[Gene-Yo]

I am trying to find a fairly inexpensive variable speed controller and power supply to run a small R/C type of engine. As an example here's a possible R/C 8.4VDC engine :: http://www2.towerhobbies.com/cgi-bin...&I=LXBYM9&P=TF

This R/C engine can draw up to 12 - 15 amps under heavy loads but I believe typical running amps is much less.

The only items I find on the web are 'put it together soldering kits' which I don't want because most kits I've ever made don't work. Or they are very high end motion controllers costing $100's if not $1,000's of dollars.

There's got to be a $79 - $99 solution somewhere for this small of a motor but I can't seem to find it. Any help would be greatly appreciated............

Also, I plan to run this off standard 110VAC outlet and not batteries. So I'm sure a DC adapter will be required??

[Al_The_Man]

Once you get down to lower voltage a power supply will be needed, many of the lower voltage ones do not include it, or are pricey.
Are you sure you cannot find someone to put something like this together for you, if you are apprehensive?
http://www.electronickits.com/kit/co...tor/ck1400.htm
Thier stuff is a piece of cake to put together, I have used their PIC programmers with no problem, you would need a power supply for up to 15amps however.
Al.

[Gene-Yo]

I looked at this kit.. My hope is to find this or something similar already assembled. And the other catch is the power supply... I need something near 8VDC at 12 or 15amps.

But I may be stuck?

[Al_The_Man]

As to the power supply voltage, it is not critical as higher voltage in itself does not harm the motor as long as the mean current is regulated, as in PWM or SCR drives, you can also tailor it so the it the PWM/SCR is never on 100% at zero load to avoid over speeding.
The 8 volts is if you were going to run off of an uncontrolled supply, and then the current would have to be limited, otherwise you burn the motor out.
This is what a drive does essentially, voltage=rpm current=torque.
Al.

[NC Cams]

Get an "electronic speed controller" for an R/C car.

These will easily run a 4 to 8 cell nicad pack. Some have onboard 5V Dc regulator IC's that will easily take 12 volt inputs and regulate it to the necessary 5 volts that it runs off of.

To drive it as a PWM'd R/C "electronic speed control" (ESC), you use a 556 IC with one side configured as a multivibrator trigger that feeds the second stage configured as a one shot.

As you stretch the duration of the one shot, the ON duty cycle of the speed control gets longer until a 100% duty cycle on is achieveable.

There are a number of digital proportional servo driver plans that use the 556 on the internet for R/C applications.

Since the electronic R/C speed controls are essentially an "electronic servo that controls speed", a 556 configured as a servo driver will give you the proportional speed control you're looking for.

Another more elegant option involves the use of a UC3637 switch mode servo driver IC. This is a PWM motor driver that will drive a DC motor at a low to 100% duty cycle in either direction.

Get the U-102 application note from the TI/Unitrode website for the "how to" create the control circuit as well as a mosfet based power driver for the motor.

The charm of the UC3637 is that it also does pulse by pulse current overload monitoring as well as PWM speed controlling.

[Gene-Yo]

O.K. I'm getting somewhere... So if I went with the $25 kit for this motor then is it o.k. to get a 12 volt 12.5 amp power supply or a 12 volt 17 amp power supply even though this motor is rated at 7 to 8.4 volts?? I just want to make sure I'm not going to burn something up.

I can get a 12 volt 12.5 amp power supply for $45 at this link: http://www.powersupplydepot.com/prod...oduct=12422+PS

[Al_The_Man]

It is excess current through the motor that will burn it up, if you have 12v supply but the mean current is controlled by PWM etc, Then there should not be a problem.
Typically drive manufacturers, for example recommend 10% min. above the motor rated voltage.
The only thing to watch is you do not go over the max rpm, If you wish to find this out, put a known DC voltage on it unloaded, 3 D cells or whatever and measure the rpm at the known voltage, the max rpm is a direct ratio of this at 8v.
Al.