Pushing powered off robots?

[Jeffy]

I have seen a few claims lately that pushing a robot while it is off is a bad idea because it sends electricity back into the speed controllers. Google and CD search didn't bring me any luck to finding the answer.

My simple knowledge of physics acknowledges that motors can be generators, but does not see how it can do any harm without a path for charge to flow through. I do notice that the spike realays light up when a motor is driven (by hand) while power is off.

Does this really hurt your speed controllers? Can you explain why?
And, how much is too much? I have seen many robot applications where an arm falls (slowly or quickly) at the end of the match, is that enough to harm the controllers?

[Chris_Ely]

Last year, my team did not have a cart to move our robot, so we pushed it around the compitition. Later, two of our jaguars stoped working. One of the jaguars completely fried and released blue smoke. We believe that tis happend because of the electricity generated through the motors by pushing the robot. Also, when we pushed the bot, the lights on the jags lit up. We later got a cart and replace the jags and have not had any failures since.
Do not push your robot! Carry it or get a cart.

[Jeffy]

Originally Posted by luckof13

Do not push your robot! Carry it or get a cart.

For the record, we are not planning on pushing it at the competitions. We have a cart, and always have, but pushing makes robot positioning pre-match and during practice sessions alot easier.

[sanddrag]

Done it for a decade with Victors with never a single failure because of it. I can't comment on the Jaguars.

[Hawiian Cadder]

depends on how hard you push it, if you are doing minor adjustment, it doesn't matter because there are diodes in the jags to protect the processors from electrical damage, however be careful because you can destroy the diodes and put some real current through the jags.

[Mr.G]

We have fried at least 4 victors over the years from students pushing the robot fast down long halls at the school.

Trust me don't do it.

[Al Skierkiewicz]

There is no real damage that can be done to speed controllers from pushing the robot if the robot is turned off. Each of the speed controllers has reverse diodes built into the FETs that are part of the output circuitry and these diodes pass current generated in the motors back to the 12 volt buss. However, you cannot possibly push at the top speed of the robot, so it is unlikely you can generate enough voltage to exceed the 12 volts. You will see the LEDs on the Victors turn on and you may see some other indicators come on while pushing. When you push, you are generating voltage similar to the robot in "coast" when the throttle is zero.