Measuring motor speed

[Hangtight]

I've got a couple of motors sitting around, including an SRC high torque that was in a bone yard gun I bought recently. Great magnets, no idea how many TPA or what sort of speed it will run at. I bit of poking the interwebnet failed to produce an answer. So how do I find out?

A bit of lateral thought later I've downloaded a basic audio recorder to my tablet and stuck a flap of tape on the motor pinion. Record the sound of the tape hitting your finger nail and then measure the time difference over a number of peaks in the audio signal. A bit of maths and it turns out an SRC torque motor with Neo magnets does a touch under 22K rpm on 7.4v unloaded. Which on 18.65:1 gears should translate as around 19rps.

At some point I'll get the gun together again and let you know if this is anywhere near right .

 

[Hangtight]

Although if anyone has a rough idea of the relation between loaded and unloaded motor speed that would be handy.

 

[Sitting Duck]

bit less 17rps I'm guessing

I "THINK" they test/run them on 8.4v to equate speed spec

However under load a figure of 25k say goes out the window completely

might get 18rps but my gut is saying just over 17rps max

end of the day - it is nigh on free and if it is a little less whack up the juice

the amps will be lower or use for a 13:1 build

or wtf - a 16:1 DSG build for $hits n giggles

(or a DMR on 11.1v etc.....)

 

[Hangtight]

I'll build for 25-26, then when it gets 17 on 7.4v I'll liven it up with 11.1v.

It was in the RPK I got cheap last weekend. Only thing it needs is a piston, the rest of the internals are barely worn. So now I'm going to take one of the longest AK variants and turn it into something a lot shorter...