Bad MiniCIMs... failing to consistently start?

[ThaddeusMaximus]

We're running into a case where our MiniCIMs (two of them, exhibiting near identical symptoms) have odd starting issues (weak/no torque), and in fact, are bad enough that we can place the motors in an orientation such that they will not start at all, even when supplied a full 12 volts. I'm darn sure it's not a motor controller issue.

To add to this, they will run perfectly fine in one direction, but see this sporatic starting in the other direction.

Some background on the motors:
The wheels attached have been running as flywheels on a shooter, direct output. A 1/2" hex output shaft was press-fit onto the end of the CIM shaft. The setup is very quiet, but beforehand they were run through a bunch of adapters that resulted in a very messy and rumbly situation.

Has anyone encountered anything like this, or have any recommendations?

We're going to be replacing the motors and doing the press fits for the next hex adapters by taking the CIM and windings out of the motor, so we press on the shaft itself rather than the bushing (if for some reason we were causing damage beforehand).

[electroken]

It's 6AM and I'm only marginally coherent, but I'm nearly certain we're not allowed to disassemble (and then use) motors for any reason.

[Mechvet]

Not sure what could cause erratic motor performance without digging into more detail.

To start with, have you started with elimination-style troubleshooting? For this case, it would start at the PDP and end at the motor itself. I'd personally start with a second speed controller/harness, and swap one bit of the system at a time until the problem went away.

Secondly, We found a solution to adapt a CIM to 1/2" hex shaft that might work for you. It's so far help up to fairly intense testing on two separate robots. We bored one side of the hex to 8mm, then fixtured the hex and slit it up the shaft just far enough to fit the 2mm key. The key gets put into the motor shaft, the hex shaft gets slid on, then a hex shaft collar "clamps" the split shaft together, also retaining the key stock. So far across four motors on two robots doing arguably too many test-shots, we haven't had a single mechanical failure or any adverse wear. It's not elegant, but it works.

[GeeTwo]

I had a similar issues with a much smaller (1" diameter) DC motor a few years ago. When I disassembled it, one of the brushes mountings was damaged so that it appeared that the brush didn't make consistent contact with the rotor.

[Dad1279]

Originally Posted by Mechvet

.......
Secondly, We found a solution to adapt a CIM to 1/2" hex shaft that might work for you. It's so far help up to fairly intense testing on two separate robots. We bored one side of the hex to 8mm, then fixtured the hex and slit it up the shaft just far enough to fit the 2mm key. The key gets put into the motor shaft, the hex shaft gets slid on, then a hex shaft collar "clamps" the split shaft together, also retaining the key stock. So far across four motors on two robots doing arguably too many test-shots, we haven't had a single mechanical failure or any adverse wear. It's not elegant, but it works.

Great idea!

[FrankJ]

Originally Posted by electroken

It's 6AM and I'm only marginally coherent, but I'm nearly certain we're not allowed to disassemble (and then use) motors for any reason.

R30 is what you are thinking of. But it covers modifying the motor. Disassembling the motor to press on a shaft adapter and then reassembling the other unmodified motor really isn't modifying the motor so would be allowed under this rule.

As other have posted, it sounds like an issue with the brushes. When the bag motors first came out they had this issue. Maybe you have an old one?

Thread on the subject with fix

[Michael Corsetto]

Originally Posted by ThaddeusMaximus

Some background on the motors:
The wheels attached have been running as flywheels on a shooter, direct output. A 1/2" hex output shaft was press-fit onto the end of the CIM shaft. The setup is very quiet, but beforehand they were run through a bunch of adapters that resulted in a very messy and rumbly situation.

This is likely your issue. I would not recommend placing wheels with axial or radial loads directly on the motor output shaft via an adapter. The motor output shaft is not designed to handle these sorts of loads. You should really be running a simple belt, gear or chain system to a separate shaft that has your shooter wheel on it and is well supported by the proper bearings/bushings.

