Hovercraft
 

I know that this has crossed other teams minds and so I'm just going to throw it out there. It comes down to who can build and control it better anyway...

Rule R-06 states that we must use the wheels provided to "provide traction between the ROBOT and the ARENA." However if we throw caution to the wind and think about the idea of a hovercraft the shirt used to hover doesn't provide traction, it reduces traction. Then fans provide thrust.

This would normally make you more easily pushed but this year everyone is going to be getting pushed around (I've seem the math, with wheels alone you simply cannot get more traction). This could give you more maneuverability and better control of your bot (and with four CIM's available and a compressor I'm sure it's doable).

Is it allowed?
Would it work?
Am I crazy?

Re: Hovercraft
 

Try it out and tell us how it goes. [=

Re: Hovercraft
 

From what my team talked about, and this may not be right, but the way we interpreted it is that they would probably get you on the friction between skirt and the ground. It definitely seems like as far as moving components, they don't really want anything touching the ground, except manipulator parts or w/e.

Of course, I'm not authority, this would be a question for the GDC when the forums go up if you really can't find anything about it in the manual.

Re: Hovercraft
 

Also you have to remember that you are dragging a trailer, that will be pulling you down, and I think that has to have wheels, which can make it for a vulnerable bot.

Re: Hovercraft
 

From my point of view, at the start of the match, your skirt will be touching the ground and thus be considered as providing friction between the robot and the arena, in violation of <R06>.
Not to mention, I don't see much advantage in having a hovercraft. You're better off with rover wheels, in my opinion...you might be able to get up off the ground, butI doubt the fans you're going to use for thrust will get you very far. Granted, I've never messed with many hovercrafts, so I can't say anything on that for sure.

Re: Hovercraft
 

I think a pure hovercraft would be a silly idea. Throwing away the traction that you ARE allowed from your wheels and opting instead for an even harder to implement and control drive system doesn't seem like the right idea.

However, using a fan to augment your acceleration and deceleration might work. The wheels can only give you a maximum of about 26.7N of acceleration¹ force. If you build a fan that's good for a few newtons of thrust², then that can be a substantial increase in your robots straight-line handling, allowing you to outrun someone intent on dropping rocks in your trailer (and maybe even causing a bit of aerodynamic drag against them).

¹: Maximum mass of robot: 54.54kg. Weight = 54.54 * 9.81 = 535N. Maximum traction: ff = uFn -> ff = 0.05 * 535N = 26.7N

²I know nothing about fans. This may very well be outside of the possibilities for a 12V fan, but it would be worth running numbers on.

Re: Hovercraft
 

First of all, crazy is relative. For instance, for the next six weeks my relatives think I'm crazy. :)

It could, possibly, work. I figure that with wheels your maximum pushing force will be about 9 lbs (150x.06). More, of course, when you're on the carpet at the edge of the playing field, which may become a factor.

With proper gearing and blades, it would be possible to generate at least a few pounds of thrust using the CIMs. The catch, of course, is that you will have to put a serious safety cage around your propellors.

You will also have to have your motors running at pretty much full blast the whole time you are playing, and will actively have to stop your robot, rather than just relying on wheel friction to bring it to a stop.

So while a hoverbot would be extremely cool, I suspect it would offer more disadvantages than advantages.

But perhaps, if you take the hovercraft idea and run it in reverse, you might come up with an idea to give you an edge. Let's just say... what if your hovercraft.... sucks?

Jason

P.S. R06 states that "robots MUST use rover wheels to provide traction", so perhaps the hoverbots aren't allowed unless they have a token roverwheel touching the ground at all times.

Re: Hovercraft
 

I personally also brought that idea to the table, before the idea of a hovercraft. But after reading R06 a few times a vacuum under the bot would be considered a "traction device" would it not?

Re: Hovercraft
 

This is a question that should be posed to FIRST, and I hope they vote in the affirmative that you can make a hovercraft.

And to pose the question as to if we can suction ourselves to the floor is another good question.

