28BYJ-48 Motor Shaft Locking

Hi everyone,

I have been running these motors via arduino and provided drivers. Everything is going well thanks to all the help from this forum!

I noticed that the shafts of these motors are effectively locked even when they are not powered. I understand that this is not incredibly common in stepper motors and I wonder how this is being accomplished in this motor.

It actually is quite helpful for my application but I am interested in what mechanism is causing this.

Thanks for the help!

Are the steppers geared? A geartrain can make the output shaft hard to turn (back drive).

The "locking" is simply due to the high gear ratio, which amplifies the high shaft and surface friction in the cheap plastic gears. If you try to force the output shaft you will probably strip one or more gears.

These motors exist primarily for one application, to move vanes that control air-flow in vehicle
heater/air-conditioning systems. Thus its a good thing they cannot be readily back-driven, or they
would lose alignment.

They are commonly used for hobbyists because they are cheap, which is because they are
produced by the million for the original purpose.

Various types have slightly different gear ratios too, which confuses people - but once you
know the original purpose you realize they are not needed to have an integral number of
steps per revolution. They have approximately 2050 steps per revolution, within a percent
or two - some types are exactly 2048 steps, some are not.

Mark,

Thank you for the detailed response. Do you know who actually manufactures these motors (or similar motors) at scale?

I believe it may be a Chinese company (with tons of distribution outlets here in the US), but I am curious about who is actually making these.

These devices are all ASSEMBLED by one company that purchased all the parts from other Chinese companies.

Then other Chinese businesses sell the assembled motors, so no one company actually "MAKES" the motor you buy.

Paul