HI,
ive been secretly working on disecting a R/C truck and equiping with sensors
and all, its tuning out realy cool, but im wondering do i need to have a “pot” in a servo controller that i took out of a servo???
to use as a motor controller?
The potentiometer in a servo tells the electronics where the output shaft is, and lets it know which way and how fast to spin the motor in order to get it to where it should be.
In this instance - using a servo board as just a DC motor controller - you’ll still need something going across the leads that attach to the pot. This can be either a simple resistor bridge with the same resistance on either side of a center tap, or it can be a potentiometer. Using a pot has the advantage that you can easily adjust the “center” position where the DC motor will be off, simply by turning the pot’s shaft, rather than having to tweak all sorts of values in your software. I prefer multi-turn trimmer pots in this application, as they’re more precise, and less prone to “accidental readjustment” by bumping them. Depending on the type and construction of the servo you’re gutting, and how carefully you disassembled it, you may be able to use the pot that was originally built into the unit.
Also keep in mind that a servo’s control board is designed to drive the motor that was in the servo originally. Asking it to drive a motor with significantly higher current requirements can let the magic blue smoke out. It should work fine, though, as long as you’re careful with the motor that you choose.
thats okay,the motor is only 3vdc
and will it work like this
http://i122.photobucket.com/albums/o255/wowy5/untitled.jpg
The resistor bridge that you illustrate would work in place of the potentiometer, but you’ll lose the ability to tweak the “center” manually, and have to do it in software. The pot or resistor bridge acts as a voltage divider to provide feedback, but in the interest of keeping everything as close to design spec as possible, you might wish to match the resistor bridge to the pot it’s replacing. The values shown in your sketch (two 5K units) would be a direct replacement for a 10K pot. Personally, I’ve never had any problems with replacing the pots with whichever trimmers I had around, but I usually went with something as close as I could get to the stock unit.
As has been noted in other threads regarding using servo driver boards as speed controls, the rated voltage of your motor, while something to consider, isn’t quite as important as how much current it will consume while running at the applied voltage. The H-bridges built into a servo’s control board are designed to handle a certain amount of current draw, based upon the motor that it was paired with in the servo. Replacing that motor with a different one imposes different current requirements on the switching circuitry. One small three-volt motor may work fine, while another that looks physically similar, but is designed to provide higher torque at the same voltage, may draw enough power to smoke the board. While I am inclined to believe that you likely won’t have any problems, I can by no means say this definitively one way or the other.
well thats good news, cause i had those to resistors for over a year and they where from a bumper switch that i got from LM but i had no use for them cause i never used the bumper
so thats good 
well thanks for the help 