I am seeking some input on the structural support of the kitbot transmission plate. I am contemplating options to cool the CIM motors and would really like to blow the air vertically rather than horizontally across the motors. The plate really interferes with that preference of mine. How much structural support does it supply? Can I achieve the same purpose by using two 1" angles of aluminum. The large fan fits perfectly between them using the bolt pattern on the transmission boxes. I have not weighed the plate and compared that to the angles. What does the plate offer in support that two angles could not provide?
Is there any advange to keeping the plate and removing a 3 or 4 inch hole for the air flow from the fan?
Actually…why would you ‘have’ to cool the motors? They’re good motors and they havn’t burned out. We actually raised our robot and had it go full speed foward and had the wheels run for lik, 20 minutes or so and the motor didn’t even get warm.
At the point your CIM’s get warm to the touch, they’re probably flaming hot inside; the CIM’s have a pretty thick metal casing. And like what Stonefan said, the CIM’s are pretty robust motors.
You could always cut it short or use different supports(prefrebly L or C channel aluminum extrusions) mounted underneath the transmissions. They have three rows of those slip holes, and atleast one depending on your set up should be overhanging on the inside of your robot. Should work well for what you need.
Okay i also forgot to say that before we had the robot running with the electronics, we actually had a guy make a backing for it and a 90 lb guy, short light guy, was sitting on it, and we also had a 160 lb guy on a rolling chair tugged by the robot and went across our football field, also getting all of us in trouble. It was sorta cool, not very smart though, and the motors are still in practically perfect condition. They weren’t hot at all from towing about give or take 150 pounds. We also had them getting currect directly from the battery, also not very smart…so ya. I’ve found old CIM motors in our closet and people have dropped them quite a few times and they still run as if they were new…well…sorta…but they’re okay. But those CIM motors are really powerful and also very durable.
I don’t know if our CIMs will heat under a load yet. I am anticipating that they might.
What I am hearing from replys to this and another post is that adding a cooling fan outside the case of a motor is of no consequence. Cooling by an external fan does nothing to prevent damage inside.
I can’t say if we have our transmission geared correctly in the power curve but am trusting the FIRST volunteers who designed the kit transmission. We are using the unmodified stock kit componants with the 8" x 1" wheelchair casters in a four wheel drive configuration.
I still consider it prudent to add some air movement to aid in the radiant cooling of the motor cases. I will not consider it a top priority in the design and just find a location to intall a fan to get some air moving in the vicinity of the motors. :o
The gearing this year is definitely adequate to prevent excessive heating. The final ratio (counting the sprockets, not just the transmission) is 17:1 I believe. Last year we ran successfully with a 13:1 ratio, the motors would barely be warm after 10-15 minutes of driving around. They even moved the bot around with a 4:1 ratio, but they were definitely too hot then.
Unless your going back and forward quickly, or in a shoving match for most the 2:15 I would expect the motors to be fine for the match and quite a bit afterward.
Why is it that people keep saying that? Even at a reasonable load, the motor can easily be outputting 100+watts of heat. Even if the motor can radiate that safely itself, it is going to be hotter (significantly) than if it had some active cooling. Now say you do have a short spike in heat output. We can all agree that we would much rather have their cooler motor to start with spike, then the hotter one.
Sure its a bad idea to rely soley on cooling in your design to protect your motors, but you can definitley get more out of your motors if you cool them.
Max,
Run some numbers and I bet you find that the CFM of the fan vs. the radiating effectiveness of the motor case cannot get rid of 100 watts. (actually, if you are running the kitbot trannys then it is more like 250w/motor @ 40 amp input) If you blow air on the wire end of the motor (this is the end with the brush assy.) you may reduce the case temperature a little. If you were to add cooling fins and fan, you might be able to get the outside of the case down to ambient but there is no direct thermal connection to the armature where much of the heat is generated. If you end up far enough under wiegth to add fans, my bet would be on blowing them at the wire end of the motors. It might not do much, but if it makes you feel better than do it.
