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Official Armadillo Q&A thread

Posted by: John Carmack - Tue Jun 15, 2004 8:01 am
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Official Armadillo Q&A thread 
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Post    Posted on: Mon Aug 18, 2008 3:33 pm
Mark-
"could you explain how the work on the methane engine for NASA works. Did they come to you or were they out shopping for someone to do this work? Also, did they indicate an application for the engine?"

I think Matt covered it a few paragraphs back in a response to Dan. Not really my area of interest (biz stuff= ugh.) Welding=Yea!
We applied for it. I do not know if Nasa had an application.

TJ

I do not do interviews, not really comfortable in front of press/people. All of us have done them, but by far John gets the most press. He definitely has more presence in the game world currently. I expect when we get to sub orbital and eventually orbital, he will have a big presence in the space industry.
AA did have a booth at Quakecon 07. Four of us went and it was lots of fun. We did not get to do it this year due to the current AA schedule. The kids really loved it. I thought it was great.
We have done a few space related conventions, and it is always fun to see the positive reactions of people, how their eyes light up when they see what is being done.


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Post Stainless Welding   Posted on: Mon Aug 18, 2008 8:15 pm
Do you have any issues with warping? I always trying to figure out ways to counteract the major pulling I see when I weld stainless.

Rotar table a must to avoid starts and stops.

Are you using the Miller Dynasty 700?

I'm using a 300DX and I can't imagine what you can do with the 700.


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Post    Posted on: Tue Aug 19, 2008 2:01 am
Mark-
You said "Lastly, what kind of welding do you do on the engine? Is the wire composition matched to the engine metal or do you have to worry about that?"

All of the welding is done with GTAW (tig). In general, you try to match or exceed the base metal requirements. A lot depends on what service it will be put into.
In the case of our injectors and chambers:
High temperatures
Quick temperature cycling
Oxidation due to temperature and LOX exposure

310 SS is an excellent metal that is readily available, is machinable and weldable. It has excellent corrosion resistance at temperature, and good crack resistance from thermal cycling.

Scienkoptic-

I do have issues with warping after welding, and I have not been able to eliminate it. The warping is not really an issue for us currently though as it does not yet affect injector performance, it is mainly an annoyance. There are large volumes written on controlling distortion. Mainly I try to reduce amps if I can, clamp or fixture the workpiece well, use peening to reduce stresses if possible, etc. The AWS section of large libraries usually has some good books on welding techniques, distortion usually is covered. It is pretty unpredictable in my experience.
I am using a Dynasty 700. I have used a Dynasty 300, and overall it could do most of the work we do now, except for the tanks. They require more amps and a higher duty cycle. But from what I have seen, the 300 is a very capable machine.
I really enjoy the 700 overall, I feel it has been instrumental in getting the tensile rates we have measured in our pv burst tests. I am able to reduce overall heat input and the width of the HAZ of the welds with far greater control of the parameters than standard welders.


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Post    Posted on: Tue Aug 19, 2008 11:13 am
When welding the tanks, do you use a wire feeder? I can't imagine having to stop for new rod.

I made a steady progression from Oxy fuel Gas welding to GTAW.
My first machine was/is a Miller Aircrafter and I ended up using a Dialarc.
Going from the Dialarc to the 300 is like going from ultralight to Concorde.

Stainless has such a different warping tendancy than any other metal.

Several years ago I saw pictures of the spherical aluminum tanks being welded. I always wondered how difficult it must be to keep those things from going haywire.


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Post    Posted on: Tue Aug 19, 2008 12:49 pm
Wirefeeder- yes. It allows keeping the root weld as consistent as possible. Without it, there would be more variance in root qualities (at the stops and starts, amount of root penetration, etc). I did end up making our wire feed gun, because I could not figure out why the liners/wire kept binding up. It was very annoying as the wire speed would change, or stop completely during the root welding. I had a lot of rework because of it. Now it feeds nicely. My only gripe is the wire helix does some funny stuff with the wire twisting around when fed into the puddle, and I would like to find a way to fix that.
Sometimes the tank welding can be a bear. But it gets better every tank. Usually.


