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Gadget Freak Case #226: Speed Regulator for Rotary Tool

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armorris
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Platinum
Re: Company confidential information
armorris   10/31/2012 11:12:46 AM
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Here is a much more readable version of the patent application on my motor speed regulator. Google Patents is great! No TIFF viewer is needed and you can download a PDF version of it.

http://www.google.com/patents/US20030107341

 

Cadman-LT
User Rank
Platinum
Good solution
Cadman-LT   10/8/2012 1:43:04 PM
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Nice gadget! That's a good solution for cheap rotary tools without speed control.

armorris
User Rank
Platinum
Re: Resolved overload protection issue
armorris   9/25/2012 12:48:15 PM
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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.

William K.
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Platinum
Re: Speed control for rotary tool
William K.   9/24/2012 9:03:18 PM
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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.

William K.
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Platinum
Re: Speed control for rotary tool
William K.   9/24/2012 6:06:45 PM
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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.

armorris
User Rank
Platinum
Re: Handy project!
armorris   9/24/2012 2:47:44 PM
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BTW, Myke Predko's name is spelled "Myke". I have two of his books and I verified it.

armorris
User Rank
Platinum
Re: Speed control for rotary tool
armorris   9/24/2012 8:23:17 AM
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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.

mrdon
User Rank
Gold
Re: Handy project!
mrdon   9/23/2012 9:16:43 PM
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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.

mrdon
User Rank
Gold
Re: Speed control for rotary tool
mrdon   9/23/2012 9:07:09 PM
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William K, It would be interesting to see the circuit schematic diagram of your design. Sounds like a possible Gadget Freak article to me!

William K.
User Rank
Platinum
Speed control for rotary tool
William K.   9/23/2012 5:51:58 PM
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In 1979 I designed an inexpensive PWM speed controller for use with a 12 volt DC motor. The control kept the torque at maximum because of not having a voltage drop, other than the Vce of the switching transistor. And the design was not patentable, so I was home-free there as well. It use a 556 dual timer chip with one section as an oscillato9r and the other section as a comparator for the ramp waveform and the setpoint voltage. One intermediate transistor buffer stage and it drove a 100 volt 5 amp switching transistor, which I don't recall the number. The BOM cost, except for the control pot, was just under $5. Probably all of the parts are still available, and there is probably a much better output transistor available today. Possibly even a FET of some type.

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