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RC Flight Question: Counter-rotating props?

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DigiTan

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I'm trying to build a mini-UAV that is based more-or-less on the **broken link removed** or the V-22 Osprey airframes. The problem is that I can't find a set of propellers that are reverse-pitched for counter-rotation. I've tried online and walk-in stores like HobbyTown USA, but nothing has come up. The project has been grounded for a long time because of this.

I tried taking a chance with co-rotating props, but the torque against the plane was so strong, the craft began spinning before it even left the floor. The gyroscopic effect would also be too extreme for the plane to manuver safely.

Basically I'm looking for any plastic prop with an 8-12 inch diameter. I'd prefer a 3-blade design to 2, but that's not critical. The type I had in mind was something like the reduction series **broken link removed**. Right now I'm using these **broken link removed** with an 8.4volt power supply that can dissipate over 55 watts. I'd need between 200 and 250 grams of thrust from both propellers (for vertical mode).

Does anyone have recomendations as far as where I can find these propellers? If they came in pairs, that would also be helpful.
 
If you are still interested, I would suggest looking into creating your own polymer molds. It's not too hard, you can do it with some supplies. Look on google for "plastic forming" or "vaccuum forming." If you could make your propeller out of something like wood, or clay, or whatnot, you could mold it into a plastic form and make several for yourself. Just an idea.

--mindctrl
 
Oh! I was afraid of that! :lol:

Would you recommend any tools in general for this? Do they come in kits?
 
Digi Tan, time for you to visit a woodworking hobby shop and get some basic carving tools and sandpaper and a lump of wood that's easy to carve. Varnish and polish the final product to a high perfection, your propellors finish is only as good as your master pattern.

You only need to carve 1/2 of a blade, make it with a part hub. That way you can cast 4 identical 1/2 blades and arrange them as a 2, 3 or 4 blade prop. First you must make a mold into which you pour your liquid resin later. The mold is easily made by pouring latex around your carved pattern. I suggest you do some googling or get a good book on the subject.
From there you accurately position the identical 1/2 sections into a 2,3 or 4 blade prop from which you then make another mold and cast your final product. This gives you a perfectly symmetrical prop which should need little or no balancing.
The latex molds are easily peeled off the hardened finished prop and can be re - used over and over.

Look at it as a challenge, once you mastered this simple procedure you will be much in demand from your fellow RC modellers, to supply more counter rotating props. Perhaps a business opportunity? :lol:

You will have to source a suitable material to pour your props from so they withstand the forces that a prop is subjected to.

Have fun
Klaus
 
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