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By captainobvious
#189348
Hi, I'm fairly new to this hobby with my only real experience being a dc gear motor with basic 2 way switch for raising and lower a panel mounted to linear slides a while back.

I have an application where I need to have a laser pointer (about 12" length and 1.5-2lbs weight) alternate between pointing about 45 degrees left sweeping to 45 degrees right and back, continuously. I also need it to be very silent. Speed should be can either be fixed or controllable via a potentiometer, but I'm looking for it to complete a motion of starting left, sweeping right and returning to left in about 2 seconds (and continuously repeating this back and forth sweeping motion). I was hoping there would be a motor that I could mount the pointer to, to avoid any additional moving parts (to keep noise potential at a minimum) and control with a very simple controller.

Ive ordered from Sparkfun before and really liked the quality of the stuff I purchased, so naturally I came back for this project. Any assistance you can offer would be greatly appreciated!



Thanks!
By captainobvious
#189365
It looks like a rear wiper motor may do the trick. They have the linkage built in to provide the alternating sweep motion and it seems like simply a matter of using something like PWM speed controller along with a potentiometer. Just have to find a motor that is extremely quiet now.
By jremington
#189372
Stepper motors can be very quiet, especially if you insulate the motor from its mount with rubber disks. No need for gears or position encoders, either. You can salvage small "pancake style" stepper motors from old hard disk drives -- like the one at the bottom of this image:
Image
By captainobvious
#189379
I need to move the laser, yes. Technically, it's a laser along with measurement microphone. (hence the need for silent operation)

With a stepper, won't I need a more sophisticated control device?
The simplicity of the wiper motor is that the motor rotates one direction, but the linkage creates the push-pull motion which alternates a threaded bolt. I just don't know how quiet they can be.

Thanks !
By lyndon
#189382
A stepper is likely to be the quietest solution. The reason being that windshield wiper motors or other motors slow enough will be geared down and gears are noisy (otherwise I'd suggest an R/C servo). You *could* try submerging the gearhead in an oil bath to quiet it, but I don't know how much effort your are planning on going to. Also, linkages add noise.

One way around the problem of gearing motors down and keeping them quiet is to use belt drive reduction, but that adds parts you may not have.

I have some Maxon motors that are almost completely silent, but they're also $200 each :-(