Hello,
Your project sounds like fun. Can you provide any more information? What type of environment will the robotic car be traveling over? Is this a road vehicle? Will it be expected to go up and down hills? How fast do you want it to travel. Are you going to build it or is this a design exercise. How much do you expect the person to weigh? That will give you the amount of weight you have available for your chassis and what not.
Conscripted