"brian whatcott" wrote in message
...
I expect, like me, you thought you knew what heading hold gyros were all
about? If you haven't been around model helicopter enthusiasts lately, you
have no idea! Try googling 'heading hold gyro'.
It turns out, that radio control modelers stick a heading hold gyro on
their model helicopter and hook it to a fast servo that modulates the tail
rotor pitch. The device takes over when a rotate ("pirouette') command
stops, and stops the tail dead on that heading - fast, and holds it
against wind-drift and weather cock effects.
The HH gyro runs $40 to $150 and a fast (digital) servo might add another
$40 on it.

Think of the possibilities for a heading stabilize function in a
homebuilt!
A HH gyro driving a big servo, controlling a servo tab on the rudder.
Something similar could be arranged for pitch hold (a sort of super cheap
altitude hold/augment?)

Brian W

The heading hold gyros are rate gyros and use a microcontroller integrate
the error. They hold heading real well but drift over time. Most of the
time we can trim out the drift well enough to not be a problem but remember
most model helicopter flights last no more than 15 minutes and if a constant
heading was held for an entire 5 minutes it would be a long and boring time
for the pilot.

But gyros in model helicopters do make a world of difference. When I
started trying to learn to fly model helicopters (1981) gyros weren't very
common. I tried for years and was never able to hover out a tank of fuel
before a crash. After purchasing a simple mechanical rate gyro, I flew some
70 full tanks of fuel before crashing, and that crash was a result of
getting too far away and losing orientation (the heli turned black in the
bright sky!).

On my larger model helicopters I have gyro's that once sold for nearly $400
and a servo that sells for $130, I bought most of my stuff used and
sometimes crashed. By that time I had so much experience rebuilding crashes
that I would buy heli's needing work for a fraction of the new cost. I have
my own home machine shop and make most of the shafts simply by cutting drill
rod to length and cross drilling the holes for the bolts, a $20 main shaft
costs me about $2 + 10 minutes.

RogerN