FabLab Academy 2012

Manchester Lab

David Forgham-Bailey

Week  16: Machine Design

This week's task was to automate our machine - the FabScan3D_mod.

The electronics design has yet to be finalised. The aim is to produce electronics which can be easily replicated by any FabLab.

Currently we are designing a system which utilises components from the Fab inventory.
We aim to use the A4985 Stepper Driver Chip (620-1344-1-ND) - and the USB to Serial chip (768-1007-1-ND) - with the control chip ATTiny 44 - or the ATMega 328 (both in the inventory).

In the meantime I manufactured the Fabkit i/o (aka Fabduino) and the hello.stepper boards to create a development rig to test out software routines for control of the two stepper motors and the Laser.


Programming the Fabkit proved difficult - the chip used was the Mega328 but Arduino only recognises the Mega328P chip which is fitted to the commercial Arduino boards.
At one stage I managed to get the bootloader to complete - (by editing avrdude.cfg), and the led on the Fabkit flashed ... however when the FTDI cable was attached the board did not function...

I decided to try to reload the bootloader but this time it failed to complete...(bad decision)..
Upon further investigation I found that the FTDI connectors did not match the FTDI cable - Rx/TX wrong way round on the board...  More work required to bootload the board correctly, and resolve the FTDI issue...

I decided to use a commercial Arduino Mega 2560 - with two stepper motors from the Fab inventory (PF35T-48L4) - connected to pins 8-11 and 4-7, and a diode in place of the Laser - connected to pin13. Using the Arduino programme I made up a routine to sequence the motors and the led - stepper 1 moves one step - the laser turns on - the second stepper moves through 1/4 rev and returns - then the first stepper moves again to repeat until one full revolution is achieved... (these steppers can be driven directly from the Arduino and have 48 steps per rev - the motors we will use in the final machine will need a 12v supply and have 200 steps per rev - so the routine will need to be modified accordingly.

ard01   ard02  video

Once we have designed and manufactured the final electronics boards, this routine will be created in 'c' or Python.