Physics of T-boning

[DampRobot]

Originally Posted by rnewendyke

254's 2014 bot was pretty good at avoiding t-bones like that as well as t-bones in general. They used an alternative bumper material (I believe it is sail cloth, but I'm not certain) and is at least 20 pounds under the 120 pound limit. In most t-bone situations it either bounces off of the other robot, slips off of the other robot, or does a combination of the two. It's not quite as un-t-boneabe as a 33 or other butterfly/butterfly-esk drive trains out there, but it does appear to have an advantage over other traction setups I have seen.

IIRC it was sail cloth. They switched after SVR (as well as I believe strengthening the bumpers to better stand up to Arial Assault), and from watching their videos, I agree they did see performance increases.

One dirty little secret about bumpers is that the best teams in the world have been using "alternative" bumper fabrics for years. Just take a look at some 67 or 2056 bumpers from the last few years, they clearly aren't the recommended fabric (Cordura?). It just seems like 971 and to a lesser degree 33 have precipitated a conversation about pinning this year, and suddenly these innovations have come into the light.

[Gdeaver]

With Swerve there is the rotate out maneuver. It does take a driver allot of practice to learn the timings of this action.

[Racer26]

Seems to me then, that an optimal drive train for avoiding a t-bone friction pin may in fact be a swerve drive with omni wheels, as counterintuitive as that sounds.

[IKE]

If you are going to have a physics discussion about T-boning, some discussion about the Traction Circle should be brought up. Basically, for a wheel to carpet that has consistent traction (say colson), the effective CoF (coefficient of friction) in lateral and longitudinal are teh same. Then you get into sliding conditions, the effective CoF follows a circle. thus if you are eqaul side slip as longitudinal then the effective CoF of either component direction is reduced to square root of 2 or 0.707.

This video does a decent job of describing:
https://www.youtube.com/watch?v=JjCcFsGLpaM

Another item needs to be static vs. dynaminc CoF. Once you get into a slipping/sliding condition, you are in the Dynaminc CoF which is lower than static. thus you have a dramatic reduction. (10-30% reduction depending on surfaces and materials).

Lastly, you need to look at the torque it would take to pull off of the "T". This one is a little trickier. I will see if I can draw something up about this one. Ultimately though, CG placement for-aft will mean taht the robot stands a decent chance of pulling out in one direction, and no chance in the other direction (assuming the CG is not the exact midpoint.

[JesseK]

Are there any gearbox/drive train innefficiencies that arise out of a T-bone? For example, the bearings are designed to deal with a radial load and R-rated bearings have very nice efficiency when doing so. When under lateral load, what does that efficiency decrease to, and how does that affect a robot's ability to get out of a T-bone pin?

It may be a factor in why 33 was hard to pin.