On Wed, 23 Sep 1998, Oyvind Kaurstad wrote:

> >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.

You need sufficient GBW at 50 kHz to get rid of a certain residual signal
from the sensor. You will see.

> I'm not sure of how much resolution I will need on the ADC, and I'm not

Sensor output ~= 0.3..0.8 mV / (degree * second)

> 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.

Oh ! I had thought that you'd done this before... (interfacing to PWM
RC servo circuits). You need to do some reading here. Mixing with the
signal is DEFINITELY not the way to go.

Also, there are some implications to make a closed loop servo (hint: the
stability of a loop with gain and respectable delays and dead-bands built
in).

> 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.

Look again, I am quite sure that the DC component is not eliminated unless
the circuit is meant to do that (i.e. rate of rate gyro == rpm
stabilizer).

> >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?

Until the ground stops it or radio liaison is re-established, whichever
happens first... ;) This assumes that the heli knows how to auto-rotate
w/o help (ok, skip the flare, use a shovel instead, but it's still
better than a *sieve* and *magnifiying glass*).

> 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....

You can do that.

> 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)

I was thinking of a safety feature here. If the total degrees over a
certain time is too large, assume that the sensor died and turn off servo
loop.

Peter