Dean,
Most of the small inexpensive dc speed controllers either use a 10K potentiometer, or 100K potentiometer.
It is also important to note, that the requirement on the potentiometer have a linear taper, rather than an audio or logarithmic taper.
The speed controls responds correctly when the resistance changes in a smooth linear fashion.
Another important specification to note is that the controller have a speed range from 0- maximum voltage, or 0-100% control.
There are some controllers on the market that vary the speed from 5% to 90%. If you use a 200 rpm motor and have it slow down to 5%. That would mean that you would only slow a 200 rpm motor down to 10 rpm, which is not what you want, when your lift your foot off the pedal.
Essentially, you need a foot controlled device that can vary the resistance of a variable potentiometer from 0 ohms to 10K, or 100K ohms - depending on the controller.
If you using a pedal, the normal arc range of a standard foot pedal is about 20 degrees. i.e. if a round potentiometer is connected to a 20 degree pedal, the pedal would only rotate for 20 divided by 270 degrees. This would mean that you would only have a very small speed control range.
To eliminate the issue, I chose to use a pedal that uses a rack and pinon design to drive the potentiometer by the use of a rack, or cogged straight shaft connected to the underside of the foot pedal. Then, as the pedal descends from full up, to full down, the rack or cogged shaft will rotate 270 degrees or the full standard rotation of a variable resistor.
The pedal type that I like to use is a rock guitar amp pedal called a WAH pedal. These are robust all metal heavy du ty pedals that will stand up to years of service wrapping rods.
Here are various examples of NEW Dunlop Wah pedals.
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www.jimdunlop.com]
Rather than spending the money for a new pedal, and then completely eliminating all of the parts in the pedal with the exception of the rack on the underside of the pedal. I also keep the mounting hardware for the potentiometer.
I do not use the potentiometer from the typical WAH pedal, because the typical WAH pedal uses and audio or logarithmic taper that does not provide the control that is needed for the speed controller.
However, sometimes one can run across a Linemaster rack and pinion pedal style that is normally used for wire feed welders. The down side of these pedals is that the cost is normally quite high.
Also, the design of this pedal resulting in a high foot position fo rthe foot that is placed on the pedal during rod building. It is nice to use a pedal that allows the foot to be quite close to the foot - during normal operation.
To find the Dunlop wah pedal in the used category, I check for hits on a pedal search from the local Craigs list.
Also, the on line @#$%& sites can sometimes reveal a pedal that is for sale.
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By the way, if using only the pedal for control the speed controllers own potentiometer is eliminated and the speed is completely controlled by the foot pedal potentiometer.
But, if one wants to use the wrapper for applying finish and to act as an overnight dryer, then it is nice to incorporate the speed controllers own pedal and have a switch such that the variable speed potentiometer that came with the speed controller be used, or the foot pedal that you wish to use to control the speed. The switch essentially uses either the hand dial, or original potentiometer that came with the controller or the potentiometer that is in the foot pedal.
Feel free to ask any more questions.
Roger
