Quote:
Originally Posted by martin417
Theoretically, a CIM should be able to swing that 12 x 3.8 prop at 8500 rpm, giving you 4 1/2 lb. thrust, and only using .35 HP. Sounds like a good candidate to me.
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The no load RPM spec on the CIM is 5310 @ 12V. Trying to remain 1:1 is the basic problem. I don't see how you can do it without a much larger dia. At a torque load and RPM that will give you the required shaft horsepower for this prop at 8500 RPM you would need to gear it up about 1:2.75. But those numbers are really for a normal prop, not a slow fly. SF props at this size are not safe at this RPM even for airplanes. When you add the likelihood of shock induced tip flutter from collisions it's a bit scary.
We are using direct drive FP motors and our thruster is still optional. We were originally planning to machine a custom prop but are now planning on off-the-shelf adjustable pitch props with a custom machined 3 blade hub to get us a 1 - 2 pitch in a pusher configuration.
As another poster pointed out, careful attention to the shroud will help.
I suspect we may see both geared up CIM's and Direct Drive FP's with total thrusts approaching 10 lbf (at the start of the match).