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Post    Posted on: Tue Aug 19, 2008 6:56 pm
Just found this:

http://www.forbes.com/technology/2008/0 ... rmack.html

Saw another article that mentioned they would be doing a test flight of the RRL plane a couple of weeks ago. James? John? Can anyone comment on if this has happened yet?


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Post wirefeed   Posted on: Tue Aug 19, 2008 9:33 pm
I've noticed that as well when using a Mig (GMAW) gun when using AL wire.

I suppose it has something to do with how the pinch rollers and the grip the wire and the memory that the filler wire has from unrolling from the spool.

If you are using small 2# spools this might be worse than with larger spools. might be worthwhile to figure out some strategy for conditioning the wire before it enters the sleeve.
(if I'm understanding you correctly)

Did you base your feeder off any other product?


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Post    Posted on: Tue Aug 19, 2008 11:44 pm


Hehe, I see they ended up using the "sandwich" photo after all.

fatron wrote:
Can anyone comment on if this has happened yet?


Nope, sorry. That's for the Rocket Racing League to comment on.


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Post Question on RRl Attitude   Posted on: Wed Aug 20, 2008 7:24 am
Hi Matthew,

Would you comment/speculate on why the Rocket Racing League is so secretive or negligent in announcing anything you guys are doing for them? Are they simply less concerned about public interest?

Also, would you speculate on the mystery participants in LLC '08? Any ideas who they might be?

Lastly, in terms of nozzle steering, does John use any fuzzy logic programming to "balance" the body of the rocket on top of the engine?

Marc Hopkins
Orange, CA


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Post    Posted on: Wed Aug 20, 2008 2:33 pm
Scienkoptic- "Did you base your feeder off any other product?"

We use a cold wire feeder from Profax. It is basically the same as a mig wire feeder, but has a lightweight gun (that I did not like at all for .065" aluminum wire) that has no provisions for carrying amperage. It is strictly for feeding wire. I did make my own gun for it that feeds much smoother though. I will have to take pictures and post to flicker. It was really simple and works much better than the original.

"If you are using small 2# spools this might be worse than with larger spools."

We are using 16 lb spools. The helix is a lot less than with the 2 lb spools. I think it would be easy to make something that reverse pinches the wire as it comes off the spool, so I may try something when things slow down some.


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Post feeder   Posted on: Wed Aug 20, 2008 5:11 pm
I thought I had seen purpose built GTAW wire feeders in the welding journal.
I figured that was what you were using.

I've just noticed that this curling occurs with any Spool Gun (Spoolmate) that I've used so it might also be an issue.

It usually is not a problem when GMAW welding except when you are working in a tight space and cant get the tip as close as you need to the puddle.

For GTAW applications it would seem that directing the wire into the center of the puddle is critical.

might just be a matter of rotating spool axis perpendicular to direction of weld and adjusting for curvature of wire.

I'd like to see the pictures of the feeder. I've thought about building one for an application that I have.

What certifications does a welder for AA require?

Have you ever used a gas lens? I was doing structural repairs on a 4130 airframe and was ready to cut the thing into pieces before I got hold of one.


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Post    Posted on: Thu Aug 21, 2008 4:30 am
Our wire feeder-
http://media.armadilloaerospace.com/200 ... Welder.jpg
The picture is from when we got it. I have since pulled the feed cable and made one to fit. Just lathed out some aluminum ends and stuck a teflon feed tube we got from McMaster in them and epoxied them in. Russ got me a little micro switch for a button and viola!
I am sure the same could be done from a standard mig wire feeder. The most difficult part is starting the torch heat before you start adding wire. Once you have some experience it is really great for consistency. The root welds I do look much more like an automated weld.
Wire placement in the puddle for the tank welding is tough. I have found that I have to keep it riding an inner and upper edge of the v-bevel during welding. Usually I am aiming for an area about .060" in diameter. Going outside causes problems with oxidation and porosity from the wire bringing in atmospheric gases. The same when adding to the center of the puddle. It also happens when the wire rotates in the tube 360 degrees from the helix cast, and whacks into the tungsten. Oops!
The only other problems I have are when the wire slows down or stops (hard to see when you are welding and the wire slows down), and the puddle overheats suddenly and a hole blows out in the root area. Extra re work that is fixable, but it is nicer when you have a 100 percent complete root weld from the start.

