Stepper motor precision screwdriver

Hello, has anyone built a stepper motor screwdriver?
Perhaps this has been already made?

The idea is having a way (encoder) to set to turn (stepper motor) a selected number of steps (on lcd screen), then having options like turning 1 full revolution, half revolution, 1/4 rev, 1/8 rev.

Turn forward and reverse obviously selected on LCD.


Perhaps this has been already made?

Have you measured the torque required to turn the screw?

Paul

That sounds easy enough... As long as you know how to run a stepper motor, drive an LCD display, and read a few buttons or a knob... If you don't know how to do any of that, work on one thing at a time before you try to put it all together. And of course, you'll have to adapt a screwdriver tip to the motor.

What are you going to use it for? If it's for some kind of adjustment, most stepper motors are 1.8 degrees per step so you'll probably have to gear it down for finer adjustment.

If you're going to use it as a screwdriver you're going to have "torque problems". Either you'll run out of torque, the motor will "slip" and you'll loose count of the steps, or if the motor is big enough you'll strip the screw.

Normally you run the motor as fast as possible and use a mechanical torque limiter to disengage the drive so that the momentum of the motor doesn't strip the screw thread.

DVDdoug:
If you’re going to use it as a screwdriver you’re going to have “torque problems”. Either you’ll run out of torque, the motor will “slip” and you’ll loose count of the steps, or if the motor is big enough you’ll strip the screw.

Agreed. This is a major issue. And the amount of torque needed may vary even between apparently identical screws.

If the motor has too little torque the whole idea is pointless.

If it has the essential excess of torque then you are relying on it stopping after the required number of turns and before any damage is done. Can you determine the correct number of turns?

I guess you could have a slipping clutch that was set at a higher torque than is needed to drive the screw but which is still low enough to prevent damage. But determining that setting might not be easy.

To my mind a traditional DC motor with a suitable clutch makes a lot more sense. You could mount a rotary encoder on a regular screwdriver so you could measure how far it turned.

…R

I have a commercially made torque limiting screwdriver that we use when fastening enclosures together with screws. The torque is set by limiting the current to the motor. When it stalls, the correct torque has been applied.

There is no way you are going to accomplish the same operation with a stepper motor.

Paul

Paul_KD7HB:
There is no way you are going to accomplish the same operation with a stepper motor.

I can see how an exact number of turns would be a good or even better substitute.

…R