Re: Hovercraft
 

To continue this train of thought and get an idea of what would be possible. Note that neither of these would be legal:

A $2600USD model aircraft jet engine puts out 59N: http://www.trimair.com.au/index2.html. However, it is petrol powered and obviously illegal.

A $740 set of ducted fan components can put out 13-15lbs of thrust (57.9N), but uses a minimum of 3200 watts, which is 6.6 times how much power a FIRST robot can use.

Re: Hovercraft
 

You could put free rolling wheels under the skirt so that on start-up, the skirt lifts the robot off the wheels. Also you could use several of those silver motors to power a centrifugal fan similar to this one. They are commonly used in commercial hovercraft and are more efficient at this task than a vacuum or a typical fan partially because it disperses the air evenly. Then use 2 cim's per fan for propulsion in a dual rear fan set-up.

Here's the type of fan I'm talking about.

Re: Hovercraft
 

I'd tend to think of it as a "normal force increasing device". Technically the vacuum would not provide any traction... it would merely increase the force acting on the wheels allowing them to provide enhanced traction.

I believe the Q&A needs to answer this one, though,

Jason

Re: Hovercraft
 

F1 buffs will get this one.



:yikes:

EDIT: Hmm, where did the picture go? Err, anyway...
en.wikipedia.org/wiki/Brabham_BT46B

Re: Hovercraft
 

I like that logic. Let me ask, to get a good vacuum would you need to touch the surface of the playing field or would you be able to make a duct that comes very close to the surface but does not touch?

Re: Hovercraft
 

I would think touching the surface would be required to gain significant benefit from it, however, it might just be a use for all those banebots/FP motors my team never finds a use for, if the Q/A determines its allowed (which i think is unlikely)

Re: Hovercraft
 

When does the Q&A open anyway?

Re: Hovercraft
 

The rules say somewhere (now with edit) that you cannot attach yourself to the arena surface.


<G29>
Arena Interaction –ROBOTS may push or react against any elements of the ARENA, provided there is no damage or disruption of the ARENA elements. With the exception of a ROBOT towing a TRAILER, ROBOTS may not grab, grasp, grapple, or attach to any ARENA structure

Re: Hovercraft
 

To finalize my discussion with myself about fans to augment your own acceleration, I found one designed for a maximum of 300 watts, which is in the range that a FRC robot can legally put out. It puts out 4 newtons while spinning at some mind-boggling RPMs. It would sound really cool spooling up.

So you'd have a drive motor running continuously at near-maximum output for 4 newtons of forward force. Maybe I'm not looking in the right places (after all, R/C fans are designed for applications where they are moving through air quickly), but that seems like it'd be too little force for a hovercraft to be effective.

You could build very light if you wanted maximum acceleration, but you're still hauling a big trailer behind you and you'd lose pushing matches because your absolute pushing power would be lower (you'd lose your wheel traction in proportion to your weight loss).

A maximum-weight robot would get a 15% acceleration boost by using this little fan, assuming it would be a legal thing to do, you could rig a motor and gearbox to the fan, and the constant 300 watt drain wouldn't greatly impair other robot actions.

Here is the fan: http://www.modelflight.com.au/rc_mod..._micro_fan.htm

Re: Hovercraft
 

Definitely an interesting idea, but i was wondering how you were going to get past (R18) which defines the height that the trailer must be attached to the robot - 2 and 13/16ths to the center of the Trailer Hitch from the floor., doesn't sound like it can be "floating" at different heights... which I think would occur, also they mention that it has to be rigidly attached to a fixed locations.
:yikes:

Re: Hovercraft
 

to keep going:
Thrust = mass flow * velocity
Power = (1/2) mass flow * velocity^2

For a given thrust, we could pick any combination of mass flow and velocity, but to minimize energy used, we want greater mass flow and less velocity.

max power for a single FIRST motor is 480 watts (12V * 40A). call it 500W for round numbers. So for 50 N you could do, for example, 2.5 kg/s air at 20 m/s. Now, to put this in perspective, 20 m/s = 44 mph. Seems a little high to me, but maybe not out of the question. Probably you wouldn't get anything faster than this. Now put 2.5 kg/s of air in perspective. That's 5.5 lb/s. Since a cubic foot of air has a mass of ~0.075 lb at standard temp and pressure, we need 73 ft^3/s. That's 4406 ft^3/min (scfm). That's a rather large number. Maybe not totally out of the question though.

