spherical positioning

[sciguy125]

I was just thinking up a helicopter-like device. I doubt that I'll actually make it, but I thought it was interesting.

My reasoning for the accelerometer array is that gravity is just a 3-d vector. If we had a device that could measure this vector, we'd know our orientation. But, again, this would only work if we were static. If we started to accelerate in any direction (by our own power), this second acceleration would be added to the gravity vector. This would make the measurement almost worthless.

If we had gyros (or some other sort of rotational sensors), we'd know our orientation referenced from our initial orientation. We assume that, at start up, we are on the ground, or otherwise not moving. We take a reading from the accelerometers and we can determine what direction is down. All readings from the gyros are referenced to this condition. When we start moving, we can use the gyros to determine our orientation and start using the accelerometers to determine our linear acceleration. However, we'd have to subtract gravity from the accelerometer readings. Because we know our orientation via the gryros, we know what direction gravity is. Subtract the gravity vector from the accelerometer readings and we have our linear acceleration. With our acceleration, we should be able to figure out where we are.

So, how do we compensate for drift because our initial reference point is gone?

A better way to phrase my question would be: If you were in a box and could have any instruments you wanted, how would you determine your position in space (as in your 3-d position)? I have a feeling that we'll run into some sort of Uncertainty Principle type of thing.