Broken gears on gearmotor - project guidance?

[jasonwebb]

I’ve been working on a project for the past couple weeks to spin a painting (about 2x2’ of 1/2" plywood) using a DC motor (part number 3207) and a custom, 3D printed mechanical system.

Previously I did some calculations (Advice for right DC motor to spin a painting - #2 by grant) and found that it seemed like the motor would be more than powerful enough for this application, and things were looking good until a few moments ago.

However, I’m using bike chain and bike gears to spin my painting, and when I tried to install the chain manually by spinning the motor a few degrees, the gears inside the gearbox broke. Now when I apply power I get no movement, only sound.

The piece needs to be finished by Friday, so I’m trying to figure out whether I need to source a different motor, or if I should replace the one I originally got.

If I use the same motor, but never spin it manually, are the gears likely to just snap again? I’ve never used these motors, so I don’t know how strong their gears are, but if they are rated for 300oz-in, it seems reasonable that the gears would be able to handle that spec as well.

Video of broken movement: Broken gears Pololu motor - YouTube

[VgKing]

It sounds like you are going to need a plastic steel epoxy, a Popsicle stick and a brush. Some people use thin plastic papers but I wouldn’t advise you to go that route.

[Jim_Remington]

Obviously, the torque applied by hand was far higher than the gearbox was designed to take.

I suspect that you underestimated the torque required to spin up the plywood square. It isn’t clear if you used a ball bearing support on the weight-bearing axle, but in any case the calculation described in your other post did not consider shaft friction.

Finally, it is not clear whether you have taken Grant’s thoughtful advice seriously:

[quote]You should avoid instantly applying full power to the motors as that will apply the full torque of the motor instantly, which can be much higher than your calculated value and could damage the motor or gearbox.
[/quote]

The safest approach is to measure the torque required for the typical usage scenario, and use at least twice that value when specifying the next motor/gearbox. Use PWM or voltage regulation to spin up the motor/gearbox slowly and avoid cranking the setup by hand.