Hi,

I have been reading a lot about fpv on heli which is comparatively difficult. thus question is not specific to rc models either.

How can a electronic system  detect drift on rc heli? What sensor? I know fly mentor uses ccd cam to analyze images. But this is only at a height of 3 mts.. Now what about at a 500ft altitude say??

And altitude? can GPS provide altitude which can be used in altitude stabilization?

No diy ec guys here?

Dear Srivatsa:

Regarding the drift
Gyroscope and Accelerometer sensors may be used in combination.
One measure the rate of rotation and the other used for orientation

For instance, A 3axis gyroscope shows the rate of  rotation on its X(side) ,Y(front) and Z(vertical) axes.
Z-axis(for heli) output may help to understand/co-relates the cyclic rotation created by the main rotor, accordingly tail rotor speed may be regulated to counterbalance rotational force.
Secondly, it also helps to counter balance the air pressure. where all the axis play together.

Using an accelerometer, we get axis tilt output - i.e. the tilt of the body.
For instance, a 3-axis accelerometer will provide tilt data on axis X,Y,Z.

Regarding altitude:
from GPS you get altitute data with speed, latitude, longitude, time. The accuracy of which majorly depends on the trigonometric calculation of the number of satellites tracked/visible to the GPS.
You may datalog the path of travel using lat & long data.

if you just wish to measure only altitude, you may also use a barometric pressure sensor - we have such sensor - named altimeter

Here is the link -
http://shop.sumeetinstruments.com/index.php?route=product/category&path=35_54

http://shop.sumeetinstruments.com/index.php?route=product/category&path=35_56

Thanks sumeeth, but drift doesn't rotate the heli? so I'm really doubtful if gyro outputs anything actually.

Also I'm skeptical if i can use a barometric sensor for altitude, reason being,  heli's main blades, pushing huge volume of air underneath creates an area of high pressure. so the readings will not be accurate.

Accelerometer & gyro together can be used to stop the sideway shift. I think with practical trial, a proper equation may be reached with these sensor output and accordingly the tail rotor speed and main rotor tilts can play.

say - When the heli start and lifted, it circle around (consider the main rotor as the vertical axis of rotation, the gyro together with accelerometer output may be mapped with tail rotor speed adjustment - to stop rotational affect. When this is done - you may see the drift affect - here the accelerometer output may be used to oppositely adjust the tilt of main rotor - both system has to work together for effective results.

Barometric sensor is just an option and you are correct with the air pressure issue - and GPS need clear sky or add an external antenna .... may be some kind proper housing may reduce the effect