Evil Robotics

3/30/03 Motor Test 

I set up a wood test fixture for the surplus pancake motor.  The weapon bar was a piece of 7075 Aluminum cut to 3.25 x 19 x 5/16".  It weighted 2.0 lbs.  I crudely made a shaft attachment with a drill, hack saw, and tapped holes.   

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First I tested the pancake motor at 12 Volts.  The spin up time to the top speed was about 4.5 seconds.  To hold the blade still I used a c-clamp.  The locked rotor amperage spiked at about 4 amps.  I put a spring scale under the weapon blade to test torque and it read only 1 lb at stall.  The most amperage I could draw was 6 Amps when I went from full speed and rapidly reversed the direction.  

It took 64 seconds to coast to stop.  After switching the IFI ESC to active braking it took 20 seconds to stop.    

When tested at 24 Volts.  The spin up time to the top speed was about 7 seconds.  The locked rotor amperage spiked at about 5 amps.  It drew 9 Amps when rapidly reversing the direction.  The time to stop with active braking was about 30 seconds.  At 24 Volts the spin rate was so scary fast I was afraid to be in the same garage with the weapon on.  The spring scale under the weapon blade read only 1.5 lb at stall.

I did not have a good way to check the rpm's so I will just have to use the numbers supplied by the manufacturer.  (2150 rpm and 2.4 A at 12 Volts, and 4420 and 2.6 A at 24 Volts.)  

Based on this test, I think the spin up time is too long.  To run at 24 volts, I will need to reduce the speed by a ratio of about 2:1. This should decrease the spin up time and increase the torque. This will also allow some sort of decoupling of the blade from the motor shaft and hence reduce shock to the motor.  The drawback is it will add more parts and the design will be heavy again.

To avoid self destruction, I will need to ensure that the skirt design cannot flip up into the rotating blade.  My prediction is that this weapon will cause a spectacular one hit wonder.  I just hope it is not my robot that is given the Compound Fracture.