Temperature Shutoff on Denso Motors?

[Richard McClellan]

Has anyone had any issues with the Denso motors heating up after several minutes of high loading? Our team has a 3-wheel crab drive setup this year, and each module is independently steered. We are using the two Denso motors to rotate the two front modules (directly driven) and a globe motor (directly driven) to rotate the rear module. The whole system works great during driving practice at first, but after about 10 minutes of driving, the rotation of the front modules stops working (the lights on the Jaguars are solid green, the modules aren't rotating, and the denso motors are hot to touch). Then if we wait 5-10 more minutes (which I presume is for the motors to cool down), it will start working again.

At first I thought there might be some large side loading on the output of the window motor, or binding in the lazy susans we are using for rotation, causing it to bind, but we've taken the modules apart many times and can't seem to find any issues. A picture of our robot can be seen here.

Our sister team, 2881, is also using their denso motors to drive some belts for their lift and they are experiencing the same behavior (freezing up after 10-15 minutes of driving.

Has anyone else ever experienced issues like this with the denso motors? Is there an internal temperature shutdown such as an auto-reset breaker of some kind? We are thinking of making some heat sinks to attach to these motors, but if anyone knew where we could buy some that were about the right size, that would be a lot easier.

[Woodworker88]

Yes, the Denso window motors have temperature cutoffs inside. This is definitely what is happening based on your description of the failure mode. Heatsinks and fans would help, but other than that there is not much else you can do. If they run for at least 5 minutes or so, you should be alright, given that they can cool down between matches. Make sure that everything is calibrated (trimmed) so that the motors are not stalling when the bot is just sitting there.

[Tom Line]

You may want to invest in some cold spray or a couple cans of compressed air (which when sprayed upside will spray out liquid air that is EXTREMELY cold).

That way if you get into elims you can cool them between matches to be at your best.

[R.C.]

What other motors do you have available. I know that no one wants to switch motors but you may want to use a keyang or some FP's if you still have them. Maybe even dual the rs-385's if you have time. Post back what other motors you have available.

[colin340]

put a fan on it and they will be fine

[IndySam]

Why drive for 10 minutes straight? I guarantee your CIM motors won't like that either and they don't have a cutoff. They will just cook and then fail at the worst moment.

[meaubry]

The Denso motor is used normally on Power Windows. It has thermal protection inside to keep the motor from catching the car on fire in case there is an electrical failure and the motor is stuck on drawing current.

They are not designed or intended to drawn current non-stop for long periods of time, instead they are designed to be non-backdriveable (to prevent windows to be forced open as a means of theft deterent) and to draw current for a relatively short cycle (image taking 10 minutes to open or close a window).

Also, I don't know what kind of load they are trying to move, but the less force the better - so minimizing the drag (friction) will help but it will not resolve the issue over a 10 minute time period.

Mike Aubry

[Al Skierkiewicz]

Richard,
The Denso motors are not open frame and so some of the techniques mentioned above to cool down the motor will not work very well. The thermal cutout is not part of the outside frame of the motor so anything done to the outside case will do little to the inside. A picture will help, but my guess is that your mechanism is producing significant loading for this motor. If you are like most, pulling on a chain and turning to large modules is really at the outside limit of this motor. You can see that the Globe works well in this application. We have used Globes on our crab drive for many years now. If your crab modules do not have a bearing surface at the bottom of the module, then friction at the top bearing can be pretty high, especially when the robot is moving.