This is the mechanical machine we made for a event called "Robopatrol" at IIT Guwahati. It won 2nd prize.

Mechanical structure

The base of the bot is made of plywood with gearboxes attached to it using aluminium strips. Now base is done and it can move forward, backward, right and left using the motors that are bidirectional. As we were novice in this field, We had a challenge in making the motors bidirectional during the time of making it. we needed to use push button switches as they are very easy to control the bot. But by using adaptor, we had to use 8 of that kind. Then we made a circuit of the kind as shown below and using that we can control the bot iwth 4 push buttons only.

In this circuit, using two push buttons and two different battery supplies, we can control a motor in both directions. Now our base is complete and working fine.

The next part is to make a mechanism for grabbing a tennis ball and have to place it in some pit specified. During our discussion, one of our friend suggested a rubber band idea. So we implemented. we took a plastic box and tied rubber bands at regular spaces so that the space between any two of them will be smaller than diameter of a tennis ball. So whenever we bang the box on the floor where we kept some tennis balls, those balls got trapped. Then we made a hole to the plastic box and connected cylindrical tube made out of plastic file material. This cylindrical part is supported by wooden scale. We connected the wooden scale to a perpendicular gear motor which is mounted on our base. We added some flipper mechanism at the other end of the cylindrical structure to control the balls falling in the pit.

That's our machine.

YouTube Video