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2408-21T motor and ESC Problems

Old 06-06-2007, 11:31 PM
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Default 2408-21T motor and ESC Problems

I just purchased a TowerPro 2408-21T brushless motor with an 18A ESC and I'm getting poor performance. ( http://www.unitedhobbies.com/UNITEDH...idProduct=4853 )

The problem I'm having is that the ESC/motor are not drawing the amps they should with the given battery and prop size, compared with data from aero-nuts.com: http://www.aero-nuts.com/product_inf...products_id=82 . With an 8x3.8 prop, I get about 7A with a fresh 10.8V battery (measured in series where the battery connects to the ESC), but I should be getting above 10A.

I measured the voltage across the positive and negative terminal of the Dean's ultra connector that connects the ESC to the battery and it was 9V, not 12V like when I measure the battery without it connected to anything (just touching positive and negative terminals of battery). So, that explains why I'm not getting as many amps as I should.

Just to confirm the problem I'm having, I went back and tested an 8.4V NiMH and was getting 6A, with about 7V instead of the 9V I get when just measuring the battery. It should be about 8A. I've also tested a few 2-cell lipos, and they are running at about 5.5A, instead of 7.2A. I've also tested different prop sizes as well, including 7x6, 8x3.8, 8x6, and 9x3.8. Oddly enough, there isn't much of a difference in amps between all the props tested.

So either my motor or ESC aren't drawing the volts and thus current they need. I've tried about 6 different batteries, and they all are not performing as expected both voltage and amp-wise. They are fine with other motors/ESCs. It's not my transmitter either, as I've tried two different ones (Shun Da Piper Cub and E-Sky Lama transmitters). Also, I notice the motor RPMs reach a cutoff well before I push the throttle stick all the way up.

What could be wrong? Could it be the ESC not drawing enough power from the battery, and thus the motor isn't going full RPMs? Is there anything else I can test? Thanks in advance.
Old 06-07-2007, 12:46 AM
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Default RE: 2408-21T motor and ESC Problems

Now this is something I don't understand: when the ESC/motor are connected to the battery but throttle is down, I get 12V with the 10.8V battery (same as not connected). As I increase the throttle, the volts go down. They end up at 9V. I don't get it.

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