Help choosing high accuracy motor, maybe a hard drive servo??

rwgast_logicdesign

I have some sensors and mirrors I need to mount to a motor to do 180 degree or 360 degree sweeps depending on how things end up. Since these motors are just rotating sensors they don't need to have to much torque or gearing. What they do need to do is be integrated with a very hi res encoder and be able to have precise control to stop on a trick with no backlash! I have a few encoders with a few thousand counts which are what I planed on using.

I have a stock pile of motors from hard drives, I have never used them but would imagine these things would have to be precise and backlash free? Maybe there is a better solution, Im not sure what advantages brush less motors have.

Electrodude

Hard drive motors aren't necessarily incredibly precise and probably don't even have encoders. Instead, hard drives just uses markers on the platter to figure out precisely where the head is on the disk. This compensates for thermal expansion and miscalibration and such.

GordonMcComb

Older hard drives used a stepper motor of the same accuracy you can get today with any low-cost unit. Today, the pickup heads are usually driven using a voice coil, which has no "horsepower" to speak of, and wouldn't be able to move much mass. However, it might be enough for a very small mirror, assuming you could repurpose the mechanism. I doubt you'd be able to accomplish the 180-360 rotation without a very high precision lever or gearing.

The disk platter spindle is driven by a brushless motor requiring a compatible drive. Most use hall effect sensors, and the whole thing is likely integrated into the hard drive electronics. You'd have to duplicate the drive, which can be a pain.

From the sound of your project, what you need are galvanometers (though most are limited to about 60 degrees from center). They are very similar to the voice coil on a hard drive, but packaged for easier mechanical mounting for different types of project. Good ones are expensive -- $500 to $3500. The really good ones cost more than a person might make in a year earning minimum wage.

For background, look at the open and closed loop scanners used for laser light shows. You do need closed loop if you expect to be able to accurately retrace paths, such as that needed to write letters with a laser projector.

If your system can go more slowly, and some gearing backlash is tolerable, look at the systems they use for disco lighting. Those units are gearmotor driven, and can often rotate at least 180 degrees.