Monday, December 1, 2008
Dumbbot showing off it's motors
Dumbbot was designed to be my first Sumobot. Originally I had intended to construct a much more complex bot by decided that a simpler bot would be better as a first time sumobot. The project used various circuit "bits" that I had either used before or had seen.
Not knowing how I was going to do the body construction I decided to make the base chassis the universal plate set from Tamiya. This plate is plastic, 6x?? cm and has been predrilled with 3mm holes. Being plastic it was easy to cut down to size (the magic Dremmel).
For wheels I chose the Tamiya tractor tires. Again being from the same range everything fits together. The 3mm hex axle was used. I did cut down the molding on the tire so it would sit closer to the body. This meant the width of the robot was now just under 10cm.
One of the hardest parts about a sumobot is meeting the restrictions on the size of the body (10x10cm - 500gm). To get two motors into a 10x10cm area is all but impossible with standard gearhead motors. The gearhead motors I used on Squarebot are 7cm long. So normally you need to be using motors with their drive shaft at 90 degrees to the motor body or some special gearhead motors where the gears are laid out to minimise the space used (like the Solarbotics motors).
I make a habit of pulling apart old cdrom drives for motors and gears. Luckily I had pulled apart two of the same model which meant I now had two motors of the same spec. These were approx 5cm long and rated to 9V. They weren't gearhead motors however. I needed a way to gear down the motors and connect them to the 3mm hex axles used to attach the wheels. Luckily Tamiya had something to help. They sell pulley set range consisting of various pulleys, gear wheels, etc. I used the 38mm pulley wheel on the tire axle and drove the other end of the system directly off the small (2mm) shaft of the motor. First I did some test to see if a pulley system would actually carry 500gm and also push 500gm. A few tins of mushrooms and tuna later and to my amazement the pulley system worked well pushing the 500gm tin with little issue. The only issue was the pulleys were too large for the axle and the base plate was in the way. So some more Dremmel work and I cut out some channels under the pulleys so they would run clear. I ran the motors at 3V as that produced a speed that seemed about right. The 3V power line came from 2 x AA batteries.
To attach the motors to the base plate I used some small scrap pieces of metal. I made a template of where the mounting holes were on the motor and used this to drill out the metal as required. One was good, the other needed a bit of filing to fit. Doing it again I would spend more time making the template. A bit of sheet metal work and I had custom engine mounts for my recycled motors.
On the opposite end of the chassis I had room for the 9V battery mount. This way the majority of the weight was as low as possible.
I intended to mount the circuit board above the engines and pulleys. So I used some 3mm screws and spacers to gain the height needed to mount the board.