The Car

I have the mk.2  car back!  It went together very well, though it was perhaps too tight in some places – the short loops and forks that hold the drive wheels to the gears needed to be shaved a little.  I added 0.1mm to the perimeter of all the shapes, and on thinking about it, it seems likely that it should have been more like 0.08 mm or so.  Needing to make adjustments that tiny is a strange business indeed!

Anyway, here is the finished product in all its lasered glory:

This time there were only two things amiss:  First, I didn’t account for the width of the AA batteries in the bottom compartment in addition to the holder for the power transfer gear, so it can only hold 1x AA in the bottom bay and 2x AA in the top – although you could probably pack a bunch of those squishy Lithium ion batteries in with no problem.  The other problem lies in trying to make the design too cramped – on each side, one wheel is attached directly to the motor, and one wheel is attached via a wooden axle, to a point behind the motor that powers the opposite side.  The current design is so compact, though, that there isn’t really enough room behind the motor for a solid fixture, and it has a tendency to fall off.

Widening the design by 3mm would solve both of those problems and the whole plan would stay well within the 181 x 181 mm limits set by Ponoko though, so I’m pretty pleased with the design.  Ideally I’d like to be able to keep the base design small enough that it can form the basis of a miniature robotics platform, and be able to have room on a P1 board to put holders for sensors or a small robotic arm. Stay tuned!

Arduino Enclosure

I also needed to make an enclosure for the Arduino Duemilanove as part of another project I’ve been tinkering with. After looking online I found surprisingly few examples anywhere – in particular a total absence of  compact, fully-enclosing cases, so I designed one and got it cut.  At first I was going to get it made in 3mm MDF as well but Heather suggested that an acrylic would be more pleasing and I agree.  It looks like this:

There are pass-through holes for the three holes in the Duemilanove board,  so it could be bolted to another object.  I offset the pats for this design by 0.1mm as well, and unfortunately, acrylic is a lot more brittle than MDF, which has meant a couple of small parts snapping off when I tried to force them.  Other than that, though, the design is perfect and the tightness has meant it keeps together really well!

The other good thing about sticking the Arduino in an enclosure is that you can stick other things to it – in this case I wanted to guarantee the orientation and position of a compass module on top of the unit, which is encased in the small box on top.

Once I made the enclosure design (and was able to verify that it actually works), I decided that it would be worth looking into making the interlocking parts more automatically.  I was inspired by Jared Tarbell’s Cubes to start thinking about how to generate the map automatically.  It’s still very much a sketch, but the principle is straightforward enough to automate most – if not all- of the process.

Lay out the lines of a shape by clicking, adjust the tooth width with the slider and hit ‘clear’ to clear the shape.  Enjoy!

Tamiya motor EPS download

They can be purchased on the sparkfun website, and I think they are the same as the ones on pagermotors.com, and the ones manufactured by JinLong Machinery.

Vibrate motor EPS download