16 Stage Optically
I built this coilgun
in 1994 but never got round to completing it. The thought of wiring up all those
opto sensors made me lose interest. It spent years lying around in my workshop
until recently. It's getting a new lease of life and this time I'll finish it.
Unfortunately at the time I built it I wasn't sure what I was doing from a theoretical
standpoint so the physical design is less than optimal. The accelerator is about
300mm long, made from brass, and is slotted to reduce eddy current losses. Originally
the accelerator tube wasn't slotted, this was the first thing I changed after
blowing the dust of it. I also wound off some of the wire from the coil formers,
these were packed full of wire and made for a poor coil geometry, not to mention
an inductive nightmare.
The images below
show 2 of the 16 coil formers and the optical gate components. The formers are
turned from Acetal engineering plastic. The infrared diode and phototransistor
are mounted in a small plastic plug which fits into the former, they are locked
in place with grub screws.
I've finally finished
the mounting and wiring of the mosfet switches. I'm using IFRZ44A mosfets mainly
because I had lots of these lying around. Click on the images to get a high resolution
version (hint: if you're using IE hold down shift when you click a link to spawn
a new window). The MOSFETs are isolated from the aluminium mounting strip using
thermal conduction pads (little rectangles of rubbery-plastic material). Commutating
diodes are mounted underneath the coils.
I need to work on the triggering circuitry...