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Mar 08, 2007, 11:42 PM
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Meet Astro Blinky


So finally got a blinker, the smallest, cheapest, and hardest to find battery balancer in the world. It supports 6 cells, for U Trex 600 fans. Now for the first time, your closest look at The Blinker.

The Blinker is just a PIC which takes analog readings of the cell voltages every 2 seconds. It shorts all the cells except the one with the lowest voltage until they're all equal or within a certain range. Any cells over 4.2V are discharged regardless of the other cell states.

The maximum current during the shorting is 150mA, so you can't charge the batteries too fast and expect them to stay balanced. The more
unbalanced they are, the closer to 150mA of charge current you have to provide. Still need a "don't do anything STUPID" battery protoboard for measuring unbalance after flight.

The Blinker gets the job done; unfortunately, the blinker has 2 limitations. If 2 cells are 3.7V and 1
cell is 3.5V, it discharges the 3.7V cells to bring them to 3.5V, a lethal condition. After charging, if 1 cell self discharges faster than the other 2, it discharges the other 2 to match the faster discharging rate.

The solution is to only use the blinker during charging, don't leave it on for long periods after charging, and top off the blinker before
flight.

The perfect battery balancer would charge each cell on a different circuit, not possible without adding enourmous weight for connectors.

In other news, the next test flight was supposed to be a tail lock using gyros. WRRRRROOOOOONGO! Reviewing the source code, discovered it takes a full 3 axis magnetometer to do the next flight. Heading lock was never possible using inertial navigation alone. No-one has dissected one, but suspect all heading lock gyros use magnetometers of some kind.

Another $160 gone. Total spent so far: $320 At least it isn't Euros.
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Mar 09, 2007, 09:05 AM
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>Discharged like astronauts.
he, he, he


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