One of the first sketches of how I might get the robot to steer.
I think I was trying to sketch out a vision of how the whole thing might look down the line.
Blurry image of the blown-up joint for the center of the robot.
It lets the robot control steering at the center, but there's also a pivot/twist so that it can keep four wheels on the ground more often in rough terrain.
Here's how I put the drive train in the chassis. The differential/shafts are from an hobbyist RC car catalog and looked about the right size for what I wanted. I fabricated the motor and gear reduction by cutting up the housings of some cheap electric screwdrivers from Harbor Freight; seemed like plenty of torque and speed. The wheel axles are on some roller skate bearings that sit in custom aluminum carriages that my uncle CNCed for me.
Chassis with the drive train installed.
Me working in my basement electronics shop, junior year of high school. via my dad.
This is the robot at its most finished state thus far. The solar arrays are from Harbor Freight and trickle charge the drive batteries (NiMH). There are limit sensors and switches at both ends, as well as limit switches on the turning mechanism so that it never tries to rail the turning. There's also a car door remote receiver so that I can start the program remotely. I never got the bluetooth connection working so that I could update the program in real time, but bluetooth was far less reliable in 2007 when I was working on it.
RoVAAR: robotic vehicle for automation application research

This is a robot that I built in my basement in high school and entered in the ISEF International Science and Engineering Fair (alumnus '10, '11, '12). The main controller is a Direct Logic DL06 PLC with two ADC/DACs to control the steering (PD loop) and driving (PI loop). There are a number of sensors so it can run autonomously: some limit switches to prevent oversteering, some bumper collision sensors on both ends, and some infrared collision avoidance sensors. The DC motors are stolen from cordless drills run on NiMH batteries, and a lot of the drive components are taken from hobby RC cars.

Brian Cherbak
Engineer at MindTribe Product Engineering San Francisco, CA