Quad encoder problems

[smitty505000]

Hi Darrel,
Thanks for your input! Please forgive me for not explaining everything. I understand inertia and centripetal force and I totally agree with you. However, the plane this unit is going into is slow and very stable. Yes it can do loops and rolls but I do not plan on doing any (or at least I don’t expect the reading to mean anything if I do). I plan on just slow gentle flying and gliding. For this, I believe my setup should work just fine. Please correct me if I am wrong.

Smitty

[Darrel Taylor]

I still think you'll have problems with the weight swinging back and forth, and wild readings in general just do to the different G forces.

If you're just looking for a way of finding which way is down during level flight. Perhaps as an aid to setting the trim. I think it'll be a lot easier to use an accelerometer. It's not going to give an artificial horizon, but it can find which way is Up. It can also give other interesting info like the G force of a turn or the amount of turbulence.

There's a nice one at Parallax for pretty cheap. And it works with PULSIN, so no interrupts or quadrature encoders to deal with.

Memsic 2125 Dual-axis Accelerometer
http://www.parallax.com/detail.asp?product_id=28017

Understanding the Basics of an Accelerometer
http://www.parallax.com/html_pages/r...s/cat_acce.asp

HTH,

[SteveB]

Having a little experiance with this from the operator end, Darrel is right, at any flight speed. It is inconcievable that you will only be flying in straight, unaccelerated flight, and this is the only time your concept would be accurate. Even at slight bank angles and accelerations, your "gravity" based system would not give you useful or accurate infomation.

Doing a little searching, found an adequate explaination of why this the the case.

Steve

[Darrel Taylor]

Darn 40 posts per page.

Smitty, if you missed it, go back to post #40, page 1.
Steve and I both hit it at the same minute
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[smitty505000]

Crud! You guys are convincing me that this will not work. I didnt think the forces would be that bad. I guess it is like walking and carrying a glass of water, and we all know how it sloshes around.

Ok so a Parallax dual accelerometer shows where down is? Is it effected by inertia?

What about a pair of Mem's inclinometers from Digital ADIS16203?

I need to do some more reading I guess.

Smitty

[Darrel Taylor]

Is it effected by inertia?

Yes it is. That's why it can't give an artificial horizon.

What about a pair of Mem's inclinometers from Digital ADIS16203?

At $48 a piece for a single axis, It's makes the dual axis for $29.95 look a lot better.
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[smitty505000]

I am a little confused. Will inertia effect the ADIS16203 digital inclinometer as well? Dosnt it work off the earths magnetic field?

Is there any way I can make this artificial horizon work without a PHD in astrophysics?

Smitty

[sayzer]

....

Is there any way I can make this artificial horizon work without a PHD in astrophysics?
..

I was about the say that this issue is getting too complicated for me to follow.

[SteveB]

Here is a quote from the datasheet of the ADIS16203:

The ADIS16203 is a calibrated digital inclinometer that provides a full 360° of measurement range in any rotational plane that is parallel to the earth’s gravity. A dual-axis accelerometer provides the base-sensing function, which resolves the earth’s gravity into two orthogonal vectors, as displayed in Figure 23. A power-efficient approach to a common trigonometric identity converts these orthogonal vectors into an incline-angle measurement.

It is an accelerometer. Thus, in flight, will only be accurate when the plane is in wings level, unaccelerated flight. In other conditions, it will be giving you the resulting sum of all accelerations on the plane, which will certianly not be the same as the acceleration of the earth's gravity.

Steve