.. _build:

Construct the plotter
=====================

This tutorial takes you through the process of building a plotter with 8cm arms. 8cm arms are
suitable for drawing an area approximately 14cm wide by 9cm high. This fits well onto a sheet of A5
paper.


Components and materials
------------------------

You'll need:

* a Raspberry Pi
* three servo motors (recommended model: TowerPro SG90 - see :ref:`servo motors <hardware-servos>`
  for more information)
* sticks or stiff card to make two arms, each about 10cm long
* jumper wires and GPIO pin header to connect the Pi to the servos
* a clothes peg
* a board or sheet of card, about A4 size
* strong adhesive or a hot glue gun


.. _assembly:

Assembly
-----------------

The image below shows the basic construction of the BrachioGraph plotter and the names of some key parts. In this
example, the drawing sheet is A5 size.

.. image:: /images/basic-construction.jpg
   :alt:


The shoulder motor
~~~~~~~~~~~~~~~~~~

The shoulder motor needs to be affixed in the right position. You can work out a suitable position using the image
above as a guide, but even better, print out the supplied :download:`template grid
</supporting-files/template-grid.pdf>`. Affix that to the board. The motor's spindle will need to be placed at location
0, 0 according to the grid, as shown below:

.. image:: /images/template-grid.jpg
   :alt:


The servo motor needs to be raised by a few millimetres (4-6mm should be OK), for example with some layers of card.
Glue it into place.

.. _mounting-details:

.. image:: /images/servo-mounting-details.jpg
   :alt:


.. _build-inner-arm:

The inner arm
~~~~~~~~~~~~~

Glue the servo *horns* - the little plastic arms that attach to the motor spindles - to the inner arm, so that the
centres of rotation are **exactly** 8cm apart.

.. image:: /images/arm-inner.jpg
   :alt:


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 **exactly** 8cm apart.

.. image:: /images/arm-outer.jpg
   :alt:

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 the :ref:`close-up above <mounting-details>`.


Video - building a BrachioGraph by Rob Bricheno
-----------------------------------------------

..  raw:: html

    <iframe width="810" height="456" src="https://www.youtube.com/embed/7hI-9dHqTeg" frameborder="0"
    allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture"
    allowfullscreen></iframe>