Was wondering if any teams had any practical experience with how long it takes to destroy the various motors used in FRC when stalling?
For example have read here on cd 3-4 seconds for a 775 pro to release its smoke, and somewhere around 20-30 for a cim. What about mini cim, bag motors and so on?
Click on a motor then scroll down to the locked rotor stall test. It gives you a general idea of the motor’s stall performance.
Not sure how I missed that on vex site? Thank you though.
So if I am reading correctly @12v looks to be about 20-25 seconds on a bag motor
You shouldn’t plan on doing this often. The bag and cim motors don’t have any good way of transferring heat out of the rotor, so they’re going to stay good and hot for quite some time after that. Also those tests start with the motor cold. If you’ve been running the motor previously, it’ll be rather warmer to start with.
There has been some back and forth on wether to use a cim or dual bags, so trying to make a pro con list for each setup.
Use a CIM rather than dual BAGs, it has more power and heat capacity, and you can buy heatsinks for it.
I agree with your conclusion, but heatsinks are not a reason. Heatsinks help only marginally in a stall situation where the rotor is heating rapidly. The rotor has no good thermal path to the case of the motor.
The heatsinks don’t help much during the stall, rather they’re there to help keep the motor cool before the stall.
The motor will not be “cool” if it has been used heavily during the match (like a PTO from the drivetrain).
And if the motor is dedicated to the lifter, and not being used until the end of the match, a heatsink will be lipstick on a pig.
Oh, duh. You’re right.
Leaning towards cim even prior to posting, but the weight savings of the dual bag and the real estate savings were/ are considerations as well
Heatsinks really don’t do much for CIMs, unless you really design around them (ie, add some sort of airflow over the heatsinks).
For dual BAG, also consider the extra weight and complexity and real estate requirements of the second motor controller.
Please remember that motor testing is done with a well regulated and high current power supply at a constant 12 volts. Your mileage will vary from that. Also remember that while there is very high heat generated within the rotor of the motor during stall, the failure comes from the breakdown of the insulation on the wire in the rotor. Some motors have lower temperature failure on the insulation than others. Some motors do not adequately insulate the rotor and so high temps result in the windings shorting to the motor frame.