Although it seems pretty trivial decision, however while deciding on the shape of our robot we had plenty of discussions within the team. We experimented with different shapes and decided on the octagon. Here is an explanation as to why.

When we started designing this robot, we thought about using the usual robot chassis that is available from most websites. 

However we decided to design our own chassis as we wanted to build a robot that would have lots of add-ons and a number of possibilities. Just using an off the shelf chassis did not give us the freedom to design our add-ons according to how we wanted to place them on the robot. 

After discussing many different designs and going through different prototypes and versions we ended up with a Octagon shape. We considered a circular chassis, a hexagon as well as the traditional shape shown in the image above. The reason for choosing an octagon shape was it gave us plenty of room to add sensor modules which are usually straight or rectangular in shape. Refer to the image with the Sonar sensor. 8 different small sides gave us 8 spaces to mount sensors that needed to be at the boundary of the base plate (the chassis). For this reason we did not use the existing chassis shape as well as the circular shape.