>> I've read that they all use the "Gyrostar ENC" sensors from MuRata.

>mostly correct, all others seem to be copies thereof...

Close enough....

>> These gyros are usually very expensive. (more than
>> twice the price of a conventional one here in Norway)

>so someone is trying to rip you off... they are CHEAPER actually, they
>were expensive when they were a novelty. You should not pay more than $110
>for a one-axis one, complete sealed in the box with warranty, and this is
>the high side price.

I suppose the marketing guys have a certain influence here...

"If it is better we can charge more for it, it doesn't matter if it is cheaper
to manufacture. We will make more money that way..."

>I'll never understand why a mechanical contraption with a whole collection
>of closely toleranced moving parts can be sold for less money than the
>equivalent solid state design, once the novelty stage passes.

I couldn't agree more...

>> The sensor itself is not so expensive (approx 25 dollars) and I believe that
>> the other components needed besides the PIC will cost approximately
>> the same (an op amp, probably quad, and an A/D plus some discretes and
>> probably a temp sensor to compensate drift).

>No drift or temperature compensator is required, the gyrostars are rate
>gyros. The A/D can be inside the PIC. If you do not have gyro
>horizon/compass requirements then a 12C671 and a CA3260 or such are all
>the hardware needed. When I investigated this, I used a 16C71 and LM324.
>The 324's performance could be improved on (thus the 3260).

I assume there are lots of other opamps that could be used, also.
But it should be low-noise, low power types, I suppose.

I'm not sure of how much resolution I will need on the ADC, and I'm not
sure how to do the mixing with the incoming signal from the receiver.
Does it sound ok to kind of overlay the gyro signal on the receiver signal?
With adjustable gain, of course.

I saw an example amplifier circuit on the Murata website, but they used both
a highpass and a lowpass filter on the signal, thus eliminating the DC 
component.
In the case of a model heli gyro this will be undesirable, I think.
If I do that I will not be able to detect if the helicopter is continuosly 
pirouetting, for
instance.

>The nice thing is, these gyros require so little power and weigh so little
>that they can be used with electric helis.

I'm not into electric helis, but obviously this is a great asset.

>> The inputs from the receiver and the outputs to the servo can be connected
>> directly to the PIC since the signal levels are TTL compatible.

>Yes. You can even make the chopper turn slowly if the radio signal is
>lost... which is a very good idea in view of the price of the bird imho.

But how would you determine for how long it should turn?

>> What do you think? Doable or not?

>Doable, but there will be a reasonable amount of effort required to get
>the low-pass filter and the digital integrator deadband right. Gyrostars
>have an offset that varies fom unit to unit and this must be allowed for.
>A trimmer is not a good idea an a heli but a 93c46 could be.

What about an initial zero read routine in the gyro software?
It would of course have to assume that the heli is not rotating when it is first
powered, but that is usually the case, so....

Why would you want to integrate the signal?
Isn't this kind of a closed-loop thing? You apply opposite tail rotor until the
rotation stops? (Or until a preset deadband is reached)

-Oyvind