Propulsion that does not involve driving wheels [Archive]

DonRotolo

04-01-2009, 16:07

Several threads discuss wheels, friction and traction.

I propose moving a robot around like a swamp boat (http://www.vacationdaysmagazine.com/blog/uploaded_images/a_airboat-766839.jpg). A 27" fan on each end, driven by 2 CIM motors each, with steering vanes, might allow for a far greater acceleration than wheels on the ground.

You'd still have wheels of course - I am not proposing a hovercraft (or eels) - they would just be mounted as casters, with no function other than supporting the weight of the robot against the playing field.

Two fans running in the same direction would push the robot. To slow down, reverse them both (no need to turn around). Run them both blowing outward, maybe you can blow moon rocks away from your trailer as the other alliance lobs them to try to score...

Steering is a little bit poor however. For this, we use a horizontal reaction wheel (think bicycle wheel with a heavy rim, spinning parallel to the floor). Driven by two FP motors at about half speed (to allow speed headroom both faster and slower), you would slow it down quickly - conservation of momentum would cause the rest of the robot to spin in the opposite direction. The same effect would occur, but in the other direction, but sharply accelerating the wheel. the wheel would be brought back to idle speed somewhat slower than during a steering maneuver.

An alternative to this would be a vertical flywheel (the axle would be horizontal) in the center of the robot which is turned opposite the direction you want to steer the robot. Gyroscopic effect would work to keep the wheel from moving, so the robot beneath it would move instead. This idea is not mine, I give credit to C J Reeves (http://www.chiefdelphi.com/forums/showpost.php?p=791064&postcount=6).

Thoughts and comments on these ideas are requested, along with other ideas for propulsion not involving driving wheels.

Don

.

Wayne C.

04-01-2009, 16:20

Don- were you in my back seat driving back from NH? Uncanny....

will the battery allow it?

WC :cool: - tis the question

DonRotolo

04-01-2009, 16:47

Don- were you in my back seat driving back from NH? Uncanny....

will the battery allow it?
Great minds think alike?

Anyway: The battery will certainly allow four 2.5" CIMs to be driven to near maximum output - our robot does that almost every year. Maybe we'll be near the limit after 2:20, but that also depends upon how it is driven. The real question is whether this will provide more propulsive force than 4 or 6 (or x) wheels on the graound, driven conventionally.

Test results will be posted ASAP.

dtengineering

04-01-2009, 16:53

antoineft

04-01-2009, 17:21

MrForbes

04-01-2009, 17:25

We were thinking of using a smaller high speed blower (leaf blower type) but decided that would not be safe because of the high air velocity.

Hopefully someone will build a swamp buggy on ice prototype soon

Bongle

04-01-2009, 17:34

Mathematically, this concept is possible. You'd need some extremely high-volume fans (4000 cubic feet per minute for 50N), and as your trailer filled up you'd lose a lot of your propulsion. The size of the fan required rules out quick reverses, not to mention that the structure of your robot ahead of the fan would reduce its efficiency.

I'm not sure why you'd want your wheels undriven though. You might as well make use of the 26 newtons of frictional force that the wheels provide. There's no good reason to simply have them be casters when they can provide as much propulsion as a big fan.

To see someone who ran the numbers, read drkiraco's post here (http://www.chiefdelphi.com/forums/showpost.php?p=790031&postcount=20)

clark_noah

04-01-2009, 17:35

Also, does it seem conceivable that you could have the fans blowing overtop of your trailer all the time to stop all/some balls from being scored? Does this seem like a cheat of the game?

Team 2609

I wouldn't think it would be cheating, but it would have to be pretty powerful to stop them if they are being directly dumped into your trailer....
it might work but it would have to be very very powerful, which means heavy most of the time....

roboraven15

04-01-2009, 17:36

we have begun to descus the options of a fan boat type effect, but u have to remember those huge fan boats have very poor acceleration on the water, and from what we saw in the kickoff video the robots could accelerate just with some slipping and stuff. the fan you would use on your robot would be even smaller, and probally have less power to work with you can only pull 40 amps at max. the fans ability seems doubtful to be any better than wheels.

Creator Mat

04-01-2009, 17:37

i was talking about this in another thread. see URL="http://www.chiefdelphi.com/forums/showthread.php?t=71037&page=8"]http://www.chiefdelphi.com/forums/showthread.php?t=71037&page=8[/URL] well my idea for this is to mod a off the shelf floor fan (something with a protective cage) to use the CIMs to power the fan blades and then use servo turned fins to "guide" your air flow for steering. Then for your wheels you would just stick them on casters.

then for the power situation but if using my past experience becuse last year we where using 4 CIMS to move a robot (120lbs) on wheels with high friction/wieght and a pnuematic system. this drained most of our battery last year. but if we where to use only the fan idea it would be 1-4 CIMs moving at most 5 pounds of fan blades (im being very heavy). Then with no other major draw of power the batterys most likely won't have a problem with this type of drive train.

King Duke

04-01-2009, 17:45

http://www.treehugger.com/files/2008/08/lotus-concept-ice-vehicle-moon-regan-antarctica.php

relevant... maybe
cool..... yes

feilmeier

04-01-2009, 18:17

At Bongle, did the 26 Newtons of frictional force come from each wheel, or from all of the wheels together, and how heavy was the robot? Anyways, a mentor and I had the same idea of having fans blowing like in a swamp boat. We calculated that a battery with an 18AH life would be capable of holding out for the length of the match, with a bit of time left over.

RobotLady

04-01-2009, 18:29

On blowing balls away from the trailer, could you use pneumatic tubing to direct the force and just dump pressure from a tank to create an air jet of some sort?

Michael Hill

04-01-2009, 18:37

hint: mini turbine-engine :D

tjwoodin

04-01-2009, 18:46

Also you could use a fan to blow above your robot to force it doen and increase traction but maybe thaat is a violation of the rules?

DonRotolo

04-01-2009, 19:25

On blowing balls away from the trailer, could you use pneumatic tubing to direct the force and just dump pressure from a tank to create an air jet of some sort?You can use a pipe-like thing to direct the air. But anything regarding pneumatic tubing, or air ultimately from the on-board compressor simply does not have enough volume to be useful in this way.
Also you could use a fan to blow above your robot to force it down and increase traction but maybe thaat is a violation of the rules?I don't know why it would violate any rules, assuming the safety aspects were covered. An increase in "weight" (more accurately, downforce) would provide more friction and therefore traction.

sxysweed

04-01-2009, 20:05

DonRotolo

04-01-2009, 20:14

(do we have to use wheels are can we use like little bearing things?)
<R06>
ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA.<snip>
Yes, you can only use the specified wheels, nothing else.

,4lex S.

04-01-2009, 20:34

You may be forced to use the 'rover wheels', but you could concievably create caster attachments for them.

Uberbots

04-01-2009, 21:19

Interesting idea...
Big fans.. Maybe. Depends on the coating and the weight of the robot. Seems conviecable but you'l have to work out the number of wheels (do we have to use wheels are can we use like little bearing things?) for the least friction...

Why a big fan though? By not build a series of duct fans like on the Big RC Jets? Build a nice fat one or custom make a few by gearings the motor out and making it run 2-3 duct fans. That way you could direct the fans. You could either go for downforce or for power....

1124 ran a small test with a large downward facing fan (it was powered by a .25hp motor, about 26" in diameter, so it probably wouldnt fit on a robot), but that fan and the downforce it provided gave a significant boost in the amount of friction between the robot and the ground. it actually became hard to push (we dont have the proper instruments to give you guys how much force was required to move it, but it was a lot more than without the fan turned on)

MrForbes

04-01-2009, 21:28

The instrument could be a bathroom scale or something simple like that, use it to push the robot with and without the fan running.

gorrilla

04-01-2009, 21:33

Matt H.

04-01-2009, 21:38

A fan in a cage is no more dangerous than an intricate chain system or some of the launchers we saw last year--at least in my opinion.

Uberbots

04-01-2009, 21:44

I dont think FIRST would let a team have a large,SHARP!, spinning object on the robots, i mean they already get on us about the sharp corners.....

imagine what would happen if there was a collision, and the fan blade shattered and sent pieces flying everywere:ahh:

if its sufficiently caged, mounted, and protected, the above shouldn't happen.
shouldnt.

ill see if i can get the team to use the scale for force measuring tomorrow, when we are back in the high school.

gorrilla

04-01-2009, 21:44

A fan in a cage is no more dangerous than an intricate chain system or some of the launchers we saw last year--at least in my opinion.

i highly disagree with that.....

Uberbots

04-01-2009, 21:49

A fan in a cage is no more dangerous than an intricate chain system or some of the launchers we saw last year--at least in my opinion.

And yet, people still found (and were required to find) ways to protect these systems and reduce how dangerous they actually are.

RogerHebert

04-01-2009, 21:57

I don't know why it would violate any rules, assuming the safety aspects were covered. An increase in "weight" (more accurately, downforce) would provide more friction and therefore traction.
There is <R06> which states "No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted."

hipsterjr

04-01-2009, 21:59

Why not the best of both worlds? Have two cims driving the wheels and two on a fan set up. You have the same driving characteristics of everyone else with an added speed and some handling boost. The wheels alone can brake so the fans dont have to be reversed.The fans can help turning a little and best of all help blow moon rocks away. If you really get fancy, you could come up with a herding system with the fans and blow them around on the ground like a leaf blower.

computerish

04-01-2009, 22:08

I think RogerHebert is right that you can't use a big fan on top, but what about the idea of pointing a fan (kind of like a leaf blower) over the trailer to deflect balls? Is that legal?

