I ordered a total of 6 motors from China, 5 of them are working normally.
If you measure the resistance with a good quality meter, 12 Ohm is normal. This one is showing a short circuit.
*do* measure the resistance of every motor before wiring it up
Attachments
short1.jpg (209.59 KiB) Viewed 6301 times
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good? Stacie - tidy flipper; 4wd driven by hair bands
On a related note re the N20's ..
I have had the simple "bent metal" brushes fail on these.
There appear to be some N20's made with "proper" carbon brushes.
Does anyone have more info about this, sources, etc?
I found that my cheap home meter behaves somewhat like a random number generator, my guess is that it's putting AC or some switched voltage through.
The good meter (pictured) is in Reading Hackspace and consistently gives 11-12 Ohm for the good motors. It also depends slightly on the shaft position, because not all the windings may have the same resistance.
After I have finished dealing with Banggood about getting a replacement, I will post a tear-down of the failed unit.
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good? Stacie - tidy flipper; 4wd driven by hair bands
The 0ohm short-circuit motor, I decided to use as a "mechanical prototype" that I could bash around as much as I wanted, trying to make it fit.
Essentially, I connected it mechanically to my flipper and started bashing it around a bit.
To my extreme surprise, it seems to have "recovered". I tried powering it from a bench supply, and it now runs!
So I guess it was an internal mechanical problem with the brushes which fixed itself with enough abuse. I didn't open the motor.
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good? Stacie - tidy flipper; 4wd driven by hair bands