Day 2: Power Diversions

Intending to start discussing and working on the MC14500B processor board, I had to change plans when I saw voltage regulators in the mailbox this afternoon. These beauties are 3Amp LM323 +5V regulators in a gorgeous TO-3 package. They scream vintage electronics! No modern switch-mode power here, just the tender warmth of a linear regulator. In a weird stroke of luck (or an odd feature), two mounting holes in the chassis and the large cutout in the middle fit the TO-3 package almost perfectly.

Even if you are not familiar with the TO-3 package, you might quickly notice that there appear to be only 2 terminal pins for a transistor or regulator that typically has 3 pins. For purposes of our 9V to 5V voltage regulator, we need input voltage (9V), output voltage (5v), and common ground connection. The TO-3 package supplies each of these, but the ground is provided by the metal case of the device. As a result, unless we want the robot chassis to be at ground potential, the regulator and its screws must be isolated from the metal mounting plate by some insulators. Unfortunately, the chassis screw holes are not quite big enough for the insulators and I drilled them out to 11/64". Of course, that meant I had to disassemble everything first. So once everything is insulated from the chassis, you still need to make the connection to the case of the TO-3 component with a little eye lug terminal on one of the machine screws holding everything together. It is all delightfully mechanical.

I was so proud of myself and thinking that I might get to hook up a battery to the voltage regulator, then directly to the motors and give it a (uncontrolled full speed) test run. Not so fast... as I was putting everything backtogther, it was clear that the motor mount screws were just barely touching the voltage regulator screws. It probably would not be too big of a deal to just have everything grounded, but it took the wind out of my sails. Too late at night to use power tools to shorten the motor mount screws.

Note the flat white plastic insulator that extends through the holes in the chassis (middle to left of photo), the grey silicone(?) insulator on the other side (barely visible though some of the extra screw holes), the long and thin round terminal sticking through the insulators (extreme lower left of photo) and the metal fittings holding it all together... and of course, the horizontal motor mount screw barely touching the grounded mounting nut.

Parts list once I fix this issue.