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May 19, 2003, 04:12 PM
"Simplify, then add lightness"

Altitude control for FP micro-heli


I had been flying my HB outside only on calm days, but lately there have been too few of those days. The problem I have is not so much directional control in the wind, the major problem I have is altitude control even in light gusts. A gust comes along, and the HB takes off for the stratosphere, and as soon as I get the throttle adjusted to stop the climb, the gust stops, and the HB starts to sink like a rock. It is hard to work the throttle fast enough to compensate for the gusts, and not much fun. Does a CP heli act like this also?

I have been thinking that it would be nice to have something to stabilize the altitude, the way a gyro stabilizes the yaw. Does such a thing exist? If not, I might try building one. An simple ultrasonic range finder should be able to detect height above ground, up to about 20-25 feet, and can be built fairly light, with only a microprocessor and two ultrasonic transducers. It could connect inbetween the throttle channel and the main ESC, the way the gyro connects between the rudder channel and the tail ESC. Maybe use an extra channel to turn on and off altitude hold. Anyone else have any ideas? Maybe I just need to improve my piloting technique a bit more.

Jeff
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May 19, 2003, 05:28 PM
"Watch this!" SMACK!
jaggies's Avatar
The issue is one of control stability at low head speed. As you lose head speed, you lose cyclic authority.

With a wind gust, a helicopter wants to take off because of the additional lift. As a consequence, you drop the collective (throttle, actually). On a CP machine, this is no problem. But with a decent gust on a FP machine, you have to practically stop the blades to get it to come down.

If you could increase the head speed (by reducing the pitch, for instance), you'd get back some control by raising the head speed in descent.

If you feel like experimenting, you could trim off some of the trailing edge of the blades.

Or you could just fly inside or on a calm day

Another technique for altitude regulation could be a
pressure transducer to detect altitude or changes in altitude, rather than absolute distance. Ultrasonics are only good for 10s of feet and depend on angles and types of surfaces.

Another possibility is an accelerometer.


--jim
May 19, 2003, 07:11 PM
"Simplify, then add lightness"
Thanks Jim,
I do have an old set of blades that I might try to trim, but it looks like I'll either have to get a CP heli, or else get a bigger house. I do fly it in the house and garage, but I have a lot more fun flying outside where I have more room. I wonder if Century is ever going to come out with a CP kit for the Hummingbird.

Jeff