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Apr 19, 2001, 02:47 AM
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I need help with motor timing.

Like a fool I moved the endplate on my new promax cobalt 4014 before I marked it. Now I have a few questions. Everyone talks about reversing the polarity and adjusting the timing, but I installed a apc prop backwards (tractor for a zagi) and I don't need to reverse the polarity. I don't understand why everyone talks about reversing the polarity and adjusting the timing. Did I do something wrong?? Why does everyone talk about it? I set my timing to be about 20 amps static with an apc 6.3x4. Is this way above the efficiency curve? The stats say max 20 amps, but I assume the amps will drop to about 18 amps at speed. Does anyone have suggestions for what kind of current I should see with this prop. Should I go for a 7x4 or maybe a smaller prop. I don't have a lot of experience in propping electric motors. I need any advice anyone has. Thanks for your help again everyone.
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Apr 19, 2001, 03:30 PM
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anyone have any suggestions?
Apr 20, 2001, 08:06 AM
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If you are going to run a motor designed or pre-timed for tractor operation as a pusher, using normal tractor props, then you do indeed need to reverse both the polarity, AND retime it for reverse rotation.
"Advance timing" means the brushes are positioned 'earlier' in the rotation. When you reverse polarity, the brushes are now 'later' in the rotation - you need to rotate them so that they're 'earlier' again, by the same amount. Measuring sometimes works (many motors come with prescribed or printed marks just for this purpose) or measuring current draw, as has been described here many times..
Jun 09, 2001, 11:12 PM
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I screwed up the timing (I don't have a whattmeter), so I sent it back to MPI to re-time it for pusher configuration, maximum efficiency. It's on a Zagi, and I am trying both a APC 7x4 and 7x5. Now it screams. Goes absolute vertical 150+ feet. Learned my lesson - won't touch the timing now!

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