Uberbots

04-01-2009, 22:08

There is <R06> which states "No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted."

However, these fans arent providing more traction- they are increasing the normal force which in turn causes the wheels to have more traction.

perhaps this is a question for the Q&A?

xtraman122

04-01-2009, 22:14

I'm pretty sure they'd rule that out as something with means to increase traction and therefore would be disqualified. Although adding lead weights on the top woulkd effectively be doing the same thing as far as interactions between the wheels and the surface so maybe there is an argument there.

Creator Mat

04-01-2009, 22:16

I dont think FIRST would let a team have a large,SHARP!, spinning object on the robots, i mean they already get on us about the sharp corners.....

imagine what would happen if there was a collision, and the fan blade shattered and sent pieces flying everywere:ahh:
you could get around that by buying a off the shelf floor fan or something like it that comes with its own cage and just use its motor (might break a few rules unsure tho) or rip out the motor use the fan blades and cage and power it with CIMS

smurfgirl

04-01-2009, 22:18

However, these fans arent providing more traction- they are increasing the normal force which in turn causes the wheels to have more traction.

perhaps this is a question for the Q&A?

I'd say the call is quite clear... this goes against the spirit of the rules, even if it is not explicitly forbidden in the letter of the rules.

Tom I

04-01-2009, 22:25

The fan on top pushing the robot down is definitly a question for the Q&A... While technically the fan would not be changing the traction, only the Normal Force, and thus the friction, it does get into the whole "lawering the rules" that is frowned apon. If they say we can do it in the Q&A then most certainly go crazy! But until then, it is kind of a dicey issue...

hipsterjr

04-01-2009, 22:27

I'd say the call is quite clear... this goes against the spirit of the rules, even if it is not explicitly forbidden in the letter of the rules.

I have to disagree. I dont see how it is against the spirit of the rules at all. The rule said you had to use the stoke wheels to support the robot, but says nothing about how those wheels have to be propelled. With fans, the wheels are the only thing in contact with the floor and that is 100% in the spirit of the rule.

smurfgirl

04-01-2009, 22:30

I have to disagree. I dont see how it is against the spirit of the rules at all. The rule said you had to use the stoke wheels to support the robot, but says nothing about how those wheels have to be propelled. With fans, the wheels are the only thing in contact with the floor and that is 100% in the spirit of the rule.

Oh, I think you misinterpreted me. The original idea of the thread, posted by Don Rotolo, with fans propelling the robot horizontally, sounds completely in the spirit of the rules. The idea of using fans in the vertical direction to increase traction sounds against the spirit of the rules. I think we really do agree.

SteveJanesch

04-01-2009, 22:36

First of all, there are a lot of great ideas here. Thanks, Don!

Second, the idea of using a fan for downforce (either blowing down from above or creating a partial vacuum below) is Q&A material, but here's my opinion anyway: I think it's legal, as it doesn't change the traction devices - the wheels - but improves their ability to grip. The last sentence in R06 is pretty clear on its intent:

The intent of this rule is that the ROVER WHEELS be used in as close to their “out of the box” condition as possible, to provide the intended low-friction dynamic performance during the game

- Steve

hipsterjr

04-01-2009, 22:43

To SmurfGirl, I'm sorry, I did misinterpret you. I think using a fan vertically is still legal, but a little useless. Think of all the wasted space (if you wanted an efficient fan) and energy you would sacrifice! Why not just add weight bars!?

efoote868

04-01-2009, 22:46

There is <R06> which states "No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted."

<R06>ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA. Any number of ROVER WHEELS may be used. The ROVER WHEELS must be used in a “normal” orientation (i.e. with the tread of the wheel in contact with the ground, with the axis of rotation parallel to the ground and penetrating the wheel hub). No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted.

A giant fan on top does not contact the ARENA, it's still the ROVER WHEELS. The other forms of traction are things other than the wheels that contact the ARENA.

chmp09

04-01-2009, 22:47

I don't think that you could use a fan as an effective defense. The shape of the game piece does not make it very resistant to air. Its also kinda heavy, not that heavy, but heavy enough to make it hard to stop.

mrnoble

04-01-2009, 22:54

Don, you are psychic. I hope to see lots of great and waaaay out of the norm ideas coming into play for this game. There may very well be some classy, Newton-era type devices on display this year.

EricH

04-01-2009, 23:03

ebarker

04-01-2009, 23:05

The Pre

04-01-2009, 23:07

i really wana see someone build a hovercraft or swamp boat :D

definitely going to be a great year

i think it would be legal (vert or horiz fan orientation) but i think Q&A would be a great way to figure it out

GUI

04-01-2009, 23:25

I think the biggest problem with using a fan to propel a robot is safety. It takes a bit of work to get an FRC bot moving, and with a fan that sould mean moving as much air as possible as quickly as possible. This presents very real dangers to anyone near the field when debris on the field (or even a grain of sand) is blown into their face or body. It's a great idea, but too risky to everyone involved.

sdcantrell56

04-01-2009, 23:34

Using a vacuum to create downforce, as long as nothing other than rover wheels are touching the ground should not be illegal or against the spirit of the rules. This would be an innovative solution as you would not be adding anything extra between the physical interaction of the ground and the robot, and as such would not be adding traction. Also the Cof is remaining the same no matter how much downward force is applied, the only thing changing is the normal force which is not friction.

BigWhiteYeti

04-01-2009, 23:42

The biggest problem that arises with a slippery floor is the difficulty in precision maneuvering. Large fans or leaf blowers will allow for even less precision than the wheels, so it doesn't really solve anything (it would look cool, though). The only way to increase your stopping distance, turning radius, etc. is to increase your normal force without increasing your mass, as the post above describes. Other than that, your pretty much stuck with the oil slick.

GUI

04-01-2009, 23:46

Assuming traction and friction to be synonyms, then anything designed to increase normal force is illegal. Friction is the product of the coefficient of friction and the normal force, so increasing either coefficient of friction (explicitly prohibited by wheel requirements) or increasing normal force will increase traction, which is in violation of R06.

BigWhiteYeti

05-01-2009, 00:03

The rule specifically describes ways to change the coefficient of friction like putting rubber on the tires, not changing the normal force. Coefficient of friction is different than friction.

Besides, the only way I can think to change normal force without changing mass is a large fan, which would be impractical and be more pain than its worth.

Dominicano0519

05-01-2009, 00:07

hey you can always wear the wheels in such a pattern that it would be really rough and grippy or ad a chemical that would do that

and for propulsion

i have three words pneumatic rocket boosters

nitsua60

05-01-2009, 00:14

...
Besides, the only way I can think to change normal force without changing mass is a large fan, which would be impractical and be more pain than its worth.

Another way to increase the normal force: give yourself a nice hydraulic suspension and bounce your way along like an El Camino down the strip -- at the lowest part of the bounce you'll have increased the normal force and can apply more power to the wheels at that time (assuming you don't want your wheels to spin out). Of course, at the top-side of the bounce you've a smaller F_n and can apply less power.

If you don't like how that affects your shooting/tracking/&c., mount ballast (or your batteries, or your control system) on a piston inside your robot and wiggle that up and down to the same effect.

An idea that came over from another thread: an imbalanced two-wheel design. If CoG is forward of wheels so that the trailer (through the hitch) is effectively holding down the back of the robot, then you'll have a higher F_n than solely due to robot weight.

EricH

05-01-2009, 00:20

hey you can always wear the wheels in such a pattern that it would be really rough and grippy or ad a chemical that would do thatYou might want to go read <R06> more carefully.
ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA. Any number of ROVER WHEELS may be used. The ROVER WHEELS must be used in a “normal” orientation (i.e. with the tread of the wheel in contact with the ground, with the axis of rotation parallel to the ground and penetrating the wheel hub). No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted. The surface tread of the ROVER WHEELS may not be modified except through normal wear-and-tear. Specifically, the addition of cleats, studs, carved treads, alterations to the wheel profile, high-traction surface treatments, adhesive coatings, abrasive materials, and/or other attachments are prohibited. The intent of this rule is that the ROVER WHEELS be used in as close to their “out of the box” condition as possible, to provide the intended low-friction dynamic performance during the game. Translation: Your proposed method for more traction is illegal.

darkChozo

05-01-2009, 00:24

Have you considered the safety factor of having a fan powerful enough to propel a ~150 pound robot faster than the wheels can? That's going to be quite a lot of wind. Considering that people are usually standing pretty close to the arena, I could easily imagine someone who is already off balance being pushed over and getting hurt by that. Same with light, unsecured equipment, or maybe tablecloths, barriers, etc. that can easily be blown up or away. And that's ignoring the damage that smaller things kicked up by the fan, or even worse, accidentally fed into the fan could do. It's not something I'd want to risk betting on at this point, lest it violate <S01>. I would wait until the Q&A clears things up.

Not to mention, I doubt that the crowd will appreciate being blown upon. Just a thought.

