Ok, so here's what I did this past weekend. I started by working on the steering. To start with, when I loosely put the old parts in, I realized there was a new problem. The servo has a larger turn radius than the old motor. So, I needed to redesign how the steering worked somewhat. I decided to go with a steering method similar to what was originally in the car. The first step was to figure out how long to make a lever to make use of the turn radius of the servo in order to get the full turn radius of the wheels. I did a measurement or how far a know lever turned on the motor and using tangents, I calculated the angle the servo turned (approximately 120°) as well as how long of a lever I would need. Then I redesigned the bracket in my head and fabricated it out of brass using a variety of tools. I also designed and created a new linkage, while making use of the existing tie rods for the wheels, and assembled the whole thing. I gave it a test and it worked pretty well, but the only thing I'm not too happy about is that it has a bit more play than I would have liked, since I didn't have a good way of making it easy to disassemble while securing the tie rod to bracket linkage from rotating. I may go back at this and build an improved version with better leverage that addresses the looseness problem. Also, the weld stuff does hold to metal quite good, so I'll probably make better use of that as well. It's good enough for now though and the steering does actually work for all practical purposes. I took some pictures of the linkage, but have yet to upload them.

The next thing I tackled was seeing if the rear drive motor could be upgraded. I bought a larger DC motor at Radio Shack and decided to test it's RPM on the same load and voltage as the old motor before doing a replacement. I took another motor to use as a generator and connected a gear to it. Next, I hooked up my multimeter to the generator motor to measure the voltage output. Then taking each of the motors and connecting the same gear to them, I tested how much voltage each generated when turning the generator. Surprisingly, the original motor produced more power, so I decided not to make any modifications to the rear of the truck. I reassembled it and used some epoxy to make a couple repairs while doing so, since some plastic parts that had snapped off in some crashes which probably occured when one of my kids was driving it.

Next I started looking at electronic speed controllers designs again. My biggest worry was how I was going to read all the radio inputs into the microprocessor. Most of the designs which used a pic chip read no more than 2 channels for reading the PPM (Pulse Position Modulation) value to determine what positions the controls were in. Since I wanted to make use of the 6 channel RC Transmitter/Reciever that I had, I was looking at various ways to tackle this. One that I had been considering was assigning the task of reading the PWM (Pulse Width Modulation) signal with separate pic16F84a chips and communicating information back to the main pic16f877a processor, but I wanted to see if I could find a simpler solution. After doing some research, I'm thinking of making use of an octal latch chip (such as the 74LS373) to latch in the values of all 6 channels and loop through them, which will allow me to make calculations to determine the pulse widths on all channels without channel values changing during those calculations. Then I could make use of just the pic16F877a without complicating the design too much with a bunch of other unneccesary extra parts. That will also keep my costs down and it's much easier to make software tweaks using 1 microprocessor than multiple microprocessors.

Since I have somewhat of a good idea about what I'll be doing with hardware, I'll be writing the initial software soon. For the test circuit, I'll probably do something low power like rapidly blinking an LED or 2 to give it the illusion of changing brightness as the controls move. Either that or I may just output something on an LCD display, for which I wrote some nice code to interface it about a week and a half ago.