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.
http://www.mycockpit.org/forums/attachment.php?attachmentid=10535&stc=1

http://www.mycockpit.org/forums/attachment.php?attachmentid=10534&stc=1

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/showthread.php?t=24577&highlight=scott

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

http://www.mycockpit.org/forums/showthread.php?t=28859&highlight=altimeter

And other:

http://www.cockpitbuilders.com/community/index.php?topic=2373.0;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:

http://www.mycockpit.org/forums/attachment.php?attachmentid=10539&stc=1

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

http://www.mycockpit.org/forums/attachment.php?attachmentid=10540&stc=1
Arduino has a module ready to work

http://www.mycockpit.org/forums/attachment.php?attachmentid=10541&stc=1
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/manual_usbstepper_eng.pdf

Regards.
Horacio.

[SimSupervisor]

I managed to open it up! Thanks. It looks a lot like that one from the website you suggested
http://colibrisim.free.fr/wp-content/uploads/wpid550-12062012-_DSC0203.jpg
(sorry I didnt take pictures of mine while it was openned)
BTW I am from Montreal, french is natural for me :D

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.mycockpit.org/forums/attachment.php?attachmentid=10575&stc=1

http://www.hobbyking.com/hobbyking/store/__11737__HobbyKing_Ultra_Micro_Servo_1_7g_for_3D_Flight_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.

[SimSupervisor]

I didn't know about those linear servos, looks quite interesting. The gears outside do lots of revolutions, might be perfect. It would certainly be more interesting than most other zero-sensing methods I have tought about.

[xplanematt]

The problem with a servo is that you have an effective resolution of *maybe* 1,000 steps or so...and that's for a high-end servo in ideal conditions. The problem with the altimeter is that the bellows makes extremely small movements to make the needles move quite a bit. With a stepped worm drive, your resolution is limited only by the gearing of the stepper. Higher resolution just means more steps required for movement of the needles. The only other piece of the puzzle, as you say, is detecting the zero/home position. I don't think this would be a huge problem to overcome, and would certainly be worth the hassle for the smooth and precise movement that would be possible with the stepper. A light sensor behind a tiny hole in the altimeter face is one possibility, or an optical switch that is interrupted by the bellows linkage at the precise point at which 0ft/sea-level is indicated.

Matt

[SimSupervisor]

The below linkage had been severed, I'd think by corrosion. I still need to confirm the dial gears are functional. I am working on my tachometer right now, but this is next up my list.

You are right, it is going to require quite a small, tiny precision movement. I am pretty sure I will have to get some gearing going. Thing is, I have no local store where to get hobby gears. :(

[SimSupervisor]

after some cleaning, and trying to see if the first gear was stuck or what, it appears the gear is no longer on its shaft. I don't know if it happenned before I got it or is it me trying to see if I could make it turn, but its no longer in place.

I had tried prior to that to see if I could get into the gearbox, it is held in place by two brass screws. Thing is, one of them is stuck in place and is getting damaged by trying to unscrew it.

http://www.mycockpit.org/forums/attachment.php?attachmentid=10587&stc=1
here's what the front plate just under the faceplate looks like. I decided to go ahead and just drill the bolt down, and am getting to the insides.

here's the inside of the gearbox:
http://www.mycockpit.org/forums/attachment.php?attachmentid=10588&stc=1

plus two gears shown bellow. The small one goes on the right side, you see discoloration where it goes, and I believe the bigger one is supposed to be part of the small one, and give the below's access to the motion. Everything else works fine (except the middle needle, that would go with the below's gear)
http://www.mycockpit.org/forums/attachment.php?attachmentid=10589&stc=1

Can a set of those two gears (in one piece), plus a gear that would fit the specs of the below's gear (and interface with the "faster" needle) be made/purchased somewhere?

Or should I simply gut it out and find something else? It woudl be a shame, as most of the gears are still functionning.

[hyamesto]

Simsupervisor: That´s it your name? :lol:
Let me disassemble my altimeter to better understand what is missing in your setup, but basically, you have a 1:10:100
gear train (1 is connect with 100 ft needle, 10 with 1000 feet needle, and finally, 100 with 10.000 feet needle).
I don´t think you can use that gear train. If your sim is based in a C-150, you can´t fly over 13.000 feet (at least in the real plane), and using this gear train with a stepper, to calibrate to zero, you need at least 100 or 200 turns of the 100 feet needle.
Another thing: the altimeter that you have got has a max operation range of 20.000 feets. (no need to use the full scale of the 10.000 feet needle)
There are better solutions.
I´m building my instruments from raw materials, cutting gears in acrylic, others pieces with plastic or MDF with a CNC laser, and using steppers and servos. (cheap service from a laser CNC shop near my home)
For the altimeter, i use 1 stepper for the 100 feet needle, a gear reduction of 1:10 for the 1000 feet needle, a servo for 10.000 needle, and another servo for the kollsman setting, drive by an encoder. To zeroing, the altimeter needs to turn 10 or 20 times the 100 feet needle when i turn on the control card, before start Flight Sim.
Regards.
Horacio.

