Extremely long time since my last entry.
I've been busy, of course. Been trying to draw up a new mechanical scheme for the USB webcam mount, and have a lot of parts for the CNC:
(3) bipolar Crouzet stepper motors
(1) WinSystems LBC-586 single-board computer
(1) 510MB laptop hard disk and adapter for the SBC
(15) UDN2954 full-bridge PWM control chips
(1) long heat sink big enough for six of the power chips
(1) roto-zip style cutout tool...very high speed, we'll see if it works...was cheap
Several cables soldered up to test the single-board computer.
That SBC was a really good deal. I picked it up on eBay for about $40. This board is what controls John Carmack's Armadillo project. It has IDE, floppy, diskonchip sockets, ethernet, 4 serials, keyboard, vga, flat-panel, 48 dedicated I/O, a parallel port, and simm socket. Winsystems still sells those boards...for approximately $600. Some are still left on eBay. Pick up one up now.
I also got the full-bridge chips on eBay. A great find...they can handle up to two amps continous per coil, and 3.5 amps starting. I will need two chips per motor. The great thing is that I don't have to design a chopper circuit. When trying to run a stepper motor at high speeds, you can't just switch the rated voltage on the coil. The inductance won't allow the current to reach the rated value before you have to switch it off and move to the next step. This means that the faster it runs, the less power you get. When using a chopper circuit, the stepper coil is driven by a much higher voltage than rated. This give a very fast current risetime in the coil. When the rated current is reached, the control circuit shorts the coils, and the current recirculates until it falls below the rated current. Anyway, this is all included in the chip, so I can set the desired current with an external resistor, and the chip does the rest.
All I need now is a power supply and some minor logic for controlling the steppers. There is a retrofit CNC endmill at work, which no one ever uses. I'll try to use that to make some of the parts I'll need.
Otherwise, work is boring, and the job market is gloomy. Engineers just aren't cool anymore.