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I have an n20 DC motor which has a gearbox with a 55mm m4 threaded shaft (see image below for visualization of the motor). I'm compressing a spring with this motor, so the motor needs to work relatively hard to compress the spring.

I am noticing that the spring compresses significantly less (3/4 the expected compression) after the 2nd or 3rd subsequent time that I try to compress the spring (I take about a 1 minute break between runs). I am noticing that the motor is slightly warm after 1 or 2 of these spring compression runs.

Is it expected to see such a large difference in spring compression?

Also, does the motor wear out over long time of use? I have been using this motor for about a month and am wondering if all of this use is causing degradation?

I've attached an image of the specs of the dc motor. The gearbox has a reduction ratio of 1/52 and I am using the 6V motor. You can see our motor's specs highlighted in red.

Could it be that the m4 motor shaft is wearing out over time and causing friction as a result? What about the m4 insert I am using (could that be causing friction over time)?

Here is the spring we are using: https://www.mcmaster.com/9657K371/

Thank you very much for the help.

n20 Motor with 55mm m4 threaded shaft

n20 dc motor with gearbox specs

Jason Easton
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    You haven't said anything about what's powering the motor. – Simon B Feb 26 '21 at 11:09
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    This sounds like you're powering the motor off a small battery. In which case, measure the battery voltage and current during both first and second operations... –  Feb 26 '21 at 13:36
  • Also, possible duplicate of https://electronics.stackexchange.com/questions/549599/how-do-i-find-the-best-dc-motor-for-my-rack-and-pinion-system and (https://engineering.stackexchange.com/questions/40524/advice-on-spring-launcher-project). Is he working on the same project? –  Feb 26 '21 at 13:39
  • In other words you may need to start with a proper analysis of required torque and current as in his question. –  Feb 26 '21 at 13:44

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Increased temperature of the motor windings will increase the winding resistance and reduce the maximum torque that can be produced with a given applied voltage. You could compensate by applying a higher voltage, but that may cause the motor to be damaged. You probably need a larger motor. Along with a larger motor, you should use a motor controller that will limit the motor current electronically. The current needs to be limited to a level that will produce the required torque but not damage the motor with the operation vs. rest duty cycle that you need. It may be difficult to find a motor with a published duty cycle rating.