So, unless I messed up the math, I'd guess that 50N of thrust could be achievable without violating the laws of physics or any FIRST rules, but I don't think it would be cheap or easy...

Re: Hovercraft
 

I did math myself starting with your equations and got the same answer, so you're probably correct.

Now, how big would the swept area on this hypothetical fan be? You've got a column of air 18.5 meters long (for my calcs) long passing through through every second, that contains 2.7kg of air, which is 2.11 cubic meters.

V = pi * r * r * h
2.11 = pi * r * r * 18.5
sqrt(2.11 / (18.5 * pi)) = r
0.19 = r = 19cm radius fan, or 7.5 inches. That's a pretty big fan, but not unusably big. This could be do-able, but the speed out the back and the CFM rating seems pretty insane. I searched for 4000CFM fans, and came up with stuff sold as "whole house fans", and I doubt that those would put out the kind of velocities needed.

Is this a correct calculation?

Re: Hovercraft
 

Don't want to get into all the math, I don't really remember it, but from fooling around with a human-carrying hovercraft a few years ago I have a couple of things for you to consider:

First: You have to be careful with the center of mass when using a hovercraft- any manipulators carrying over the curtains will tip it. Tipping makes the air curtain hit the ground (a rule violation) and will make your 'craft drift because of the uneven airflow.

And second: Yes a hovercraft will float the 120 lbs of robot. It will do so for awhile too. I remember using two car fans and the same 12 volt batteries we use now to carry myself as well as the weight of the actual craft and batteries (probably a little over 120 back in the day)

Re: Hovercraft
 

O.k. Being less far-fetched, from this I've gotten that using fan(s) to boost a drive trains output is possible but to cut out the drive completely is just stupid (or not prudent).

The hovercraft would have been sweet though. Oh well :)

Re: Hovercraft
 

I did the math a little differently and got 7.2 inches for the radius. Probably a round-off difference between you and me. If anyone was seriously considering this, it would probably be better to make the fan bigger, thus it could run slower.

Re: Hovercraft
 

I was thinking about this some more, and I realized the original spec of 50N is a bit ridiculous. Sure it would make your robot fast, but once your fan spooled up, you wouldn't be able to stop (without cutting and reversing the fan, which would take a long time). 5-10N as a booster would be more reasonable. I'd bet that 50N is more in the range of what an FRC robot gets on carpet, as it implies acceleration of nearly 1G for a max-weight robot. You'd have a 120lb rocket. (Edit: this is wrong. You'd have acceleration of 1m/s^2, which is nearly 10 times less than 1G. I need to go to bed).

I made an excel sheet to play with these numbers:
If you had a fan with a radius just wide enough to fit on the short length of your robot (35cm), you'd only need an output velocity of 3.1m/s for a 5 newton boost. It would only require 7.8 watts. For a 10N boost with the same fan, you need a 4.5m/s output. However, since a lot of that boost would get caught on the trailer (thus slowing you down), you'd need more.

Edit: But it occurs to me that a giant fan would pose an entanglement risk, and so probably isn't practical, if QA allows it at all.

Re: Hovercraft
 

Just for arguments sake, remember robots actually weigh about 150 pounds. The 120 base that passes inspection, plus a 13 poundish battery, plus 15 pounds of battery.

Also, can you provide some documentation about motor outputs? I though CIMs output about 300 watts. :confused:

Re: Hovercraft
 

I'm going by what we're allowed circuit-breaker wise. We have a 12V system with 40amp breakers. Thus, the most power we're allowed using for a single motor is 480 watts. Due to conduction losses, the most useful power we're allowed is a bit less than that, but it is in that region of power.

I don't know the specs for the individual motors, it is possible that 480 watts through one of the kit motors is impossible.

Re: Hovercraft
 

This might sound stupid but where would you go looking for fans / propellers? And what kind of gearing would get a CIM to spin the most efficient.

