Our robot has several elevator bearings less than a quarter inch away from our drive motors. Several other parts are quite close to the motors as well. Does anybody know how hot a CIM motor can get after 2 back to back matches?
It all depends on the use case. Last year many teams (including ourselves) ran into issues with overheating CIMs due to required motor stall to keep elevator position. If its something like a drive or elevator motor, it could get quite hot, a shooter motor sees less load and would not heat up as much. If you have room, you could always add a Cooler For CIM from andy mark. Itâs not much, but it will help.
(You can also keep compressed air cans in the pit to cool the motors (turn the bottle upside down)
Cooler For CIM
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If the concern is radiant heat from the motor cooking an adjacent bearing, the answer is ânot enoughâ. They can get easily get too hot to hold after heavy use, but they arenât going to hurt anything that isnât in direct contact with the can.
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What if something does occasionally contact it? Can it blow a bearing?
To expand on this a little:
Many people consider anything over 130°F âtoo hot to touch.â ~135°F can cause minor tissue damage after extended contact.
Theelevator bearings weâre using are rated up to 240°F. Thatâs âinstantly cause 1st or 2nd degree burnsâ territory, or âwater droplets vaporize almost instantly.â
Iâm not sure what a CIM motor is rated to temperature-wise, but often motors are fine even if theyâre far too hot to touch. A little more background info.
Somewhat tangential to this⌠Designing your elevator to reduce the forces, and amount of time your spend at stall is a good thing. Counter weights/springs to reduce the lifting forces are helpful, as are driving techniques that minimize the time you spend with the elevator lifted. The critical factor you need to manage is the current at stall as this is what is generating the heat. Lowering the required force, lowers the current, which reduces the heat.
Having said that, we ran a fairly heavy elevator mechanism last year, powered by a CIM, mounted in a non ideal location (enclosed space with minimal ventilation). It would get warm to the touch after a match, and hot to the touch after back to back matches. We did manage to cook a CIM when doing demos, and running it continuously.
CIMs are tough motors and very good at dealing with the heat generated by stall conditions (large thermal mass). The unfortunate flip side of that design is that they are not particularly good at getting rid of the heat.
What are the bearings made of? If they are steel, you wonât have any motor heat related problems. If they are made of something that melts at a really low temperature, you might want to worry a little about it.
Consider that many gearbox designs mount the CIM motors directly to a plastic housing, with no ill effect. While they can get too hot for our puny human hands to hold, most of the stuff on a robot is a great deal more heat resistant.
A perhaps likely exception here is some 3d printing materials. I can imagine a PLA or similar printed motor mount getting hot enough to soften and move on you.
The energy that heated up the motor while it was stalled to hold the elevator carriage in position came from your battery. If you have a âhigh current drainâ drivetrain, the stall current of the elevator motors will cause the system voltage to drop even more, making it easier to go into a brownout condition. Methods for decreasing the motor current have already been mentioned. You may also want to consider a brake because, properly designed, it consumes almost no energy to hold position.
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