Best way to cool CIM motors?

[Sperkowsky]

I recommend liquid nitrogen.

[rainbowbear998]

Originally Posted by Sperkowsky

I recommend liquid nitrogen.

Oh god... Please no.

Thanks to MrForbes for clarifying that rule.

Back to my surgical tubing idea!

[rich2202]

Did you check the jumpers on your motor controllers? There is a jumper that lets the CIM freewheel (coast) or brake. Make sure you have the Motor Controllers in Brake mode. That will apply some counterforce, without having to power the motor. On our robot, brake mode is enough to keep the totes from dropping.

[JamesCH95]

Two CIMs should not be heating up during a match unless they are being very over-worked. Gear your mechanism more effectively to solve your real problem, don't address the symptom of over-heating motors.

Our 'totem' can support between 2 and 8 totes, plus the tote-grabbing bars, with a single stalled RS550 motor with no ill effects after two district events and lots of practice. We are using a 64:1 reduction with a 0.88in diameter spool to wind up cable.

[Ether]

Originally Posted by JamesCH95

Gear your mechanism more effectively to solve your real problem, don't address the symptom of over-heating motors

@OP: If you're willing, please tell us about your gearing. How many motor turns does it take to raise the boxes 1 foot?

[rainbowbear998]

Originally Posted by Ether

@OP: If you're willing, please tell us about your gearing. How many motor turns does it take to raise the boxes 1 foot?

I didn't design or build the mechanism, so I'm not entirely sure about the specifics. However, I do know this. As a capstan, we have a metal 42 tooth belt pulley. This is connected to two CIM motors on a tough box mini.

At the moment, I'm thinking that using surgical tubing or bungee cord to take some of the strain off the motors. The other option my team is considering is a bar that locks up under the carriage holding our forklift mechanism while we drive. Thanks for all the great responses!

[asid61]

If it's possible, disc brakes are really good.
Constant-force springs might last longer than surgical tubing, depdening on stretch.

[s_forbes]

Originally Posted by rainbowbear998

I didn't design or build the mechanism, so I'm not entirely sure about the specifics. However, I do know this. As a capstan, we have a metal 42 tooth belt pulley. This is connected to two CIM motors on a tough box mini.

At the moment, I'm thinking that using surgical tubing or bungee cord to take some of the strain off the motors. The other option my team is considering is a bar that locks up under the carriage holding our forklift mechanism while we drive. Thanks for all the great responses!

Any chance you can post a picture of your mechanism? It makes it easier to identify potential fixes.

Using springs/bungees to offset the weight of everything is the first thing I would recommend. If you have a way to put a brake on the transmission (which might be as easy as a pneumatic piston jamming some rubber between two gears) then your motors will probably remain cool for the whole match. If you do either of those effectively, you can probably even get rid of the second motor.

[Richard Wallace]

Originally Posted by Ether

@OP: If you're willing, please tell us about your gearing. How many motor turns does it take to raise the boxes 1 foot?

Ether's question is directly on-point.

As an example: my team is using one CIM motor to drive our elevator. The CIM drives an AndyMark RAW Box (am-2372) with reduction ratio 14.2:1, which drives a second reduction stage made from VexPro gears with ratio 84:30, which drives a 36 tooth 5mm pitch timing pulley, which drives the elevator belt.

So, our overall gearing is calculated as follows:

At the pulley: 36 teeth/rev x 5 mm/tooth = 180 mm/rev belt speed

So our elevator moves 180 / 25.4 / 12 = 0.59 ft per pulley revolution, so to takes 1/0.59 = 1.69 pulley revolutions to raise our elevator one foot.

Multiplying this by our gear ratios gives 1.69 x (84/30) x 14.2 = 67.3 motor revolutions to raise our elevator one foot. At full voltage the CIM motor turns at ~5200 rev/min = 87 rev/sec, so the CIM motor could raise our elevator 87/67 = 1.3 ft in one second, if there were no load on it.

----

Using the same method to calculate for the system with a Toughbox and a 42 tooth pulley gives 18.5 motor revolutions to raise the elevator one foot, and a no-load speed of 87/18.5 = 4.7 feet per second. This speed is probably too high, considering gamepiece loads and likely sources of friction, so it is not surprising that the CIM motors are running hot.

[rainbowbear998]

Thanks for the great responses everyone!! Our final solution is a bar that will rotate up and provide a hard stop at the height we will be carrying our stacks at. Hopefully that wil minimise the time we have the motors stalled.

[aciarniello]

Originally Posted by rainbowbear998

Thanks for the great responses everyone!! Our final solution is a bar that will rotate up and provide a hard stop at the height we will be carrying our stacks at. Hopefully that wil minimise the time we have the motors stalled.

If you have concerns about weight, I'll suggest our solution to a similar problem that didn't cost any weight. Or rather, ask a question: Can you strategically afford to be holding up totes less often or for shorter durations?

We do not hold our large stacks off of the ground to score them, they are pushed along the ground by the robot. This way, your lift CIMs don't have to run in reverse to hold up the load...let the ground do the work!

Perhaps not strategically or mechanically an option for your robot, but just a thought!

[LeelandS]

It was mentioned earlier in the thread, but having a worm gearbox driving your elevator is a viable solution. We used the RAW Box from AndyMark this season and we were relatively pleased with it.

The RAW Box is backdrive-resistant, and once you have your motors hooked up to it, it can easily hold the weight of several totes and a can without any power from the motors. The only time we found the elevator would be forced down is when we were carrying 6 totes and a can, but 5 totes and a can was fine. We had the motor controllers (Victor SRXs) in brake mode, and combining that with the natural resistance of the gearbox (which took the brunt of the force), our elevator motors typically ended extended practice sessions at a slightly warm temperature. I think we enjoyed it more because we didn't have to devote more time and resources to a "proper" braking system.