I still remember the first robot I built at home. Although I have no photos of it I still remember the mess I made putting it together. I spent hours cutting and carving Styrofoam to make an oddly bullet shaped pancake that was about the size of an A4 sheet of paper. Tiny foam balls flew everywhere and statically stuck to everything as I tried to insert my Basic stamp education board by squashing it into the square “like” hole I cut into my robot chassis. My 2 modified servomotors (for continuous rotation) were positioned awkwardly at different angles and heights, held in by screws even though sticky tape would probably have sufficed.
Wires hung and dangled on the floor and in the air connecting the micro, sensors, power and actuators with extreme complexity so that no-one (not even I at times) could determine where they were connected to. While putting it on the ground a small and gratefully unused chunk of the robot chassis broke off. My robot maiden run was not going so well. However I had managed to scrape together some decent code off the internet so my PING sensor managed to keep my robot from bumping into obstacles and loosing any more pieces of itself.
The robot had many flaws. It would not drive straight (due to the positions of the servos in the chassis not being aligned), it would break apart and leave foam all over the place (due to the chassis material being too brittle) and wires would come loose shut down the robot and I could not work out quickly where to put them back (due to poor wiring and messy prototyping). All of these issues could have been solved with some forward planning and measurement rather than just trying to cobble some “stuff” together. My first robot was not just a failure in building and construction, it was a failure in planning.
A robot chassis is the skeleton of a robot and good working robot requires that its skeleton be robust and precise to ensure its correct functioning. A robot will never work properly if it is not created with its intent, environment and construction planned out before you design it. Whenever you begin to design mechanical parts I have found it best to ask the following questions:
- What do I want this robot to do?
- What will be its operating environment/conditions?
- What method/process will I use for construction?
The first question will highlight the critical aspects of your chassis design. For my first robot I wanted it to drive around and avoid obstacles therefore it needed to have equal motor drive balance. So making my robot symmetrical with both motors balanced was critical, something I definitely did not do. What your robot is intended to do will form its skeleton.
The second question will help you to determine what your robot chassis and rest of the body should be made from. Is your robot going to be operating outside on the grass, underwater, on tiles or wooden floors or will it be on carpet inside the house.The environment in which your robot operates will give you the requirements of what it must handle in its life, so you should design accordingly. My robot needed to be robust enough to handle just being handled, to that criteria it failed. I cut the foam for its chassis too thinly and it could barely hold the weight of all components when handled without cracking and breaking. Some 10mm perspex sheet would at least provided some rigidity to hold the robot together and not fall apart.
The final question is a must for designing anything. How will this be made? With your materials selected from the last question you can now see how to make parts using that material. All processes have their strengths and weaknesses. You may be limited to what tools you have access to so that may also limit your construction abilities and techniques. You MUST design with the way it will be made in mind, my robot was carved out of foam using a knife and a short battery powered wire cutter. My first intricate and dimensioned drawings of the robot had no chance in reality of being produced by hand with those basic tools. I was not able to make the proper measured and accurate cuts that a machine could do without issue. Rigid materials for robot chassis’ require power tools to cutout with speed and accuracy.
I have completed the build instructions for the Prototype robot chassis/shell. I do not have as many photos as I would have liked, but I did not think of writing this blog until half-way though finishing. The method used for this shell is the same used for fiber-glassing boats and making models. It provides a very strong structure and can be finished with paints. I hope to use this method in the future to complete a robot, but that is for another time.