Weeks 9 and 10: Machine design and automation
As this was a group assignment and our supernode Fab Lab León hosted a weekend session for all the students to meet and work on the machine: McNulty MachineMachineBuilding_v4 from Marta Verde on Vimeo.
I got a little late to the MTM session at Fab Lab León, not really late, but some of my colleagues arrived León on friday and started setting up the tasks and started setting up the boards. So on saturday morning when I got there Marta and Borja were already connecting the boards. They’ve never used a laboratory power supply with voltage and current regulation so I explained them a little bit on current limiting and voltage supply.
As Fab Academy 2015 students also met at León for the MTM assignment, the FTDI cable, connection board and cables were already made. So we started installing Python and required dependencies like Pyserial and Pygestalt on our computers to test the boards. When we first run simple_node.py from Pygestalt examples, we were able to connect to serial but then the LEDs wont start to blink and ask for identification on the bus.
We wanted to discard a problem with the firmware and practise with programming firmware into the avr from different OSs. So we had two firmwares available 086-005a.hex and 086-005a_boot.hex and we were seeing that different labs used different hexes selected as the “working ones”. And after a while having problems also after flashing (rewriting fuses then burning the firm… test, nothing) I decided to disconnect everything and start fresh re-checking connections, power supply and firmwares.
That’s when we discovered a cable on the wrong position that gave us hope. So we plugged everything right, flashed all four (by that time labeled) nodes and started single testing each one of them. To our surprise two of them (#1 and #4) worked but the other two didn’t and showed a message on the console “RUNNING IN BOOTLOADER MODE” while the working ones showed “NOW RUNNING IN APPLICATION MODE”. So we reflashed boards #2 and #3 with 086-005a_boot.hex, repeated the process and everything worked. We run the single_node.py for every board and motor and discovered that one of the motors was vibrating when stopped, so we discarded that the board was the fault, and changed the motor as we only needed 3 motors with an axis.
The next step was to get all four motors working and then check on the power consumption and see what power supply was needed once we install a dedicated power supply. The consumption will depend on the load, weight to move and speed. At speed 2, and without any foam on the plate, the consumption was around 0.88 A which seems very low and gives us room to use a 5A supply for all motors and nichrome wire.
Now the electronics were set up, we focused on getting an simple code to be able to test the cutting before leaving León. There were some documentation foam cutting machines from last year that we’ve been following during the weekend. But we wanted to start in the middle from scratch to a fully working version for a very similar machine. So we picked xy_plotter.py example from pygestalt htmaa machine example. Since we can still work on the code and improve it, and even for distributed programming while we were there, we set up a git repo at gitlab, but not git.fabacademy, but gitlab.com. Later we realized that we have to have it on the fabacademy archive.
About the name, when I've started the GitLab repository, thinking of it as something just to share code while we were on the Fab Lab, I put the name McNulty one of the main characters on The Wire### tv series as a pun, since we were building a hot wire cutting machine. Monday when we got back to our weeklife, as nobody proposed any other name, it became McNulty for the machine too.