# Thread: Altimeter gear compound train help

1. ## Altimeter gear compound train help

Since Mike Powell´s book is not longer available, i need a little help for making a gear compound train for a kollsman altimeter.
I had seen a web (Scott Hendry) with a simple system (with the numbers of teeths) ,but the URL no longer exist.
I have a photo, but i don´t understand the numbers of teeths for a 1:10:100 ratio.

altimeter gears.jpg

In the photo, the larger gears are 50 teeth, and the smallers are 16 teeth, but the ratio does not seem correct.
Can anybody help me?
Thanks in advance.

Horacio

2. ## Re: Altimeter gear compound train help

I was thinking about:
60-30-12
or
80-40-16
or
50-25-10

but i haven´t a clue to put gears in a 2 axis system.
Thanks.
Horacio.

3. ## Re: Altimeter gear compound train help

Why not buy a real altimeter off ebay and convert it. Much easier in my humble opinion as all the gearing is done. You just need to change out the drive mechanism.

4. ## Re: Altimeter gear compound train help

Those gears produce a 0.1024:1 ratio. Not the exact 1:10 that you want, but probably close enough for a simulation while still using easy-to-get parts.

5. ## Re: Altimeter gear compound train help

It's 24 to 48 out to the idler shaft, then 12 to 60 back to the concentric shafts. The first gives you a 2 to 1 reduction; the second gives you a 5 to 1 reduction. The net reduction is exactly 10 to 1. A key fact is that the sum of the diameters of the first two gears is the same as the sum of the diameters of the second pair. If this were not the case the gears would not be able to mesh properly.

I don't know how Scott was planning to use the gear set you pictured. Possibly he was not going to develop a 1:10:100 reduction train. He may have planned to simply use three separate, offset motors to individually drive three concentric output shafts.

6. ## Re: Altimeter gear compound train help

That´s the right answer... Just before your reply, i find the solution with 12 to 24, then 12 to 60.
ALTIMETRO KOLLSMAN 1.jpg
Many thanks Mike !!!!!!!!

7. ## Re: Altimeter gear compound train help

Originally Posted by Mike.Powell
It's 24 to 48 out to the idler shaft, then 12 to 60 back to the concentric shafts. The first gives you a 2 to 1 reduction; the second gives you a 5 to 1 reduction. The net reduction is exactly 10 to 1. A key fact is that the sum of the diameters of the first two gears is the same as the sum of the diameters of the second pair. If this were not the case the gears would not be able to mesh properly.

I don't know how Scott was planning to use the gear set you pictured. Possibly he was not going to develop a 1:10:100 reduction train. He may have planned to simply use three separate, offset motors to individually drive three concentric output shafts.
LOL, that's because those weren't my gears. I used the ratios Mike set out above and in his book, but I cut my own from aluminium and brass.

P1060112.jpg

I used an old altimeter as someone else suggested, which gives the benefit of the external knob to drive the kollesman setup mechanism.

P1060288.jpg

My new URL is at the end of this post, but I had to remove soome of the sim pics when I started building the Nynja. If there are pics of any sim bits that I did that anyone would like copies of, just PM me and I'll gladly send them.

8. ## Re: Altimeter gear compound train help

Hello 737NUT,
interesting post. How do you change the drive mechanism? Using stepper motors will be difficult since it requires 2 turns to find its position with an optical sensor. So that would mean using an altimeter you already have passed 200 or 2000 feet just for finding the position. Any ideas? I am having the exact the same problem.
Many thanks
nils

9. ## Re: Altimeter gear compound train help

Hi Nils,
Welcome to the forum, take alook at What Rob did.
http://www.cockpitbuilders.com/commu...73.0;topicseen

Les

10. ## Re: Altimeter gear compound train help

Thanks Les! Very interesting

Originally Posted by iwik
Hi Nils,
Welcome to the forum, take alook at What Rob did.
http://www.cockpitbuilders.com/commu...73.0;topicseen

Les

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