RunRyder RC Helicopter Topic - Robbe Heli Command.

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Aerial Photography and Video > Robbe Heli Command.

Gary Evans
Heliman
Location: Mesa, Az, USA

Helicommand

I was aware of the pop up windows but some of them like "gain" leave a lot to be desired in terms of clarity.

03-24-2007 11:14 PM

AceBird
Elite Veteran
Location: Utica, NY USA

Quote
My understanding is that in order to make a GPS signal work to move a heli from point A to B you need a means of knowing the heli's attitude.

Isn't GPS three dimensional? Don't you already have elevation from sea level with GPS?

Ace
What could be more fun?

03-24-2007 11:30 PM

BigguyOz
Key Veteran
Location: Forster, New South Wales, Australia

I would be very surprised if the resolution of the altitude provided by a GPS would be fine enough, even if it was accurate to one foot.

It would be incredible to believe that relying on "rough" accuracy like this from two GPS units spaced a couple of feet apart could be of any use in measuring the attitude of the helicopter - a difference in height of even 6 inches front and back of a helicopter represents a relatively extreme angle....

Sorry Ace, back to the armchair.

03-25-2007 12:24 AM

Harris
Senior Heliman
Location: Cyprus

Quote
Isn't GPS three dimensional? Don't you already have elevation from sea level with GPS?

GPS gives you an estimate of your position with an error that can be anything from 2 meters to more than 30! Yes, it gives you elevation above sea level but with the same error margin. However, it doesn't tell you anything about relative height from the ground. Also, the update rate is very slow (about 2 Hz).

To control a heli effectively you need an update rate of at least 20Hz and an accuracy of 0.1 degrees. There is no way you can get all this from current GPS technology!

Even if you can have 2 GPS units one at the canopy and another at the tail of the heli that update fast enough, are accurate enough, and 100% full-proof (no loss of signal), you can still calculate the attitude of the heli only along 2 axes. You will still miss the roll axis.

And don't forget that GPS only works outside.

So for all these reasons I think GPS is not good for attitude estimation. Just look at full scale aircraft and you will know. They tend to do things right...

03-25-2007 08:51 AM

HOMEPAGE

AceBird
Elite Veteran
Location: Utica, NY USA

Quote
a difference in height of even 6 inches front and back of a helicopter represents a relatively extreme angle....

I'm just thinking out loud. I assumed that the GPS could tell the distance between each signal better (resolution) whereas it doesn't matter exactly where (accuracy) they are in space.

Hmmm ... you think full scale dictates technology vs. a model? I thought they used models to determine what would work in full scale.

Ace
What could be more fun?

03-25-2007 02:31 PM

Harris
Senior Heliman
Location: Cyprus

Quote
I'm just thinking out loud. I assumed that the GPS could tell the distance between each signal better (resolution) whereas it doesn't matter exactly where (accuracy) they are in space.

No problem at all with that! This is a free speech forum after all! Don't feel that you have to defend your ideas simply because somebody else disagrees with you.

Quote
Hmmm ... you think full scale dictates technology vs. a model? I thought they used models to determine what would work in full scale.

Well, they use models for some things (like aerodynamics for example) but not for all. Certainly not for avionics, as far as I know. And, yes, most of the technology used in full scale aircraft is years ahead of what we use in our models. For more specific examples see turbines, main rotor blades, autopilots, etc. Of course most full scale helis don't flip and roll very well, but that's something to be expected. They carry humans after all!

03-25-2007 09:17 PM

HOMEPAGE

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