How can we drive on this new floor?

[dtengineering]

One thing to watch for when designing the robot is turning ability when using skid steering (tank drive).

If you notice the coefficients of friction for the wheels, you will see that inline dynamic is .05 while transverse dynamic is .10. In a skidding situation the wheel will be twice as resistant to going sideways as it is to going forwards....

That means, as I read it, that your wheel is not going to want to slide sideways very easily if you use 4wd tank drive.

In fact anyone planning on going with skid steering will probably want to really look at using at least six wheels to minimize the amount of skidding required in a turn.

Jason

[writchie]

Originally Posted by dtengineering

One thing to watch for when designing the robot is turning ability when using skid steering (tank drive).

If you notice the coefficients of friction for the wheels, you will see that inline dynamic is .05 while transverse dynamic is .10. In a skidding situation the wheel will be twice as resistant to going sideways as it is to going forwards....

That means, as I read it, that your wheel is not going to want to slide sideways very easily if you use 4wd tank drive.

In fact anyone planning on going with skid steering will probably want to really look at using at least six wheels to minimize the amount of skidding required in a turn.

Jason

It may be even worse than it first appears. Unless you've already broken traction, skid steering has to overcome what could be as high as the static transverse friction (if you want to turn as you are starting out). At first glance it appears 6 wheel drive raised center is the way to go for skid steering (whether tank mode or joystick mode on the controls). Also the abnormally high differences between static and dynamic coefficients is probably worth a bit more analysis. In past years static vs. dynamic and inline versus transverse were relatively minor differences that could often be more or less ignored. Not so this year. Don't count on being able to control the bot until you do the math

[Raul]

Originally Posted by markulrich

...
Has anyone felt the new playing surface? How much does it cost? Would plane old hallway concrete be a suitable substitute?

We bought two 4' x 8' sheets of that "ice" material ($30 per sheet) for the floor and did some testing. We compared traction on the "ice" the carpet and plain old tiled floor. The ice was the slickest. The carpet was slick but not as bad. The tile was surprisingly almost the same as the ice. So, to answer your question, if you cannot afford to buy some of the ice material, use a tiled floor as your best simulation.

[gburlison]

Originally Posted by Raul

We bought two 4' x 8' sheets of that "ice" material ($30 per sheet) for the floor and did some testing. We compared traction on the "ice" the carpet and plain old tiled floor. The ice was the slickest. The carpet was slick but not as bad. The tile was surprisingly almost the same as the ice. So, to answer your question, if you cannot afford to buy some of the ice material, use a tiled floor as your best simulation.

Did you collect and numbers to help us compare?
I was thinking that we might stretch a large sheet of plastic over a tile floor and tape down the edges. If the plastic is thick enough, hopefully the robot will not wrinkle and tear it long enough to practice.

[sdcantrell56]

So does anyone want to chime in about using these wheels as omniwheels. Would it even be possible. I am feeling slightly lost since all of my preseason designs involved mega-traction and multi-speed high torque transmissions

[dtengineering]

Originally Posted by sdcantrell56

So does anyone want to chime in about using these wheels as omniwheels. Would it even be possible. I am feeling slightly lost since all of my preseason designs involved mega-traction and multi-speed high torque transmissions

Omniwheels are specifically designed to have a lower coefficient of friction in the transverse direction than in the inline direction.

These wheels, according to the manual, have a transverse coefficient of friction that is about twice that of the inline direction. They are, by my reading... anti-omni wheels.

Jason

[GaryVoshol]

Originally Posted by Raul

We bought two 4' x 8' sheets of that "ice" material ($30 per sheet) for the floor and did some testing. We compared traction on the "ice" the carpet and plain old tiled floor. The ice was the slickest. The carpet was slick but not as bad. The tile was surprisingly almost the same as the ice. So, to answer your question, if you cannot afford to buy some of the ice material, use a tiled floor as your best simulation.

Did you do any testing on terrazzo floors? (The stuff where a slurry is poured, and then polished after it hardens)

[gorrilla]

Originally Posted by Thermal

There is another rule stating that the wheel's rotation MUST BE inline with movement of the bot, so that the axle the wheel is on is perpendicular to the bot and wheels movement

could you find this and link to it?

[Racer26]

Originally Posted by gorrilla

could you find this and link to it?

Originally Posted by FRC 2009 Game Manual

<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

Seems to me it says nothing about requiring the wheels be oriented so MOTION is in the direction of the tread, only that they be mounted with tread touching the floor (i imagine to foil us lateral thinkers that might try to cantilever the wheels and use the flat face of them to try to move forward)

[Branden Ghena]

Originally Posted by 1075guy

Seems to me it says nothing about requiring the wheels be oriented so MOTION is in the direction of the tread, only that they be mounted with tread touching the floor (i imagine to foil us lateral thinkers that might try to cantilever the wheels and use the flat face of them to try to move forward)

Darn, the first thing I thought was that we should make a walker bot using the wheels sideways.

[Zyck_titan]

It seems to me that heavier Bots will do a lot better, and I'm sure everyone will be maxed out on weight, so the question is how do you add weight....without adding weight.... *Hint hint Nudge nudge*

[thefro526]

Originally Posted by Zyck_titan

It seems to me that heavier Bots will do a lot better, and I'm sure everyone will be maxed out on weight, so the question is how do you add weight....without adding weight.... *Hint hint Nudge nudge*

That's an easy assumption to make.

But what about momentum? Changing directions with a heavier bot it's going be be a bit harder I think... Or maybe not, I'd like to get some input on this.

[Zyck_titan]

Originally Posted by thefro526

That's an easy assumption to make.

But what about momentum? Changing directions with a heavier bot it's going be be a bit harder I think... Or maybe not, I'd like to get some input on this.

Well what if you could control how much you wanted, you know actively change from a heavier bot to a lighter bot in the middle of a match, you could start moving by being light, "make" yourself heavy if you don't want to be pushed etc.

I do have an idea for this, but I'm trying to stimulate the thinktank, see what else people come up with

[gorrilla]

car steering might make a comeback this year......seeing as how tank drive wouldent turnas well,(drifting around with the trailer would take some getting use to though)

[DanL]

Some quick suggestions off the top of my head:

Giant Flywheel. For resistance to bumps and bruises, spin up a giant flywheel to help you conserve momentum.

Traction Control. This was mentioned before, but I'll summarize the idea of a traction control system. In a car, you compare the speed of the powered wheels to the unpowered wheels. If there is a difference, that means one set is slipping while the other isn't. The computer cuts a bit of power to the driven wheels until both spin at the same rate. For a 4-wheel vehicle, you can use an accelerometer to get the differential measurement.

Mariocart for Driver Training. Mariocart invented drifting. Blue sparks may be a safety hazard, though.

Pneumatics as Thrusters. Satellites use gas thrusters to control direction. If the surface is low enough friction, this could act as a nice stability augmentation.

Antilock Brakes. Antilock brakes don't necessary cut down on braking distance, but rather they give you control WHILE braking. If you slam on a car that doesn't have antilock brakes and you lock the wheels, the car basically keeps moving in the direction of its momentum vector, regardless of which direction the steering wheel is pointing (conservation of momentum). With antilock brakes, you're switching between static friction and dynamic friction, and in a nut shell, this gives you some control (ie allows you to swerve around the object you're braking for).

Physics 101. Actually, Physics 8.01. For the truly adventurous, check out Walter Lewin's physics videos on MIT's OCW, specifically the lecture dealing with friction. http://ocw.mit.edu/OcwWeb/Physics/8-...il/embed08.htm. This is roughly equivalent to an AP Physics class.