9

Controlling stepper motors with Arduino

SCHOOL OF MAKING

tepper motors are used in scanners,

ink-jet printers, 3D printers, laser

cutters, CNC machines, robots,

and all kinds of devices where

precisely controlled movement is

required. They’re motors that turn in

set increments, such as a quarter turn, rather than

regular motors which simply continue to rotate while

power is applied. Using this, you can move machinery

a precise distance.

Stepper motors are brushless motors with multiple

coils, so they require additional electronics to drive

and control them. There are two main kinds of

stepper motor: unipolar and bipolar.

UNI VS BI

The main difference between them is the way that

the coil windings are connected. A unipolar motor has

a connection at the centre of each of the two main

windings. This is called a ‘centre tap’ and is usually

connected to the positive voltage. The small 5 V

‘hobby’ unipolar steppers you see on eBay (e.g.

28BYJ-48) usually have five wires – one for each coil

end, and a common wire for both centre taps.

Unipolar steppers can use a simple, cheap

ULN2003 Darlington array chip to protect your

microcontroller and switch the coil phases on and off

in turn, thus rotating the rotor one step at a time.

The main disadvantage of the unipolar design is

that at any given time, only half of each winding

can be energised. This means that both torque

and efficiency are significantly lower than if the full

windings could be used. This is not usually much

of an issue for hobby projects, where cost is often

the deciding factor. A 28BYJ-48 and driver can be

bought on eBay for as little as £1.42, if you’re willing

to wait a few weeks for delivery from China (eBay or

AliExpress). If you’re in a hurry, you can buy locally for

a bit more.

Bipolar stepper motors don’t have centre taps, so

they only require four wires to connect them (the

two ends of each coil). This is a much more efficient

design and gives more torque, but it comes at a

cost. The required drive electronics are a bit more

Make precisely controlled, repeatable movements with steppers and Arduino

Controlling stepper

motors with Arduino

S

Alex Eames

RasPiTV

Alex Eames loves

making things and

regularly blogs/

vlogs at RasPi.TV.

He makes a living

designing and selling

RasP.iO products.

Above

Stepper motors are

available in a range

of shapes and sizes.

They can all be

controlled by Arduino

and driver board