The first problem I stated on was the motor controller, unlike last year I wanted to use PWM and solid state devices to control the speed.
I started off using a fully integrated H-bridge IC, this was a single device with everything built in, sufficed to say this didn't work, I went through 3 devices before I gave up and started looking for a different solution. I am not really sure why it didn't work I think it was due to overheating, I switched on the h-bridges using a solid logic signal rather than a PWM signal this meant that it was running at full power and I don't think it was designed to do this.
After this didn't work I decided to go back to making a controller from scratch, something heavy duty and reliable. Someone else must have done something similar in the past so I decided to check the Internet, it didn't take me long to find a suitable motor controller. The only change I made was to use higher power parts than was recommended, after building many different motor controller circuits to have none of them work I was very surprised when this one did. This is a very good circuit, I am using it in this robot and in my balancing robot and it performs perfectly. I have only tried it with a PWM input not a steady logic signal like I did with the integrated IC's.
You can find a full circuit diagram on the authors page, as soon as I find out what parts I used I will list them here