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Old Jun 29, 2004, 03:09 AM
Eljimb0 is offline
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Idea

contra rotating prop brushless


I had this great idea this afternoon. and it works
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Old Jun 29, 2004, 03:18 AM
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The drive shaft for the back rotor is inside the front rotors prop. I found a pair of opposite pitch props as a replacement part for one of those aero wanker birds with two motors. ONE cc phoenix 10 drives both motors.
Both motors start about 1/2 the time the other half one or the other starts only. It makes a wonderfull sound. I don't know how to read the prop rpm?
do I set the tach for 4 blades or 2. It rips all the way to WOT.
jimbo
Old Jun 29, 2004, 03:24 AM
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wow


That looks great you have to do an in depth on the build ,ive had a play with back to backs and 2 on a common shaft but that a great inovative application just think no torque reaction no fuz twist and the dreaded wing tuck under. are they standard winds? some motor tests would be great also.
Old Jun 29, 2004, 03:37 AM
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It actually works
Please do post some more pics, especially how the two shafts tie up!
Goof luck
Old Jun 29, 2004, 03:45 AM
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The motors are from mini disc players (17mm. dia stator) For the sake of simplicity and speed I used the stock winds on the motors (I knew they would be the same).I cut the aluminum mount up and ca glued it to the back of another
Old Jun 29, 2004, 03:45 AM
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T(w)ooCool! *all thumbs up*
Old Jun 29, 2004, 03:55 AM
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this is how the drive shaft works
Old Jun 29, 2004, 03:55 AM
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Quote:
Originally Posted by Eljimb0
I had this great idea this afternoon. and it works

This is one I saw @ Aspach 2002:

Old Jun 29, 2004, 05:50 AM
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Very good job jimb0!
Have I any chance to find a slow flyer inverted pitch prop somewhere? I'm thinking about a twin, with counter rotating engines, but I've never seen an inverted pitch prop in any catalogue.
Thanks, Piero.
Old Jun 29, 2004, 06:47 AM
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Jimbo


How about a black line on the rear drum to get the RPM ? mmm could fit one into a delta pusher , was there any make and model number on the units you salvaged ? is there an optimum distance between the props ? I wonder if it related to the air foil of the props. you got my attention
Old Jun 29, 2004, 08:06 AM
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Quote:
Originally Posted by Eljimb0
ONE cc phoenix 10 drives both motors.
Both motors start about 1/2 the time the other half one or the other starts only. It makes a wonderfull sound. I don't know how to read the prop rpm?
do I set the tach for 4 blades or 2. It rips all the way to WOT.
jimbo
Thumbs up to your efforts! Highly interesting.

If I may suggest further tests, it would be interesting if you could hook up another cc phoenix 10 and measure how much less current the rear motor draws in %. Then you could vary the speed of motors to see how much difference you need to cancel out all the torque -I would think holding a mounting in a hand (safely!) would tell you by feeling if there is a a measurable difference. Static thrust tests would be interesting as well -compared against the thrust by only one motor running.

RPM measurement: set you tach to 4 blades, it gives you the rpm of each motor (4 blade result multiplied by two divided by two). Since they run out of one ESC, the rpm is synchronized but current must be different.
Old Jun 29, 2004, 09:38 AM
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That's awesome Jimbo,
I like the way you think! Must be a common thing to banjo pickers!
Old Jun 29, 2004, 09:44 AM
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Quote:
Originally Posted by Eljimb0
The drive shaft for the back rotor is inside the front rotors prop. I found a pair of opposite pitch props as a replacement part for one of those aero wanker birds with two motors. ONE cc phoenix 10 drives both motors.
Both motors start about 1/2 the time the other half one or the other starts only. It makes a wonderfull sound. I don't know how to read the prop rpm?
do I set the tach for 4 blades or 2. It rips all the way to WOT.
jimbo

??? Tried Googling, what are they?
Old Jun 29, 2004, 03:16 PM
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aero wanker birds ;
Hobby Zone- "firebird outlaw"
two props 4X4? $2.50 US. Part number HBZ 4540 Horizon Hobby
jimbo
Last edited by Eljimb0; Jun 29, 2004 at 03:23 PM.
Old Jun 29, 2004, 03:41 PM
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Thanks for the compliments all.



"If I may suggest further tests, it would be interesting if you could hook up another cc phoenix 10 and measure how much less current the rear motor draws in %. Then you could vary the speed of motors to see how much difference you need to cancel out all the torque -I would think holding a mounting in a hand (safely!) would tell you by feeling if there is a a measurable difference. Static thrust tests would be interesting as well -compared against the thrust by only one motor running."
Peter
I will do a bunch of test on this thing after I get some sleep. The project from idea to product took about 10 hours most of that time should have been spent "counting sheep" .


With regards to RPM; because the props blades cross each other 4 times per
cycle the tach numbers wouldn't hold still. I figured it out at 10,000 rpm WOT


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