Re: HDPE or ICE FLOOR
 

We certainly know the idea has been floating around in the GDC's heads for a few years:


http://www.chiefdelphi.com/media/photos/22422
:p

Re: HDPE or ICE FLOOR
 

Oh man, talk about putting images in my head!!

Most of all, I keep seeing Dave's "Boot-Drive" robot that keeps showing up in his game animations. Every year a drive train like that hit's our design considerations process. Every year we laugh, then move on to more serious concepts. Maybe this year we will consider it a bit more seriously. Hey, take a look at the new Vex leg wheels. It makes you really think:rolleyes:

Re: HDPE or ICE FLOOR
 

Except played with a ball instead of a stone?

Re: HDPE or ICE FLOOR
 

Ahhhh....that explains the first part of Game Hint #2!

Re: HDPE or ICE FLOOR
 

More like hockey played with brooms and a nice big ball (say, a little smaller than a playground ball). Oh, and you don't wear ice skates. The groups I've played with used street shoes. Evidently, that isn't the only way to do it.

Re: HDPE or ICE FLOOR
 

Like I said earlier, surface area doesn't matter.

HDPE and ice are as close as possible to an "ideal" surface from a physics standpoint. The reason surface area might matter on carpet is because the tread can interlock with the carpet.

On ice or HDPE the surface is totally slick, so there is no possible way for the tread to interlock with the HDPE, and thus surface area does not matter, only coefficient of friction and normal force.

Re: HDPE or ICE FLOOR
 

HDPE is what milk jugs are made of. We have made several robots out of HDPE. Very easy to work with and we keep lots of it on hand. Very strong and durable.

Re: HDPE or ICE FLOOR
 

For the stack attack game, we found that McMaster-Carr Grip all neoprene rubber had very good traction on HDPE. Our problem was that it gripped to well on carpet (4" wide wheel). If we had less width and more power than the drill motors it would have worked well.

Re: HDPE or ICE FLOOR
 

the conveyor belts they make are for moving bags around an airport, they are a like tiny little plastic plates with rubber tread on them, were you thinking like timing belt kinda thing?

Re: HDPE or ICE FLOOR
 

Traction is directly related to frictional force. Force = mu * N, where mu is the coefficient of friction and N is the normal force (force directed directly away from a surface that something with friction is on). Notice the lack of area in that equation? Yep, there's a reason for that. Namely, surface area doesn't matter.

There's been discussion of this issue already, some years ago. Look it up.

And, the only way to increase mu is to increase the coefficient of friction. You can a) change materials or b) dig one material into the other. If you try doing b) to an HDPE section of the field, I'll call a rules violation, assuming there is a "no damaging the field" rule again.

Re: HDPE or ICE FLOOR
 

i know, i think ive read that......

i was thinking treads becuase i felt they would give the most stable platform on a slick surface

really its either that or wheels, and i dont think they would make the entire floor HDPE.........

Re: HDPE or ICE FLOOR
 

Ah, stability? Again, not determined by surface area. It's determined by some other things, like CG and wheelbase.

Let's say you have a rectangular robot at max dimensions, with the wheels (or treads) a little bit inside the max. It looks like this:
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That's the wheelbase as seen from the top. As long as you keep your CG above that area, you won't tip. As soon as the CG goes outside that area, you've got a split second to get it back before the big crash. If you have treads, you'll still have the same area.

Re: HDPE or ICE FLOOR
 

ah, wheelbase(couldent think of the word for it) thats what i meant......

i never implied that they were going to be wider than a wheel..............

there like this
http://www.chiefdelphi.com/media/photos/28106

except flat

Re: HDPE or ICE FLOOR
 

Erich - Don't forget to remind your audience that inertia exists, and that it makes a moving robot do things that a stationary robot would not (like tip over even if the CoG is within its wheelbase)...

Re: HDPE or ICE FLOOR
 

Oh, Newton's first law?:p

That is true, especially if there's a sudden stop or change of angle involved. See, in physics (and in Statics), you can usually get a really, really good approximation of forces and how they'll react with each other by finding the CG and having all the forces act from that, unless you're dead sure that the force acts elsewhere (like friction, which gets as close as it can to the floor, or an impact from another robot, which should be within the bumper zone).

If you've got a robot traveling at constant speed, the only forces acting on it are weight, the normal force (cancels out the weight), friction (applied to the wheels) and whatever force you need to maintain equilibrium (applied to the wheels). Now, a sudden stop! The force needed to maintain equilibrium has been effectively distributed through the robot, and there is a sudden forward force at the CG (for simplicity--there's a rule saying I can move it there, I just forget which one) and a reverse force on the lower section of the frame. This creates a moment, causing the robot to rotate forwards. If a corrective force is not applied, the robot continues to rotate and goes splat. This effect is not helped if the CG is high, as there is now a much bigger "lever" for the forward force to act on, and it takes much more force to stop due to the way moment is calculated.