How do I use dial to manage power output to CIM motors?

Technical
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Hey guys. I just finished my student career and. I have some CIM motors. I want to connect to my scooter but need a way to control power. How do I use a dial to control the power? Thanks again.

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Easiest way would probably be to use an RC Servo Tester and an FRC Motor Controller or Brushed Motor ESC that accepts a Servo type PPM signal (which pretty much all do in my experience).

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I think the CIM is actually about a 32 or 36 volt motor (check the drawings/specs) - the minimum is 12 v so it barely performs for FRC robots. If you can take advantage of the higher voltage, you get much better performance.

I don’t know what motor controllers to use at 36 volts; I’ve never done that. Some fork lift trucks can go to 48 volts so maybe that equipment would be a good place to start research.

I have no idea if Bang-Bang control or take back half is a useful control strategy for a scooter but they are simple and a small computer to turn a relay on/off would get the scooter to move - just not sure how smoothly.

4

A cordless drill trigger is an option. Possibly recovered from old brushed drill.

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Check the rating of you use an old drill (usually stamped on the part). Many are rated for 20amps and the Cim motor will likely draw more than that in this application. This can produce the magic smoke!

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@Pogepoge64 Running a CIM motor at 12V does not appear to cause it to overheat, even when run for extended periods of time. Running it at higher voltages may lead to overheating so it would be best to monitor the temperature using some sort of sensor. Please note you really only have access to the outside case and not the rotor where the heat will be generated.

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The temperature of the motor depends on the wattage that runs through it over time. So if you run 12v at 20 amps that is 240 watts. IF you run 6V at 40 amps that is also 240 Watts (V * A) so the same heating effect over time

As for controlling the motor. I’d probably 3dp a box put a pot in it and an Arduino Nano and a BTS7960 And write some code to adjust the PWM duty cycle based on the input Voltage. Then You got to power it. You could use a real live Battery for that. I’d probably connect and AMmeter too so I can also read the load. Then you could diagnose efficiency and load too. Maybe I put something like this into my project queue

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Right. OP needs to be careful and check specs if possible. The FRC model isn’t on the CIM web site anymore (as far as I can see). (Current links below.) Maybe I can find it on an old backup of my computer.

There is some evidence that I am wrong about it being a 36 vdc motor. Looking at current models there are 3 at 12 v and one at 230 vdc. I see scooters use a lot of 36 vdc motors but I don’t notice that voltage on motors similar to the FRC CIM. Sorry about maybe leading to a dead-end. I might be right about 36 vdc but I might be horribly wrong.

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I have to guess the killer heat is at least in part from the I squared R of the windings. For the same load I think 12 v and 20 amps through the 10 Ohm winding gives more heat than 24 v and 10 amps. That’s what I meant by more efficient. Other losses I don’t know how to quantify (I miss our electrical engineer who had to leave the team several years ago). But I may be completely wrong about CIM being 36 vdc as replied nearby.

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Yes - but also CIM is a 12 V motor. So the brushes and insulation and all the math is based on 12 V or thereabouts - usually < 15 on a 12V motor. Now it might run ok at 24 but who knows for how long. Also the rpm are usually pretty linear to Voltage. so a nowload CIM at 12V runs at about 5300 rpm. So at 24 V it should run in the neighborhood of 10k rpm and that might be too much for its bearings etc in the long run. Stall torque is at about 120 Amps that means that the windings are about 1/10 ohm. And wattage stays the same - lets say 24 watts at 12 V is 2A and at 24 v is 1 amp. But still the same power. Now heat comes from the efficiency and peak efficiency is at about 12V/20 amps at somewhere around 65 % (from memory - check the spec sheet) so that means 65% of the 240 watts goes into mechanical power so about 180 watts (if you run it over an hour you get .18 kwh and kwh is now the preferred way to measure power over hp) so the remaining 60Watts of power become heat in this example which starts in the windings and then transfers outwards and radiates to the environment.

So over time it will warm up the motor. If you stall it then you are running 120A at 12 V which is about 1400 watts in heat and 0 in motion (as its stalled) Now you get into all kinds of trouble quickly as that is a space heater producing enough heat in theory to warm a room. But before this happens it probably fails as the gauge of the wire in the winding is way too small to “live” with that kinda current, they are going to get glowing hot and the insulation will melt/evaporate off. and you will get a short - unless the brushes burn off first or the wires to the motor get white hot and set the insulation on fire or hopefully you got a fuse in the circuit that blows. So some will say “but I stalled a CIM” and I will say “so have I” but only for seconds. I know at 30A it will get hot to touch within a few minutes - how do I know? I have tested and stopped the test and added a fan to the motor to continue the test. Also the gauge of the wire comeing out of the motor is 12 and I don’t want to run anymore through them for an extended time. Going to a higher voltage you reduce the gauge of wire you need for the same power but you still produce the same amount of heat and in my guess probably more as the efficiency rating (ratio between mechanical and heat energy) is probably/likely lower. So running a CIM at 24 or 36 or 48 v for extended times will probably be an exercise in paying about $35 plus shipping to VEX or Andymark

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Thanks for the detailed explanation. I appreciate it.

I couldn’t find a 36 vdc reference for an FRC CIM but I did see that there apparently were 2 versions - the model with a 44 in the number and the model with a 45. Only one of them is in the current CIM catalog and at 12 vdc.

On the drawing there is a duty cycle specification which I cannot parse - doesn’t quite make sense to me - but it is labelled “Intermittent” which may be troublesome for a scooter usage (I could guess what the duty cycle means but I’m already in enough trouble). The rating is at normal load of 27 amps
image

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I’ll give you a hand with the duty cycle spec. @Richard_Wallace actually posted how to read something like it some years back, and he can correct me if I’m wrong.

To test: Turn on CounterClockWise for 3 minutes, off for 2 seconds. On ClockWise for 3 minutes at 64 oz-in of torque, off for 30 minutes. It should last for at least 1000 of those cycles (which probably means that CCM tested a few motors using that spec).

The “Intermittent” is in reference to that 30 minutes off. If you can operate for 6 minutes in 36, that’s pretty intermittent… like a typical FRC drivetrain use*, which is CCW/CW alternating suddenly for 2:30, cool for 30 minutes to an hour or two, use again. A scooter would be more like “CW 20 minutes at varying speed”, which is a continuous-duty motor.

*Or the original design use of the FRC CIM motors, which IIRC was trailer jacks. Those move very intermittently…

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Thanks. I was not sure where to place the missing commas and implied “off.”

And it seems unlikely these were intended for 36 vdc since trailers are near a 12 vdc battery.

Maybe the 36 vdc I remember was the other model since there were potentially two (there is only one model for sale now) or 36 vdc is the maximum allowed if accidentally over-voltage and NOT for normal use.

So the OP is warned that the scooter might not make it very far down the road.

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CIMs can get plenty hot running on 12VDC, it depends on their load : CIM Motor Data Sheet/Operating Temperature

There’s the big CIM, and mini-CIM: Home - Electrical - Power - Motors - AndyMark, Inc

The FRC PWM speed controllers work with Arduinos. Configure the Arduino output as a servo. Yes, it works, I’ve done it. You can wire a pot (potentiometer) to one of the Arduino’s analog inputs to control the speed.

Wear a helmet.

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I’ve also heard some unsubstantiated lore that they were used in marine winch applications, which again lines up with that spec of extending unloaded and retracting loaded.

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