After starting a few threads on RC Groups forums, and giving the design some thought, I’ve decided that the way I will be starting is with a quadcopter (was tricopter).
Change to a quad was dictated by the design of the frame. I couldn’t come up with an elegant and simple solution to design a body using few fabricated parts. A quad design uses much fewer fabricated parts. So far I only have to drill some holes in some aluminum angle. Simple enough.
I will use 3 tail rotors (HK-500GT Metal Tail Holder (Align part # H50073)) since they are pretty cheap, at $13. That’s about the cost of one good prop.
Using HK450 tail units instead of the hk500 tails. The 450 has cheaper components.
One central motor will drive the whole system, which will be located in the center of the craft, and will drive the rotors using the belt system that comes with the tail rotors.
No rotation mechanism will be used on the rear rotor, as I will use a few vanes, and adjust their angle to direct the thrust. This should simplify my build considering, and it won’t interfere with the belt drive system.
I will eventually duct the props, for increase efficiency, and safety (so failed blades won’t kill anyone). Speaking of ducting, there a great thread here on construction of a ducted propeller build. Need to finish reading.
Found some interesting info on propsizes and thrust produced here. Need to give it a look.
Interesting: variable pitch heli tails not as efficient as a prop…here.
Another interesing post to read here, regarding variable pitch rotors.
Another Hong Kong shop for heli parts, here.
Forum post on SAFE lifting weight of different sized RC helicopters. Did a plot, and the trend seems to be exponential.
No 205mm blades, but from this, I’d estimate a safe lifting weight of 0.42lbs (190g). Not quite what I expected.
Servo choices: I looked at the recommended servos for a 250 and 450 sized helis. They seem to recommend similar size servos for both copters. 1.8Kg-cm servos seem to be recommended. So 3 servos should be able to put out 5.4Kg-cm of torque. I am also looking for a digital servo, so that raises the price a little, but I think I found a 3.5Kg-cm digital servo at just over $11. Less torque, but I think should be adequate.
I should use this servo torque calculator to estimate a torque, to see if my choice is correct.
Torque tube upgrades: Tarrot Torque tube upgrade