Gyroscope repair

15.01.2011 23:10

On Tuesday I wrote a rant about how my indoor model helicopter didn't work correctly. It turned out that my hunch about a bad connection to the gyroscope was correct. After some exhaustive continuity testing of the nets associated with the gyro SMD I found out there must be a fault somewhere on the tiny break-out board that carries the gyroscope.

After I unsoldered it from the main part of the PCB, the problem was obvious:

Murata Gyrostar on a break-out board

The first pad (ground connection as it turns out) is mostly missing! Probably there was only a crack at first and the rest of the pad peeled off when I unsoldered it. Since I couldn't do anything about the missing pad I soldered the board back in place and made a bridge on the top side with a piece of wire (it's way too thick, but that's the smallest gauge I had at hand):

Fixed ground connection to the gyro

Here's a photo of the components on the bottom side of the circuit board (the black thing out of focus in front is the IR receiver):

Bottom side of the PCB inside micro RC helicopter

Now that the sensor ground has a proper connection the gyroscope offset is well within the trimmable range and the chopper flies as it should. I also managed to take it apart and reassemble it without breaking any of those hair-thin wires or stripping any of the tiny screws. Yay!

Micro helicopter flight test

(Click to watch Micro helicopter flight test video)

Interestingly, I first wasted time by focusing on the Vcc connection. The helicopter was rotating clockwise, which according to the Gyrostar datasheet should mean that the sensor output voltage was too low (i.e. erroneously reporting counter-clockwise rotation). But since the ground connection was flaky it was actually too high. So either the datasheet is wrong or my clocks are running backwards.

Also of note is that the reference voltage output of the gyroscope isn't used (only ground, Vcc and sensor output pads are connected).

Oh, and finally, remember that I said the web site of the company that sells these always throws a PHP error? Well, not if you set the preferred language to Austrian German (de-at) in your browser.

Posted by Tomaž | Categories: Analog

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