Sensor ideas needed

[joe@tech-mp]

Here is the problem:

In a tandem helicopter (Chinook type), the yaw (rudder) is controlled by differential cyclic on the roll axis. To yaw left, the front rotor tilts left and the rear rotor tilts right. So, the yaw axis on a tandem is controlled by the roll axis. As many of you know, roll control sense does not change whether the model is right side up (RSU) or up side down (USD) like rudder and elevator. When a tandem is flying RSU everything is fine, the yaw gyro sense is correct. When flying USD the controls and gyro (yaw) are inverted but the roll axis is the same. The result is reversed rudder control with the gyro correcting in the wrong direction. Currently, this is a barrier that limits tandem 3-D flying.

Here are some potential solutions already on the table:

1. Use a pilot controlled invert switch on the Tx. - Old school way of handling it.

2. Change the yaw signal polarity based on Tx collective pitch position - This has been experimented with and had
limited success. The stick position does not exactly follow the lift vectors of the rotors.

3. Use a sensor or group of sensors to accurately detect the RSU or USD position.

I like the number 3 approach the best. The sensor(s) would be inputs to a tandem mixer (TH-2) which would process the signals and apply the polarity corrections. The sensors must work both outside and indoors with artificial lighting. Also, they must handle the effects of gravity and centrifugal force from any 3-D flight manuver.

Any Ideas would be appreciated.

Joe

[Mr.RC-CAM]

Can you limit the design to outdoor use? If so, then this is one application where the inaccuracies of the thermal IR sensing method would probably not be a significant issue. Thermal IR is free of inertial influences that may trigger a false RSU/USD position. So, try hacking a Co-Pilot sensor (just add microcontroller and stir). :)

[sfsjkid]

Most heli pilots have an idle up for inverted flying, and some pilots 3 of them. Couldn't one of the be used to also reverse the direction? This might be limited to the higher end radios though.

[Tophinater]

KISS, go with the first one.

[Blue Sky]

Here's a thought.
Why not use a magnetic field sensor?
You could use a Hall effect or magnetoresistive sensor or
compass module set up as an inclinometer.
Ther earth's magnetic field is largely vertical not horizontal.
Where I live the field is tilted about 70 degrees from the horizontal.
This means that if a sensor has it's faces set vertically it's largest and
smallest readings will always follow it's vertical orientation despite
actual compass heading. If you were actually trying to guide the helicopter
using the sensor or trying to establish an artificial horizon, it wouldn't work.
But if you just need to know if you are RSU vs USD a single axis sensor that has a
large hysteresis, that is ignores all but the large and small readings should work.
The big problem might be keeping it far enough away from the motor.
A more sophisticated 3 axis sensor that compensates for stray fields and compass
heading might even be better and could supply other useful information.
But even a very simple setup might work.

-Dave

[joe@tech-mp]

Thanks for all your input :)