motors burning out

[Paul__B]

The next step up is going to be RC hobby servos. A little overkill for your application since you don't need accurate positions.

You reckon?

my project is a musical one. so the actuators are used in combination of sticks and pedals to strike percussion instruments.

That's not your average RC model servo.

[wvmarle]

Have a look at this thread, particularly the video link of #5. Look like what you're trying to do. Looking at the video it seems he's using solenoids to push down the drum sticks, and a rubber band to get them back up.

[taterking]

That's me and my daughter in the video! LOL.

[MarkT]

Are you sure there's a motor in those door actuators? Not a simple electromagnet?

Most modern door actuators are motors, you can hear them work!  This one obviously has a motor unit and a
rack-and-pinion section from the shape.

They are certainly not rated for continuous use, nor for use under continuous stall (I suspect the circuit driving them senses stall and cuts the power automatically - modern motor control is smart)

Basically any electric motor encased in plastic is likely not for continuous use, motors need ventilation or metal heatsinking to work continuous due to the high power densities involved.

I'd be tempted to see if the plastic casing can be partially removed to help cool the motor part.

[wvmarle]

That's me and my daughter in the video! LOL.

Didn't look at the user name, didn't realise it's the same.
Of course you really should have posted it yourself, as it'd have shown everyone here right away what you're up to, and we may have been able to come with solutions already instead of wasting a full page to even get to understand the application.

[Paul__B]

So clearly you need heavier-duty motors.

Another odd, but quite serious suggestion would be to take a leaf out of gaming PCs and water-cool the motors!

Wrap copper tubing around the motor housings.  Probably more effective (and quieter) than forced-air cooling.