Last week I spent my evenings redesigning my holonomic platform. It had te be wider in order to get the center of gravity (relatively) lower. I also wanted to gear it up to make it more agile. And I wanted the brick to be better accessible, especially the USB port. Two other demands remained from Sidbot, the wheel angle should be adjustable so that the robot can be used both on a flat surface and on top of a large ball. It also had to be sturdy.
As it had to be sturdy I decided that the motors should be fixed to the frame. Sidbot had its motors adjustable to make the wheel angles adjustable. The wheels have to be adjustable on the new robot as well, this meant that the hinge point had to be between motor and wheels somewhere in the gear train. I tried different designs and gears but I always ended up with grinding gears. At last I ended up using a 5×7 liftarm to house part of the gear train. This effectively stopped the grinding but resulted in a very wide wheel housing as well. This is not so pretty so I’m still trying to improve this part. However, I now got a 2:1 gear ratio. With a motor speed of 120 RPM and a wheel diameter of 48 mm this gives the robot a top speed of 30 cm per second.
The frame of the robot consists of two triangles stacked vertically. The triangles are made of three 11 stud liftarms connected at the ends with 3 and 4 stud liftarms. This makes a very rigid frame, the brick lies on top of it making it easy accessible. The motors are mounted horizontally with the flat side down. This gives the robot width and also the ground space that is needed when riding on a ball. To prevent torsion between motor and frame I made a housing with L-shaped for the motors.
I used light bluish gray and dark bluish gray for the color scheme as these are the colors the motors and brick are made from. The result is a bit dull but still rather nice looking. It resembles a Starwars like vehicle. Maybe I should mount some laser guns on top.
The resulting robot does meet all my design specifications. But I have not been able to test it yet as I’m one 40 teeth gear short. I hope to get it this week.
The robot still needs a name. If you have a good suggestion you can post it in the remarks. There is a nice price for the winner a second hand Hitechnic gyro sensor. Submit your entry before November 2011.