CNC fun

On Monday we spent most of the evening trying to get EMC to work on a donated PC, and then with Martin’s stepper driver board. Alan did some good work persuading the rather picky realtime Linux distro to work at all, and then we set to work.

The board consists of a breakout board connected to the parallel port of a PC, which opto-isolates its inputs before amplifying them up a small amount to be used with stepper motor drivers. These drives generate quadrature output from two input signals, a step signal (or clock) and a direction voltage. The job of the PC is to directly step each motor, and the accuracy with which it can do this affects the maximum frequency of steps that it can generate.

This is a hard real-time task and so a Linux kernel is used that allows tasks to be prioritised above nearly all of the kernel tasks and drivers. This kernel will not work with binary graphics drivers, and quite a few other drivers that are incompatible with its priorities, hence the difficulty in setting up. Once this obstacle was overcome we traced the stepper control lines to the right pins of the parallel port (in Martin’s absence) and eventually puzzled out the power supply to run the stepper motors themselves, admittedly pretty slowly to be on the safe side.

In lieu of having a mill to connect them to, we found some software for playing tunes via gcode and soon we were graced with at least the higher parts of the Super Mario Bros theme, played about 4 octaves too low.

May Day

The NSME May Day re-opening is now 3.5 weeks away, on Monday 2nd May. As part of this we’re having a stall ourselves (wiki page for organising here) in the afternoon and in the evening, a BBQ and hack session focussing on glowing in the dark! Whatever you’re making on 2/5, make it glow, by any means you like.

Next meet

Next meet is on the 18th April and will feature Mat talking about his quadcopter, how he built it, and how he controls it. This is also the only meet to test any contraptions for display or use at the NSME open day, so make the most of it!