Originally Posted by ATLAS COPCO
monster stocks the com seems to be a bit on the small side now but boy dose she go why is this, and what diamiter could i go to without all the segments coming apart
I'm not Eric, but I can probably shead some light on this topic.
As the com gets smaller, the brushes develop more "wrap" around the com. This results in more RPM. At the same time, the motor becomes less efficient, and heats up more in a run.
Generally motors with a bigger comm can make the same amount of power, they just have a powerband that is more in the lower RPM ranges. You can still maintain the top end speed by gearing up a bit with a larger com. It will generally run a bit cooler and fade less with a larger com as well because there is mroe copper to disipate heat, and there is slightly less "wrap" around the com.
I won't run any standard size com any smaller than .270 inches. They start at .300 (I think) before they are cut for the first time. For the larger mid com motors like the Reedy quad mag 19T and the Reedy Kr, I wouldn't run them any lower than .310.
Some motors tend to have a sweet spot for the com dia, but it varies from motor to motor. It;s hard to tell just off hand what a specific motor will run good at. Hope this helps a bit.