Today, our team’s main builder and I were working on the robot and we ran into a problem with the 4 drive motors (2 motors geared together on each side for front wheel drive). When we pushed the joystick channel all the way up for forward ( same thing with backward) the motors would run at full speed for a couple of seconds and then stop for a second, then resume running for a few moments only to stop again for another moment and so on in a continuous cycle. we hypothesize that this might be due to friction, which we have a lot of and are currently trying to fix. i would like your opinions on if this is actually due to friction or something else, and if it is friction, then why doesn’t it affect the speed as a whole and only in waves? thanks.
What you are experiencing is motor overload (a.k.a. motor stall). In short, you are asking too much of your motors, they are overheating, and their internal circuit-breaker (called a PTC) is tripping. After a few seconds, the PTC cools down and you can drive again, albeit at a lower capacity than you could before (and you are more likely to trip again and again after that).
So, “asking too much of your motors” can result from many sources. One is excessive weight compared to the number and speed of the motors on the chassis, another is excessive friction from any source, or trying to push/lift something that’s just in excess of the capacity that the motor can do.
Read all the details in this article I wrote: https://renegaderobotics.org/motor-overload/
well actually the motors run for a few seconds and stop for barely an instant and start running again for a few seconds, then stop for an instant, and repeat. So it is most likely friction, correct? Because this happens even when the wheels aren’t touching the ground
Yes, this sounds more like friction to me. Tripping the PTCs should stop the motors for noticeably longer than an instant. The first things I would check are that everything that should be parallel/perpendicular actually is and that the gears are actually meshing properly, which are related. You also might look at the gears to see if one is deformed/damaged in a spot.
As to why just at moments, it sounds like the sort of problem that happens when something theoretically circular (or a chain attached to sprockets - no circular but same idea) and aligned is slightly off. Then you can get situations where the problem only occurs each time that particular gear or whatever completes a full cycle from the last time the problem occurred. An easy example to see an understand would be a gear that has one tooth that is too large or has debris between two teeth. Then it will work fine when that one spot is out of the way. But when that one spot is supposed to mesh with the next gear, it will have trouble fitting through because it’s too large. There will be a much larger resistance for a moment. Then, once it’s passed, the gear will work fine until the next time that spot has to mesh up.
No guarantees that’s exactly how this problem is coming about, but when you have a cyclic problem like that in a drivetrain, I always look for such problems in the rotating components first.
The most likely cause is indeed the gears, however, if both sides are experiencing this problem at the same time, then it is not mechanical, and most likely the result of a misplaced wait in your Driver Control. If this problem just randomly started, you may just need to re-download the code.
This is probably what is going on…we will check if there is something wrong with the gears. thanks a lot