Dominicano0519

05-01-2009, 00:25

no im saying those wheels have a concave surface so you make you grind out as much of it as you can

Dominicano0519

05-01-2009, 00:26

EricH

05-01-2009, 00:29

no im saying those wheels have a concave surface so you make you grind out as much of it as you can
Umm... Excuse me? Re-read the bold portion of the rule in my last post. There should be something about altering the surface profile. Grinding down the surface is doing just that.

Dominicano0519

05-01-2009, 00:41

no grinding is one thing practicing all everyday with that set of wheels for three weeks is another thing im just saying use the most worn out set of wheels that you have it will give you an edge

Rossetto07

05-01-2009, 04:03

I think RogerHebert is right that you can't use a big fan on top, but what about the idea of pointing a fan (kind of like a leaf blower) over the trailer to deflect balls? Is that legal?

Our team did some tests to see if a leaf blower could deflect an incoming cell, but we had very little success even though the leafblower was significantly stronger than any fan that a 12V CIM could power. The design of the balls just doesn't have enough surface area for them to be affected by air movement.

Too bad.

GaryVoshol

05-01-2009, 08:37

no grinding is one thing practicing all everyday with that set of wheels for three weeks is another thing im just saying use the most worn out set of wheels that you have it will give you an edgeYou could take the robot outside and run it a few laps around the cement parking lot to scuff the wheels too. Just try to pass inspection after that.

XXShadowXX

05-01-2009, 08:48

Using the said fan idea is nice, but you would need a skirt to keep an air pillow between the robot and the ground, and to contain the air. This is how current hovercrafts work, and it would provide you with good steering, and manuveurablity, but horrible friction one bump and you would go flying seeing as you have nearly no contact with the ground. Not to mention that you will have trouble picking up balls off the ground, and your skirt will need to be lower then the bumper zone so you can have regulation bumpers.

Dominicano0519

05-01-2009, 09:08

You could take the robot outside and run it a few laps around the cement parking lot to scuff the wheels too. Just try to pass inspection after that.

man just pop those bad boys on after you pass inspection have some other tires on

GaryVoshol

05-01-2009, 09:10

Don't try that on my field - I'll have you reinspected.

Dominicano0519

05-01-2009, 09:54

Don't try that on my field - I'll have you reinspected.
god you guys cant take a joke

my team is not competing this year so of course i won't try it, besides i was just kidding that would be against the spirit of the rule i mean its obvious that what im proposing is illegal

Tottanka

05-01-2009, 10:00

god you guys cant take a joke

my team is not competing this year so of course i won't try it, besides i was just kidding that would be against the spirit of the rule i mean its obvious that what im proposing is illegal

A 'joke' stops being funny after 5 times.

sdcantrell56

05-01-2009, 10:13

Seriouslly... You have proposed numerable illegal and unethical measures to increase traction. It really isn't funny and appropriate after the 4th time. Although you might not be serious, what happens if a rookie sees this and thinks that this thinking is acceptable in FIRST?

sxysweed

05-01-2009, 11:23

I'd say the call is quite clear... this goes against the spirit of the rules, even if it is not explicitly forbidden in the letter of the rules.

But isn't the spirit of the compition innovation?

I don't think that you could use a fan as an effective defense. The shape of the game piece does not make it very resistant to air. Its also kinda heavy, not that heavy, but heavy enough to make it hard to stop.

Not necessarily a fan as everyone seems stuck on. But for those that have experience in RC Aircraft, the duct fans provide LOTS of pushing power. I'll have to try it out, but I think it could move the ball. Have them point at an angle upwards (posssibly 45*) and you should be able to blow the balls away if they are thrown. If they are otehrwise placed in, that's another story.

The 45* would also give some forward movement and traction, but how much and how useful it is, is uncertain. My question is (haven't read the rules yet), is it legal to deflect the balls like that?

Ziaholic

05-01-2009, 11:54

For those of you saying that a downforce would be legal:

I'm 99% sure that it's not legal. The wording in the rule is clear: if it increases traction, it's not legal. The idea is to increase the normal force, which increases available frictional force (not friction), which increases traction. That's increasing traction, which is illegal.

The other 1% says to ask Q&A when it comes online and see what they say.

I've gotta' lean in this direction also. Very well put. Downward force does increase traction which would be illegal.

So while this vertical force is most likely not allowed, the arguement for horizontal forces is not as simple, unless you could argue that it's not perfectly horizontal ... a sneaky team might try to offset their swampboat's thruster to provide a small downforce.

I'm guessing that they'll refine the rules to include phrases that say that the wheels must be the locomotive force of the 'bot.

hipsterjr

05-01-2009, 12:18

This thread is way off topic. The main idea was to drive a robot with horizontal fans. Someone mentioned a vertical fan to increase traction and now everyone is arguing about that. IMHO a hybrid driven wheel and propulsion fan drive system is most defiantly legal and has some interesting advantages.

martin417

05-01-2009, 12:54

For those of you saying that a downforce would be legal:

I'm 99% sure that it's not legal. The wording in the rule is clear: if it increases traction, it's not legal. The idea is to increase the normal force, which increases available frictional force (not friction), which increases traction. That's increasing traction, which is illegal.

The other 1% says to ask Q&A when it comes online and see what they say.

The way I read the rule:

<R06>"No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted

Increasing downforce does not provide traction. I know this is a semantics argument, but I think the rules are very carefully worded. Traction is provided by whatever contacts the ground. If it doesn't contact the ground, it cannot provide traction.

Bongle

05-01-2009, 13:39

I think the "fan as downforce" concept is fundamentally flawed, anyway.

So you take a fan producing x newtons.

-If pointed horizontally, it could accelerate or decelerate your robot to the tune of x newtons
-If pointed vertically, it generates x newtons of downforce, which increases the amount of friction you get by 0.05 * x (mu * normal force increase). This is far less useful than a horizontal fan.

Kevin Sevcik

05-01-2009, 15:01

I agree with Bongle that using a fans pushing down to increase downforce is a little silly. I don't think it's going to be illegal, however. The super strict readings of <R06> I'm seeing don't seem sensible to me. If you're saying the fan is illegal because it's increasing downforce and thus increasing traction.... Then wouldn't the entire robot be illegal because it's adding additional weight, increasing downforce, and adding traction? The rule specifically says that the intent is for there to be a "low-friction" dynamic. Not a "low-traction/pushing power" dynamic.

Anyways, back to the gyroscope, because I think it's brilliant, and I want someone to try it. I don't know that the appropriate way to use the gyro is as a stiff structure to turn against. It would certainly work, but the dynamics are going to be weird, and I don't know if it's the most efficient use of a gyroscope. Specifically about the dynamics, if you wind up the gyro to a good speed and then try to rotate against it, it's going to generate an overturning moment perpendicular to the axis of rotation of the gyro and the axis your robot is rotating about. Which is going to try to flip your robot front to back, side to side, or something, depending on the orientation of the gyro at any particular moment. (Cool, huh?)

I think the better, if more complicated, use would be as a control moment gyroscope. If you remember the old science trick with a spinny chair and a bicycle wheel, you've got the basic idea. Here's some videos to jog memories just in case:
Cornell Video (http://www.youtube.com/watch?v=UKf50CJU-Dg)
Honeywell Video (http://www.honeywell.com/sites/servlet/com.merx.npoint.servlets.DocumentServlet?docid=D3B 6B31DD-A0D5-4E8B-8270-0615E647A80D)

Using a control moment gyro is a little more complicated, as you'll need to keep track of the absolute angle of it, and try to keep it vertical, but the axis of rotation will always be the same relative to your robot's direction of travel, so the over-turning effects will be more predictable. It should really do a very good job of keeping you pointed in the proper direction. I'll have to do some math to work out just what sizes and speeds we'd be talking about to get a useful effect, but it's definitely something I'm seriously considering.

feilmeier

05-01-2009, 19:37

As I read through this post, I notice a number of discrepancies that alter some people's view points.

1) A rolling wheel has the same coefficient of friction as a static wheel, since as the wheel rolls, each part of the wheel stays in static alignment in respect to the piece of ground that it contacts. Therefore, the coefficient of friction provided by rolling, non-slipping wheels is .06.

2) By having a vertical fan pointing downwards, you simulate additional mass. This increases not traction, but weight. The mass of the robot stays the same, but the weight increases.

3) Unless your fans are a lot stronger than that I am imagining, the falloff for most air flow from the fans is quite sharp, reducing the potential for anyone being knocked over, or being hit by flying debris. Remember the inverse square law people.

Thanks for listening to me. As you can see, I just finished a section on friction in my physics class.

EricH

05-01-2009, 20:12

2) By having a vertical fan pointing downwards, you simulate additional mass. This increases not traction, but weight. The mass of the robot stays the same, but the weight increases.

Thanks for listening to me. As you can see, I just finished a section on friction in my physics class.Weight, when directed perpendicularly to a surface such as the ground, is also known as Normal Force for purposes of determining friction between an object and the surface. This increases the frictional force that is available, increasing the traction.

professorX

05-01-2009, 20:23

Of course, once you've got the fans, you could also use them to suck air from underneath the robot to increase your traction.

Jason

I believe that you are not able to do this.

