I am running 4 cim motors (2 per side) for my drive system
My robot is ~100-120lbs
I ran the drive slowly (~25% max throttle) for ~ 5 mins for some drive tests.
When I touched the motors, they were all uncomfortably hot. Not hot enough to burn skin, but uncomfortable enough to be unable to leave my hand on there for >5 secs. (Sorry, I dont have a FLIR camera on me or anything to get a specific temperature)
Based on my calculations, this CIM motor setup should be able to handle the weight no problem. I was wondering if this is normal, or if there is excess friction in my chain system
CIM motors do get hot pretty quickly, even over the amount of time you used them. That said, your description of their heat seems to point to more than just normal use.
Based on your other thread about how you are having difficulty with the chain, I would think that friction in that system would be the culprit.
You mentioned how the chain wore down both plastic and metal idlers. That would cause a huge amount of friction. I recommend either using an idler sprocket like you mentioned in the other thread, shortening the chain, or both.
Edit: There is also a chance that you have the robot geared too aggressively, causing the motors to overwork. It never hurts to double check your calculations here if all else fails.
What gear reduction, wheel radius, and wheel type (CoF) are you using? With that information, you can calculate the current draw per motor using JVN’s calculator. Ether’s motor calculator will then show you how much power (and what % of input power) the motor loses to heat.
That said, for a standard AM14U3 at that weight the description isn’t totally crazy–these motors are designed for short runtimes, and not long runtimes like you see in FRC practice. Once CIMs get up to temperature inside, they really don’t have an efficient way to get rid of that heat and it slowly dissipates out to the can (and your hand). That’s why you see people doing things like fans and forcing air through vented screws to try to help it along. The performance gain from doing that is a matter of debate, but putting a fan on the outer can does meaningfully cool the exterior of the motor can if that’s of value to you.
We had an overly-aggressively-geared mechanum in 2017. After a particular half-hour practice sessions, we clocked the exterior of the motors at at least 250 degF (it may have been higher, but it was at least that from what I recall).
We promptly stopped using the robot, and gave it a rest. Motors seemed fine after that?
I ran the numbers quickly, and it looks like you are in a decent range. Assuming a fully-weighted robot and a CoF of 1.2 (probably close for pneumatic tires on asphalt), you should be geared for 8.1 ft/s free speed, 6.6 ft/s adjusted. And each motor should draw about 55 Amps at stall. From my experience, that’s a pretty reasonable current draw for a drivetrain.
Putting that into Ether’s calculator, you get that the motors are running at 60% of free speed (close to max power but with a little buffer room for load spikes) and the motors are 49% efficient (compared to 65% at max efficiency). Overall, I think your gearing choice is not the problem. You may just need to drive a bit more calmly.
If this is really a problem, you could look into adding another CIM per side, or switching the 2 CIMs for 3 Mini CIMs (same power, better heat dissipation).
It’s unlikely, but possible that if you were giving the motors 25% throttle, that you were just barely moving the motors past stall, ending up on a really inefficient spot on the motor power curve and burning a lot of heat.
CIMs will get noticeably warm after 2-3 minutes of intense driving on carpet with high traction wheels. Maybe give the motors a little more power to bring them to a more efficient spot on the power curve? This is probably not what’s going on but at least it’s worth mentioning.
You mentioned you turned a couple of times in your test. Do you have a drop-center drivetrain? How long is your wheelbase? If your robot really struggles to turn t could build up a lot of heat in the motors quickly.
Do the motors still get noticeably warm if you run them in the same conditions while up on blocks? (No load on the drivetrain other than friction) Do any of the motors not get warm at all?
All of your gears properly greased and aligned? Good chain tension?
A picture of your drive base would help us understand if there are any obvious mechanical issues.
Based on the picture he posted in the other thread, it would appear the drive system is a flat 6WD (no drop). This could very well be at least one of the causes of the heating issue.
When I read the first post here, my initial reaction was that this was probably a gearing issue, under normal use (IE, not pushing things, just driving around), CIM motors really shouldn’t get that hot if your gearboxes are geared properly.
Using the gearing posted earlier in this thread and the wheel size, it looks like you might be a little on the high-end, JVN calculator estimates around 41amps during normal use, which combined with 25% power setting and the wheel scrub caused by the flat drive base could be causing the issue.
The 18t sprocket should drop that current draw down to ~35amps per motor which should be much more manageable under sustained loads
Not sure if they have it in Canada or what the equivalent would be, but I would highly recommend Lucas Oil Products: Red “N” Tacky Grease for gearbox gears. It’s generally available in auto parts stores or online and is relatively inexpensive. In my experience, I tend to avoid white lithium grease as it has a tendency to loose effectiveness more quickly.
Additionally, your chains and sprockets might benefit from some DuPont Teflon Chain-Saver (or equivalent), though most chains do come pre-lubricated so this is a less significant issue.
If you’ve been running your gearboxes a while without grease, it might not hurt to inspect the gears when you take them apart to grease them and make sure they’re not worn down too much already and you don’t have any gears binding.
If you still get heat buildup on the motors when the chassis is up on blocks, I’d check you electrical system, and make sure you don’t have motors fighting each other (unplug all but one motor at a time and check to make sure they’re spinning in the correct direction), and make sure your speed controllers are calibrated (if using PWM control) and not in brake mode (since brake mode can cause motors to generate quite a bit of heat if used frequently).