I just bought a BP-21 from my LHS on impulse after having seen them online for cheap. I also bought BP's 15A ESC to go with it. Costs: $14.95 outrunner + $23.95 esc.
My concern is... I know you get what you pay for... but, I ran the motor to test it using 8-cell Nimh 2/3 AAA pack (yeah real powerhouse
) without any prop on just to see if it ran correctly. It felt so "clicky" when I turned it by hand earlier that I wanted to be sure there was no binding anywhere. Well, besides the funny boot up tune, the motor got up to speed, BUT it started to get real warm. I checked the temperature of the can <100'f, and the coils were 125-140'f, and surprisingly it was hot enough that I couldnt touch the base mount for too long. I ran it for barely 10-15 seconds bursts along the throttle range, with NO prop attached. Do these BP-21 heat up under no load normally? Then I decided to attach the smallest prop I had lying around, 11x4.7 just to see if that made any difference with moving air. Sure enough, the motor stayed hot through the throttle range, as if I had not changed anything. The ESC the whole time just got a little warm, but nothing unusual.
I noticed that if I throttled down very low, the motor would actually slow down at one point in the revolution, and then speed up a little bit after it got over that area. I'm thinking I may have a bad motor, or is that to be expected from these? I've previously enjoyed trouble free use from E-flite's 450 and 480 before crashing, and I know they didn't heat up that much just running without a prop on.
Of course I plan on getting an 8x4 and 9x4 GWS prop to test it for use on my Slo-V using 6-8 nimh cells that I have.