Ok, I have now been through 4 replacement motors on my Wild Thumper 6WD 75:1 chassis. I am using a Pololu Orangutan X2 with a wixel for remote control.
The issue I am having is not the motors themselves, but the gearboxes keep getting stripped out. Every time I take this thing out, one or more wheels will bind up (mainly in grassy areas) and the gearboxes will strip out. I have already bought 4 replacement 75:1 HP gearmotors for this thing, and each time I get one replaced, another will die (had another one die this weekend, less than 30 minutes of use after getting the previous one fixed). The motors themselves survive, but the gearboxes get stripped (always on the gear that interfaces directly with motor). Has anyone else run into this? Are these motors just too powerful for the gearboxes?
According to this pololu.com/catalog/product/1575, only the 172:1 and above should be able to damage themselves, but the 75:1 motors keep on destroying themselves in a stall. I guess I could implement a stall detection based on current, but with three motors on one channel and considering how easily they stall, that solution seems like it would render the entire thing almost useless.
Crazy idea:
Do the encoder mod.
Mount motors with encoders.
Only drive motors at, say, 20% power, until you see that all three motors are moving. (And after it’s moved, only count it as “moving” for a very short while before going back to 20% power.)
Interesting thought. The only problem is that 6 new motors with encoders will cost me 130 bucks, plus shipping. You have given me an idea that I may be able to implement cheaply, though. I believe the orangutan X2 will tell me how much current the motors are drawing and I may be able to detect a stall based on that and cut the power down to 20 or 30 percent, rather than completely cutting power. Whether that will actually prevent the stall from stripping the gearbox, I’m not sure, but it may be worth a try.
I am sorry you are having so many problems with the motors on your Wild Thumper. Beyond a few isolated, single-motor-failure incidents, we have not heard of others having problems like this. In general stalling motors is rough on them, and stalling the motors a lot could explain them breaking. The reason we have the warning on some of the higher-gear-ratio pages is that those motors are very likely to break if stalled. That doesn’t mean that stalling (especially repeated stalling) cannot damage lower-gear-ratio motors.
How much of a load are you driving? Are the wheels often encountering a situation where they are being commanded to go from full-speed in one direction to full-speed in the other? Also, just to be sure, could you double check that your batteries are connected in parallel, not series? (If the motors were being driven at 14V, that might explain the damage).
I am using the Orangutan X2s inbuilt motor ramp up, ramp down, and braking functionality to avoid full reverse to full forward situations. The only additional weight on the frame is from the batteries, Orangutan X2, Wixel, and breadboard. No other items have been added to the frame. And yes, the batteries are wired in parallel. I’m not going to feed 14.4 volts to a 6 volt motor.
The situations where I am seeing the motors stall, are the very situations that this chassis is designed the excel at. When attempting stair climbing, the middle motors regularly stall. In even short grass, any attempt to turn will cause the motors to bind up, pushing the suspension into full travel, up or down. Even simple carpet puts the motors into a bind at any heading other than straight forward.
Strangely, none of the replacement motors have yet died, only the motors that came with it originally. Maybe when I get them all replaced, all will be fixed. Maybe I should not give them full power. I don’t know.
I do find it interesting that Sparkfun, in their product description for the 34:1 model says the following:
"Each of the six motors are mounted on independent suspension and outfitted with 34:1 steel gearboxes (no more stripped gears!). "
That seems to indicate that I’m not the only one who ran into this problem, with the higher torque 75:1 motors.
After further consideration, it’s quite possible that I am reading too much into that statement. It’s hard to say.
Thank you for answering my questions. I am not sure what is causing the original motors from your Wild Thumper to break, but since it seems that the new motors you got from us are working well, I will contact you via email to discuss possible replacements. Have you tried taking one of your new motors apart and comparing it to the broken motors that came with the chassis?
