Andrew Morris had a problem with a small rotary tool built in China. The tool fit nicely in the hand and was useful for precision cutting, drilling, and polishing. Yet for delicate work, the tool was in bad need of a speed regulator.
Andrew had developed an analog motor speed regulator back in the mid-1990s, but this time, he wanted the benefits of a digital regulator. The digital version was just as efficient, but it was less expensive to build and easier to assemble. The digital circuit also provided more torque.
Andrew Morris' microcontroller-based DC motor speed regulator brings control for delicate work.
I have not seen a drill motor that is so easy to hold in the hand that has decent speed regulation and torque. I have a Dremel Moto-Tool that is great for big jobs, but it's awkward to use for delicate work. The Chinese mini-drill is dirt cheap and with my speed regulation technique, a piece of useless Chinese junk has been turned into an indespensible tool. I stand by its usefullness.
I own a cordless, three-speed electric floor sweeper that has my speed regulation system in it, so somebody else has found my invention useful. IMO, there is no cheaper way to regulate the speed of a small DC motor. I helped a guy in India tune the software program to run a larger motor for a CNC machine he was building. It was working for him, the last time I talked to him.
Cool that someone did this, but if I'm not mistaken these types of tools are readily available for purchase. So NOTHING NEW HERE. Can't we find more interesting and unique gadgets to feature in this segment. Maybe I'm just being a curmudgeon.
Before this article was published, when I added R10, I sent the editor an updated pdf file and for some reason, the first pdf file was published. I have resent the corrected file twice and it has not been posted. R10 is a 22k resistor connected between Q2's drain and ground. Please email me if you would like the updated pdf file.
Mrdon, the motor controller had one section of a 556 generating a triangle wave from 1/3 Vcc to 2/3 Vcc, the other section used a potentiometer to vary the reference for the second section that is used as a comparator. The signal from the comparator feeds a small transistor that drives a TO-3 power transistor.
The circuit to generate the PWM signal came from an applications note. So it is really not anything that complex. I may be able to find a copy of the circuit someplace in my archives, but that may take a while.
OK, it was a variable speed drive. What we used for feedback was the effect of the pump delivery rate, which was controlled by the motor speed. It was not clear that any feedback was used with the tool speed controller, either. Small tools seem to work better if they do slow as the load increases.
The other thing is that a motor controlled with PWM may not have as much speed drop as the load increases, since PWM control does not increase the source impedance.
William K. Thanks for your response. Was your device a controller or a regulator? In other words, how did you sense the motor speed? I can build a DC motor controller with a 555 timer, a pot, a MOSFET and a few small components. Such a device would not be a speed regulator as it would have no feedback.
When it comes to learning PIC microcontrollers, Mike Predko is an excellent teacher. I have several PIC microcontroller books by Mike and his writing style make developing microcontroller applications a breeze. His books also provide solutions on debugging software errors as well.
In our third annual contest, Design News and Allied Electronics are going to crown a winner in early 2016 for the best reader gadget submission this year, and once again, you, the readers, are the judges!
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