Well, this post is quite a bit belated, thanks to Will’s laziness :P. I’m unofficially deciding that since school is in, we’ll measure time by week rather than by day, since we usually can only meet once on weekends anyway. So this post is going to explain what we did the weekend of the first week of school.
As was evident in the previous post, we fired up an ESC for the first time. After fixing a bug in the timer driver, we were able to control throttle from the vex remote, albeit with some glitches. I learned that the ESC calibrates your arming signal as the “off” position, but the code assumed that 1ms always meant off but sent a .75ms signal to arm. Because of this, as I mentioned briefly in the video we were unable to turn off the motor short of shutting off the signal, which causes the ESC to power off only after a few second delay. Easy fix however, we’ll simply send a 1ms arming signal and also use that to signal motor power off.
We also ordered female headers and a bunch of other goodies from Electronic Goldmine. They have all kinds of random awesome stuff, like this electronic interrupter that should make excellent landing gear, or this really cheap 1×24 character LCD. Since we’re extremely low on IO lines, we’re going to attempt to drive the LCD’s data lines using a shift register. We also picked up 5 super caps for Jeff, for a possible future railgun project. And a bunch of other random stuff, like transistors, and an assortment of voltage regulators for powering various things like XBCs and wireless cameras.
I’ve been working on the final board’s schematic for a bit. Like the previous board, it primarily is just routing power and signal lines to the microcontroller and sensors, but this new board will also contain our EEPROM and altimeter, which finally arrived from Futurlec. It also contains its own power regulator, and provided I can convince Will a built in serial shifter circuit as well. The direct connection to the battery means we can also measure our battery voltage.
Since we’ve got a three day weekend, tomorrow will be our Week two meeting. We should get to construct some sort of harness to keep the copter from flying away during later testing. We’ll also measure our power draw with a watt meter, and if everything looks good fire up all four motors. After that, we should probably try out our the LiPo charger for the first time. And last but not least, work more on our board layout using the schematic. Construction of the final board should begin on Week three provided we finish the layout tomorrow and the parts come sometime this week!
Oh, and here’s my crappy board schematic, made in ExpressSCH. I used Eagle for a while, but its part list was annoyingly slow and massive, while ExpressSCH works much faster and also is more intuitive to work with. Since this schematic will never get fabbed, its also nice that ExpressSCH doesn’t keep making you worry about picking identical parts with different footprints. It looks kinda ugly right now, going to spread components out more once I’ve placed them all. All thats remaining are the boring connectors for a few spare UARTs, and the transistor-driven 12V buzzer I think.
Mainboard WIP Schematic