<R06>
ROBOTs must use ROVER WHEELS (as supplied in the 2009 Kit Of Parts and/or their equivalent as provided by the supplying vendor) to provide traction between the ROBOT and the ARENA. Any number of ROVER WHEELS may be used. The ROVER WHEELS must be used in a “normal” orientation (i.e. with the tread of the wheel in contact with the ground, with the axis of rotation parallel to the ground and penetrating the wheel hub). No other forms of traction devices (wheels, tracks, legs, or other devices intended to provide traction) are permitted. The surface tread of the ROVER WHEELS may not be modified except through normal wear-and-tear. Specifically, the addition of cleats, studs, carved treads, alterations to the wheel profile, high-traction surface treatments, adhesive coatings, abrasive materials, and/or other attachments are prohibited. The intent of this rule is that the ROVER WHEELS be used in as close to their “out of the box” condition as possible, to provide the intended low-friction dynamic performance during the game

feilmeier

05-01-2009, 20:55

Weight, when directed perpendicularly to a surface such as the ground, is also known as Normal Force for purposes of determining friction between an object and the surface. This increases the frictional force that is available, increasing the traction.

Indeed. I did not mention normal force, because of two reasons. By Newton's second law, F=MA. If you simulate an increase in mass without reducing the acceleration (ie. gravity), then of course you increase the normal force. The other reason is that weight is measured in Newtons, as is the normal force. The only difference between normal force and weight is if the object suppyling the normal force is incapable of holding the weight. If suddenly robots started falling through holes in the floor during the game, then we would have to revert back to using the term normal force. But for this case where we are certain that the floor will hold us up, the term weight is equally valid as the term normal force.

Since we also know that traction is commonly used to refer to static friction/adhesive friction as opposed to kinetic friction/sliding friction, by the very definition of Rule <R06>, to add any sort of metal to the wheels is to increase the traction of the device, and thereby banned. Come January 7th, let us ask the Q and A, and see if indeed this approach is acceptable.

comphappy

05-01-2009, 21:07

Weight, when directed perpendicularly to a surface such as the ground, is also known as Normal Force for purposes of determining friction between an object and the surface. This increases the frictional force that is available, increasing the traction.

Yes but that does nothing for your acceleration.

m*g*u=m*a
gu=a

So a robot that is 500lbs wheels will spinout like a robot that is 10lbs.
Collisions are a different story, and my thought on that will be left between me and my team for now.

DonRotolo

05-01-2009, 21:21

I dont think FIRST would let a team have a large,SHARP!, spinning object on the robotsI disagree. With proper guards it is no more dangerous than a fan in your house.
<R06>
this goes against the spirit of the rules
For those of you saying that a downforce would be legal
increasing normal force will increase traction, which is in violation of R06.
Downward force does increase traction which would be illegal.I believe that you are not able to do this.This increases the frictional force that is available, increasing the traction.

I get the feeling that all of you are serious in thinking that increasing the normal force is not legal? :confused:
I agree with Bongle that using a fans pushing down to increase downforce is a little silly. I don't think it's going to be illegal, however.Finally, a voice of reason. Thank You Kevin.

With the caveat that my proposal was to use fans horizontally to push air and move the robot and not to push downwards harder (since the effect would be somewhat, as Kevin puts it, silly) I have to say...

If increasing the normal force is not legal, then your robot must weigh nothing, since adding ANY weight at all increases the normal force. Clearly, we are allowed robots that weight something...

Put another way: There is no difference between adding a 20 pound weight atop a 100 pound robot and adding a fan pushing downwards with 20 pounds of force atop a 100 pound robot. Both "increase traction" by modifying the normal force. And if it is legal on that 100 pound robot, then it is perfectly legal on a 120 pound robot, since the rules define (and inspectors measure) a specific robot weight, not a specific downforce.

I hope someone asks Q&A, because I find the whole discussion silly (and will eat crow if wrong), but can also assure you that this is not a consideration for our robot.

What we are considering is wheels aided by fans. After all, what would you do with an extra 50% (or so) maneuverability???

feilmeier

05-01-2009, 21:27

Actually, a 500 lb robot will get more frictional force, but on the same account will have a larger inertia, thus retarding it's acceleration. By simulating an increase weight, you will increase the frictional force, but leave the inertia alone, thereby allowing you to accelerate at a faster rate.

120 lb robot will generate roughly 32 Newtons of frictional force, which will then give it an acceleration of .58 m/s^2.

A 120 lb robot with an additional 10 Newtons(120 lb is roughly 534 N) will generate roughly 32.5 Newtons of frictional force, which, when related in the F=MA equation, will give you an acceleration of roughly .6 m/s^2.

As you can see, this is a very small increase, only leading to about 0.3 m/s or so of end velocity at the end of the run of the entire 54 ft/ 16.5 m. To make this effective, a comparable amount of pressure must be induced to allow a robot to perform significantly better. In a collision, the robot that has the higher rate of speed in this game will probably win out, and because of the low coefficient of friction, the collisions will very likely be semi-eliastic.

As to the original post, my personal leaf blower can exert about 10 N when in contact with concrete. I have a feeling that the team with the best manuvability will have a nice system to direct airflow, and power the wheels

EricH

05-01-2009, 21:40

Yes but that does nothing for your acceleration.

m*g*u=m*a
gu=a

So a robot that is 500lbs wheels will spinout like a robot that is 10lbs.
Collisions are a different story, and my thought on that will be left between me and my team for now.
F=m*a
Frictional force = mu*N, where N = m*g, where g= 9.8 m/s^2= the gravitational constant acceleration

You're saying that m*a=mu*m*g, right? m cancels out, leaving a=mu*g.

However, the g has been increased by using a fan or something to add downwards force! Guess what? a must increase!

And lbs are NOT a unit of mass, they are a unit of force, which is computed by m*g. Increase g and you increase the force.

Let's look at your scenario: 500 lbs=32f/s^2*x slugs (slug being the English system's unit of mass) 10 lbs =32 f/s^2*y slugs
you are saying that 32f/s^2 * x slugs = 32f/s^2 * y slugs. Cancel out 32f/s^2 and you get x slugs = y slugs. Cancel out the units and x = y. However, because 500/32 = x slugs and 10/32 = y slugs, you get 500/32=10/32, which simplifies to 500=10. This isn't true, is it?

EricH

05-01-2009, 21:44

I get the feeling that all of you are serious in thinking that increasing the normal force is not legal? :confused:
Finally, a voice of reason. Thank You Kevin.

With the caveat that my proposal was to use fans horizontally to push air and move the robot and not to push downwards harder (since the effect would be somewhat, as Kevin puts it, silly) I have to say...

If increasing the normal force is not legal, then your robot must weigh nothing, since adding ANY weight at all increases the normal force. Clearly, we are allowed robots that weight something...

I am not saying that adding weight is illegal. However, what I am saying is that using a fan or other method to effectively increase your weight beyond the 120# + battery + bumpers is. I have no problem with teams going right up to 120.0, even using a fan. But as soon as you use some of that weight to add extra weight on top of the 120.0, then I have a problem. I would assume that the others who said that would say the same thing.

Again, I have no problem with adding stuff up to the limit; I have a problem with using some of that to go beyond the limit.

ZakuAce

05-01-2009, 22:26

I am not saying that adding weight is illegal. However, what I am saying is that using a fan or other method to effectively increase your weight beyond the 120# + battery + bumpers is. I have no problem with teams going right up to 120.0, even using a fan. But as soon as you use some of that weight to add extra weight on top of the 120.0, then I have a problem. I would assume that the others who said that would say the same thing.

Again, I have no problem with adding stuff up to the limit; I have a problem with using some of that to go beyond the limit

Spot on. This is exactly the way I feel. Now, can we please get back on track to the fans as propulsion idea?

I really hate this idea. I don't see how it is practical. Also, I feel like acting against a hit would be a problem. If you get hit while you are maneuvering into position to score, with wheel power you have at least some chance of repositioning yourself. You are using the small amount of traction you can get to your advantage, which is not something I would throw away. With a hovercraft like propulsion, I think the ability to counter-act this is much harder. Not to mention the power requirements, though like Don said, the batteries can run the CIMS at full power for a while.

HOWEVER, I think it could be a viable design if you are focusing your robot on only keeping your robot moving and keeping the opposing alliance from scoring, since being hit will send you flying away.

wizardofoz

05-01-2009, 23:02

You can't use fans on the moon since there is almost no atmosphere on the moon. If the goal of the game is to simulate a moon environment, wouldn't it be going against the theme of the competition to use fans?

comphappy

05-01-2009, 23:12

F=m*a
Frictional force = mu*N, where N = m*g, where g= 9.8 m/s^2= the gravitational constant acceleration

You're saying that m*a=mu*m*g, right? m cancels out, leaving a=mu*g.

However, the g has been increased by using a fan or something to add downwards force! Guess what? a must increase!

And lbs are NOT a unit of mass, they are a unit of force, which is computed by m*g. Increase g and you increase the force.

Let's look at your scenario: 500 lbs=32f/s^2*x slugs (slug being the English system's unit of mass) 10 lbs =32 f/s^2*y slugs
you are saying that 32f/s^2 * x slugs = 32f/s^2 * y slugs. Cancel out 32f/s^2 and you get x slugs = y slugs. Cancel out the units and x = y. However, because 500/32 = x slugs and 10/32 = y slugs, you get 500/32=10/32, which simplifies to 500=10. This isn't true, is it?

