StrongHold Pushing Match & T-Boning

[staplemonx]

In a typical t-bone with both robots having 6 wheel drop center 8" pneumatic chassis. Can the robot who is t-boning push the robot being t-boned?

Has any one tried this will full or partially full tires on one or both bots?

Let's say the robot doing the t-boning is geared at 12.76:1 with 3 cims per gear box, and semi deflated tires. Could it push the other bot easily?
What if the t-boning robot were to weigh more, say around 165 lbs. Would that allow the t-boning robot to push the second bot more easily?

In a head to head pushing match, could the t-boning robot described in the previous question easily push a robot that is not geared as high, has fully inflated wheels and weighs closer to 145 lbs?

We ask because we are waiting on our first set of pneumatic and probably won't have a second bot to test on?

Thanks for your experience.

[BoilerMentor]

Originally Posted by staplemonx

In a typical t-bone with both robots having 6 wheel drop center 8" pneumatic chassis. Can the robot who is t-boning push the robot being t-boned?

Has any one tried this will full or partially full tires on one or both bots?

Let's say the robot doing the t-boning is geared at 12.76:1 with 3 cims per gear box, and semi deflated tires. Could it push the other bot easily?
What if the t-boning robot were to weigh more, say around 165 lbs. Would that allow the t-boning robot to push the second bot more easily?

In a head to head pushing match, could the t-boning robot described in the previous question easily push a robot that is not geared as high, has fully inflated wheels and weighs closer to 145 lbs?

We ask because we are waiting on our first set of pneumatic and probably won't have a second bot to test on?

Thanks for your experience.

My suggestions would be to perform some simple testing with your drive base and a bathroom scale. Tire pressure is an easy variable to change. See how much pushing force you generate with "fully inflated" tires and "partially inflated tires" (maybe a couple different levels of inflation?). Place the scale against the wall, drive the robot into the scale and record the peak force before the tires slip, then pick whatever pressure gives you the best performance. You may also consider configuration with different pressures at different locations as that may yield a different result.

It's safe to assume about the worst case scenario for the force required to push that robot sideways is in the 205-215 lb force range. This assumes a 147lb robot on an aggressive rough top tread.

If you're planning on playing defense, you can't really plan for any possible opponent configuration, but you can certainly optimize your configuration for the best results.

If you have any other questions, feel free to send me a PM and I'll see if I can help you out.

[staplemonx]

Totally agree, problem we do not have any pneumatic wheels at the moment. So we are looking for other teams to share some of their testing results. We are expecting to have wheels in early feb if we make the purchase in the next round, but we need data now for a decision.

[BoilerMentor]

Originally Posted by staplemonx

Totally agree, problem we do not have any pneumatic wheels at the moment. So we are looking for other teams to share some of their testing results. We are expecting to have wheels in early feb if we make the purchase in the next round, but we need data now for a decision.

Okay, let me take a different tack then based on my experience, this is how I'd answer your questions.

1: Assuming the two robots in the interaction are full weight and have enough torque to break traction the result of this interaction will depend largely on bumper position as well as if the pushing robot entered the interaction at any speed.

The robot with the lower relative bumper position should have a pushing advantage, because it tends to generate a force vector that serves to diminish your opponent's traction and enhance yours. A robot using a defensive strategy will probably want the lowest bumpers possible while still maintaining clearance for obstacles.

If the "T-boning" robot enters the interaction with enough force to cause the "T-boned" robot to begin sliding sideways it may continue to push the robot (dynamic friction vs static friction), but this has a lot to do with how drivetrain software works and driver skill. If the "T-boning" robot breaks traction with the impact, you end up in the same place (Dynamic friction vs dynamic friction).

2: Team indiana Ri3D used 15-17 psi in our pneumatic wheels and saw excellent driving performance. We didn't do any testing for pushing force though and our robot was significantly underweight. Basically if there is a traction advantage with deflated tires, as long as your opponent in this scenario doesn't know that, you win. If your opponent knows: stalemate.

3: Let's look at the traction limit. The basic physics model is a pretty safe place to start (Traction = Coefficient of friction * Normal force). Let's say you can get a 10% increase by deflating the tires some known amount, which is probably a safe, high estimate for what you might be able to achieve by adjusting air pressure. If your robot is full weight (147 - 148 is about the max unless you use something to generate extra downforce) we assume a 1.397 coefficient (AndyMark stated 1.27 coefficient of friction * 1.1) you can generate 206.7 lbs pushing force. Your stated gearbox and wheel configuration can produce 370.34 lbs pushing force at stall. You'll only ever be able to use 206.7 lbs of that force.

That said, the current draw is low, which isn't a bad thing, but you may be able to go faster safely. Here again, you can simply maximize your own performance. If you don't want to be pushed sideways or to be able to push another robot sideways there may be wheels with better traction options and that would be the way to go if that is a goal for the team.

4:Head to head pushing matches are a funny thing. Unless you implement some kind of "traction control" this is going to come down to your driver. If the contact the other robot and slam the controls forward, they'll just spin the wheels.

I hope this is better, more useful info. Again, if you have questions, let me know.

Also, the JVN Mechanical Design Calculator is your friend.

[staplemonx]

Thanks

[jeremylee]

I think that gear ratio with 8 inch wheels will stall the 3 cims and brown out. I'd suggest more ratio for pushing. See discussion in this thread of others faced with a similar situation.
http://www.chiefdelphi.com/forums/sh...hreadid=142496