[SimSupervisor]

That sounds interesting, but I don't know that I can accurately print gears... :( I hope to find somewhere to buy what it takes to make a functionnal gearbox.
But I have to agree, this gear train is not in good shape, I might have to use something else.

I did complain to the used aviation parts supplier where I got this altimeter about the poor state of some of the instruments he sold me (this wasn't the worst, you should see my airspeed and my vertical speed indicators!) and he said he would send me other instruments soon. I hope it includes a replacement altimeter. I wasn't expecting to get that much corrosion inside the instruments. Aren't they supposed to be sealed??!

Regarding the kollsman indicator, I am not sure to follow you... isn't the Kollman setting an input from the instrument to the flight sim? Maybe I completely miss the point, but normally you would setup the reference barometric pressure and leave it as is, which in turn would infere a proper value to the instrument, to display as accurately as possible the altimeter....

I was thinking of reusing the current knob and disc for display, and interface a potentiometer to the knob's gear for input trough the Arduino, letting the software know what is the current Kollsman setting.

[hyamesto]

Tomorrow i will try to show you my proposed solution. (If i have time...), and why i am using an encoder and not a potentiometer to set the kollsman, as well a test to understand that...
About the corrosion, the real instruments are not sealed. They are interconnected with plastic tube to a static port open for sensing the pressure surrounding the plane, and to the pitot tube.
The system must use a moisture trap, and regulary, you must purge the condensed water with a valve.
If the plane which took the instruments, was flying near the sea, the salt is very corrosive, or maybe, the plane crashed on water, and the instruments are discarded.
By the photos, all the instruments you have, seems to be scrapped, and sold as ornament. (like mine instruments)

In advance, check this post for your others instruments to come....

http://www.mycockpit.org/forums/showthread.php?t=26848

As you can see, based on reply of your posts, very few people are using real instruments, due to the complexity of adapting to a software Flight sim.
And when you get the NAV instruments (VOR, ILS) to set the OBS, everything done up here, will be the easiest part....

Regards.
Horacio.

[SimSupervisor]

Less people working with actual instruments is yet another reason to post about it! Share the knowledge!!! :D

I have a Narco VOA-4 VOR/ILS Nav converter/indicator that I might try to interface later. Its all transistor circuitery from the 70s, and wasn't anywhere near being used on a cessna 150 that I base my cockpit on; so I am uncertain if I'll use up one of the empty instrument bay for that, or if I'll use its chassis for another instrument (I badly need an attitude indicator)

in the meanwhile, I am out of luck for gears on my altimeter, so far... :(

[hyamesto]

:D It´s more easy to build a 737... a couple of monitors behind a panel..........:D
I'm short on time, but wait a few days while I get a good video camera to show you what I have build and how is working with Flight Simulator.
And i will give you some ideas to replace the instruments.
My collection of real instruments is ornament now, only buyed to see the internals and to study to interface (like your tachometer) or find a way to replicate with scratchbuilding ones. (The altimeter is the next...)

Don´t hurry, building my cockpit took to me 10 years, and never is finish.:roll:

For example, i made an Attitude Indicator, or Artificial Horizont, simple like the original cessna, and weeks laters, a friend give me a real broken one from an Aero Commander 500, with Flight director needles and two warning flags (gyro and steer). I want to remake mine, adding the Flight Director and the flags too..
Wait for photos and videos.

Regards.
Horacio.

[SimSupervisor]

I found a clock mechanism that I can dismount to have access to triple centered shafts if I can't manage to work the original gearbox.

here's what the clock shaft gears look like on the top/below separation plane inside my altimeter. I would modify the gearbox casing to hide my gears and still use the Kollman dial, and will have to make the clock shafts shorter (not an issue), but could manage my three needles from there.
http://www.mycockpit.org/forums/attachment.php?attachmentid=10611&stc=1


http://www.mycockpit.org/forums/attachment.php?attachmentid=10612&stc=1



I still need to manage my own gearbox to get the 1:10:100 ratios.


How do you manage your own gears?

I can't wait to see your instruments in action.

[hyamesto]

Be patient.......
Meanwhile, i can show you my real altimeter.
Your missing piece is this shaft, with a gear......

http://www.mycockpit.org/forums/attachment.php?attachmentid=10614&stc=1
With a piece of paper to better contrast....
http://www.mycockpit.org/forums/attachment.php?attachmentid=10615&stc=1
Its a 12 teeth gear, one point connected to barometric part, and the other to drive the gearbox....

