Motors randomly stopped working

[Potatonator]

Last Saturday we got our kit of parts, which included two motors. Those motors worked perfectly fine when we manually turned them then for testing. After testing them, we built them into gearboxes, and then stored them in a box with other parts. Today (Wednesday, four days later), we took out the motors again, and they could barely turn at all. Nothing about them has been modified, aside from putting them in the gearboxes. Any ideas what our issue could be?

Thanks in advance =D

EDIT: Fixed a wording error.

[sergioCorral842]

Pictures of the setup (wiring, etc) will be useful for people to determine the problem.

[nighterfighter]

If you take the motor OUT of the gearbox, and connect it directly to a battery (assuming it is a 12V motor and safe to do so), does the motor turn?

If so, then the problem is in your gearbox. Is your gearbox assembled correctly? Did you grease the gears?

Is the gearbox designed to turn slowly?

Edit: I'm assuming the gearbox is NOT the gearbox provided in the KoP for the kitbot. If it is, then disregard the last question.

[Potatonator]

Oh, I worded the question badly. We haven't actually wired the motors up and run them, we just cranked them by hand to test them. So the issue is just that today, it was much harder to turn. Sorry for my mistake, I'll fix it quick.

[nighterfighter]

I would recommend that you test the motors first.

Also, how were you cranking the motor by hand, when it was in the gearbox? Are you attempting to turn the output shaft by hand?

[Potatonator]

I would recommend that you test the motors first.

Also, how were you cranking the motor by hand, when it was in the gearbox? Are you attempting to turn the output shaft by hand?

After doing what you said and testing it with a battery, it *seems* to run fine.

So today we learned that we need to test stuff before we panicked. Thanks to the people who stopped by to help us with our non-problem =D

[FTC5110]

If you accidentally had the motor wires shorted together the shaft would become much harder to turn by hand. Perhaps that's what happend.

Permanent magnet brushed DC motors are also DC generators.

[MrBasse]

The motor will be considerably harder to turn because you are now turning the gearbox as well. Compound that with the fact that you are trying to turn a small output shaft to rotate a gear set designed to increase torque in the opposite direction to turn the motor means that you are fighting the laws of physics in a way that will cause you to use more effort to get the job done.