Servo - December 2014

8 SERVO 12.2014

Q. I am building a two-wheel balancing robot, but I’m not sure that a 2 x DC motor with encoder or a 2 x stepper motor is better for that kind of robot. Also, should I use two batteries (one for the motors and one for the Arduino circuit and sensors) or just use one battery for both (with a regulator for the sensors)?

— Jackie Su

A. I have actually fielded this question before in other places. The stepper motor seems to have a mystery or panache about it that just makes us want to use it in our robots. Stepper motors have a different driver configuration and control sequence than DC motors do, and let's face it, they just sound cool. A stepper motor is very good at moving precisely to a chosen position and getting to the same exact place every time. This kind of motor is also very good at holding that position firmly, without using complex PID algorithms and specialized encoding schemes.

( Wait for it ...)

But ...

A stepper motor is not very fast (compared to a DC motor — either brushed or brushless). It is also larger, compared to a DC motor with a similar torque rating.

Figure 1 shows a size comparison between a stepper and a DC geared motor. The one on the left is a bipolar stepper motor (typically stronger than a unipolar), and the by Dennis Clark

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for Mr. Roboto. In the last couple of months, I have introduced you to a great new IDE (integrated development environment) for Arduino and chipKIT projects. I also discovered 4D Systems who has excellent graphics displays and design IDEs whose costs rival other manufacturer’s LCD displays alone. Here is a whispered hint to those of you that actually read my introductions ... I am going to be reviewing a couple of fascinating new products from them in the next couple of months — as soon as I build projects worthy of their "coolness" factor!