Need help with pulse width modulation for motor for aiming laser pointer

I'm trying to build a model with a small remote control laser pointer aiming system. I'm not exactly a mechanical genius and, I don't want to spend over $100, or much over $30 if I can help it. I figured I could set up a simple pulley system with some cord running from the laser pointer to two small electric motors, one for right and left and another for up and down. I don't need the laser pointer to swivel 360 degrees, just about 90 vertically and horizontally would work fine. If I were to attach a few monetary switches, I would be able to run the motors one way or the other, and get the laser pointer to point wherever I want.

The main problem I am having is that every electric motor I find has a RPM in the thousands. Such speed would jolt the laser to one side or the other without any means of fine adjustments in aiming.

I've looked around and it seems to be the general idea that either a PWM (pulse width modulation) controller or gear box are the best options to get lower RPM out of a motor. I don't have much room to work with where I want to mount the laser pointer, so I decided to go with a PWM controller and spread the components around the model to save space.

I've been doing my best to construct this....
www.discovercircuits.com/PDF-FILES/SIMPLEPWM2.pdf
... but my knowledge of circuitry is rather limited, having only take a college course on basic circuitry, I'm in a little over my head.

Could someone please identify the component labeled "PULSE WIDTH ADJ" (center bottom, between the two diodes) is it two 250K resistors in series with the lead to the left acting as a resistive load or something else? Also, what is the component labeled "IRFD024" (far right below the motor)

I would be very appreciative for any information that would aid me in getting a PWM controller to slow a motor down to around 50 RPM. If some one has a better idea all together, I would be willing to scrap the motors for another project and start from scratch.

SIMPLEPWM2.pdf(675x484) 98 KB
The component labeled "Pulse Width ADJ" is just a 500k potentiometer octopart.com/3386p-1-504lf-bourns-104679 and are fairly common.  The second a transistor, specifically an N-Chanel  MOSFET octopart.com/irfd024-vishay-7371317 You should be able to use any n-channel MOSFET with similar voltage and current ratings.

That said this doesn't seem like the greatest way to go about solving the problem.  My suggestion would be micro servos, which you can get for 10-15 a piece, maybe less on ebay, but you would still need some kind of controller.  An Arduino would work, but would add another $20-35. If you're interested in this approach there should be some similar projects on Instructables, maybe look for pan-tilt mounts.
cruton (author)  advancedMischief7 years ago
I hadn't considered micro servo's. They may be a little larger than I like, but I might be able to get a couple small ones to fit. The price doesn't seem too much higher than my original idea, and the overall installation seems easier.

The only thing I'm a little concerned about is the Arduino. Having never used one before, I don't entirely know how it works. I'm sure that there are some tutorials around somewhere. I'll see what I can find.
caitlinsdad7 years ago
You might try stepper motors instead.  Look up the instructables on homemade CNC rigs that control the movement .  You should be able to get ideas from there.  Good luck.
cruton (author)  caitlinsdad7 years ago
I thought about using a stepper motor at first, but a few problems arose.

First, stepper motors are expensive. I should, if I don't burn out too many components in the process, be able to assemble a PWM controller with a motor for less than the price of a single stepper motor. Also stepper motors require controllers and drivers witch cost about as much as the stepper motor it self or more.

Also space is a major issue. A stepper motor, driver, and controller take up a lot of space, which I don't have, and I need two motors in order to get the thing to work correctly.

Also, what degree of programing knowledge is required to control a stepper motor? Aside from router configurations (I should be going for my CCNA certification in 4 months)I really don't know all that much programing.

Unless you know where I can get tiny stepper motors, drivers, and controllers for $15 a piece or less, than I don't see any way to make use of stepper motors.