Current prototype assembled from laser cut acrylic
The big task of last week was moving from the foam-core prototype to one made out of acrylic so that we can begin attaching the motor and other electronics. The version pictured above was drafted with AutoCAD and cut on the laser printer. It contains no gears but demonstrates how all the joints will work.
As someone whose background is in digital media, it has been a lot of fun watching Sid and Eilidh (both product designers) build stuff with their hands (and the laser cutter). This is a process I will be careful to never underestimate in any future projects.
Sid attaching the stepper motor
Once we were happy with the way the scale moved, we had to begin thinking about how to attach the motor. We considered using a belt system, but once we discovered a discarded printer in the school’s dumpster, we began experimenting with the gears inside that. In the end we decided to attach a gear taken from the printer to the scale and laser cut a smaller gear that would attach directly to our motor.
At this point, Sid has found a new best friend in the laser printer. We are using this tool to do everything from etching text to cutting highly customized gears. But besides using the laser printer, we have been in the electronics labs soldering wires, the wood shop seeking advice on materials, the metal workshop cutting screws, the glass studio sand blasting acrylic and in the IT office seeking discarded printers to hack.
Eilidh soldering a power supply to the motor's driver board
The problem we are currently facing is power. Once the motor was fixed to the scale and connected to our Arduino board, we were very relieved to see that it was actually working. The gears fit and the motor moved the arms quite smoothly. But the problem was it could hardly lift a plastic dish, let alone anything that would be placed in that dish. We experimented with stronger power supplies but in the end the problem appeared to be with our motor’s driver board. We are presently working with Vinay to assemble a driver board capable of handling more power. Hopefully then the scale will actually be able to move with things placed on top of it.
Driving the motor with the Arduino
Besides the motor, we also connected two limit switches. They are placed below the gears and act as a safety mechanism. Once the arm goes too far to either side, it will hit the switch and turn the motor off. They will also be necessary for measuring the amount of steps the motor will take to move the scale from one side to the other. With this measurement, we can begin thinking about how to calculate the movements that will take place when different food items and weights are placed on the scale.
We have made some good progress during the past week but our to-do-list is still frightengly long (and getting longer). Once the motor is working properly, we will need to attach an RFID reader to one arm and a load cell (weight sensor) to the other. And then we have to program everything. It also might be good if the object looks nice, as opposed to clear acrylic with wires everywhere. And then we have to put together a presentation.
