Hi,I understand the issues about using simple rate gyros with an autopilot - i.e. you can't unless teamed with accelerometers etc - but could one use a head-lock gyro for stabilisation via aileron control ?Max flight time would be about 10 - 15 mins.Simon
Interesting comments !
bGatti's original response reminded me of the occasion I watched a model jet aircraft being expertly flown straight and level down a runway, whilst continuously rolling around the x-axis; not too sure then how you'd use the gps vectors to correct the roll axis gyro.
The Sparkfun gyro is c $30, add an integrator plus assoc electronics and we're looking at around $70 which compares reasonably with the Co-Pilot IR solution at c $75. However I had in mind an ESky EK2-0704B head lock gyro which is promoted as incorporating drift cancelling. It doesn't claim 'zero drift' but certainly seems, on initial testing, to be pretty stable. I guess I'll just have to try it.
Given that U-Nav doesn't own the idea of a turn-rate wing leveller... I am REALLY shocked that there is no DIY-spawned open source or competing product at a much more reasonable price. It would be the World's simplest test case for a simple Kalman filter in aircraft stabilization: predictions are done by integrating gyro in yaw axis, and the update cycle comes with each GPS update. Simple. $400 for a Pico-N board??? I think NOT! The LISY-AL300 gyro is only around $10, and Sparkfun sells it now.
Even head-lock gyros drift over time. A heli only needs to hold a vector for a few seconds. A plane needs to know where "down" is for for many minutes.
The better Analog Devices gyros have a noise density of 0.05 deg/sec/sqrtHz.
To be generous, assume your aircraft has a pretty slow response frequency of 15Hz, so you only need to sample your gyro at 30Hz. This means a noise density of about 0.25 deg/sec. You need to integrate the output of your rate sensor to get your rotational position (which is what you are controlling for), which basically means to find the worst-case drift you would just multiply the noise density by the time in seconds. 15 degrees per minute is not a negligible error. Luckily, three-axis accelerometers are getting very inexpensive thanks to hard drive protection mechanisms in laptops, and gyros are thanks to image stabilization in consumer cameras. We may be getting close to a tipping point of affordable inertial stabilization.
Comments
bGatti's original response reminded me of the occasion I watched a model jet aircraft being expertly flown straight and level down a runway, whilst continuously rolling around the x-axis; not too sure then how you'd use the gps vectors to correct the roll axis gyro.
The Sparkfun gyro is c $30, add an integrator plus assoc electronics and we're looking at around $70 which compares reasonably with the Co-Pilot IR solution at c $75. However I had in mind an ESky EK2-0704B head lock gyro which is promoted as incorporating drift cancelling. It doesn't claim 'zero drift' but certainly seems, on initial testing, to be pretty stable. I guess I'll just have to try it.
The better Analog Devices gyros have a noise density of 0.05 deg/sec/sqrtHz.
To be generous, assume your aircraft has a pretty slow response frequency of 15Hz, so you only need to sample your gyro at 30Hz. This means a noise density of about 0.25 deg/sec. You need to integrate the output of your rate sensor to get your rotational position (which is what you are controlling for), which basically means to find the worst-case drift you would just multiply the noise density by the time in seconds. 15 degrees per minute is not a negligible error. Luckily, three-axis accelerometers are getting very inexpensive thanks to hard drive protection mechanisms in laptops, and gyros are thanks to image stabilization in consumer cameras. We may be getting close to a tipping point of affordable inertial stabilization.