EDIT: Talking about using this to give a drive a little boost not to push an entire bot around.

Re: Hovercraft
 

This is an R/C fan that generates 4N, but spins at a pretty crazy RPM to do so: http://www.modelflight.com.au/rc_mod..._micro_fan.htm.

I think it would be worth your time putting a standard house fan on a physics cart and use a spring scale to see how much force it generates. Then you could maybe replace the house fan motor with a CIM and speed it up a bit.

Again, I note that you probably don't want to invest too time or money in this idea unless QA says it is legal. Their "only traction must come from rover wheels" rule could potentially be interpreted (FIRST has reached pretty far in their rule interpretations in the past) that you can't get thrust from fans either.

Re: Hovercraft
 

You're right, max output of a CIM is somewhere in the 300 W range. For these back of the envelope calcs, I was assuming 100% efficiency in the CIM motor (and in the gearbox, and in the fan). 12V * 40A = 480W is the maximum input to the motor. It's not 100% efficient. But, you could always use two of them put together if you wanted to...

Re: Hovercraft
 

This question has been vexing me as well. My good friend (http://en.wikipedia.org/wiki/Propeller) tells me that propellers max out around 80% efficiency. I'm afraid that we won't get anywhere near an optimum prop, so let's assume 10% efficiency with 300W of CIM, yielding 30 W. When your robot is moving at 2 m/s, 30 W should translate to 15 N, about 3 lbs. If you power your fan or fans with 2 CIMS, you get 6 lbs of thrust, which would make a nice adder to the 7.5 lbs you get from traction.

Now, if someone who knew what they were doing made the prop a mere 30% efficient, then they would have an additional 18lbs of thrust; enough to push anyone around.

Unfortunately, I have no idea where you would purchase or how you would design this propeller. There are some big RC planes out there, but I can't find much information on thrust produced or efficiency. Anybody have any leads?

Re: Hovercraft
 

This one is for EXARKUN666... You posted somewhere that you were unsure of the numbers that were used in the "LUNACY: initial game layout" in chapter 7. I realized that the <=7 on the carts and the 13-20 mean
the 13-20 is starting count for the moon rocks for that station 20 is max and if u load moon rocks on your robot before start, which max is 7, then that explains where u get the 13 moon rocks at start from, because you would have taken 7 from 20 to put on robot. And the <=4 is indicating that you will have 4 or less of the empty cells at start. I believe that you can load moon rocks and/or empty cells on your robot before start, but i don't see why you would put empty cells on your robot before start.

this is out of context from this thread but i could not find the thread that u originally asked about this so i quoted u here and posted here. Not to get off topic.

Re: Hovercraft
 

I think everybody's best bet as of now would just be to check out some hobby shops to get a look at propellers used for RC planes, copters, airboats or anything similar.

Re: Hovercraft
 

lol, i think it will be more like a game of air hockey

Re: Hovercraft
 

hey you guys, your thinking to hard...
You could do the opposite and get more grip... Like that model car that can go on the ceiling! I don't know if that would work... What do you guys think?:cool:

Re: Hovercraft
 

is the coeficient of friction independent of surface area under the present conditions

Re: Hovercraft
 

i think that someone already discussed earlier in this thread using a fan to generate downforce, effectively increasing the normal force on the wheels.

my question is, how would you calculate the amount of suction force that a fan can generate against a solid surface like the playing field? using drive motors to power a fan is really only worth it if there is a significant traction increase.

also, is it legal to generate downforce with a fan?

Re: Hovercraft
 

it is illigal to genarate downforce with a fan

Re: Hovercraft
 

I think you're not thinking hard enough, since you asked.
Yes, as coefficient of friction is a property of the interaction of two surfaces. But I think you want to know about pushing power, which theoretically remains the same because a larger area means a smaller force per unit area, but in reality a larger surface contact area means a very slightly increased pushing power.
Can you quote a rule please? Or is this speculation?

Re: Hovercraft
 

I've built hovercrafts before and let me tell you that by time your robot is all said and done, you won't be able to hover. I mean, it could be possible, but that would require so much power that it's just not plausible. I just seriously doubt that you could build a hover craft and efficiently complete the mission.

