The old power supply circuit, the drive motor speed control circuit, and the directional control circuit still work. They are now connected to my laptop via the Phidget 8/8/8 (see below) and I have written new speed control and direction control software in C. Rather than only 10 speeds, Mike now has 200 speeds (100 forward and 100 reverse), for finer control.
I had considered replacing the drive motor speed control with a new DC motor controller, which would have handled the drive signal pulsing in firmware and also provided valuable signal feedback, but I ultimately decided to keep the legacy boards in place where possible. This means that I wrote my own speed functions, delivering from 0 to 100 pulses to the drive motors every 100 microseconds. Fun to do and I’m glad that it works. Down the road, however, this circuit may have to be upgraded or replaced: The legacy speed control circuit delivers the same signal to all drive motors, which are wired in parallel. Separate speed control of each individual drive motor is not possible and Mike’s geometry calls for this feature.
The directional control appeared at first to not function, but it turned out that the drive current was being limited by too great a factor. Probably because my Microtron is powered by a motorcycle gell cell instead of the original old-style liquid acid car battery that Todd’s Mike used. The 4.7 Ohm 10 Watt resistor (limiting the drive current) will need to be replaced with one of smaller value. But like the speed control circuit, the “proper” step in this case would be to use a full-blown motor controller.
Phidget 8/8/8 mounted on Microtron Robot, in former location of the directional control circuit. The new aluminum sheet on which it is mounted matches Mike's classic 1980s appearance. Visible at the bottom of the photo are part of the battery cage and the new battery charging cable.
All that remains for Mike to be somewhat autonomous is the addition of sensors. Probably fixing the impact sensors (ie, bumpers) and/or adding the ultrasonic detector will be next. Then transferring Mike’s new “brain” from my laptop to some sort of on-board SBC.
Synertek’s SYM-1 microcomputer, programmable from the hex keypad, with 6-digit LED readout.
The SYM-1 appears to be dead. It does not give its customary “beep” when powered up, the display remains blank, and there is no response to any key presses. Further, some of the chips appear to have rotted. I have removed it from Microtron in preparation for the robot’s long-awaited system upgrade. Also gone are the original A/D converter circuitry, the bumper-hit detection circuitry (both circa 1982), and a slew of old wires.
My current thought regarding most of the legacy circuitry is to keep boards if they work; remove or replace them only when needed.
The Phidgets library compiles and installs on my Lemote YeeLoong. The netbook appears to need 20 volts while Microtron’s battery is 12 volts – so I’ll either add a boost-up circuit or use something else for Microtron’s on-board processor.
In the meantime, I’ll be ready for coding when the 8/8/8 arrives.
Microtron knows which direction it is turning because of a potentiometer that reports the current position of the turning wheel back to the central processor. The original potentiometer that was installed in 1981 had apparently disintegrated at some point while the robot was in storage.
As one of the steps needed to get Microtron working again, I replaced the pot’ and pressure-mounted dowel today.
Pictured above on the right is what is left of the old potentiometer, and on the left is the new replacement pot’ and dowel.
The joystick has been assembled and wired to the A/D converter, using a 16-pin IC connector and ribbon cable. It was originally used on our Apple II.
The Directional Control Potentiometer has been attached to the front wheel using the same dowel method described by Tod. Instead of a screw, however, I used super-glue to hold the dowel in place. I also had to add a small block of wood (held on with Elmer’s glue) beneath the aluminum mounting bracket.
Completed the speed control circuit.
completed circuit, mounted on the right side of the triangular frame:
Completed and installed the Power Supply Circuit.
Completed the Directional Control Assembly. This includes the framework needed to hold the directional control motor in place and the gear on the upper shaft of the front wheel. I had the gear attachment ring made at the NAPA (Rt. 9, Natick) machine shop.
Completed the battery cage, altered from Tod’s measurements to fit a pair of 6v gel cells (in series).