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New to Motors (help please!)

Hi Pololu -

I’ve been trying to figure out a project for almost two years now, on and off. I don’t have much aptitude for this subject, despite having gone through the “Making Things Move” book and asking a handful of more-experienced people. I’ve probably got a thick head.

Essentially, I’d like to find a solution for replacing the motor/gear system in old, broken tape recorders. Since there are gearbox-based motors with powerful torque, it seems like there could be a cheap, easy way of running these old machines.

To get started, I’m thinking I’d like to start with a particularly powerful motor that has the capacity to run at a particularly slow RPM. I’ve been looking at the 1000:1 Micro Metal Gearmotors - but having a hard time deciding which one to get. I’m also wondering if there are any cheaper options that might work, since $25 is pretty expensive for a motor I will likely fry in the prototyping stage :slight_smile:

I am looking to have variable speed control, to some extent… which I know changes the potential torque efficacy. My fear is that if tape gets caught or stuck, whether or not the torque will be enough to break the tape without damaging the motor/gearbox…or if there is another safeguard. I’m still pretty hazy on torque, stall torque, stall extrapolation, etc… I think I’m looking to find a number that gives me a baseline weight that a motor can move without reason to worry.

Finally, on top of all of this - I’m trying to figure out how to drive the motor. I have a 12v 3amp bench supply - and a variable voltage regulator that should give me the ability to change the speed. I’m slightly worried about overheating or burning out the motor, though - there are so many details on the datasheet, I’m having trouble understanding what my driver circuit needs to be and what the motor can handle.

Any counsel would be greatly appreciated. Thanks.

Hello.

You can check out this force and torque blog post to see if the information there can help you get a better idea about what you need, but if you really have no idea where to start and are looking for a lower-cost alternative to our Micro Metal Gearmotors, you might consider doing your initial testing with one of our plastic gearmotors. Once you have an idea of the amount of torque you will need from the motor, then you can try to find a motor that can apply that torque around its maximum efficiency point. By the way, if the documentation for a motor you are looking at does not include its maximum efficiency point, then a good rule to follow is to not use a motor for loads greater than 20-25% of its stall torque.

The best way to control the speed of a brushed DC motor is to use an appropriate motor driver or motor controller. To be safe, I recommend using a motor driver which can continuously handle a current greater than the stall current of your motor.

-Patrick