Figure 2 - Tippy will have a differential type of drive like a front end loader
I recently acquired an old power chair for parts and found that the dual gear head motors had amazing amounts of power. These motors had a 1 horsepower 3000 RPM 24 volt DC motor connected to a huge gearbox, outputting to a 3/4 shaft turning at around 250 RPM. These motors were absolutely perfect to build medium to large scale all terrain robot platforms, so I found some rusty old scrap square tubing and began to make a simple frame.
The plan was to create a square frame to hold a set of machined car axles and drive them through a belt and pulley transmission. The two front wheels would also create a differential steering system by altering their speed and direction. The rear wheel would be placed on a swing arm, so it could just follow along, much like the way a front end loaded drive and steering system worked. The frame box would also have enough room for the battery pack, which would be placed as low as possible in order to help keep the robot balanced.
Figure 3 - The pivoting rear swingarm will steer along with the front end
To create a front end loader type steering system, a pivoting swing arm was added to the rear of the frame. The pivot is provided by a pair of bearings and a shaft hacked from an old snow blower I found at the dump. To keep the frame horizontal to the ground, the front drive wheel bearings are placed face up in the frame and the rear wheel bearings are going to be places face down on the swing arm tubing. This will place all 3 axles at the same level, keeping the frame horizontally positioned.