# RPM's

How many rpm’s is manageable for an FRC robot? And also, does anyone know the speed reduction in a 2007 KOP transmission box.
Basically I’m trying to figure out whether a KOP transmission box is provides sufficient speed reduction… And sorry for the multiple questions, but is it possible to mount a wheel directly to a globe motor? (specs)
or are globe motors more for arms and lifters?

thank you! :]

Math error: see post below.

In general the KOP transmission does not provide enough reduction to directly drive your wheels without an additional chain-sprocket reduction.

However, there are sprockets provided in the kit (2007) for this purpose, which will give you enough of a reduction to drive at a reasonable speed.

You could mount a wheel directly to the globe motor, but it is not a good idea for two reasons.

Reason one: Globe motors are more for arms and mechanisms like you said, rather than drive motors. They rotate at about 90 rpm, iirc, which is very very slow for a drive system. In addition, they need to be geared down further to provide any sort of torque.

Reason two: Globe motors are notoriously bad at handling side loads. Mounting a wheel directly to the output shaft is asking for trouble, as eventually the motor will go bad.

In general, the drive motors in the KOP consist of the 2 small CIM’s, the 2 large CIM’s, and the 2 Fisher Price motors. You’d have much better luck using any of these.

I don’t believe this is correct. Assuming it has a 12:1 reduction, it outputs ~442 rpm which works out to 11.6 ft/s with a 6" wheel.

It has been done. 330’s 2002 robot used them to drive a mini-robot for extra points. However, that was maybe 4lbs of metal and wheels. More than that I wouldn’t do. (We also used them on an arm in 2004–we used two of them for that particular arm.)

CIM Motor RPM = 5310
Reduction = 12:1

Reduced RPM = 442

How’d i mess that one up…

6 * 3.1415 = 18.849" circumfrence

18.849 * 442 / 60/ 12 = 11.5 Feet Per Second

Wow, must have hit the wrong button somewhere. Thanks Cory.

Remember that this calculation is for the CIM’s free speed. The motor will never achieve that speed on a robot because of load, so the actual output speed is probably something closer to 45/50% of this.

hmmm so according to AndyB, the reduced free RPM’s or a 2.5’’ CIM motor would be 442 rpm…so how much more reduction would a sprocket provide?

That depends on which sprockets you use, but 2:1 reduction is typical.

actually lots of RPMs do the work for our team- our Raider Parent Mentor organization…

haha very funny Mr. Cokeley
just wanted to let you know that this question is a result of the KOP gear box you lent us…thanks a bunch

Something like this inexpensive digital tach might be useful for measuring and calculating a robot’s actual top speed:

http://www.meter-depot.com/tacho.html