Which motor is better?

[EricH]

Originally Posted by KenWittlief

are the CIMs still enclosed?

the drill motors and FP motors have internal blowers for cooling, and openings to let the air through.

CIMs have no openings in the case, except for mounting screws, the axle, and where the wires come out. It's the same for both types.

[Andrew Blair]

Not quite. The Large MiniBike CIM actually has one more small hole opposite the output shaft, on the plate holding the back of the armature.

The big one is definitely not, but is the small CIM water resistant? If you take the motor apart, you'll notice that there are rubber gaskets between the different case parts. The only real hole that isn't gasketed is to the output shaft hole.

[Joe Johnson]

There are many things that go into this, but in my opinion, based on power conciderations alone, the CIM motors are the only real choice for the drive train (with the possible addition of the FP if it is not the only motor used).

There are only 2 questions then:

1 motor per side or 2? And Which CIM motor?

If you go with 1 only, the extra power of the 330W motor and smaller size & lighter weight is too attractive too pass up. If you go with 1 motor, I recommend that you strongly consider shifting.

The question of multiple motors per side is tricker.

There are various combinations:
CIM 340W + CIM 340W = 680W
CIM 340W + CIM 270W = 610W
CIM 340W + FP 170W = 510W
CIM 270W + FP 170W = 440W

I think any of them can work but to be honest, I would stay away from the FP in a drive train because they tolerate heat and abuse less well than the CIMs.

It is sort of a toss up for me between the top two above, though I am leaning toward the 680W version.

I used to be firmly in the "1 Motor + Shifter" camp, but I have since become a believer in the merits of 2 motors per side for 2 reasons: it makes your robot peppier in terms of acceleration and it gives you two (2) 40Amp breakers to feed your drive motors.

As to shifters, with the advent of the Andymark.biz shifter and the NBD whitepaper on how to adapt a CIM to a 3 speed XRP Dewalt Drill Transmission, shifters are easier than ever to implement, even for a team with limited resources.

So...

...here is the bottom line advice, this year's Stylish Robot will have 2 CIM 340W motors per side + shifters.

You read it here first...

Joe J.

[Biff]

Just a side note, The torque at stall on the mini bike motor is almost twice that of the small cim. If you want to keep it simple and not shift you might consider that. And if you want it all Check out the Andy mark conversion kit to run one small cim and the large cim out of the kit transmissions.

[Joe Johnson]

Originally Posted by Biff

Just a side note, The torque at stall on the mini bike motor is almost twice that of the small cim. If you want to keep it simple and not shift you might consider that. And if you want it all Check out the Andy mark conversion kit to run one small cim and the large cim out of the kit transmissions.

Yes it is true that the FP CIM has 66% more stall torque than the smaller CIM, but the Smaller CIM has 97% more free speed.

Stall torque and free speed are accidents of birth. You can always trade more of one for less of the other (by gear ratios).

The Peak Power (=Tstall*Wfree/4) is your immutible figure of merit for a motor size.

For example, I can put an extra 1.66:1 gear ratio on the smaller CIM and get 1.66X the stall torque which will match the FP CIM's stall torque. BUT, this reduced smaller CIM will be running 25% faster than the FP CIM loaded to the same torque.

I like the FP CIMs, they are nice motors that will probably run nice and cool even when abused (as they surely will be), but they have 25% less power than the smaller CIMs.

Joe J.