Hello, I´m a starter and this is my 1. project => I´m trying to build a RC-car control via serial connection, which includes 3 servos + a DC-engine. I´ve already written the software on the Arduino UNO (, by the way) + on the PC and can control the servos fairly well. Today I´ve added the DC-engine control and as i presumed the DC-engine + the servos can´t be controlled together on 1 board without external power supply because when I start the engine, at a certain level of power the Arduino switches off, because the load draws too much. So I´m thinking of an external circuit, which is powered by a 11.1 volts battery pack. I want to control this via transistor with a digital Pin from the Arduino (PWM), so my question is which transistor would you recommend for this job?

thanks so much in advance!!

Bipolar Transistors come in two flavors: NPN and PNP. Because you are switching a voltage higher than the Arduino's supply voltage you will want to use an NPN transistor between the the Load (motor) and Ground (the negative side of the battery.

Here is a tutorial about using a transistor as a switch: http://www.electronics-tutorials.ws/transistor/tran_4.html

Transistors are rated by the maximum voltage they can safely switch and by the maximum current they can safely carry. You need one that can handle 11.1V and as many Amps as the stall current of your motor. There is also a value called the "Beta" or "Current Gain". This is the ratio of how much current passes through the transistor to how much current you feed into the Base. You can safely feed about 0.030 Amps (30 mA) from an Arduino pin so a transistor with a Current Gain of 100 can pass up to 2 A (0.02 * 100). If you need higher current you will need higher Current Gain.

While you should comprehend the need to have the ground of each of the circuits connected to one another (and there are some tricks about that), I do hope you are not attempting to power the servos either from any part of the Arduino.

Logic level mosfets are cheap and plentiful enough these days , easy to use for simple on /off .

I don’t know anything about engines. I only have experience with motors. Sorry.