Propulsion that does not involve driving wheels

[R3V34L]

Originally Posted by EricH

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]

Originally Posted by R3V34L

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]

Originally Posted by EricH

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]

Originally Posted by EricH

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]

Originally Posted by ebarker

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]

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]

Originally Posted by comphappy

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]

Originally Posted by Rossetto07

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]

Originally Posted by dtengineering

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.

We tried this in 2006 as well, with results that weren't quite good enough to implement.

[AlexD744]

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.

[Jared Russell]

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]

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]

Ah, well. Bill has beaten us.

Originally Posted by Bill's Blog, today

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)

[Justin Stiltner]

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

[GregT]

Originally Posted by Steven092391

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).