Best way to cool CIM motors?

[rainbowbear998]

After competing in the Australia regional, my team have found that our winch motors (two CIMs on a tough box mini) get quite hot during matches, as we have them running to compensate for the weight of the boxes so we can kept them off the ground.

What is the best way to cool these? From what I've read, the heat sinks aren't that effective. At the moment, I'm working on mounting a 120 mm computer fan to cool them. Has anyone tried this? Does it work?

[theawesome1730]

For immediate results in a pinch, you can use an can air duster upside down so it blows out liquid. It works well in a pinch, but the best solution to your problem is to equip some kind of braking mechanism like a bike disk brake and caliper attached to a servo or pneumatic cylinder so that you don't have to constantly run the CIMs at stall to hold a stack. A fan may work reasonably well, but trying it out is the best way to see for yourself.

[MrRoboSteve]

Don't know about your design, but you might also want to look at a counterweight or constant force spring to help reduce the load.

[ay2b]

Keep them cool by not running them. It may sound a bit snarky, but in this case it sounds like you're basically spending a lot of time with the motors stalled (i.e. putting power into the motor, but getting no motion out). That's a good way to both heat up your motors and run down your battery fast.

I'd suggest looking for alternate solutions to the gearbox. Many worm-gear drives are not back-driveable. You may instead be able to add some sort of break system. Look for solutions that allow you to hold the totes off the ground without running motors to do so. Many teams use window, van door, or snow blower motors to drive winches. They aren't as fast or as powerful as CIMs, but they also aren't back-driveable (thanks to the attached wormdrive gearbox).

[theCADguy]

At the New York Finger Lakes regional in 2014, Team 20 had a similar problem. As a result of 3 back-to-back matches, we had noticed that our CIM motors had become exceptionally hot, due to heavy defense. For the remainder of the event, we cooled our motors using canned air.

Upon returning, we decided it would be best to have a more permanent solution, so we redesigned the wooden block that we used to secure our robot on our cart. We added 4 powerful computer fans donated by a local company, placing them so that they would sit under the drive motors when the robot was placed on the cart. It worked well for us, especially during our summer IRI drive practices, as our practice field is not air conditioned.

Edit: If you are using a computer fan, make sure it is not attached to your robot during a match.

[rainbowbear998]

Thanks for the ideas everyone!! I saw a team with a pneumatic disk brake system which seems to work quite well. Unfortunately that won't work with our design though. I'll look at using the window motors we got in the KOP, but our carriage that our forklift mechanism is attached to is made of 2mm steel tube, so it's quite heavy.

I agree that a physical mechanism is the best method, but due to budget constraints we don't have any pneumatics. Can I ask why computer fans shouldn't be mounted to our robot?

[MrForbes]

Some computer fans can be mounted to your robot.....specifically, the ones that came in the Kit of Parts this year, or the ones available from FIRST Choice, this year. Other computer fans, no.

Fans are considered to be motors, and there are very specific rules about which motors you can use on the robot.

[theCADguy]

There are only certain motors allowed on the robot, listed under R18. The only computer fans allowed on the robot are the tiny ones included in the kit of parts, or that come with COTS motor controllers. I wouldn't expect any of these options to be very successful in cooling a CIM.

The fans we used were very large, and were designed to cool large server computers, and could provide a flow rate of more than 100 cubic feet per minute.

[rainbowbear998]

At the moment I'm considering a loose piece of surgical tubing going from the top of our frame down to the carriage, which will tighten as it lowers. It won't be enough to fully hold the carriage, but it should be enough to take some of the stress off the motors.

Thanks for all the replies!

[MrForbes]

This one is pretty good sized, and will move a lot of air

http://firstchoicebyandymark.com/fc15-117

We use several pieces of surgical tubing to help hold up our container arm, and reduce the load on the motor. works good!

[Dale(294engr]]

Large mass of CIM is too great for air cooling to be effective within a match (between matches it may help depending on time to next match)

suggestions:

Alter gearing to reduce the hold current (at cost of speed-time to position)

(assuming CIM use=servo position mode w/sensor feedback to "hold" position)

or

Conduct CIM heat to largest robot frame for most effective thermal transfer during match

otherwise:
perhaps a latch via pneumatics or disc brake though this adds "time" to position/re-position but reduces CIM generated added heat during a "hold" to zero

the heat in the "held" CIM is produced by V^2 / R:
12^2 =144 / ~.1ohm 14.4 watts

or I^2*R of which I is being constrained to hold a position
decreasing hold current by more gearing is effective: generates less heat

(less I effectively produces less average voltage proportional to PWM duty cycle)

"R" contributors:
1. commutator:carbon-CuBrushes + 2. armature wire & crimp resistance

CIM heat is primarily removed via conduction via shaft & bushing closest to commutator

between matches the fasted way to reduce CIM temp would be to have a massive pre-cooled heat sink ready to physically attach to the CIM/Gearbox/Chassis area in prep for the next match

Good luck...

[rainbowbear998]

I just read R18 in the game manual, and with regard to fans, it states:

"Hard drive motors or fans that are included in the 2015 Kickoff Kit, 2015 FIRST Choice, are a part of a legal motor controller (including manufacturer provided accessories), or COTS unlimited computing device"

Would any computer fan be counted as a COTS unlimited computing device?

[Sperkowsky]

I recommend liquid nitrogen.

[MrForbes]

The fan has to still be in the COTS computer device, for it to be legal. Read through the Q&A for an explanation.

[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!