burning question - HSI?

Sounds good.

The TO/FROM can both be on one side of the CDI needle slot. The problem here is that as you turn the plane and the CDI plate turns, so do the TO/FROM arrows. So either we create some logic that flips them on the turns or we need a different way to mount them so they don't spin.

Put a small tab between the LEDs to prevent light bleed-thru.

The flags are hidden under the outer ring which is where you have the 4 supports at. A simple shaft to a flipper/solenoid down in the housing could handle them.

Also two of the support gears can be used to connect the front panel knobs to. Or would we want them to go to a pot somewhere to feedback the position info? If we build position sensors into the rings, then we can connect them directly.

Ah - now I see the problem. You're picturing a King-style TO/FROM e.g.http://www.esmofly.net/HSI-esm.jpg whereas I'm picturing the F-16 style e.g. http://home.priorityonesystems.com/hsi/HSI_layout.jpg :)

Should be straightforward enough to mod the design for either.

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Originally Posted by AndyT

Also two of the support gears can be used to connect the front panel knobs to. Or would we want them to go to a pot somewhere to feedback the position info? If we build position sensors into the rings, then we can connect them directly.

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The approach Mike Powell used in his book is to have the knobs as rotary encoders, which drive the steppers to position to ring, rather than have the knobs geared directly to the ring. I'm gunna go with what I know for now! :)

Ok, I see what you mean. Yes, should be pretty easy to handle either.
This is beginning to sound like a combo of the two you have pictured above.

The encoders are perfect for the knobs.

Can anybody figure out the gear trains? The big gears have 120 teeth, and it would be nice to gear them to commonly available 24- or 48-steps/rev stepping motors so that we can move the rings in 1/2 degree or maybe 1/4 degree steps?

We need a position sensor on each main gear so that when it powers up, it can calibrate itself. All we have to do is have either a small tab that breaks an optical sensor or trips a micro switch when it hits the 360 mark. Then the software can do the math on its own. Once its done that, it can set itself to the whiskey compass.

Ooohh...Bit of a stretch calling me a machinist ;) I have the machines, but the talent is pretty raw. Nonetheless, I think we could probably work something out in trade services. Don't want to do cash as that implies I'm open for biz. I'll phone tomorrow. Today's full on with the boat.

Ruprecht:
Love your drawings mate. Here's some practical considerations. The CDI needle needs to be elastically attached to the servo. Servos can rotate through about 180 degrees and from experience, when the sim is first powered up, there's always the chance that a servo will run feral. If the pointer is rigidly mounted to the servo, you'll get some damage at worst or some mis-alignment at best.

I like the idea of using LEDs for the to/from flag. Simple and elegant.

Gear trains are straightforward. At 48TPI, just divide the number of teeth by 48 and that is the working diameter of the gear. Halve that and you have the working radius. Add the working radius of the two gears that must mesh and you have the centre distances. Your gears look great in the 3DS, but you don't need to be that fancy. Just draw circles at the appropriate working radius.

The three gears you have in the drawing are going to be difficult to "home". As you've discussed, we'll need some kind of sensors on the gears. If we use opto-interrupters, there will need to be a LOT more space between the gears. Another option is to place small magnets on the gears and position reed switches around the periphery of the gears.

Also, the gears/compass plate/CDI card/Heading bug carrier need to be supported somehow.

I know all this sounds like criticism and it is, but constructive criticism. We'll get there with this.

BTW, I have a copy of the actual facia of one of the BK gauges and it's a bit frightening how small this unit is and how much stuff has to go inside.

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Originally Posted by cscotthendry

The CDI needle needs to be elastically attached to the servo.

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Good thought, noted.

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Originally Posted by cscotthendry

Gear trains are straightforward.

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I've got it sorted in terms of fitting the gears together, I meant more the gear ratios. For instance, it would be nice to be able to move the CDI assembly in half-degree steps. If I have a 12-tooth gear on the pinion of a 48 steps/rev stepper, and mate that directly to a 48-tooth gear on the CDI assembly shaft, 48 steps will give me 90 degrees of shaft rotation, or 1.875 deg/step. So what different and/or intermediate gears are needed for 0.5 deg/step?

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Originally Posted by cscotthendry

The three gears you have in the drawing are going to be difficult to "home".

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I've got something in my head about where to put optointerrupters, will get that into the design tonight.

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Originally Posted by cscotthendry

Also, the gears/compass plate/CDI card/Heading bug carrier need to be supported somehow.

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Also in my head ;)

No worries at all with constructive criticism, this is a collaborative process.