…but I’m getting other things done while it floats over by the Trade Currents. It really should be here tomorrow. Meanwhile, battery chargers and battery maintenance equipment are also on the way. This is turning into a usual engineering project for me – that is, it ALL gets done in the last week.
Things that are done:
- Powertrain mechanics
- Battery pack
Things that are not done:
Throttle assembly Electronics mounts / side panels Instrumentation Wiring
- ..and Aaron, I didn’t forget this time: Cutting self and ranting on MySpace!
Pics from the past few days:
Hey, it’s my R/C signal faker. The 100A controller requires a 1-2 millisecond duration pulse every few dozen milliseconds. This is not exactly something a potentiometer can do by itself, so it requires additional circuitry. The schematic used to build the prototype was transferred over to a 2-year-old reused-thrice burnt-flux-covered piece of Radio Shack perfboard. It’s akin to using the same sheet of toilet tissue three times, once on each side and once by creative origami.
DC-DC converter! I realized that the little tiny 5 volt regulator chip would most likely detonate, and in the process detonate everything behind it, if I layed the full battery voltage through it. A bit of asking around got me these 9-36v in, 12v out converters that conveniently mount on a PC board.
Part 2 of the important electronics is this RC power analyzer. Devices like this are dropped in between a battery and its load, and read information such as volts, amps, amp-hours, watt-hours, watts, and other combinations of SI units. It will form the instrumentation of this contraption since I’ll be needing all my dead reckoning skills to prevent actually becoming dead.
Conveniently named the “Watt’s Up” meter, it is an even more convenient possibly-illegitimate cousin to the Astroflight “Whattmeter”. With a name like that, Astro will never notice.
DC-DC converter and associated equipment mounted on another piece of old perfboard. Now I’m digging napkins out of the trash can. The two are connected on the underside, and soldering this whole assembly was a precarious balancing act to make sure the tiny wires didn’t snap.
The large pic is labeled with the “pinout”, if it can really be called that. I stole a bunch of 0.1″ headers from circuit boards lying around, and regular R/C connectors slip over them in standard fashion. Only I know which way they go.
Which means this whole thing is about to detonate.
Here’s the “ghettoboarding” on the underside. This is what happens when you don’t have PC-board making equipment and freelance it using plucked strands of a 12 gauge wire. The DC-DC converter sticks out past its own board a bit, and so I glued the two boards together using it.
When I first switched everything on, there was no smoke, but there was only a shaky 7 volts coming out of the 12 volt converter. As a result, the 5 volt regulator only could push out 4 or so. I wasn’t sure why. A bit of reading on DC-DC converters found out that this thing needed capacitance on the output. A
Equate it to using a bucket to move water to a different level. The capacitor acts like a tank to smooth out the water flow on the other side. I plucked one from the nearest switching power supply board and the problems went away. Testing was done on 18 volts, but 36 shouldn’t be much different.
So I came to the conclusion that tying all my expensive electronics to the back wheel forks wasn’t going to hold up to any sort of engineering (or practical) scrutiny. Therefore, this pile of standoffs and cap screws will form the anchors for aluminum side plates, onto which everything will mount. I don’t have a concept sketch yet, but imagine big plates parallel to the wheel forks on either side of the wheel. This has the added bonus of being a starting base for a wheelie bar, and protecting the giant motor from hitting the ground, which *might* be bad.
Anyway, Hong Kong Express mail better hurry up with my controller. Who knows, the thing might take its maiden flight into the wall within the week…
This must be done.