What you said is very WRONG check your equations before correcting me!!!

http://upload.wikimedia.org/math/0/c/0/0c02725f116ef3cad99527413171d4bb.png

m*a=u*m*g
becomes
a=u*g

therefore mass does not matter, now if you are useing downdraft gas then the "mass" part of Fn will not equal the mass of the robot. But that is not what I was talking about. Watch your equations.

Justin Stiltner

05-01-2009, 23:25

As a long time participant in FIRST (10 years) I think a few of you are "reverse lawyering" the rule about traction. To me it is pretty clear that the intent of that rule is just what most think, the rover wheels are the ONLY thing that can act against the floor to provide motive force. They actually mention legs, other wheels, etc. I think that a robot with a fan would be a great idea, and something I would look into the feasibility of. I am sure this will be settled soon via the Q and A. What you are talking about doing is done in all motor sports (cars anyway) the car uses down force generated from the aerodynamics of the vehicle to provide extra normal force, and the end result is more traction. If it were properly designed, and guarded I would have no problems with a robot that had normal force increasing devices, but be ready for a lengthy inspection, and have your engineering numbers ready if you designed it yourself, or the data sheet of the fan from the mfg.

To go ahead and comment on various other posts ideas, and take these as you will...

WORN WHEELS
If a team came in with worn in wheels I dont see a problem, It is the same as a team that has run in a previous regional and not changed their wheels, If you are going to say that you cannot have worn wheels then you would need to make everyone change their wheels every few matches. However the manual does state that the profile of the wheel may not be modified. But one thing to ponder, if we assume these to be ideal surfaces, then the surface area of the contact patch doesn't matter.

FANS FOR PROPULSION
Dont think of a fan which is normally moving a relatively low volume of air and relatively low velocity. Think of a helicopter rotor, by using this you can get an off the shelf product, that has been tested to certain rpm limits, and the best part, instead of reversing the rotation of your "fan" you only have to change the collective pitch of the rotor blades, (done with a servo on model helicopters). I have not tested the numbers myself, however there are reports that a heli with a 27.6" rotor diameter was lifting itsself as well as generating 5lbs of upward force, this while consuming about 420W via a brushless motor. However you would need casters to turn if this was all you had, which could result in a wild ride when you had a collision.

FAN FOR DOWNFORCE
To me, a fan blowing up alone would help, however you would most likely see more of an effect if you were to use your fan to generate a low pressure area under the robot. The force in this case being pressure differential multiplied by the area of the robot under this low pressure. Assuming you could affect the entire underside of a full legal size robot with a lower pressure you would have 1064in^2 of area, with something this large, the differential would not have to be much to have a rather large increase in force. For instance a random fan mfg. I looked at quoted 50cfm at 2inches of water (.072PSI), this doesn't sound like much, but over the full area of the bottom of the a fore mentioned maximum dimension robot you would achieve an extra 76lb of downward force, assuming a 120lb robot and a coefF of .05 that would be 6lb of linear force before the blower, and another
3.8 if you could establish -2IWG of pressure under the robot meaning you get 63% more force if you can establish the low pressure.

Take all of this with a grain of salt, plenty of off the cuff calculations there, and food for thought. I also think a good traction control system would be worth its weight in gold!!!

EricH

05-01-2009, 23:47

What you said is very WRONG check your equations before correcting me!!!

http://upload.wikimedia.org/math/0/c/0/0c02725f116ef3cad99527413171d4bb.png

m*a=u*m*g
becomes
a=u*g

therefore mass does not matter, now if you are useing downdraft gas then the "mass" part of Fn will not equal the mass of the robot. But that is not what I was talking about. Watch your equations.Frictional force (static) = Ffs
Max frictional force = μ*N, N = the normal force. So far so good, right?

N = m*g, where m = the mass of the object (robot) and g = either 9.8 m/s^2 or 32 f/s^2 depending on your system of measurement. Am I not correct?

For the condition where nothing is slipping or about to slip, Ffs <= μ*N. When the object is about to slip, Ffs = μ*N. When the object slips, you get into Ffk, or the force of kinetic friction. I'm still correct in this, right?

By your equations, you are assuming that the wheel is about to slip. That is, F=m*a (the standard force equation) == μ*N. But wait! Where, oh where, does Ffs come in? It is the force exerted by the static friction, so it is m*a also, I'm assuming. Please correct me if I am wrong here.

Now, on to business.

Ffs = m*a = μ*m*g, assuming a flat plane. I think this is quite reasonable considering the application and that you're about to slip your wheels.

So, m cancels. a = μ*g. You are correct. The mass does not matter.

HOWEVER: you add a fan using your available mass (which doesn't matter) which adds additional force going downwards, correct? mu is constant due to the rules, so we can set that aside. That leaves g and a. a = g. g is a component of the normal force, under N = m*g. The normal force is equal and opposite to the weight m*Ag , such that W (weight) + N = 0. So far so good, right?

When you add the force Ffan going downwards (or upwards), you now have W + N + Ffan = 0. Ffan would be added to either W or N if the fan were pushing down, and you have W+Ffan = -N or N + Ffan = -W.

Your full new equation, therefore, would read: m*a = μ*m*g + Ffan. (Frictional Force = Normal force times mu plus Fan force) Correct me if I am wrong here.

Fan force is dependent on area and speed, is it not? There is not a mass component there, because it is already accounted for. So you can no longer divide out mass. (basic algebra)

As for your other comment, YOU also need to watch your equations. Unless you can point out what is wrong with my response to your example of a 500 lb and a 10 lb robot, that stands. I could also run it in metric if I wanted to.

GameSlammer7

05-01-2009, 23:55

I noticed that the question was raised as to whether the 26 N was for each wheel or all combined. That's a physics answer I'll nab: it does not matter. Increased surface area does not affect the frictional force. Only normal force and the coefficient of friction affects. So, more wheels I believe will produce same friction output. I believe.

feilmeier

06-01-2009, 00:14

comphappy

06-01-2009, 00:44

Frictional force (static) = Ffs
Max frictional force = mu*N, N = the normal force. So far so good, right?

NO
Lets lay down some facts
is u of static friction which FIRST has at 0.06 for static inline.
the Fn is going to be mg asumming the robot is flat on the ground.
120 lb = 54.43 kg
Fn = 54.43 * g
Fn = 533.41 N
now lets calculate the maximum frictional force that can be exerted by wheels before they slip on the surface (static friction as the wheel does not "leave the surface")
Fu = Fn * u
Fu = 533.41N * 0.06 = 32N
now lets find out the maximum acceleration because we must be equal to or less then Fu.
Fu = ma where a is the acceleration parallel to the surface
32 = 54.43 * a
a = 0.58 m/s/s

low lets try that with a robot at 10kg

Fn = 10 * g =98N
Fu = 98N * 0.06 = 5.88 N
5.8 = 10 * a
a = 0.58

Now Lets try it with the equation that I derived
a=u*g
a = 0.06 * 9.8 = 0.58 m/s/s
So with no wind propulsion which I said in my first response. mass does not mater in terms of acceleration.

N = m*g, where m = the mass of the object (robot) and g = either 9.8 m/s^2 or 32 f/s^2 depending on your system of measurement. Am I not correct?

For the condition where nothing is slipping or about to slip, Ffs <= mu*N. When the object is about to slip, Ffs = mu*N. When the object slips, you get into Ffk, or the force of kinetic friction. I'm still correct in this, right?

No the m is N you are putting that in twice, which is wrong, see the image that I slipped in my last post.

By your equations, you are assuming that the wheel is about to slip. That is, F=m*a (the standard force equation) == mu*N. But wait! Where, oh where, does Ffs come in? It is the force exerted by the static friction, so it is m*a also, I'm assuming. Please correct me if I am wrong here.

This is not right, see above.

Now, on to business.

Ffs = m*a = mu*m*g, assuming a flat plane. I think this is quite reasonable considering the application and that you're about to slip your wheels.

So, m cancels. a = mu*g. You are correct. The mass does not matter.

mass is not in there twice take it out.

HOWEVER: you add a fan using your available mass (which doesn't matter) which adds additional force going downwards, correct? mu is constant due to the rules, so we can set that aside. That leaves g and a. a = g. g is a component of the normal force, under N = m*g. The normal force is equal and opposite to the weight m*Ag , such that W (weight) + N = 0. So far so good, right?

When you add the force Ffan going downwards (or upwards), you now have W + N + Ffan = 0. Ffan would be added to either W or N if the fan were pushing down, and you have W+Ffan = -N or N + Ffan = -W.

Your full new equation, therefore, would read: m*a = mu*m*g + Ffan. (Frictional Force = Normal force times mu plus Fan force) Correct me if I am wrong here.

Fan force is dependent on area and speed, is it not? There is not a mass component there, because it is already accounted for. So you can no longer divide out mass. (basic algebra)

As for your other comment, YOU also need to watch your equations. Unless you can point out what is wrong with my response to your example of a 500 lb and a 10 lb robot, that stands. I could also run it in metric if I wanted to.
I have pointed it out, in metric (not sure why that mattered). As for above with a fan you can accelerate a little more. although the equations above for the fan suffer from the same error as the wheels.