The next photo, is your broken 2 parts gear. Its a Gear compound....
http://www.mycockpit.org/forums/attachment.php?attachmentid=10616&stc=1
The bigger gear has 40 teeth, and the smaller gear has 13 teeth. This are a gear compound, that is the gears are fixed to one another.
The next photo it´s the location inside the gearbox...

http://www.mycockpit.org/forums/attachment.php?attachmentid=10617&stc=1

The gear system is:
Pinion 12 teeth pinion (direct 100 feet needle)
40 teeth -13 teeth gear compound 1
39 teeth -24 teeth gear compound 2 (Connected to 1000 feet needle)
48 teeth -12 teeth gear compound 3
60 teeth gear (Connected to 10.000 feet needle)


12 teeth pinion drive a 40 teeth gear compound 1. (3/10 relation)
13 teeth of gear compound 1 drive a 39 teeth gear compound 2. (1/3 relation)
24 teeth of gear compound 2 drive a 48 teeth gear compound 3 (1/2 relation)
12 teeth of gear compound 3 drive a final 60 teeth gear. (1/5 relation)

This is a 1:10:1000 gearbox.

A design with autocad......

http://www.mycockpit.org/forums/attachment.php?attachmentid=10618&stc=1

But again, be patient, because this gearbox can be cut in acrylic.... but it´s no good for a simulated altimeter (remember the zeroing...).
With this gearbox, you need at least 100 turns minimal to zeroing the altimeter.
I recommend work with 100 feet and 1000 feet needle gearbox (10 turns to zeroing) and work the 10.000 feet needle with a servo.
Remember, the real altimeter has a effective range of -1000 feet to 20.000 feet for a Cessna.

Read this:

http://www.unitedinst.com/Products/SpecificationsSheets/d126281.aspx

In the weekend, i will try to upload a video of my others instruments...

Regards.
Horacio

[SimSupervisor]

Thanks a lot for those pictures and explanations. I never worked gears before, this will be my first time. I was hoping to just "use the original gears"...

I would be happy to have to drive "only" two motors. At the current point (without gearbox) I need to drive three, and would be happier with only two. If I would have the original gearbox I'd be OK to have a longer zeroing, but if I am to build it from scratch, you are right it makes no sense.

The only gear I am really missing, is the 40:13 gear compound. I still have the "center" 12 teeth gear, but its shaft was broken. I was hoping to manage another one. On my altimeter, the 48:12 teeth compound is passing trough the gearbox and the 39:24 teeth gear is on the other side compared to the 43:13. These still work. If the compound wouldn't be damaged, I'd be trying to interface to it with some motor.

But things being what they are, I am looking at making another gearbox. I'll see what I can come up with.

And post pictures of my trials and error in the process. ;)

[hyamesto]

I´m sorry, but the 43:13 gear it´s really the most necesary part. Mine gearbox is equal to yours (the 48:12 passing trought gearbox too).
If you are interested in scrachbuild the original gearbox but with bigger gears (not change the functionality at all), i can make a Coreldraw file (every laser cut service accept this format) and send you the gearbox ready to make a laser-cut gears in acrylic, and with some brass or aluminium tubes and wires, you can reuse the rest of the instrument. I give you a list of materials, dimmensions and a guide to doing this.
Only need the exact dimmension (diameter) of the "circle" of piece in which is placed yours gearbox, and the shaft diameter of the stepper.

http://www.mycockpit.org/forums/attachment.php?attachmentid=10619&stc=1
Maybe you should enlarge the holes of the needles to match the tubes.

Or, if you can wait, i must begin to design my altimeter, with servos and a stepper, and scrachtbuild the overall instrument.

Regards.
Horacio.

[hyamesto]

A beginning of design of my altimeter.....
http://www.mycockpit.org/forums/attachment.php?attachmentid=10627&stc=1
Regards.
Horacio.

[SimSupervisor]

that could be interesting! I will look around for a place that does laser cutting, I guess I would have to order online.

How do you manage the needle shafts from the gears?

Thanks for teaching me about those kind of mechanism.



My original piece is 73mm wide, but where it sits in the original instrument, the border narrows the usable to aprox 66mm. Also, I will have to pass a geared potentiometer trough one of the holes to interface with the kollmans dial that is still geared to the kollmans knob. pierce on the area away from the three holes, where the actual knob is.

I still have to choose the stepper.

The way I see it, most of the time the instrument will be near ground at power-up, zeroing could in theory be done going down and wouldn't need the whole 100 turns every time. I don't think I mind the extra zeroing time.

[hyamesto]

How do I manage the needle shafts from the gears?, easy.....
Using K&S aluminium tubes, like

http://www.ksmetals.com

In Montreal, you can find in:

https://udisco.com/index.php

This are the telescopic aluminium and brass tube from my instruments and some music wires (not showed), gluing the laser cut gears to them....

http://www.mycockpit.org/forums/attachment.php?attachmentid=10644&stc=1http://www.mycockpit.org/forums/attachment.php?attachmentid=10645&stc=1

Regards.
Horacio.

[SimSupervisor]

That's a great idea!
I'll get tubes and manage my design from there.

This is going to be interesting to learn :)

[SimSupervisor]

That's a great idea!
I'll get tubes and manage my design from there.

This is going to be interesting to learn :)