We are using the denso motor to direct drive a pincer.
Normally, there is little load on the motor, and the motor drives smoothly in both directions with about 3-4 Volts on a bench power supply. We have a bushing support on the end of the shaft to minimize cantilever loads.
However, if we run the motor into the hard stop (thus, applying a sizeable backdrive torque) the motor will not run in reverse. Even after unloading it, we need to run it up to 12V to get it unstuck.
Has anyone seen this kind of behavior with the densos?
We’ve never had this kind of problem before.
I would guess that you’re damaging the plastic gear inside when you run it into a hard stop. I suggest you do something to prevent that from happening–limit switches are one possibility. And replace the motor with another one.
We are using the window motors too and have had this issue. We decided to make sure the the motor doesn’t come under a lot of stress because that causes it to lock up. Just do everything you can to avoid using a hard stop.
Those motors have a worm gear set inside them, and as such with greater applied torque you have greater friction within the geartrain. I have not experienced the issue you have there, however I wager that if you were testing using a victor and a 12v battery you would not see this issue. Most variable voltage bench supplies cannot supply the current needed when these motors stall, or even to operate them at max efficiency. If your system reverses reliably with a 12 volt supply that can give the motor the current it wants (limited to less than 20A) then I wouldn’t worry. The proper way to address this would be to put a limit switch so that the motor stops just a bit before the hard stop.
The Denso window motors provided in the KOP are designed such that they will lock when sufficient backdrive force is applied. Removing the locking pins is, as expressly stated in the FIRST rulebook, the only motor modification ever allowed.
Of course, when I tried to disassemble one to remove the locking pins for practice, I ended up stripping the screws. By hand.
From the Team 1640 wiki, the following quote:
"These locking pins lock the drive coupling in one direction in response to excessive torque. "
Does this really describe what the locking pins do, or are they really related to the anti-backdrive function? If the former, I will have a student take the locking pins out tonight. If the latter, than we may not want to remove them.
Thanks for the other comments. We will indeed be using limit switches into the Jags to remove power before hitting the hard stops. The problems we see are based on the bench test setup.
We used the window motors last year for 4 wheel independent steering swerve drive. The locking pins caused friction and lockup. Lock up is most common when small changes are made at small PWM values. Note that our problems with the Denso motors did not totally disappear until we switched to victors. With the victors our steering worked perfect. There must be some PTC heating caused by the high frequency PWM of the jags. The 2 don’t mix. A denso motor can be back driven with the locking pins removed. You will have to determine what is right for your application.