Re: Hovercraft
 

I'd like to see one of your hovercraft's, they must be crap. out of cim motors and first batteries i've built a hover craft that moves me around, and I'm not talking a hovercraft in the shape of a circle with a shop vac on the blowing port. a full blown movable steering hovercraft. (two cim motors on car radiator fans for lift)

after several years of building model hovercraft's more or less the exact same size as a first robot I'm positive you could lift a decent weight (i wouldn't do 150, it'll make it hard to steer) and move.

on this low traction force with a well maneuverable hovercraft and a driver who actually knows what their doing, that team could out run, out push and plainly out preform the wheels. in this low traction surface i have no doubt a 60lbs hovercraft with a a 20" fan could push a 150lbs robot with those wheels.

driving is sorta an art, like drifting, everybody believes they can do it, because it looks easy, but really once behind the wheel the most frequent thing done is a spin out or end swap.

now i do think it would be dumb to have a complete hovercraft, with the little traction, you want all you can get....not less. my idea is to have a standard chassis, but have some thrust fans with rudders, to get you up to speed faster improve braking and turning. are there any rules that this would violate?

Re: Hovercraft
 

If you wish to make a suction device tell me when you find a Unobtanium retailer because that would require something that both makes an airtight seal and has a µ=0

Re: Hovercraft
 

Well lets not assume you need 100% effcientcy.

Any lowering of air pressure under the machine will provided additional Normal Force. So if you had skirts that are within 1/2 inch you would get a reduced pressure when you started vacuuming air out of the area.
Have I done the numbers? no...
Is there a prototype in the works? Yes.

It may not provided enough of a difference to use but I can't dismiss it out of hand.

I suspect a week before we decide yes or no on the idea.

Re: Hovercraft
 

just a thought, but a hovercraft would provide a defensive advantage.
The fan could in theory push cells and rocks away from the trailer.

Re: Hovercraft
 

I dont think that the fan in the back would be a good propeller on its own, but used with the wheels it may give a minor advantage.

Re: Hovercraft
 

Would you mind quoting the specific rule?

Re: Hovercraft
 

It's pretty clear that anything that provides additional traction is ruled out by R06:

<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

Note the OR OTHER DEVICES INTENDED TO PROVIDE TRACTION.

Re: Hovercraft
 

I don't think that a downward force would be "creating traction" but be closer to "increasing" traction, which I guess depending on how you look at it could "create" traction.

Re: Hovercraft
 

I have to agree with T3H_K3YM45T3R on this one. If you consider any device that creates a normal force to be a traction increasing device, then ballast isn't allowed (actually, anything with mass isn't allowed). This doesn't seem realistic.

Re: Hovercraft
 

haha! If u get that working post up a video! People are craving to see if it works..:D

Re: Hovercraft
 

In the late 1960's, Jim Hall designed a racing car, the Chaparral 2J, that used auxiliary fans to create suction. It greatyl increased traction, so much so that the rules were changed to make it illegal.

Here's a photo of it:


Others have made smaller versions:



This technique would certainly be possible on an FRC robot, but the question is: would it be legal?

We'll have to wait and see what FIRST says.

Re: Hovercraft
 

there is no way the compressor/motors will be able to keep the skirt inflated AND provide thrust, its just out of the question, another thing to remember is battery power...

Re: Hovercraft
 

Actually, the first to use the fan concept was Jim Hall with his Chaparral 2J in 1970. Jim was a great innovator and most of the aerodynamic ideas used in racing today originate with him. His most successful from a winning standpoint was the 2E which used a moveable wing to provide downforce in corners but which could be leveled on the straights to provide minimal drag.

As usually happens, his ideas were proved so effective that they were outlawed after 1 or 2 seasons.

One of the things that happens in racing is that if you come up with a really brilliant idea, someone will try to ban it in the name of "level competition". As you write the rules tighter and tighter, there becomes less and less possibility for really great leaps of creativity...just think of NASCAR.

I worry that FIRST is going in that direction.