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CatgutViolin

Weapon-Carrying Exoskeleton, EE-03 'Siegfried'

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Right, I don't know why I neglected to make a thread on this when I started. My team has worked on 'mech suits' or unpowered exoskeletons for several years, mounting a variety of weapons to them and using them at fields where special rules are provided.

 

Ballahack Airsoft in Virginia did a 'battle suit' competition in late October. My team decided to build a new suit from scratch and enter it. The result was Rasputin:

 

Jac7B5G.jpg

 

(More pictures here)

 

To briefly summarize: EE-02 'Rasputin' is an unpowered exoskeleton, using a padded ALICE frame to distribute the weight of its weapons systems, which are mounted to arm pieces held up by gas pistons. The pistons hold the guns at a level position, making it easy for the operator to wield a considerable weight in firepower. Rasputin also included significant armor, an active ventilation system, and cameras mounted to each gun shield and routed to display screens in the cockpit. We were all excited for the competition, where one teammate would man Rasputin, and the other teammate and I would act as support.

 

Except at the time of the competition, I was quite ill, and we reluctantly decided it best if I don't attend.

 

While my teammates were at the game, doing quite well for themselves, I was annoyed by the injustice of the situation and started thinking of how I could improve on the Rasputin design. When I heard they won 1st place in the competition, I got mad. I build things when I'm mad.

 

First, I started brainstorming. One of the things I disliked about our prior exoskeleton designs was that the arms were designed to hold a level position, and were difficult to pull down (against the gas spring) or lift up (against gravity). I was inspired by the ingeniously simple spring arrangement used by desk lamps and Steadicam rigs, which uses a pair of linked, parallel bars connected by a diagonal spring. With this design, raising the arms upwards increases the angle of the springs relative to the bars, increasing the torque they provide. And lowering the arms decreases that angle, which reduces the tension. This simple mechanical system allows the spring arrangement to keep the arm roughly in whatever position it is placed.

 

However, the biggest complexity in building something like a Steadicam is designing the arms. Getting the springs to run inside the track of the supporting bars, while having those bars be strong enough to sustain a 15+lb load, is no easy task. I didn't want this project to involve significant machining, since I don't have a machine shop, just a drill press, chop saw, Dremel, and hand tools, so building the arms represented a significant problem. It then occurred to me that I could design an arm system where the two parallel bars are offset, and thus avoid machining entirely: I could make the arm segments out of aluminum bar stock, and run bolts through them to serve as the axes.

 

I had purchased one of the CA M132 Microguns used by Rasputin to temporarily donate for the competition, so I knew I could use that as a primary weapon. As a secondary, I wanted something capable of sustained, low-rate-of-fire suppression, with better range and pinpoint accuracy than the microgun. My MG42, lightened by removing all extraneous parts, fit the bill perfectly.

 

This was the output of that weekend:

 

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(continued in next post)

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This initial prototype revealed some significant problems. For starters, by just being mounted to the back of an ALICE frame, virtually all of the weight was forward of the attachment points to my body, which meant that it pulled hard on the securing strap just to stay upright. As well, the ~40lbs of the combined system is a lot of weight to carry on one's shoulders. Despite the success of Rasputin on the field, my teammates reported significant fatigue from extended use.

 

This got me thinking about my intended use for this: I could just add armor plating and make my own equivalent to Rasputin, or I could do something different. The thought occurred to me that my local fields are less receptive to special rules than my teammates', so something that would be effective without any special immunity to BBs would be more useful. If I could then solve the issue of fatigue, I'd have a more general-use weapons platform, not intended for durability and 'shock troop' operations, but rather to help carry and sustain much heavier firepower than I could otherwise.

 

In my industry research for real-world exoskeleton designs, I ran across Lockheed Martin's FORTIS exoskeleton. This is, again, an impressively simple design. The Steadicam-esque tool mount is connected to a pair of legs, attached at the bottom to the user's shoes, and stabilized with ankle supports. As long as the user is standing near-vertically, the legs sustain the load, and the ankle supports keep the legs straightened. This seemed like my magic ticket- with the suit sustaining its own weight, fatigue would no longer be a problem. With design goals now set, I continued our team's naming scheme of quasi-mythological figures by dubbing the suit 'Siegfried'.

 

I copied the basic layout of the FORTIS, with some tweaks. I placed the supports behind the thigh rather than around the ankles, since this was much easier to build than a wraparound brace. For the shoes, I decided to build a homemade 'shoe' out of ABS, using rubber to make a homemade sole, and securing my boots with snowshoe bindings. Since this didn't require spring assists like the arms, it was much quicker to implement.

 

OMOEpoY.jpg

 

However, testing this showed that it wasn't a terribly practical solution. While it did the job of sustaining the weight of the suit, the shoes themselves felt very awkward and unnecessarily tall. I could walk easily, but the prospect of jogging, let alone running, felt very unstable.

 

I scrapped the shoes and, on a whim, decided to try testing affixing the legs directly to a pair of boots. It worked surprisingly better than anticipated.

 

 

After that proof of concept, I built up a more permanent solution.

