Help me gut my altimeter!

[SimSupervisor]

Greetings. I am still new here so sorry if I posted in the wrong subforum or am using a wrong nomenclature, I still have much to learn.

I have this (used, non-working) altimeter that I want to interface to an Arduino. Problem is, I can't get the internals out of the enclosure.
I removed the knob/faceplate/glass but am stuck at that point, as the altimeter doesn't want out of the enclosure. Short of opening it with a can opener (joke) does anyone know of a way to remove it out?

here's some pictures if it can help.




any help would be greatly welcomed.

[hyamesto]

Hi:
This is my point of view:
The internals are useless. You only can use the faceplates, and the needles. To remove the needles, just pull-out carefully, they are just pressed over a group of tiny concentric tubes. When you remove the 10.000 feet needle, you can find two small screws, and the faceplates are out. Some gears out, and the internals are free.
To interface with arduino, today it´s no easy. You need at least 1 stepper motor for the needles with a gear train, one servo or another stepper motor for the kollmans window faceplate, and encoder to adjust the pressure (kollmans scale) and a sensor in every stepper to set the zero point.

Check the following links:

http://www.mycockpit.org/forums/show...ighlight=scott

Others guys, are using only a servo to "press" the aneroid capsule, but the movement must be micrometric.

http://www.mycockpit.org/forums/show...ight=altimeter

And other:

http://www.cockpitbuilders.com/commu...73.0;topicseen

Regards.

Horacio.

[SimSupervisor]

I was somewhat hoping to reuse some of the mechanism...
But I'll try to find do out how to remove the faceplate, thanks a lot for the idea.

As for steppers, what sort of sensors are you referring to?

[SimSupervisor]

Sorry seems like I doubleposted

[hyamesto]

Sensors: can be optics or mechanicals, to determining the zero point (thats is 0 altitude)

Check (in french, sorry)

http://colibrisim.free.fr/?page_id=545

http://colibrisim.free.fr/?page_id=136

This guy use a mechanical sensor ( flexible blade switch) like some found in older cassette recoders) with opencockpits USB stepper card:



Others, like Opencockpits, use optical sensors (found in some printers).


Arduino has a module ready to work


but the stepper control with arduino it´s (until now) very difficult.

Check the concept with this manual from opencockpits:

http://www.opencockpits.com/uploads/...tepper_eng.pdf

Regards.
Horacio.

[SimSupervisor]

I managed to open it up! Thanks. It looks a lot like that one from the website you suggested

(sorry I didnt take pictures of mine while it was openned)
BTW I am from Montreal, french is natural for me

The internals is ... very corroded. I don't know if the gears are working or are seized; the small activation gear from the main mechanism broke off, and without a proper shaft I couldn't simulate movement manually. I am pretty sure some cleaning and some motor would lead to a proper rotation.

I am pretty sure a stepper or infinite movement servo could do the trick, but the zeroing might be tricky.

[hyamesto]

Yes, the zeroing point is the trouble. I have two altimeters, but I´m planning to make copies of faceplates to keep the instruments as a ornament.
Regards.
Horacio

[xplanematt]

Before you go ripping out all that fine expensive hardware......

I am going to pass on a tip I got from another builder.....I think I remember who it was, but I don't want to say, in case I am remembering incorrectly. If it's who I think it is, he will hopefully chime in. A fellow builder told me he got a barometric altimeter working with minimal hackery by using a stepper-based worm drive on the small linkage that connects the dial to the bellows. Basically the worm drive replaces the bellows. This makes a lot of sense, as the amount of movement with a worm gear per-step is TINY. I am keen to try it myself. Most of my altimeters are servoed, but I have one that is not (actually two, but the other one is WAY too nice to chop up for sim use.....going to save it as a conversation piece, possibly have it re-certified and put into whatever real aircraft I eventually purchase at some point down the road).

Matt

[SimSupervisor]

Worm drive stepper motor? That's interesting. I was thinking I'd have to pass trough some gears to get the proper resolution. I was def wanting to try and use the original linkage, as long as it still works. As I said, that altimeter had LOTS of inner corosion, and I have yet to make the needle gears turn.

Another concern too is "how do I manage to detect zero)


But, thanks quite a lot for chiming in, knowing someone managed to interface to the gears and get good precision is rather positive.

[hyamesto]

You can try with a lineal hobby servo like this:



http://www.hobbyking.com/hobbyking/s...ght_Left_.html

Just google "lineal hobby servo", and you can find thousands of models and sizes..
With this, you don´t need worry about zero position.

But i don´t know how can manage to set the "Kollsmann" setting, and synchronize with Flight Sim software....
Regards.
Horacio.