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Old May 23, 2007, 07:37 PM
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St. Louis, MO
Joined Oct 2002
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Question
Dual motor rpms how close is close enough?

I have a dual pusher plane with two Mega 16/14/4's and Castle creations Pheonix 25s.

I tached the motors tonight and one motor is 300 rpm slower then the other. I do have mixing to the rudders and I have tried to trim the rpms but that has not worked. So how close do duals have to be to get a nice straight flight?
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Old May 23, 2007, 08:24 PM
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Sabrejock's Avatar
Winnipeg, MB Canada
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Switch props and try it again. If the same motor is fast, switch esc's. If the same motor is fast, start trimming the slow prop by carefully shortenning it and rebalancing. Tex
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Last edited by Sabrejock; May 23, 2007 at 08:29 PM.
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Old May 23, 2007, 08:56 PM
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Boston, MA subburb
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Great suggestion about trimming the prop (on the slower motor) to balance motor rpm. I intend to run brushed motors wired in parallel and would never have thought to do that.
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Old May 23, 2007, 10:55 PM
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St. Louis, MO
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Before I go shortening props, what is considered a good range for rpms? Of course dead on is best but what is close? With the props I have now there is roughly a 2mph difference.
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Old May 23, 2007, 11:03 PM
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UT
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I just finished a twin of my own and my rpm's were off about the same as yours. I made a phone call to someone who is experienced in twins and he said 300 rpm difference is fine. 3,000 rpm would be something to worry about.. I would just fly it and see what you think.

-Jon
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Old May 23, 2007, 11:49 PM
I havent decided yet
Indiana
Joined Jun 2006
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if you shorten a prop to make it spin the same rpm as a larger one, it would make less thrust. i think that would make the problem worse. 300 rpm difference is ok if we are talking 30,000 rpm but at 1,000 it might be a problem.
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Old May 24, 2007, 05:47 AM
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Winnipeg, MB Canada
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Prop Sync

Quote:
Originally Posted by dmiller746
if you shorten a prop to make it spin the same rpm as a larger one, it would make less thrust. i think that would make the problem worse. 300 rpm difference is ok if we are talking 30,000 rpm but at 1,000 it might be a problem.
I'm thinking mainly of the sound. Nothing worse to a full scale pilot's ears than out of sync props! Tex.
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Old May 24, 2007, 07:16 AM
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St. Louis, MO
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Oh the props sound like they are in sync, which is the reason I tached them. So sounds like I am good to go then.

Thanks
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