This is important to make clear as intuition for most people is wrong here.

comphappy

06-01-2009, 00:50

Let us get away from the mass of the robot times the gravity, and consider just the weight, since it comes in force measurements, and is much easier to calculate with. :)

Maximum Static Friction = Coefficient of Friction times the normal force/weight

If you increase the normal force, either by adding more mass, or by applying force in the form of a downdraft caused by a fan, then the Maximum Static Friction becomes larger. That's Algebra. 0.06 * 10 < 0.06 * 20

Now wheels that roll without slipping should ideally roll without friction, but as we all know, that's false. Rolling friction equals coefficient of friction times the normal force. This coefficient can also be the same as the one used in the static friction. As the tread touching the ground is at rest relative to the ground this makes it true.

If you can refute this, please point me to where you found this. I found all of my equations inside of Physics for Scientists and Engineers 5th edition, Extended Version page 118-127

Ah my friend you are oh so close, they do have friction the static friction. And yes the frictional force increases with mass, however it is harder to get a more massive object to move. As in my proof above you will see friction force down is proportional to the force to push the object (with out moving into dynamic friction ie slipping) across. All the forces are greater but only by the mass, they cancel. Its all the same until a collision. then its just p=mv with some lost to heat and deformation.

EricH

06-01-2009, 01:16

R3V34L

06-01-2009, 01:27

I am not saying that adding weight is illegal. However, what I am saying is that using a fan or other method to effectively increase your weight beyond the 120# + battery + bumpers is. I have no problem with teams going right up to 120.0, even using a fan. But as soon as you use some of that weight to add extra weight on top of the 120.0, then I have a problem. I would assume that the others who said that would say the same thing.

Again, I have no problem with adding stuff up to the limit; I have a problem with using some of that to go beyond the limit.

Not meant to insult you or anything but, by that note, if I'm using a set of 2lb spinning wheels to propel my ball out of the 28'' x 38'' x 60'' box for our robot, then I'm using my weight to reach outside of my robot boundaries. Yet I would think that this is not illegal. If you are using mechanical means, and they fit within the scope of the rules, I would say let the team use them.

My team, (948) is currently dabbling in the possibilities of a fan helping to pull our robot down. As a rough estimate, we know that the base of our robot can be ~1000 in^2. If we can generate even .5 psi difference, that's an additional 500 pounds to "add" to our normal force. If we can get that is another question however, and one we are trying to answer. To help increase the potential of a fan's use, we thought that adding a skirt along the inside of the bumper that comes within a quarter inch of the ground could help to contain our "pseudo-vacuum".

EricH

06-01-2009, 01:30

Not meant to insult you or anything but, by that note, if I'm using a set of 2lb spinning wheels to propel my ball out of the 28'' x 38'' x 60'' box for our robot, then I'm using my weight to reach outside of my robot boundaries. Yet I would think that this is not illegal. If you are using mechanical means, and they fit within the scope of the rules, I would say let the team use them.I said nothing whatsoever about reaching outside robot boundaries. The entire robot must fit within the boundaries, and anything inside the boundaries must follow all applicable rules.

A fan or vacuum is not necessarily violating any rules, but when it is used to add traction (deliberately), then I would call intent and have it removed.

R3V34L

06-01-2009, 01:39

I said nothing whatsoever about reaching outside robot boundaries. The entire robot must fit within the boundaries, and anything inside the boundaries must follow all applicable rules.

A fan or vacuum is not necessarily violating any rules, but when it is used to add traction (deliberately), then I would call intent and have it removed.

Correct, and it could be argued that the effect of the cannon is to change things outside of your boundaries, just as the effect of the fan is to change how your normal force is calculated.

Here I would say that traction is your coefficient of friction, (which is fixed by not tampering with the wheels or letting anything touch the ground) whereas the fan is affecting Normal Force. Yes the force of friction is changed, but not because of any change in traction.

comphappy

06-01-2009, 01:44

Comphappy, I see where we really differ, now that you have explained where you and I differ. What you call "u" (the coefficient of friction) is normally hand-written as "μ", which is the Greek letter "mu". I used "mu" to designate this letter, while you use "u". I then used a "*" to designate multiplication.

I have edited my last post to reflect hand-written usage. Please go through again and tell me if I am still wrong.

As for why metric matters, I am simply much more familiar with the mass/weight units in metric. I couldn't even tell you what the units for slugs (the English system version of kilograms) are.

Hah, thats what we get for being lazy and not finding "μ" symbol, what you wrote looks close for the fan. But who knows what the usefulness will be, with all those extra variables. Most of that is going to be rough math + lots of test. I am excited for all the physics this year. If nothing else all that we wrote should help others later.

Steven092391

06-01-2009, 04:32

a prediction: true or false.

"the use of a fan to increase the downward force the robot exerts on the floor will not be allowed if it exceeds 120 lb force."

you could weight or blow yourself downward up to 120 lb force. weight don't use batteries.

But the idea of using fans for horizontal propulsion even though that sounds cool would be noisy beyond description. It would bring the discussion on OSHA noise levels to a whole new level. It would create havoc on the noise front.

I have to say...as cool as the idea may seem, I do agree with ebarker in his post. Yes, I do agree that the horizontal propulsion concept is worth a shot in the Q & A, but realistically, the concept would either prove useless, or illegal.

<R11> states that, At the start of, and during, the MATCH the ROBOT shall fit within the dimensions listed below:
Maximum Width- 28 inches (71.12 cm)
Maximum Depth- 38 inches (96.52 cm)
Maximum Height- 60 inches (152.40 cm)
Maximum Weight- 120 pounds (54.43 Kg)

<R16> backs this by stating that, Once the MATCH has started, the ROBOT may assume a PLAYING CONFIGURATION that is different from the STARTING CONFIGURATION. The ROBOT must be designed such that the PLAYING CONFIGURATION of the ROBOT shall not exceed the dimensions specified in Rule <R11>. Weight is one of these stated dimensions, right??

I believe that if the same rule pertaining to this was still in effect from last year, then it would DEFINITELY be worth the shot...and if you will recall, last year's <R11> is the exact same, but <R16> varies by stating that once the MATCH has started, the ROBOT may assume a PLAYING CONFIGURATION that exceeds the size dimensions specified in Rule <R11>. While in the PLAYING CONFIGURATION, the ROBOT may expand up to a maximum horizontal dimension of 80 inches (e.g. all parts of the ROBOT must fit within an imaginary 80-inch-diameter upright cylinder). There are no height limits for a ROBOT in its PLAYING CONFIGURATION at any time after the start of the MATCH.

With this being said, I would think that this wonderful concept has deemed itself invalid due to one simple fact- if at ANY MOMENT IN TIME you place scales under your machine and they read more than 120 lbs (excluding battery and bumpers of course), IT'S ILLEGAL! And if this concept were put into play and this isn't true? It's completely useless...Just bolt a piece of steel to it...it's much more energy efficient! ;)

I hope that this is beneficial to all, and I'm wishing all of US some luck this season!

R3V34L

06-01-2009, 09:56

In last years competition, team 1771 used an extremely effective robot with a funnel and a fan at the end used to create a vacuum to pick up the game element. I've heard that they used two Fisher Price motors and a timing belt to achieve the fan's movement. I've also heard that it gave them 350 pounds of vacuum force, if you could apply that to your robot, you would be able to increase the normal force from 120 pounds to probably around 420 pounds under best conditions possible. Though, that's being very kind to the suction.

That said, this idea is still is testing, our team might try working on a prototype just to see if it is possible, but if it is, I don't see why judges would disqualify us. The fan would still be bulky, and suck up a large amount of our battery life, two possibly life killing consequences.

Heres a link to 1771's impressive robot on youtube.
http://www.youtube.com/watch?v=QeQSGmFnKAE

Kevin Sevcik

06-01-2009, 10:43

So with no wind propulsion which I said in my first response. mass does not mater in terms of acceleration.

This is important to make clear as intuition for most people is wrong here.
This is not entirely true. It is true that if you're only accelerating the robot, then mass doesn't matter. But you're also accelerating a ~40 lb trailer behind your robot. It will add some additional normal force to your robot, but, only a fraction of its total weight, as it's not resting entirely on your robot. So, briefly, assuming a third of the trailer weight is on your robot:
120 lb Robot 60 lb Robot
mr = 120 lbs ~= 55 kg mr = 60 lbs ~= 27 kg
mt = 40 lbs ~= 20 kg mt = 40 lbs ~= 20 kg
Fr = 55 kg * 9.8 m/s2 Fr = 55 kg * 9.8 m/s2
Fr = 539 N Fr = 264.6 N
Ft = 20 kg * 9.8 m/s2 Ft = 20 kg * 9.8 m/s2
Ft = 196 N Ft = 196 N
Fn = Fr + Ft/3 Fn = Fr + Ft/3
Fn = 604.33 N Fn = 329.93 N
Ff = Fn * u Ff = Fn * u
Ff = 36.26 N Ff = 19.796 N
a = Ff/(mr + mt) a = Ff/(mr + mt)
a = .48344 m/s2 a = .42119 m/s2
So, because of the trailer, mass does matter to your overall acceleration, barring windage, etc. By decreasing the relative proportion of the dead weight of the trailer, you actually increase your effective acceleration. And this isn't accounting for any frictional effects from the trailer, as well.

jgraber

06-01-2009, 14:45

Our team did some tests to see if a leaf blower could deflect an incoming cell, but we had very little success even though the leafblower was significantly stronger than any fan that a 12V CIM could power. The design of the balls just doesn't have enough surface area for them to be affected by air movement.

