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RC Ornithopter - Motor choice + Additional questions?


Old 08-07-2017, 08:48 AM
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Default RC Ornithopter - Motor choice + Additional questions?

I'm trying to build a human-size, flying robot (5.5 feet tall, weight hopefully under 13 pounds) in the shape of an extremely large insect. It's going to have an ornithopter built into it so that it can flap its wings and fly, so I need a motor that can provide enough thrust to lift the entire robot off the ground, have it hover, etc. However, I'm unsure what motor to use for this. I've narrowed down a few motors that specify 'high thrust', but I'm aware that this is just much a function of the propeller dimensions (or, in my case, wing dimensions?) as the motor itself. A few I've got my eye on are:

P80 KV120_P Type_Motors_Products_T-motor-The Safest Propulsion System - This one claims 17kg thrust, or about 40 pounds maximum. 120 KV, 3300 W of power required.
650KV Outrunner Brushless Motor 2870g Thrust MT3315 for RC Heli Ariplane eBay - I was thinking of putting together a few of these in a sun gear configuration if the above didn't work. Each claims about 2.87 kg max thrust, or about 6.3 pounds.

How do I choose a motor that would work best for generating the maximum amount of thrust with a pair of wings instead of a rotating propeller?

The power supply I have is an array of LiPo batteries that together total 11.1V at 70 Ah (or 777 Wh total). These would only provide enough energy for the system to fly for a few minutes, but I'm unsure whether I can add more without affecting the system's ability to produce lift, as they're quite heavy (each battery weighs 131g and I currently have 10).

The mechanism for translating rotary power to the ornithopter's 'flapping' is a simple mechanical piston that I intend to make of aluminum or steel, shown attached as a Sketchup model.
The wings themselves are made of 1mm diameter carbon fiber batten rods (in a similar pattern to how insect veins are arranged) so as to ensure the wing does not sag vertically under gravity, as well as 2 oz./sq. yd. fiberglass and clear resin for the 'webbing' between the battens. I am worried that under harsh enough 'flapping' conditions at the moment where the wing begins turning in the other direction, the fiberglass might snap from inertia - is this possible? The fiberglass is completely rigid near the base of the wing, with increasing flexibility going out towards the wing tip.
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