Monday 31 May 2010

Mega RepRap sheild

I've been working for a couple of weeks on a RepRap Arduino Mega shield. I've got a mix of early generation 2 electronics, a few home-made single sided generation 3 stepper boards, and old arduino with a screw-terminal shield and a brand-new arduino mega.

I designed myself a version of an arduino mega shield to connect the gen3 stepper boards using the 10-pin IDC cables, and it might be useful for anyone transitioning between generations of electronics. Headlines:
  • Single-sided for home-made boards
  • 5 stepper driver headers - x,y,z,a,b - should match existing gen3 electronics.
  • (future-proof?) UI interface header that *should* match gen4 electronics.
  • Heater 10-pin IDC (to plug in MOSFET driver board later) - should be able to drive a reprap setup with 1 or 2 extruders/ heated bed without an additional extruder board.
  • I2c header as per standard boards
  • Optional extra 3-pin headers for digital in\out and analog in : +5v, GND, and data pin. This makes it easy to add temperature sensors, kill switches, extra limit switches, etc (I'm only using the min endstops).
If you think it might be useful, the files are here :
Eagle files for Renoir's RepRap Mega Shield

I've just etched one using my laserprinter/laminator method, and I've just etched two more single-sided stepper drivers. I'll post some photos once it's been assembled.

p.s. All files (and anything on this blog) available under creative commons attribution 3.0 licence.

Monday 17 May 2010

Tuesday 4 May 2010

Home-made Steampunk cogs

I like the steampunk look, and my daughter and I fancy building a steampunk keyboard.
Alongside my PCB building, I tried building some steampunk-style cogs to use as decoration or parts. I found some thin copper foil (0.1mm) from a sculptor's and restoration supplier Tiranti.
From Steampunk cogs
It's nice stuff, thin enough to cut with scissors, but thick enough to cover corners and bend around shapes without ripping. It should cover keyboard edges well.

One of the things I wanted to try was to use PCB etching techniques to make complex cogs or clockwork shapes. I put together a couple of templates (see the end of this post) and tried a few things to transfer the toner onto the foil - the best technique ended up being the label backing paper as per PCBs. Because you need to cover both sides, I mirrored the label and folded it in half - then placed the copper foil inside the transfer.
From Steampunk cogs
A couple of passes through the laminator, and the toner is fused onto the copper. I also printed a more complex mechanism onto normal PCB board.
From Steampunk cogs

I then used standard ferric chloride (PCB etching fluid) to etch the copper. You can either dunk the boards and gently stir the etchant, or (with GLOVES) rub it on the board with cotton wool or a kitchen towel.
Etching the PCB was pretty quick: etching the foil all the way through took a about twice as long as the PCB board. The etching worked well, most of the complex detail and cog teeth coming out well.
However, the toner is much more difficult to remove. With the PCB, the board gives the copper plenty of strength so the toner can be scrubbed away. With the foil cogs, they tear easily, so you can't scrub them. I tried soaking in acetone (nail varnish remover) and this removed some, but not all the toner. An agitated acetone bath (maybe an ultrasonic jewellery cleaner?) might remove more.
From Steampunk cogs
The normal PCB came out very well. The detail is good and the board can be scrubbed to remove all the black toner.
From Steampunk cogs
One of my ideas was to place some LEDs behind the PCB to shine through the board, illuminating the hidden pattern: this backlighting does give a really nice effect (shown against a normal lamp).
From Steampunk cogs

A nice large panel with plenty of clockwork mechanisms would look good instead of a numeric keypad, or as a lit panel in a PC case. Layers could even be stacked for a greater 3-d effect. This is just the research so far, I'll post more as it proceeds.

How to make a gear template (examples)
  1. Generate a gear at - I used tooth spacing 6mm, gear 1 teeth 100, spokes 5 and show spokes on.
  2. Hit the 'print' button, then OK. My mac then allowed me (bottom left PDF dropdown) to import the PDF into iPhoto, basically exporting it to a jpg.
  3. Edit the picture in Gimp. I did the following operations:
    1. Fill the outline with black
    2. Use Select - by color and then click on the background (white)
    3. Use Select - shrink to shrink the selection by 20 pixels (not from the image border)
    4. Use Edit - Fill with FG colour to fill it with black
    5. Use Select - all and Edit - copy
    6. Use Image - Canvas Size. Click the 'link' between the width and height to unlink them. Double the height and add two pixels.
    7. Click Image - transform - flip vertically
    8. Click edit - paste as - new layer. This should give you a mirrored image top and bottom, with a small line between them.
    9. Click file - save and export when prompted.
  4. Laserprint onto label backing paper, heat transfer to copper foil, and etch.

Mendel home-made stepper boards

A productive weekend: I used the laserprinter technique to make four more single-sided stepper drivers.
I experimented with plain paper, baking paper, greaseproof paper, oiled paper, but the best transfers were with my cheap label backing paper.
To economise on the amount of label paper, I cut a section roughly a bit larger than the PCB, and stuck it to a clean A4 sheet with some of the discarded stickers. This then goes through the laserprinter.
From StepperPCBs

I then took off this section, bent it over the PCB and taped it down, then ran it through my laminator a couple of times. This transferred the toner to the PCB.
From StepperPCBs

After etching, I had four new stepper boards to build
From StepperPCBs