The physics of pushing

[Ken Streeter]

Originally Posted by Ether

Assuming you are not traction limited, that is the force the robot can push.

Or perhaps I am not understanding what you want.

Ether is right that the torque delivered by the wheels (assuming no wheel slip) is the maximum pushing force that can be provided by the robot.

However, in my experience (at least with 1519 robots), we haven't been able to actually get that much pushing force due to a different limiting factor. However, the limiting factor isn't the wheels slipping (in recent years we have used very grippy wheels) but rather the robot starting to flip itself over. (See photo below for an example.) Once teams design robots with sufficient torque and traction, the robot's own weight distribution and geometry is the next limiting factor.

For robots with high torque capabilities and very grippy wheels, "lift up" seems to be the limiting factor. Figuring this out is something that we've never actually done before on our team, but would probably be good to do. There's little point in having more torque or traction in a pushing contest than the amount that starts to result in the robot being lifted up, as that torque (or traction) can't be effectively used.

(By the way, I was hoping that this thread was taking these other factors into account...)

Example of the problem is shown in the photo below from this old CD thread: http://www.chiefdelphi.com/media/photos/35102