Too bad.

I like the idea of vacuum ground effect, and blower deflecting the balls too.
However, the Q&A could reject air-reaction concept for all purposes as being against the spirit of the game, since there is no air on the moon.

kaszeta

06-01-2009, 15:48

AlexD744

06-01-2009, 16:13

One greatest mentor, Ralph, had the gyroscope/flywheel idea. And our head student builder, Josh, had the airboat idea. We actually built a prototype air boat and drove it in the pool.:D

Jared Russell

06-01-2009, 16:58

To those that think that vertically-oriented fans for downforce are illegal because they alter the maximum tractive force your robot can achieve:

Say you have a robot with a heavy weight on a vertically moving elevator. The weight starts low and can be lifted by a motor. As I lift the weight, my downforce is temporarily increased. If I had a 120 lb robot to start, my weight exceeds 120 lbs when I am in the act of lifting. In fact, any time I change the robot CoG, I alter my apparent weight on the playing surface. If I then lower the mass, my apparent weight decreases. Try it for yourself - stand on a bathroom scale holding a textbook, and watch your weight TEMPORARILY change as you lift it up and down.

Changing the altitude of my robot's center of gravity is something that is allowed. Are we to believe that if your robot will be lifting anything this year, you must account for it in your weight?

-Jared

rilesmitch

06-01-2009, 22:17

While I agree that using a fan is VERY questionable due the fact that we are "working on the moon" However if you back and look at the moon rover built and used later on (ask your dad about) T

hey used steering technology from JI CASE (crab steer) and the tire technology I think came from Goodyear. They used a tire that was basically a "wire basket". Take a look, they were way cool!

I found my bucket.... it has a hole in it!

EricH

06-01-2009, 22:22

Justin Stiltner

06-01-2009, 22:35

So sayith first... and so it shall not be done.
But boy it would have been cool.

GregT

06-01-2009, 23:07

With this being said, I would think that this wonderful concept has deemed itself invalid due to one simple fact- if at ANY MOMENT IN TIME you place scales under your machine and they read more than 120 lbs (excluding battery and bumpers of course), IT'S ILLEGAL! And if this concept were put into play and this isn't true? It's completely useless...Just bolt a piece of steel to it...it's much more energy efficient! ;)

So my 120 lbs robot is not allowed to pick up any balls? If a robot carries a lot of balls it will have a greater normal force and more traction.

The rule referenced seems to be talking about weight, which by definition is a force due to gravity. Pushing off other objects (such as air with a fan) will result in a greater normal force, not weight.

Back in 2002 there were a lot of robots capable of lifting the primary game piece (a movable goal) specifically to gain normal force for traction. If my memory serves me, this resulted in a lot of torn carpet- but it was legal that year (R29 seems to prohibit similar strategies this year).

Kevin Sevcik

07-01-2009, 02:36

Ah, well. Bill has beaten us.
3) Don’t spend time attempting to develop a vacuum car system like Jim Hall’s sucker Chaparral car. Even a slight suction over the base of the robot will damage the field surface and you don’t want to do that (See the 2009 FIRST Robotics Competition Manual section 7 rules G-29 & G-30)
I'm not questioning whether the GDC is going to come eventually outlaw vacuum systems if Bill thinks they're going to outlaw it... But that sounds like a pretty specious justification right there. Especially as you're only penalized for damaging the arena if you damage it. If you can prove you won't damage it, then you should still be allowed to operate under that reasoning.

Matt H.

07-01-2009, 02:44

Bill's Blog is actually quite encouraging for vacuum proponents. If you can design a system which doesn't damage the field then Bill's blog implies that it would be legal.
As for the working on the moon argument--on the moon you could stick on some hydrazine thrusters, but you obviously can not do that in FISRT. There are differences between the playing environment and the moon.

DonRotolo

07-01-2009, 21:42

You can't use fans on the moon since there is almost no atmosphere on the moon. We'll be competing in Trenton, NJ, which (last I heard) has an atmosphere. And the rules don't say we can't use it.
then its just p=mv with some lost to heat and deformation.With a tiny bit more to noise...:D
one simple fact- if at ANY MOMENT IN TIME you place scales under your machine and they read more than 120 lbs (excluding battery and bumpers of course), IT'S ILLEGAL!
Oh really? As others have said, if I were to shoot seven moon rocks straight up in the air in 1 second with my 27x37x59 inch robot weighing 120.0 pounds, for a brief time the normal force my robot would exert upon the arena floor would exceed 120.0 pounds. This is perfectly legal, and if you disagree show me the rule.

When they weigh my robot, it is powered off and without a battery - by definition they are not measuring the normal force, they are measuring WEIGHT.

At this point, the argument against using a fan to push you down* is specious at best, and bizarre in my opinion. (*Think of a fan mounted at the 50 inch level - no suction on the floor involved). But, I also admit that I wasn't even thinking of implementing this at any time.

OK, so my original post was about using fans to propel a vehicle horizontally like a swamp boat. Our current progress is measuring the forces this can generate. We will absolutely also be using a conventional drivetrain - as someone said in the Hovercraft thread, why give up what propulsion you can get easily? My thought is to double the propulsive force offered by the wheels, and I am looking for a 12" fan blade with which to experiment.

Don

minisimon

08-01-2009, 00:04

Running with Don's return to the original post:

238 ran a test that involved attached a 16" diameter RC airplane propeller to the output shaft of a Fisher Price motor. We rigged it to a digital bathroom scale with 0.5 lb resolution, put our safety glasses on, and turned it on. Registered weight difference: 0 lbs.

Now, there are a variety of things that we could have done wrong. It may be that the battery wasn't fully charged, our scale wasn't one of quality, or that our motor had seen better days. We definitely weren't operating the propeller at its ideal rotational speed or airspeed. These are issues that we would love to pursue, but we're going to focus on wheels first. Let us know what you find out. Good luck!

hipsterjr

08-01-2009, 00:33

I was a proponet of the fan boat idea untill I took an old twin radiator fan out of a dodge and tried to blow a cell; it didn't move. The cells have too many holes that let air thru. So blowing balls away looks a little busted. Although last year they said the same thing about launchers and shooters and see how that turned out:p We'll see, someone will find a way lol;).

*after thought* : if could have been because I was using a dodge fan. everyone knows those things are weak:cool:

GUI

08-01-2009, 00:36

*after thought* : if could have been because I was using a dodge fan. everyone knows those things are weak:cool:

As long as it wasn't powered by a Dodge starter motor ;)

Justin Stiltner

08-01-2009, 01:41

The problem with your 16" prop especially if it was directly on the output of the FP was you had way too much prop diameter there. If you were to put the same on the CIM you would see a difference, and if you gear the CIM up by oh 1:2 then im guessing you may see even more. However, a reduction in diameter doesn't equal a increase or reduction in pitch of the prop in all cases either.
for instance try turning your 16" prop at around 4000rpm or more and see what it does!

this video
http://www.youtube.com/watch?v=ccGVZRG8DdM
shows 26" diameter blades, variable pitch up to 10 degrees or so, and a motor consuming 350 watts and that heli weighs about 1.87lb and normal rotor speed for those is usually near 3000 rpm
Here a slightly lighter heli lifts 2000grams, thats 4.4lbs plus its own 1.5lb weight. using an 11.1v battery and a 35A speed controller so he had 388W of power, granted using a brush less motor. This would be the coolest thing... both to see and feel.. thats some major air movement!!
http://www.rcgroups.com/forums/showpost.php?p=11256442&postcount=12275

EricH

08-01-2009, 19:59

OK, so my original post was about using fans to propel a vehicle horizontally like a swamp boat. Our current progress is measuring the forces this can generate. We will absolutely also be using a conventional drivetrain - as someone said in the Hovercraft thread, why give up what propulsion you can get easily? My thought is to double the propulsive force offered by the wheels, and I am looking for a 12" fan blade with which to experiment.

DonIncidentally, the GDC has allowed using propellers on the robot in Q&A (http://forums.usfirst.org/showthread.php?t=10918).

Still no word on making a nice big downforce, but one thing at a time.

gorrilla

08-01-2009, 20:58

im still leaning towards our chepo-swerve drive.....

another problem with fans is they would take up lots of space for ball collecters ans such....

GUI

08-01-2009, 21:32

A few members of our team calculated how much thrust we could get with a leaf blower (reconfigured to run on kit motors), and with 2 1/2 hp (2 FP's and 2 CIMs) it would barely provide more thrust than possible with the wheels. This is with a 120 CFM, 150 MPH (iirc, but I know it was that ballpark) blower. For such a small advantage, this would be a very dangerous system (fast moving air + any debris/dirt/unprotected eyes = bad situation).

