burning question - HSI?

[AndyT]

any loss of sync is a real problem. Not for the to / from / inop system, which simply fails to display correctly, but it's a problem for the CDI needle, which may go out of range if sync goes belly-up, and wrap itself around the backing plate with extreme prejudice. So my thought is, under what circumstances might that happen?

A power surge on power up.

The 90 degree gear is actually called a Bevel gear. Or you can do it like this:

[P1IC]

A power surge on power up.

The 90 degree gear is actually called a Bevel gear. Or you can do it like this:

Thanks. When you said 90 deg worm drive to remove the need for the cords and pulleys, I thought you meant a long lead screw arrangement with some right-angle drive on it. I am familiar with bevel gears (and I'm looking for plastic ones to interface to my existing gear collection - good luck with that, I hear you say ).

With the bevel gear, how do you drive the needle without cords? Looks like you still need to translate shaft rotation into linear movement.

[P1IC]

P1IC:
Re missed pulses on steppers. This only happens (in my experience) for one of two reasons. a) there is a binding on the stepper that is greater than the torque produced by the stepper or b) the pulses are applied faster than the stepper can physically react. The first is a construction/tolerance issue that is a real devil. The second one is easy solved.

Using worm drives, a) may rear it's head from time to time because of the sliding type contact between the worm and the gear. The obvious solution is...

… not to use worm gears? I'm hoping that the gearing ratio provided by worm gears will mean that very little load will be applied to the driving shaft upstream from the instrument. And being hard plastic the sliding friction is low. Yet more experimentation required!

[cscotthendry]

P1IC:

Sorry, My bad. I didn't mean that was the obvious solution. What I thought but didn't say was ...grease. Specifically, I was thinking of that white stuff you often find in toys.

BTW, while it sounds like I've been critical of your designs, I actually think you've been quite innovative. I didn't mean to sound critical, in my clumsy way I was trying to be helpful. I'm a problem solver. I see the world in terms of problems to be solved.

[P1IC]

P1IC:

Sorry, My bad. I didn't mean that was the obvious solution. What I thought but didn't say was ...grease. Specifically, I was thinking of that white stuff you often find in toys.

BTW, while it sounds like I've been critical of your designs, I actually think you've been quite innovative. I didn't mean to sound critical, in my clumsy way I was trying to be helpful. I'm a problem solver. I see the world in terms of problems to be solved.

Yes, Grease Is The Word - hey, someone oughta make a song outa that!

And you're right about the issues. Sometimes when people (ie., me) get totally into one line of thought, the little problems get ignored. The overall "brilliance" of the concept blinds the designer to the shadows lurking inside. It takes other people looking at it from the other side, where there is less reflected glory, to see these, and then it's really important that they point them out.

Even then, there is the temptation to make quick-fix patches over the issues, rather than looking to see if its maybe the overall concept which is flawed. Like my suggestion that some end-stop sensor on the CDI needle would signal an out-of sync condition, shutting down the instrument and saving the mechanics. That's clearly a fudge, and the overall concept may fall because of it.

That's what I like abut this thread - this critiquing happens on nearly every post, and no one gets offended.

[Michael Carter]

"Even then, there is the temptation to make quick-fix patches over the issues, rather than looking to see if its maybe the overall concept which is flawed."

Tell me about it. I've spent more wasted hours on my e-lab bench than I care to say, and then the next morning (or afternoon) a different approach resulted in the desired solution.

You guys working on this HSI are way out of my league mechanically and mostly electronically, but the same thinking on different levels can produce outstanding results if you can think outside the box.

Explore new directions and ideas that you never considered befrore.

Just a thought from a non-degreed mechanical Boeing Skunk Works engineer.

[P1IC]

Just a thought from a non-degreed mechanical Boeing Skunk Works engineer.

Listen to this guy! An icon in flight simulation, belittling his contribution. Skunky, you're tops.

[Michael Carter]

P1IC, you give me too much credit. I'm mostly a an electronics experimenter (ICBM Tech) and hardware fanagler (parts fixer).

I just use, and do, what works. You won't find many drawings in my shop. But there are a lot of squares, calipers, and rules along with the machines.

You just have to build something every now and then even if its not for the sim. Engineering in in your blood, even if you didn't study for it.

[AndyT]

I used to have a stack of 'Engineers Notebooks' for electronics and building trades. I wish I still had them. They had formulas and diagrams for almost everything you could think of.

[cscotthendry]

The overall "brilliance" of the concept blinds the designer to the shadows lurking inside.

Ho ho, been there DONE that! The surest way I know to trash a "brilliant" idea is to try and build it. Even so, it's still a useful thing to think outside the box as often as possible.

Seriously, I don't think the synchronization issue is going to be as big a problem as you suspect, as long as the mechs work smoothly, are reasonably balanced, don't require excessive grunt from the steppers and you don't pulse the steppers too fast. That sounds like a big ask, but it's not really. Just due care and attention to detail... The usual process of making things.

You say you have a lathe and mill, so I'm looking forward to seeing your progress on this. Please post some pics of what you're doing and consider setting up a website for your project if you haven't already.