Motors from Amazon

 

I bought four of these motors from Amazon as a set of four for just under $30.  They are the equivalent of five plates thick and are the same as a 2 x 4 brick in footprint.   Other people in the reviews have said they are 2 x 4 bricks, but they are two plates thicker than that.

Below are the videos that I took of testing these motors.  The first test is a very light to no load test.  The only load is an axle and large gear.  In the second test, I used one of my demo platforms which is driving a a gear as a cam and a rubber band to pull back the platform.  So in this test the load is the large cam and the rubber band.

After about five minutes the motor on the upper right start to slow down.  At first this gave the appearance of an increasing load.  Then it started getting more and more inconsistent, like it was having a hard time getting over a spot on the rotation.  Eventually it quit running.  The motor was a little warm.  The other three kept running at full speed, at least it appeared to be.  I did not measure the rate of rotation, only what my eye could see.

I only tested one motor on the demo display.  Again this started out fine, but after about five minutes it started to slow down.  Then it became obvious that it was having difficulty pulling against the rubber band.  A few minutes later it stopped.  Again the motor was warm, a little warmer than the no load test.

In all test cases, after a few minutes of being off, they started working again.  My guess is that there is a PTC type resetable fuse inside.  As the motor heats up the fuse increases in resistance, thus slowing the motor down until the voltage drop across the fuse is so great that the motor cease to work.

One test I did not do was to try and control the motor speed with a PWM signal.  Since the observed performance was not that good, I decided not to try.  If I decide to keep them, this will be something I will try.

My conclusion is that these might be good for limited light duty that is not continuous. They have limited use in any thing else, especially anything that is continuous and loaded.  I have not decided if I will return these or not.  I may a use for them in some small, lightly loaded, lightly used module.