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BP-21 outrunner, heats up with no prop on!

Old 09-12-2006, 01:16 AM
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Slo-V Flyer
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Default BP-21 outrunner, heats up with no prop on!

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.
Old 09-12-2006, 02:21 PM
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blueline
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Default RE: BP-21 outrunner, heats up with no prop on!

It sounds as though the motor is bad, turning manually it'll feel a ***** "ratchety" as the each winding passes over the magnet. Its shouldn't be "clicky" though. Also, it shouldn't be hot without a load, just warmish. Time to return or exchange it, good luck.
Old 09-12-2006, 11:22 PM
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Default RE: BP-21 outrunner, heats up with no prop on!

Well, yes the motor is ratchety as you say. Oddly enough it does spin up well, and today I tested it with a 9x4.7 GWS prop on 8-cell nimh, and it did seem to have lots of power, but again it reached about 140-150'F toward the rear area. Damn why do I always get the unlucky or troublesome occurances.

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