Best way to cool CIM motors?
 

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?

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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).

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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?

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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!

Re: Best way to cool CIM motors?
 

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!

Re: Best way to cool CIM motors?
 

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...

Re: Best way to cool CIM motors?
 

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?

I recommend liquid nitrogen.

Re: Best way to cool CIM motors?
 

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

Re: Best way to cool CIM motors?
 

Oh god... Please no.

Thanks to MrForbes for clarifying that rule.

Back to my surgical tubing idea!

Re: Best way to cool CIM motors?
 

It may not be applicable or the best solution to your problem this late in the season, but our team used a different motor/gearbox for our winch. We took the planetary gear box out of a drill and hooked it to a banebot 775 motor. This allows us easy lifting with no back driving or stalling.

Re: Best way to cool CIM motors?
 

Depleted uranium tie wrapped to the frame of the robot.




Whoops, wrong thread.

If you need more lifting than surgical tubing, lengths of bungee cord also work.

Re: Best way to cool CIM motors?
 

Time isn't really an issue for us, as we are now refining our robot for our next event, which is an off season event in June. Unfortunately here in Australia we aren't as spoilt for choice with regionals as in the US!!

It seems that having a worm or planetary gearbox is the best option to stop the motors heating up at the moment. I have one question though - will they perform ok with a few kilos of weight on them?

Re: Best way to cool CIM motors?
 

We designed part of our lifter gearbox with VEXPro versaplanetary gearboxes. However, I would check your load requirement against this document before purchasing one:

http://content.vexrobotics.com/vexpr...s-20150106.pdf

Watch out if you are planning on using a very low reduction with a CIM or a MiniCIM

Re: Best way to cool CIM motors?
 

Depending on how much you want to lift you may need a stronger motor. We can reliably lift five totes without a can. If one wanted to lift heavier weights, adjustments would probably have to be made. As for performance. We did have a problem with the motor breaking. But we found that it was caused by our top limit switch malfunctioning. This caused the winch to constantly stall against the top of our elevator, which ruined the motor. Other than that the assembly has performed spectacularly.

Re: Best way to cool CIM motors?
 

You could also make a winch:

Attachment 18662

Re: Best way to cool CIM motors?
 

1440 watts.

Re: Best way to cool CIM motors?
 

Not too long ago there was a thread talking about dry ice and its legality. Maybe that might work well ::rtm::

Re: Best way to cool CIM motors?
 

Only if you plan on using all of that load. We have a pretty fast elevator (1-2ft/sec) and we haven't run into load problems yet in the versaplanetary.

Re: Best way to cool CIM motors?
 

I love that idea! How hard was that to manufacture? How reliable is it?

Re: Best way to cool CIM motors?
 

Last year we cooled our CIM motors and Compressor with server rack blowers. They were considered legal, and worked amazingly well. You can put the KOP heatsinks on them for further cooling.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

It's built from:

AM-0145 Toughbox
AM-0396 long hex output shaft, cut down a bit
2 - AM-0069a 500 Hex hub, modded with set screws. One hub is also modded with teeth
2" of aluminum tube - 1.75" OD
Mini Cim
HS-422 servo
#10 threaded rod
3/4" x 1/2" aluminum bar as spacer for dog (has F <-> B in photo)
3/4" x .125" aluminum bar for dog
.090 servo support plate (sits between bar and the gearbox, holds the servo in position)
small qty of .090 polycarbonate to make dog actuator for servo
2 longer bolts (I think they're 1/4x20) for fastening spacer bar and plate to gearbox
#10 machine screw with washer for pivot. The spacer is tapped to accept the screw and there's one washer on the other side.
spring (random hardware store spring)
smaller machine screws (#6?) to fasten servo to servo support plate

It's probably 3-4 hours of work all together.

One key to longevity is to keep the dog from riding on the modded hex hub when the winch is operating. When we operate the winch in the lowering mode, we slightly raise it first before actuating the servo, so that the dog does not bind.

The only concern we have is that the winch is supported on only one side. We're bringing another gearbox plate and necessary hardware to make a support for the other side if that turns out to be a problem.

Re: Best way to cool CIM 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?

Re: Best way to cool CIM motors?
 

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!

Re: Best way to cool CIM motors?
 

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

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

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.

Re: Best way to cool CIM motors?
 

I'm surprised there are 36 posts and nobody mentioned the CIM Cooler. Check out some of their charts, they will show how much of a difference fans and heat sinks make. They will make a noticeable difference, and your robot safer.

You may want to check with AndyMark, but they may be able to deliver http://www.andymark.com/product-p/am-2865.htm straight to your pit in STL.

For the last few years we have been running at least 2x 120mm fans on our drivetrain motors and I do believe they improve the long term quality of the motors.

Re: Best way to cool CIM motors?
 

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!

Re: Best way to cool CIM motors?
 

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.