Build the plotter

Components and materials

You’ll need:

  • a Raspberry Pi

  • three servo motors

  • sticks or stiff card to make two arms, each about 10cm long (to give you 8cm arms with a centimetre to spare at each end)

  • jumper wires and GPIO pin header to connect the Pi to the servos

  • other small items mentioned below (such as a clothes-peg) depending on exactly how you build the machine.

You’ll also need some strong adhesive or a hot glue gun.

See the hardware section for details on what components and materials to obtain.

The system uses centimetres as its basic unit of length. 8cm arms are suitable for drawing an area approximately 14cm wide by 9cm high. This fits well onto a sheet of A5 paper. (See Understanding the plotter’s geometry and How to optimise your plotter’s geometry and drawing area.)

Assembly

The shoulder motor

Attach a servo to the base, either by gluing it or attaching it some other way; two ways are shown below. It needs to be raised a little above the level of the base.

'Options for mounting the shoulder servo'

The inner arm

Glue the servo horns to the inner arm, so that the centres of rotation are exactly 8cm apart (you can use other dimensions, but for a first build, use 8cm).

'the horns glued to the inner arm'

The outer arm, clothes-peg and servos

Glue a servo and a clothes-peg to the outer arm, so that a pen in the clothes-peg and the centre of rotation of the arm will also be 8cm apart. Glue the final servo in such a position that its horn can rotate safely, and will be able to lift the pen clear of the paper. (See also an alternative arrangement.)

'The outer arm, clothes-peg and servos'

The assembled BrachioGraph

The BrachioGraph software needs to know the length of each arm, in values provided as inner_arm and outer_arm. If you measure them carefully, both should be 8cm.

'Arms and motors'