As for gas lenses, I had an instructor that made me learn to weld without them. I always thought he was just mean, but now I think it was a good lesson. The lenses are not cheap, and they take up more room. When it gets tight, they really become a restriction. They really make stainless welding pretty nice most of the time though...

Certification- AA does not require that a welder be certified for anything currently, as the requirements for experimental aircraft are different than commercial airlines that carry paying customers. I qualify for Mil specs 1595, 2219 and AWS D17.1, and working at AA requires a pretty extensive knowledge about welding and procedures, metallurgy, etc. Demonstrating a solid feel for GTAW with the three base metals (aluminum, stainless. and steel) is a must. Most all metals react like them welding wise.


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Post Welding   Posted on: Thu Aug 21, 2008 11:21 am
Well for most weld positions, I would agree that a gas lens is not needed and does increase the bulk of the torch.

Welding .028" &.035 4130 in tight clusters requires pushing your tungsten out rather far so that you can can get into the root joints. I can't imagine any amount of practice/skill with conventional collet body/cup arrangement would make a difference. Well, maybe a very small torch/cup might work.

It certainly allows you to see the puddle when your twisted around straddling crossmembers and longerons. I suspected that was the origin of the name.

Lately McMaster has been my favorite website. What's irritating is that no matter how much I seem to order from them, I cant seem to get another catalog. I got one a few years ago and that was it. The website really doesn't encourage browsing for stuff that you didn't know existed. I find most of the cool stuff in catalogs when I'm "bathroom reading" and I'm not bringing a computer in there with me.

Do you use a tungsten sharpener? I've been considering buying one. The dynasty needs a sharp tungsten, and I'm getting tired of doing it the old way. What do you use?


Thanks for your responses, they've been truly interesting.


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Post    Posted on: Thu Aug 21, 2008 12:57 pm
"Welding .028" &.035 4130 in tight clusters requires pushing your tungsten out rather far so that you can can get into the root joints."

Agreed. I do not weld much with 4130. In that case it is probably very useful, especially when you need additional reach with the tungsten.

Tungsten sharpeners. For a long time I wanted to buy one, but then realized a cordless drill I had worked much better than doing it by hand, the tips are as sharp as I can get. From what I have seen of the production units, the quality of the grind is really high. But it comes at a price.

McMaster- I agree, having the physical catalog is more helpful for ideas. Good luck on getting a newer one. Is there a number to call?


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Post    Posted on: Thu Aug 21, 2008 2:06 pm
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McMaster- I agree, having the physical catalog is more helpful for ideas. Good luck on getting a newer one. Is there a number to call?


Hah hah. I've called it every year since I got a catalog.

I use a cordless drill and belt sander, I used to have a dedicated bench grinder.

There is nothing like watching your weld turn into a cauliflower. I learned how to weld GTAW by starting out with Gas welding. This is how most people start out in welding schools(at least around here) I fitted and welded many practice Tube clusters( at least 50) until I was good enough that my AI couldn't tell my welds from the original Piper welds. I used mild steel at the time. I had many problems with the small torch I was using in maintaining a neutral flame. I ended up buying my first machine ( Aircrafter 300ST).
This is where I got really frustrated with TIG welding. Some of those clusters have 7 tubes intersecting them.

What do you use to bevel edges. how do you maintain consistency. This must be pretty important in your application.


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