# Homemade Electric Gokart foot throttle wired to PWM speed controller Answered

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Hello, I am writing because I have a question about a project I'm working on. I've built a gokart frame and attached a 12v 600w motor to it. And I have a Speed controller (https://ebay.to/2KUnnqe) that can handle the amps the motor is drawing but right now the only way i can control the speed is by twisting the potentiometer, and that means I cant have two hands on the steering wheel. So my question is if I can wire this foot throttle (https://ebay.to/2OChMa7) to the potentiometer and if so what wires will go to what wires and will this even work to control the speed.

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What would be best, is if we could see a circuit diagram of this controller. However, I realize an actual published, available to the public, circuit diagram might not exist.

So the next best thing, is to examine the traces on the controller, and discover which trace goes where, and also discover how it doing what it does, in particular the role of the potentiometer. Reading the heiroglyphics printed on the ICs, and looking up data sheets for the same, can give us clues also.

However, in this case, I think we can learn a lot about what the pot is doing, just by measuring the voltages present on it, while the controller is operating.

Typically, for something like this, the pot is acting as a voltage divider. Also typically, the signal output by the pot is just an analog DC voltage.

https://en.wikipedia.org/wiki/Potentiometer

https://en.wikipedia.org/wiki/Voltage_divider

So when you put your voltmeter probes, on the pot... I am naively guessing that you will see:

The voltage across the full resistance of the pot will be some constant DC voltage, like 5 or 10 volts DC, or some constant DC voltage, independent of the position of the knob.

The voltage measured between the wiper terminal, and one of the other terminals, will be some proper fraction (i.e. a number between 0 and 1; like 0.2, 0.5, etc.) multiplied by the full voltage that appears across the full resistance of the pot. Moreover the voltage between the wiper, and one of the other terminals, changes, depending on the angle of the knob.

Maybe you can see where I am going with this story? Or maybe not.

What I am saying is, it would be a fortunate coincidence if your pot also had 5 volts DC across it, with the voltage on the wiper, somewhere proportionally in between 0 and 5 volts, depending on the angle of the knob.

Because if it did, then it would be behaving the exact same way, as that throttle pedal gizmo, is promised to behave, with an input of 5 volts DC, and output in the range 0 - 5 volts, depending on the angle the pedal is depressed.

Maybe? I guess the voltage signal for the speed controller could be inverted. Meaning the low end of the voltage scale corresponded to a command for high PWM, and vise-versa.

I guess what I am saying is would be a lucky coincidence if the output from this throttle pedal gizmo, is an exact match for the voltages that would be output from the potentiometer knob.

But who knows? You might get lucky, since 0-5 VDC is a popular range for analog sensors and signals.

If the voltages are not the same, maybe you could come up with some op-amp circuits? Like for to map one analog voltage range to another; e.g. map 0-5 VDC to 0-12VDC, and invert it if you had to.