I am guessing your set up is slowly but surely causing your motors to fail. I agree with others that brushes seem to be at least part of the failure mode.

Pictures would help too.

Best of luck!

-Mike

[ThaddeusMaximus]

Originally Posted by Michael Corsetto

This is likely your issue. I would not recommend placing wheels with axial or radial loads directly on the motor output shaft via an adapter. The motor output shaft is not designed to handle these sorts of loads. You should really be running a simple belt, gear or chain system to a separate shaft that has your shooter wheel on it and is well supported by the proper bearings/bushings.

I am guessing your set up is slowly but surely causing your motors to fail. I agree with others that brushes seem to be at least part of the failure mode.

Pictures would help too.

Best of luck!

-Mike

I agree that that should be the setup, but it's pretty hard to turn back now; team picked a packaging that makes that difficult.

These motors were ran with adapters that caused lots of noise, originally, so I'd imagine that's what really caused them to fail, since we were noticing similar behavior but never really bothered to investigate. I think swapping to the new hex adapters (which reduce noise to only the sound of air flowing) will vastly improve motor life, since they'll be taking less radial loads.

I will post pics of the commutators and such when I get back to the shop today, or whenever they take apart the motors again.

Originally Posted by FrankJ

As other have posted, it sounds like an issue with the brushes. When the bag motors first came out they had this issue. Maybe you have an old one?

Thread on the subject with fix

These are MiniCIMs, not BAGs, but I'll take a look to see if we can save the old MiniCIMs.

[Michael Corsetto]

Originally Posted by ThaddeusMaximus

These motors were ran with adapters that caused lots of noise, originally, so I'd imagine that's what really caused them to fail, since we were noticing similar behavior but never really bothered to investigate. I think swapping to the new hex adapters (which reduce noise to only the sound of air flowing) will vastly improve motor life, since they'll be taking less radial loads.

You appear to be assuming that, because of your improved set up, "less noise" means "less radial loads". This is not the case. In fact, load could be transmitted more effectively to the motor shaft in a tighter set up with less slop. It could be that your new set up is actually worse for the motors, even if you get better results (less noise, stronger shot, etc.)

-Mike

[JackFisher]

How tight was the press fit onto the motor shafts? If it was too tight, and you didn't support the other end of the motor properly while pressing them on, this would probably be the most likely reason the motors are damaged.

[SJaladi]

As Mike already mentioned, running shooter wheels directly off of the motor shaft is not the best option due to the radial loads the ball puts on the shaft (1923 did this in 2013 and 2014 and it was definitely not the best idea). However as it sounds that you are constrained by your design, a better solution than pressing the hex adapter onto the shaft, which may cause damage to the internals of the motor, is to use the 8mm to hex adapter which is available from both andymark and vexpro.

http://www.andymark.com/product-p/am-0588.htm
http://www.vexrobotics.com/vexpro/ha.../217-3255.html

Alternatively if you have access to a lathe and the correct broach you can make your own adapters very easily. (We made ours with a drill press but it was a last ditch effort as we didn't have access to a lathe, and the COTS ones were out of stock)

[philso]

Originally Posted by Michael Corsetto

This is likely your issue. I would not recommend placing wheels with axial or radial loads directly on the motor output shaft via an adapter. The motor output shaft is not designed to handle these sorts of loads. You should really be running a simple belt, gear or chain system to a separate shaft that has your shooter wheel on it and is well supported by the proper bearings/bushings.

I am guessing your set up is slowly but surely causing your motors to fail. I agree with others that brushes seem to be at least part of the failure mode.

Pictures would help too.

Best of luck!

-Mike

The team we were with in 2013 damaged a Frisbee shooter motor by doing exactly what the OP was doing, though without the adapters. The side loads from only 3-4 shots, with high compression (and high side load), was all it took to damage the sleeve bearings at the "bottom" end of the motor.