Let's Make Robots!

Control DC motor easy



I what to finally make my firs robot, but I have one problem:

I found for my base nice RC car. Its perfect and also have  power supply (6V 620mAh Ni-Cd ) with charger. Also servo in front. So its perfect, but it have very powerfull DC motor... Is can use more then 4 Amps of current (if wheels are blocked). If car is lifted and  wheels are spinning free it uses about 0,4A. Then starts a moment use about 1 A. All my tests were with my 6V Ni-Cd battery.


What is the cheapest what to control it?  O need only one direction (foward) and nothing fancy. I what to control it using my arduino board. But I need something like transistor or relay. Also it would be perfect if your suggesting parts can be available in my local store "Lemona" www.lemona.lt.

Thanks! If you need Additional info. Just ask :)



I found things like this one: http://www.dealextreme.com/details.dx/sku.13020

Is it OK for me ? And ist easy to use with arduino? Can ir control speed?


I add video of my motor Amps usage.

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The BEC controller from dealextreme will not work, it's for a brushless motor. Your motor is a normal brushed DC motor. If you only need the motor to go forward, a simple N-FET will do the job. I would recommend a Logic Level type, like the IRLI540N. It's s available at lemona.lt .You will further need:

  • a Gate resistor 1kOhmto the Arduino
  • a Gate PullDown resistor of 100kOhm
  • a Flyback Diode (3A Shottky type) for the motor, SR360 f.e. 
  • a heatsink for the FET

You can control the speed simply by using an PWM port of your Arduino.

My electronic skills are sketchy at best so I might be completely wrong, but du you need a resistor on the gate? I thought FET’s where voltage controlled opposed to a normal current controlled transistor. I agree upon the pulldown resistor but are uncertain about the gate one.

Yes you are right, FETs are voltage controlled. But real life is more complicated. The gate acts like a capacitor which needs to be charged and discharged when the FET is turned on or off. The gate resistor limits the current and increases the time to charge the gate capacitor. Without the resistor the current could be to much for the microcontroller, especially when using PWM.

Maybe it will work without the resistor or a much lower resitor value (100..500Ohm). I'm too lazy to do all the math, so I always use a gate resistor more for safety reasons. Here is an article about this.

Thank you for the information and the link. I have so much to learn!

What type resistor (a Gate PullDown resistor of 100kOhm ) should I use? Is 10W is enough?

Thanks! :)

10W on the Gate side isn't needed. A normal 1/4W or 1/8W is ok. For the gate series resistor 1kOhm is maybe too much, 100Ohm 1/4W or 1/8W should be better.

That shouldn’t be a problem, the resistor is only there to keep the gate from floating. Just use a regular 1W.

Really thanks! I'm going to order that parts. :)

Please say I'm I correct: 

Arduino pin > 10K ressistor > Transistor base;

Power + > Transistor collector; 

Transistor emitter > 100K resistor> diode > motor + 


Is it right? Or I get something wrong? 

Here is a schematic, I've used for the blower motor from Mr. Red-Adair.