Hello all.
I am having some difficulties finding a smaller DC motor to perform a specific action I need. To start off, I am not sure if my math is correct in trying to find the right motor.
Essentially, I need the smallest (yet reasonable cost) DC motor that will crank a nitro powered engine over. I am going off the base requirements of a typical nitro field starter. The specs on the starter are:
Volts: 12
RPM: no load 4500rpm, load 3100rpm
Measured torque: 310 oz-in at stall
Essentially, at the end of the gearing it needs to basically push 300 oz-in stall, at 3000 rpm’s.
I have been looking at various DC motors without gearboxes, as I need to specifically create my own. In my search, I keep coming across values on motors such as “Max Efficiency Torque” and “Stall Torque”. I believe I understand what the difference is, but not the overall impact to the motor’s lifespan.
Take for example this motor I found on www.robotmarketplace.com:
Click Me
Speed : 16,000 rpm @ 12V
Angular velocity constant: 1560 rpm/V
Amps @ nominal: 1.2 Amps
Efficiency: 71.4%
Peak Power: 0.36 hp
Stall current: 91.8 A
Stall torque: 78.7 oz-in
Weight: 7.50 oz (213 grams)
Diameter: 36mm
Length: 65mm
Shaft diameter: 1/8" (3.2mm)
Shaft length: 11/32" (8.8mm)
Assuming I used this motor, and put a 5:1 reduction gear box on it, the stall torque would then be 78.7 * 5 = 393.5 Oz-In, while the RPM would be 16000 / 5 = 3200 RPM.
I am not factoring any efficiency loss through the gears; but is that correct on basic math? Based on these figures, using a 5:1 gear box, would this meet my requirements?