I was just wondering how I would go about making a pedal that controls the speed of a motor. It would also have to include reverse motor capability. My tech book at school already has a circuit for reversing motor direction but might not be compatible with what you might come up with. Thanks.

EDIT: oh, also what would I use to limit the amount of electricity that can go through a wire.


closed as too broad by Rev1.0, Daniel Grillo, Dwayne Reid, PeterJ, Ricardo Mar 29 '15 at 12:33

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  • \$\begingroup\$ What sort of motor is it (AC, DC, brushed, brushless etc.) what voltage does it run on, and what is the maximum current and/or power that you want it to draw? Can you show or describe to us your reversing circuit? \$\endgroup\$ – Bruce Abbott Mar 27 '15 at 22:57
  • \$\begingroup\$ Don't have motor yet but would have to be big enough to power electric car/go cart. As for limiting the current I don't know but my source of power will be variable ie. solar panel. And here is the circuit I talked about. It starts with the dc source loop and on the left there is a push to make switch. When pushed, it activates a relay switch. Thus \$\endgroup\$ – TheDude Alex Nuzum Mar 27 '15 at 23:12
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    \$\begingroup\$ This is a pretty dangerous and high power project, if it's for motors for powering a go cart. Perhaps you should find someone nearby that can help you with the project, especially for the high power aspects \$\endgroup\$ – KyranF Mar 27 '15 at 23:15
  • \$\begingroup\$ I guess this project would be basically a car battery or two with two big 12V motors (perhaps salvaged from an electric wheelchair, and then gears down for speed rather than torque) using some high power 80 Amp ESC (electronic speed control) for each motor to drive them. A pedal can be connected to a potentiometer to give a variable output voltage, which can sometimes go directly into a ESC to vary the output speed. \$\endgroup\$ – KyranF Mar 27 '15 at 23:41
  • \$\begingroup\$ KyranF - how would you go about connecting the esc to a pontentiometer? \$\endgroup\$ – TheDude Alex Nuzum Mar 28 '15 at 0:46

The simplest way to vary the speed of a DC brushed motor is to simply wire a rheostat (variable resistor) in series with it. However at part throttle the rheostat gets hot, wastes power, and provides poor speed regulation. Speed regulation can be improved by connecting both ends of the rheostat to make a potentiometer, but this wastes power even at full throttle.

Both efficiency and regulation can be dramatically improved by using an electronic controller which rapidly switches the motor on an off with a variable duty cycle. This technique is called PWM (Pulse Width Modulation). Commercial PWM speed controllers are readily available, or you can make your own using a handful of electronic components. here is an example:- PWM Motor Speed Controller.

A motor large enough to power a go-kart might be rated for 250W on 12V, and draw about 20A at its rated power. When starting up it will try to draw a lot more, however a solar panel 'automatically' limits the maximum current available. For example a 140W '12V' (17.5V open circuit) solar panel might have a short circuit current (in full sunlight) of 8A, and two in parallel would supply a maximum of 16A.

You can use a relay to reverse motor direction - just make sure that the relay contacts are rated to suit the current being drawn.

  • \$\begingroup\$ This the circuit for motor direction turn: plus.google.com/105592975420002072022/photos. \$\endgroup\$ – TheDude Alex Nuzum Mar 28 '15 at 1:01
  • \$\begingroup\$ So will I ad Pmw just before motor? \$\endgroup\$ – TheDude Alex Nuzum Mar 28 '15 at 1:05
  • \$\begingroup\$ I can't see your direction change circuit, but if it uses a relay then it should be OK. A PWM circuit (like in the link I provided) is all you need to control motor speed. Just make sure the FET and diode are powerful enough. For 20A motor current use an 80A+ FET (eg. STP80NE03L-06) and 3A+ Schottky diode (eg. 1N5821). \$\endgroup\$ – Bruce Abbott Mar 28 '15 at 1:37

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