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Old Sep 24, 2011, 06:36 PM
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Contra rotating motor question

Does anyone have any experience with this motor?

http://www.hobbyking.com/hobbyking/s...tor_Mount.html

I am looking for info on how well built it is and how many watts it is capable of.
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Old Sep 24, 2011, 07:17 PM
Jack
USA, ME, Ellsworth
Joined May 2008
16,924 Posts
I can't help but wonder if the term "contra rotating" as used for that motor is not being used to say that the two motors will be rotating in two different directions since the two are essentially mounted back to back (one magnet housing on each end and the base plates bolted together).

The motor appears to have only a single shaft and I assume that it is long enough that both motors are fastened to and driving the single common shaft.

There are also contra rotating motors where one prop turns with a hollow outer shaft and the second prop turns in the opposite direction on a shaft that runs down the center of the hollow shaft. Both props are on one end of the motors and closely spaced, the two motors are back to back but can turn independently of each other.

Or am I confused?

Jack
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Old Sep 24, 2011, 07:32 PM
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C₄H₁₀'s Avatar
United States, AK, Fairbanks
Joined Aug 2009
12,410 Posts
Reading the reviews, it looks like the shaft we see is coming from the rear motor. It is indeed a contra-rotating setup and one prop simply bolts to the case of the forward motor rather than being attached to a second external shaft.

As for the motor's max wattage, it should be good up to a little over 2.5kW on 8S or something like 2000W on 6S (per motor) if their current ratings are to be believed. I wouldn't run it past about 60A per motor; they claim 80.
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Old Sep 24, 2011, 08:49 PM
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I think you are correct with how the props mount. They don't show any prop hardware like thy do on the other contras. I will order one and see what happens.
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Old Sep 24, 2011, 09:19 PM
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Chattanooga, Tennessee, United States
Joined May 2003
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By their figures it should be close to 4800W... 80A @ 30v per motor... but I'd suggest that they are blowing smoke... better that they blow it than your motors do!

700g for the total weight @ 3W/g is only 2100W.
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Old Sep 24, 2011, 10:29 PM
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Yes I think the numbers are too optimistic. One option would be to rewind the motors with quality wire like Dan sells. Do you think a custom rewind and good bearings would help it get closer to the promised performance?
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Old Sep 25, 2011, 04:36 AM
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South Wales U.K.
Joined Mar 2003
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Milo, if you can obtain a copy of the current RC Model World (UK, October 2011), there is an interesting article on a contra-rotating prop drive. (Page 38). It's a gearbox based system mounted on a single motor. Contra-rotating drives using a gear system has been used by some of the F3A fliers.

It appears that an American company is involved in producing some as a commercial venture - contact - CONTRA DRIVES - BRENNER_SHARP@YAHOO.COM

Here's a link to the magazine - http://shop.traplet.com/magazine.aspx?m=mw mainly to show the issue involved, but there is no information there regarding the drive.
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