Tuesday, March 29, 2011

She canna take much more o' this, cap'n!

I'm givin' 'er all she's got, Cap'n!
All she's got isn't good enough. What else do you got?

The supposedly "low power" part of the engine room is quite low-powered compared to even the tail rotor, but: it draws about 50mA for the CPU, probably about 20mA for each light on the arduino, and 20mA for EACH of the little infrared LEDs inside the opto-isolator. When all the motors are running, this means that the engine room is drawing ~200mA at 5V, or one full watt.

This was originally designed to be powered by the LiPo battery and 3.3V regulator on the Logomatic, run through a boost converter to get it up to the 5V that the Arduino wants.

Something interesting though: The regulator on the Logomatic is set to deliver only 150mA. Now this is enough to run the LPC chip, a couple of sensors, and maybe a GPS, but certainly not 200mA above and beyond that (actually a bit more, since it is at 3.3V instead of 5V). So, it tries to go into thermal shutdown (the part is uncomfortably hot on the board!) but that darn boost converter just keeps sucking as much power as it needs to get 200mA for the 5V side. The Arduino is humming along like nothing is the matter, while the 3.3V line on the Logomatic drops to a mere 1.7V! This puts the LPC into brownout reset, of course.

So, teensy tiny design flaw number 2:  The Bridge cannot power the Engine Room. Well. We have a tempting 11.1V just on the other side of the line in the engine room, but three motors made of pure inductonium ready to put nice big fat voltage spikes on the wire at the slightest provocation. I am serious about protecting the low-power controllers from the motors. So, attach a 9V battery to the VIN of the Arduino, by soldering it in to the engine board underneath the Arduino socket.

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