Gear or direct drive??

[Chris]

Can anyone shed some light on the benefits of gearing a motor for use in a very small (as in 2 to 3 ounce, 12 to 15 inch wing span) model? I know part of the reason is to enable a motor to spin a larger prop, but is it still useful when the intended model will only use a prop of about 3 inches?

Thanks in advance.

[jimwalker]

If I understand what I've read correctly, there is another reason for gearing. Electric motors are most efficient if allowed to rev up and run at close to their unloaded rpm's. Unfortunately this is usually way to fast for slow flyers like ours (10,000+). However, when reduction geared, the motor gets to spin at it's efficient high rpm rate, while the prop spins at a much lower rpm better suited to the slow flyer envelope. I haven't flown indoor much, so if you are using 4 cells or less, what I'm saying here might be irrelevant in your case. There are several good articles in the online past issues of RC Microflight on just this subject.

Happy flying!

[Jason Nowell]

Chris:

Jim hit the nail on the head, indoors or out. The main reason for gearing is to reduce the current drawn by the motor, therefore extending the flight time. I build and fly small stuff like you're talking about and I generally use a Lite Stick (GWS DX-A) motor direct drive with a 3.5" prop. The "A" version of the motor has a BUNCH of torque, so it can spin up pretty good with that small of a prop on it. I'm experimenting now with N-20 motors (Wattage B-2 replacement motors) direct drive with a U-80 Union Prop from Cloud 9 RC. These motors draw about half the amps of a stick motor and put out 75% as much thrust. Using 50mAh cells with this setup produces a light aircraft with a bunch of thrust.

Good Luck,

[Chris]

Thanks guys,

I wondered if it also had to do with the efficiency of the propeller at higher speeds. I was looking into using some pager motors or possibly the motors from some old servos and wondered if gearing was necessary. In the end, I guess I can't go wrong just buying a KP-00 - motor, geared and everything for around $20.

-Chris

[ 04-26-2001: Message edited by: Chris ]