DonRotolo

08-01-2009, 21:39

Still no word on making a nice big downforce, but one thing at a time.IMHO I don't think that trying to create downforce will bear much fruit. Use that force for propulsion instead.
and with 2 1/2 hp (2 FP's and 2 CIMs) it would barely provide more thrust than possible with the wheels.Indeed. So if we take this one step further: Mount the leaf blower AND use driven wheels... then you'd be something like twice as fast maneuverable as anyone else... Think that'll bring any advantages?

Kevin Sevcik

08-01-2009, 22:20

I don't think leaf blowers are the appropriate model for an air-based propulsion system for a robot. They're very much about accelerating a fairly small amount of air to rather high velocities in as small a space as possible. They generally do this by generating a (relatively) high pressure differential using an impeller. This isn't nearly as efficient at producing thrust as something like a propeller or fan. These are designed for moving much larger masses of air, but at somewhat lower speed and vastly smaller pressure differentials. So, I think you're much more likely to generate a useful amount of thrust with fans or propellers, as opposed to leaf blowers.

EricH

08-01-2009, 22:33

The Q&A question referred to a model aircraft propeller in a "ducted fan" configuration. If you can do it...

ShadowNinja

08-01-2009, 22:34

Actually none of this is neccesary..the floor is drivable..you just need to think how to use it too ur advantage

ZakuAce

09-01-2009, 08:17

minisimon

09-01-2009, 08:59

Hi Justin,

I'm going to admit that I'm confused by your apparent suggestion that the FP motor spins slower than the CIM. I believe that the CIM's no load is around 5,000 RPM, while the FP's is around 15,000 RPM.

I think that the helicopters have two big advantages - variable pitch and more efficient motors. The variable pitch rotors allow pitch adjustment to match their current airspeed; our prop was optimized for some airspeed greater than 0. I believe that the brushless motors that RC planes and helicopters use are more efficient than our brushed motors. Although the CIM and FP can consume 480 W legally, they only output ~200 W at sustainable currents according to their curves.

Working from this, it makes sense for someone to try and get their hands on a variable pitch prop and try it with a couple of motors, eh?

xxsumz

09-01-2009, 09:08

this idea is amazing. just needs a prototype for testing

Justin Stiltner

09-01-2009, 11:09

What I really meant by saying use a cim was that a FP motor cannot direct drive the prop that you had on the shaft. A prop could be sized for that motor and would be very small relatively 3" or less most likely. The CIM however has more torque directly on the shaft at a slower RPM and would be more likely to be able to direct drive this prop, however it would most likely be too slow also.

If you could measure the speed of that prop on the FP motor Im sure it wasn't going nearly as fast as it needed to be.

If you read back in some of my posts here I do suggest using a model heli head assembly as your variable pitch prop setup. Or even the tail rotor assembly form a rather large model heli, would be a bit simpler to implement.

I do however agree that the motors available to first are less efficient, and never disputed that. I dont expect to see the same amount of power output from these as from a brush less motor. I would also not think of using only a prop as propulsion, only as an aid to propulsion, I think ever little bit will help this year!

EDIT: reading MINISIMON's post agian, wow I didn't realize that those motors were THAT inefficient.

Selijdice

09-01-2009, 12:44

In '06 we were contemplating a robot with fans that would sit underneath the goal and attempt to blow the poof balls away. The poof had a bit too much mass, but in this application.... it will be interesting to see how much air movement is required to deflect an orbit ball.

Of course, once you've got the fans, you could also use them to suck air from underneath the robot to increase your traction.

Safety is a concern, of course.

Jason

My team (3013) tested what is the lowest wind speed need to move the orbit balls. We used a little wind tunnel that is used for model rocket wind test. We found that it was around the wind speed was around 5.2, but that just slightly moved the orbit ball. but i belive if you can get a small fan that can produce a wind speed of a little more than that then it would work. The only problem that my team sees with the fans is that it might interfere with driving the robot. But we have not build and tested one yet but hopefully we will have our prototype done by tuesday or wednesday of next week. When we get it finished and tested I well post the results.

Mentor #2340

09-01-2009, 14:23

What about compressed air? Rather then fighting friction with driving wheels. Of course you will need a well built machine for the increased collisions. Use the walls-think billards!

nathanww

09-01-2009, 20:45

In '06 we were contemplating a robot with fans that would sit underneath the goal and attempt to blow the poof balls away. The poof had a bit too much mass, but in this application.... it will be interesting to see how much air movement is required to deflect an orbit ball

Team 1678 tested this with a leaf blower--basically there are a cpuple of problems

The air has to be moving pretty fast to actually safely get the ball away from the trailer. The only way we were able to do this was by colimating it so tightly that it wouldn't be very useful anyway
It's only effective against shooters--if the ball is dumped into the trailer it doesn't have enough time to pick up velocity
The trailer has to be free to move, which means that you either need to track it or have a HUGE jet of air

Theoretically, you could solve all these problems just by moving enough air--but that might be a bit impractical.

DonRotolo

09-01-2009, 23:19

Actually none of this is neccesary..the floor is drivable..you just need to think how to use it too ur advantage
I agre with this. I believe getting every little bit of traction from the wheels, make them all powered, steer, and just practice driving a lot.Yes, and having an extra 50% ability to move about could be of no advantage whatsoever

The nature of the competition is to creatively solve problems to gain an advantage while maintaining compliance with the rules. If I can get going better and out-maneuver you easily, I can drive around you and dump my orbit balls into your trailer while you're still trying to get up to speed.

Who do you think more likely to win a match under this contrived situation? And who do you think is more likely to end up in Atlanta, the team that wins all its matches, or the team that doesn't?

writchie

10-01-2009, 01:21

Our best numbers at the moment are that realistic static thrust could be on the order of 27N/kw.

The kilowatts are mechanical power. Input power to the motor is irrelevant. The peak power point on the CIM's is 337 watts but that takes 68 amps and 12V and we have neither.

A pair of CIM's operating at 40 amps each could produce about 0.4 - 0.5kw net on the shaft for a static thrust of about 10N - 13N. You can get these numbers only by matching blade size, blade angle, RPM, and torque. Motors produce maximum power when torque is 1/2 the stall torque and speed is half the no-load RPM.

I caution teams that airplane propellers are designed for flight. The blades are usually stalled until moving at considerable forward speeds. Same for most ducted fans. Large helicopter rotors may be the best bet and have the advantage of adjustable blade angle.

Jared Russell

12-01-2009, 12:37

Well, the GDC giveth, and the GDC taketh away (http://forums.usfirst.org/showthread.php?t=11025).

Any vacuum/suction/fan system that alters the traction characteristics of the ROBOT would be considered a violation of Rule <R06>.

And just like that, a little bit more room for innovation is taken away.

Brad Voracek

12-01-2009, 13:18

Well, the GDC giveth, and the GDC taketh away (http://forums.usfirst.org/showthread.php?t=11025).

And just like that, a little bit more room for innovation is taken away.

The way I read that rule is that using it for -traction- I haven't read the entire topic, but you could still use a fan for propulsion, as long as you have wheels on the floor.

You can't just create a low pressure surface under your robot to keep it from moving, as someone else suggested somewhere on CD, however.

Justin Stiltner

12-01-2009, 15:40

Im really not surprised in this ruling, however, I am surprised that they used that rule to do it. I thought if they did they would use the possible damage to the field rule. but in any case, this will probably be better for the health of the nearby persons... lots of plastic dust will happen this year!

EricH

12-01-2009, 17:24

The way I read that rule is that using it for -traction- I haven't read the entire topic, but you could still use a fan for propulsion, as long as you have wheels on the floor.

You can't just create a low pressure surface under your robot to keep it from moving, as someone else suggested somewhere on CD, however.Brad's right.

The recent ruling is that use for traction is illegal.

There are three other rulings relating to this topic, however. One governs use as goal-blocker. This is allowed. The other two govern propulsion. This use is allowed.

But using a fan or vacuum to increase normal force is out. If you show up at a regional with that sort of system, you'll need to remove it or face the inspectors with <R06> and the refs with <S04>.

Kevin Sevcik

12-01-2009, 18:02

Brad's right.

The recent ruling is that use for traction is illegal.

There are three other rulings relating to this topic, however. One governs use as goal-blocker. This is allowed. The other two govern propulsion. This use is allowed.

But using a fan or vacuum to increase normal force is out. If you show up at a regional with that sort of system, you'll need to remove it or face the inspectors with <R06> and the refs with <S04>.The ruling makes use as a goal blocker a rather lot more difficult, however. You'll have to mount any such goal blocking device horizontally, as any vertical inclination is going to increase your normal force. And that's going to seriously reduce the effectiveness of such a device.

writchie

17-01-2009, 22:13

Our tests today using the 9015 FP motor direct driving an 11 x 4 prop produced 1.6 lbf of static thrust with a motor voltage of 9.6 V rms. The voltage was low due to much longer than normal wire lengths for safety reasons. The test setup was jaguars driven from the cRIO.

Scaling things to to proper voltages and a better prop we now believe that 4 lbf is readily achievable with a pair of FP motors and off the shelf 11x3 props.

With props custom designed to extract the maximum power and thrust from the FP motor, our calculations show that a pair of FP's could produce more than 8 lpf of thrust.

Andrew Y.

24-01-2009, 22:35