Posted on December 4, 2015
Airplane Attitude Indicator for the Car
When you’re off-road it’s a good idea not to flip your car over. Apparently it’s a commonly held rule-of-thumb that when the car is more than 30 degrees tilted around the ‘roll’ axis, a rollover is imminent (or has already happened).
But the thing is, driving at pretty much any angle feels really scary when you’re used to driving on roads, so for a newbie like me some kind of objective reference is helpful. In the 4wd game this kind of instrument is called an ‘inclinometer’, and I think some FJ60s came with them built in like this:
In an airplane, the same thing is expressed with an instrument called an attitude indicator, and they’re powered by vacuum which drives a little gyroscope. The gyroscope is mounted on a gimbal and stays level with reference to the horizon around the pitch and roll axes as the airplane rotates around it. So, the pilot can always see the degrees of pitch and roll without an external visual reference. I decided we needed an airplane attitude indicator for the car.
I picked up an old non-functional one from a real plane from Ebay. When it arrived and I had it apart, I was blown away by the intricacy of all the parts. Calibration must be incredibly difficult with a mechanical device like this – it has all these weights and little carefully placed adjustment screws in various places. Not to worry, I ripped them all out with the original gyroscope.
To make the unit work I used two servo-motors in place of the gyro, which are sent position data from a Teensy LC (same type of micro controller as my weather radio for the car project). The position data comes to the Teensy from an amazing 9-axis Bosch BN055 chip / breakout board by Adafruit which has onboard fusing of 3-axis accelerometer, 3-axis gyroscope and 3-axis magnetometer.
It has a little LED on board which turns red when roll exceeds 30 degrees. Right now it takes power from a micro-usb port on the Teensy.
It’s still a prototype, so the dash-mount is yet to be figured out, for now duct tape will have to do!!