How can we increase friction and traction in our FIRST Robotics Team's robot?

[Sunny1261]

Hello Everyone,

I am on a FIRST Robotics Team. This year, the game has presented us with a new challenge. The playing surface is made of rough plastic, but the wheels are hard smooth plastic. Basically killing friction, or at least reducing it by 1/6.

Now, my question is how do I increase friction/traction. Note these few things that we must accomplish.

- Robot Cannot weigh more than 120 pounds.
- We can only use the plastic wheels.
- Only the plastic wheels can be touching the ground at angle perpendicular to the ground.

What we have so far:
- We know that we need to push the 120 pound weight limit and get the robot as heavy as possible.
- We know that a low center of gravity will help in increasing friction for the robot.
- We know that using a large number of wheels will increase traction, which will result in an increase in grip for the robot.


Any help is appreciated past what we have. I also have a couple more ideas, but I want to keep those off the forums.

Thank You
Sunny G.

 

[montoyas7940]

Would you be allowed to paint the wheels with rubber cement?

Edit: Or glue on some other sticky substance?

 

[Sunny1261]

Ah, sorry about the lack of information.

The wheels cannot be altered in anyway. The field cannot be changed/damaged in anyway.

If it helps, there is a 1 foot wide strip surround the plastic flooring around the rectangular field, but so far we've seen no purpose for it. But considering it's FIRST, I'm sure it has some integral use.

 

[Dr.D]

You say, "We know that using a large number of wheels will increase traction, which will result in an increase in grip for the robot. " How do we know this? Isn't there the possibility that if these wheels are not in a perfect plane (or if the field is not perfectly planar), some wheels will lift other wheels off the ground, or at least reduce the contact force? It is not clear to me that we know this at all.

Is it allowed for you to carry on board a fan directed such as to blow fan upward and thus force the robot down against the field, increasing the contact force?

 

[Sunny1261]

Well, the field is flat. And the wheels must be angled on a place perpendicular to the robot, so in turn, I assume all of the wheels will be touching the robot. I have suggested the fan, but the power systems do not match up. We will need to create a large amount of force from the fan. Plus, most fans which are powerful enough are AC, the power we can generate is in DC.

 

[Just_Cetn]

Hey sunny! I'm in first as well, same problem, same question. I've looked at everything from vaccums to gyroscopes. I don't think there is any way around it, we will be sliding all over the place and that is preety much final. Theres no inertial mechanism or device powerful enough to have a significant effect for the weight, size, or power it will require.

The most I've though of is this, can't the wheels (keeping the axis of rotation parallel, as required by the rules) like this:
/\ /\
/\ /\
/\ /\
/\ /\

I've also thought about friction and increasing the force of it. More wheels = larger area touching the ground, but les force Per wheel. You can arrange wheels sideways and use a block of them as brakes. A wheel is roughly an inch in width so a sliding wheel has an inch of exposure versus a single point facing forwards.

Also, I thought about having a small capacitor to dump a charge into the drive motors for some extra juice to gain more 'traction" / friction force to get a robot going.

Just some thoughts our team is pondering at the moment.

 

[Sunny1261]

Hm...I don't think spinning the wheels faster will you give more traction, I think it might do the exact opposite and spin them out. If it is inevitable that we spin out, I say that a strongly coded acceleration algorithm might do the trick. Our programmer(s) are/is working to find a solution to stop the skidding using coding.

 

[Just_Cetn]

With the unpredictability of the trailer, any kind of counter torque is going to be moot. Also, motors are barely sensetive enough to detect something like this and react. Could definitely have applications though.

Also, spinning the tires faster does help; how else would vehicles drift?

Unrelated:
What are your opinions on rule R<16> and its reference to the size rule, R<11>?
If you don't know what I mean, you have to look at this immediately.

R<16> states that during the PLAYING configuration, the robot can not excede the maximum size limits (28" x 38" x 60") stated in R<11>. This also states that no part may pass beyond the vertical place defined by extruding the bumper zone line upwards.

 

[Sunny1261]

Spinning tires faster would causing drifting which isn't good in this situation.

I don't have any major problems with it. Almost all of our current designs do not fold out beyond 28 x 38 x 60 so I see no big deal. It's just another constraint which we have to work around.

 

[minger]

Drifting is not better; in fact its significantly slower than properly taking corners. Drifting is done for style only. Having said that, the frictional force will ascend to a maximum value at which point slip occurs. When that happens, the force drops a large amount and stays constant with respect applied force.

What you need is to maintain the applied force right on the verge of breaking the wheels loose. This is exactly the principle behind Anti-Lock Braking systems. You need some sort of sensor attached to a wheel/axle. You then need a method to determine slip. You could monitor acceleration and look for discontinuities...or some other more clever than me way.

From there, back off the power until the wheel "sticks." The frictional force will suddenly jump, and the wheel velocity will drop.

 

[Sunny1261]

Agreed.

We are trying to get an ABS working but our programmer is against it for some reason, hopefully your post will convince him.

 

[zaurus]

So you can only use plastic wheels, but what about a tread or other extension that comes down after the round begins?

 

[Sunny1261]

Nope. Nothing except for the wheels can be touching the ground on a plane perpendicular to the play field for the duration of the match.