Does anyone have any ideas on how to prevent motors from overheating?
At our last competition, my alliance lost by 25 points in the final match of the tournament because my team’s drive motor’s overheated. We had this problem before this match (we have a 1:2.3 gear ratio on our drive wheels) but we had lowered the motor speed from 120 to 90, and that had solved the problem for a couple of matches. As we could have easily won if our motors didn’t overheat, I feel terrible for letting our alliance down, and I definitely want to implement a solution to prevent this from ever happening again!
Also, I had previously considered plans to switch from 4 motors to 2 motors on our drivebase, but if four motors can’t handle it, 2 motors definitely won’t be able to - the two motor plan will probably be scrapped :l
We’re using four motors for our wheelbase, one per wheel, tank controls, with 4 inch wheels on the back and 4 inch omniwheels on the front. It’s geared at 1:2.3 (84 tooth driving a 36 tooth, both high performance) because we have a strong short range field robot, and need to be able to quickly move around the field. I’m definitely thinking about lowering the gear ratio, and any suggestions are greatly appreciated! Is there any way to dissipate heat from the motor while in game?
Okay so your gear ratio is too high. If you want the same gear ratio and a lot less friction switch to direct drive turbo motors. This has a better chance of working because your build won’t effect it as much. If this doesn’t work do what everyone else with 4 motors does, High speed direct drive on 4 inch wheels or 3.25 inch wheels with turbo direct drive.
Something to consider is what the internal gearing of your motors are. If they are Turbo, they will probably cut out a lot quicker. Keep in mind that the “PTC” or Positive Temperature Coefficient is what stops your motors from overheating. Normal motors come in a torque configuration, so if you upgraded your base motors, it’s probably best to slow it down by a gearing configuration.Another thing to consider is the amps that are going into your power expander or cortex. We discovered that problem when we connected our Dual Flywheel to our power expander instead of the cortex. So check your wiring and where all the amps are going to. It’s best to put the mechanisms that use a lot of energy into the cortex. Hopefully this answers your question, and gives you a little more insight.
Or you could use dust spray, turn it upside down, and spray it on your motors. Our team has this back up in a worse case scenario.
We have regular motors (geared for torque) but we’re planning on changing them to high speed and removing the external gear ratio like tabor473 suggested. I’m pretty sure our team doesn’t have turbo gears, but I can ask our teacher.
We don’t have a power expander either, unfortunately.
Since the overheating occurs during matches, we can’t really dump the canned air stuff on them - also, would the canned air cold stuff damage the motors (short circuit or temperature shock)?
I would say have a 6 wheel base (of your choice) Make sure that no wheels are connected to the motors, only chains. This spreads load evenly and I find that this configuration allows for higher motor tolerance
Motors overheat because they’re being used at a current past their duty cycle. they will heat at a rate proportional to P = I^2 R. some motors manufacturers will provide a thermal constant in terms of x degree C per watt. they will also provide a torque constant in terms of Nm per amp, you must use these to size your motors to your load. if not you can figure these constants with basic data.
this website does a good job explaining in more depth.
in general you can do you best to transfer heat out of your motor with a heat sink, can use a fan to help transfer more mass and limit your torque to your current based on your torque constant
If your motors are cutting out you are drawing too much current and therefore requiring more torque than the motors can output. You should determine your current torque and increase it either by adding more motors, or changing the internal gearing. For sake of argument disregard your external gear train.
These are the three possible configurations:
A standard motor produces 1.67 N/M torque @ 100 rpm, 1.67 X 4 = 6.68 N/M @ 100 rpm total
HS motor 1.04 N/M @ 160 rpm, 1.04 X 4 = 4.16 N/M @ 160 rpm total
Turbo motor .7 N/M @ 240 rpm, .7 X 4 = 2.8 N/M @ 240 rpm total
So you need to figure out which motor gearing you are using so you can determine your base torque. Speed and torque are inverses and therefore trade offs. The only way to keep speed and increase torque is to get a bigger motor(not possible in VEX) or add more motors to the gear train.
Once you determine which motor variant you need to use, open the internals and lube everything with grease. This will cool the motors by reducing friction. The internal gearing will always be more efficient than external gearing so choose the best motor configuration first, to reduce the necessary external gearing.