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Old Feb 25, 2010, 04:16 PM
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Would a direct-drive tail rotor work?

I was thinking that for the rc heli I'm building from scratch, it would save me a lot of trouble if I just stuck the tail rotor I made directly to the tail motor. By this I mean, no gear-pinion relationship between the tail rotor and the tail motor I'm using. The tail motor is going to be gyroed to help keep the whole thing stable.

I can't think if why this wouldn't work, but maybe you guys know?
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Old Feb 25, 2010, 04:20 PM
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How big? There are a lot of micro helicopters that use a direct drive tail rotor.
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Old Feb 25, 2010, 04:22 PM
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Its a 200 size vehicle more or less. Tail rotor diameter is about 125mm

Main rotor diameter is about 455mm
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Old Feb 25, 2010, 04:37 PM
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it will work fine then
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Old Feb 25, 2010, 06:44 PM
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DONE! I tested it with a single AA battery and it seems stable:





Can't wait to test it and mount it when my replacement lipo comes in!
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Old Feb 25, 2010, 06:58 PM
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Just wondering, how much experience do you have with helicopters? Most people start off with a mini helicopter, but know about the micros with DD.

The tail rotor looks to have zero pitch, which means it will spin fine but will produce no lift (the airfoil on the blades really don't provide lift at 0 degrees, cause which way would the lift vector go if its balanced?)
Looks like a home made mount, lite ply? I would not use that, even if its the slightest bit off, it will vibrate like a mo-fo at high RPM. The left side looks a lot longer than the right side, might be an optical illusion. Bad vibration will instakill the helicopter.
Blades also look a little too big. Try using a GWS 3x3 or something in that size range, should get you a good idea of where to start. I don't want you to loose an eye with that thing exploding.
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Old Feb 25, 2010, 07:43 PM
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Yeah I noticed that it has zero pitch. I plan on adjusting that once I get a chance to mount it.

Also, that is not plywood; its fiberglass. Both sides are perfectly equal in length, I measured.

We don't have much experience tbh, but that's part of what makes the project interesting I suppose :P
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Old Feb 25, 2010, 07:48 PM
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And once you add any pitch to them, the motor will be under load and get very hot with blades that diameter on a brushed motor that small. It will most likely cook and freeze up within minutes. As the above post already said, those symetrical blades are for a variable pitch tail heli designed to mechanically alter the pitch in flight with a servo. Most direct drive helis use a small plastic prop with a fixed pitch already built into them and only the motor RPM controls the tail. They just press directly onto the motor shaft and dont require the extra weight of anything to mount blades to like are using
That motor is only going to be able to handle a very small prop and you will still need a heatsink on it. It looks like the motor on a Nine Eagles Kestrel 500 SX heli or an E Flight Blade CP which uses a geared tail drive setup and larger prop to avoid cooking the motor
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Old Feb 25, 2010, 08:00 PM
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Thanks for your advice guys. I'll definitely order some smaller blades then. I'll look at that GWS 3x3 prop.

Or maybe a Blade MSR prop...
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Old Feb 25, 2010, 08:03 PM
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Thanks for your advice guys. I'll definitely order some smaller blades then. I'll look at that GWS 3x3 prop.

Or maybe a Blade MSR prop...
The Blade MSR is waaay too small. The entire heli is only one ounce. It will never work on a heli with a main rotor diameter of over 400mm. The Kestrel is 380mm at the main and the direct drive tail setup on it barely holds and the motor gets really hot
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Old Feb 25, 2010, 08:07 PM
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Yeah I just saw a comparison shot of the MSR and it is TINY!

I'll find something else then...
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Old Feb 25, 2010, 08:14 PM
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If I go with the GWS 3x3, I have to drill out the shaft hole right?
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Old Feb 26, 2010, 12:15 AM
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Usually its press on but with a motor like that, if you do have to drill it, do it by hand.The drill MIGHT melt the plastic if too many RPM is used
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Old Feb 26, 2010, 12:48 AM
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Thanks man. I ordered the GWS 3x3 and I also got the Esky CP3 tail rotor. I noticed that the shaft on the motor I have is probably too short for the Esky CP3 tail rotor at least so I got the tail motor that comes with the CP3 too. Should be a better fit just in case.
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Old Feb 26, 2010, 02:06 PM
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Lets see your frame? Your best bet is to look at or even use parts off some micro helicopters like a Humming bird, Trex, Blade, and there are a lot of clones that look exactly the same
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