DC Motor stutter

I have a project using a 12-24VDC Mabuchi brush motor with a gearbox; At its nominal 24DC, it spins 45rpm, draws 280mA no load, and stalls a 750mA. 7.5 in-lbs of torque and is rated for continuous duty. (description taken directly from the sciplus website)

I have it hooked up to a AC to DC adaptor which is 0.375dc, .3 amps, which gets it to run at just the perfect speed I need it to, but after being run for a few hours continuously it has intermittent stutters and stops, never quitting completely, though. It's currently installed as part of a gallery piece, and the gallery isn't very happy, thinking this motor is somehow burned out. Can such a low voltage applied for long periods of time really 'burn out' a motor so tough? I feel like I'm missing something here.

bushwickprojects: I have a project using a 12-24VDC Mabuchi brush motor with a gearbox; At its nominal 24DC, it spins 45rpm, draws 280mA no load, and stalls a 750mA. 7.5 in-lbs of torque and is rated for continuous duty. (description taken directly from the sciplus website)

I have it hooked up to a AC to DC adaptor which is 0.375dc, .3 amps, which gets it to run at just the perfect speed I need it to, but after being run for a few hours continuously it has intermittent stutters and stops, never quitting completely, though. It's currently installed as part of a gallery piece, and the gallery isn't very happy, thinking this motor is somehow burned out. Can such a low voltage applied for long periods of time really 'burn out' a motor so tough? I feel like I'm missing something here.

I'd be willing to bet it's your power supply overheating or something.

What you need to do to control the speed of this motor is run it at it's proper voltage and current, but use PWM to slow it down (use a 555 as an astable multivibrator driving an NPN transistor rated for about 1-2 amps of current; a TIP120 would work - and you might not even need much or any heatsink).

If you really are trying to run a 24V motor at a fraction of a volt then this is expected behaviour. If the stall current is .75A at 24V then it should be taking about 11mA at 0.375V - the torque at that low current isn't enough to overcome static and dynamic friction so its only just running.

Using PWM from a higher voltage may improve matters but there is a fundamental issue here that you can't run a brushed DC motor at a tiny fraction of its design speed without friction being dominant.