Monday, August 07, 2006

Propeller Test

I've finished the first round of propeller testing. The test system uses software to send commands to a serial servo controller, which is attached to the speed controller, which is attached to the motor and battery. I measured lift using a digital postal scale.

Photo of the test system. Photo of propellers.

I measured each propeller at 70% and 90% of max power. I expect 70% will correspond to hovering speed, leaving a reasonable margin for climbing, turning, and battery depletion.

I tested each prop in order, then recharged the battery and retested each prop in the reverse order. This should reduce the battery charge bias.


Prop Type/SizeLift at 70%Lift at 90%
APC 10x4.7740g900g
APC 11x3.8800g995g
APC 11x4.7940g1130g
EF 11x4.5950g1130g
APC 13x61085g1335g
MA 13x61150g1345g

Each prop is denoted with its manufacturer and two prop size numbers. The first number gives the prop diameter (in inches). The second number relates to the forward speed of the propeller. For the helicopter, I'd like high static lift, not a high top speed, so I want a low second number. (Though these experiments suggest that the second number shouldn't be too low.)

The best props from this set are the 13x6s. These provide over 1kg of lift at 70% power. The motor, gearbox, prop, electronics, and battery weigh a total of about 350g, so flying with these props should be reasonable. (Some of this lift may be due to the ground effect, though I tried to reduce that by raising the props up off the table top.)

I'm going to order more propellers near the best in this batch (e.g. 13x5 and 12x4). According to the motor specs, I shouldn't go above 13" diameter, so as not to overheat the motor.

Given the charge time for the LiPo batteries, I think I may try a gas-powered engine. More on that later.


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