 

S5XOfEO.jpg

 

Very long wood screws secure the caster plate to the sole of the boot (since reinforced by an additional screw through one of the top holes). This is intended to secure to the leg via a T-handled bolt and wingnut, allowing the shoes to be attached and removed to the rest of the suit on the field. I've since retrofitted the shoulders and hips to use the same joint, so the suit can be assembled piecemeal, which makes it a lot easier than trying to struggle into the thing without assistance.

 

With the ergonomics and function of the suit itself largely completed, that leaves wiring and finishing as the last major hurdles:

 

 

So, as of this morning, I've completed rewiring on both guns, finished modifications to the backpack (a 25mm ammo can) to run a gas line through it for the microgun, and made some ergonomic adjustments to the arms and knee joints. Tomorrow I'll be testing, and if everything goes as planned I'll upload a final WIP video and then be ready for paint.

 

As the project has gone on, I've learned a lot of little things about how to best approach certain design problems, so you may notice minor tweaks and changes I haven't mentioned across the pictures and videos. I'm hoping to break those lessons learned down into a series of videos on exoskeleton ergonomics, in the hopes that it can aid someone who wants to build something like this of their own. But that'll come after the initial build is complete.

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Thanks for the kind words, guys. I really hope to illustrate that this isn't nearly as difficult to build as it looks, it's just the conceptual parts of it, getting the ergonomics right, that are tricky. If I can share those lessons learned, it's my hope that more players can try building this sort of thing for themselves, having the hard part already done for them.

 

I'm assuming going prone is basically impossible with this for a variety of reasons, but how is crouching and kneeling?

 

Actually, while physically there's no reason I couldn't go prone, I'd have to let go of the guns to crawl so it wouldn't be very useful. Kneeling is doable, but a little uncomfortable due to some not-quite-perfect leg ergonomics that I haven't taken the time to properly troubleshoot. Crouching and squatting work great though, and I think will suffice for getting out of the line of fire. This isn't really a 'take a knee behind cover' sort of setup conceptually so it doesn't bother me.

 

Also, I got that update video done:

 

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"This isn't really a 'take a knee behind cover' sort of setup conceptually so it doesn't bother me."

 

Fair point! Looking at it I just had an idea for a more compact take on the idea. Would it be possible to engineer a similar system to support a single MG that could then be swung out of the way so that the user could have their hands freed? I guess somewhat like the Aliens smart gun set up using a steady cam mount, just modified a little. If memory served this could swing up to the chest, I'm wondering about rotating so the barrel faces rearwards and then up so that the gun sits against the user's back, like a slung rifle, but bigger.

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Fair point! Looking at it I just had an idea for a more compact take on the idea. Would it be possible to engineer a similar system to support a single MG that could then be swung out of the way so that the user could have their hands freed? I guess somewhat like the Aliens smart gun set up using a steady cam mount, just modified a little. If memory served this could swing up to the chest, I'm wondering about rotating so the barrel faces rearwards and then up so that the gun sits against the user's back, like a slung rifle, but bigger.

 

That is absolutely possible, in fact, it's exactly what I suggested (even down to the swinging upwards and out of the way) for our third teammate, who is developing a concept for a 'command' suit to complement Rasputin and Siegfried. But he's become enamored with the idea of a servo-controlled, gyroscopically-stabilized shoulder gun slaved to his helmet, though, so the gun harness idea may not come to fruition.

 

If you look at the FORTIS exoskeleton I linked to, it's basically a combination of that Steadicam rig with leg sections to support the weight. If you were using a 10-15lb airsoft MG then legs might be overkill; a chest harness would be enough, and an ALICE rig would be a suitable base. Then for the arm, all you'd need would be a Steadicam-esque design like what I used here, attached to the gun a little forward of its center of mass (so that it pitches down when not in use), and yaw/pitch (roll optional) at the connection.

 

I've already worked through some aspects of that design, as I was entertaining the idea of linking both arms on this suit to a single weapon, but I haven't come up with any airsoft-suitable gun that would be of appropriate mass and worth the complexity.

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That is absolutely possible, in fact, it's exactly what I suggested (even down to the swinging upwards and out of the way) for our third teammate, who is developing a concept for a 'command' suit to complement Rasputin and Siegfried. But he's become enamored with the idea of a servo-controlled, gyroscopically-stabilized shoulder gun slaved to his helmet, though, so the gun harness idea may not come to fruition.

 

If you look at the FORTIS exoskeleton I linked to, it's basically a combination of that Steadicam rig with leg sections to support the weight. If you were using a 10-15lb airsoft MG then legs might be overkill; a chest harness would be enough, and an ALICE rig would be a suitable base. Then for the arm, all you'd need would be a Steadicam-esque design like what I used here, attached to the gun a little forward of its center of mass (so that it pitches down when not in use), and yaw/pitch (roll optional) at the connection.

 

I've already worked through some aspects of that design, as I was entertaining the idea of linking both arms on this suit to a single weapon, but I haven't come up with any airsoft-suitable gun that would be of appropriate mass and worth the complexity.

Ah, so a predator shoulder cannon basically? I mean, cool idea, I'm not sure how practically useful it would be. Maybe do the "light" version at some stage a project of your own? It seems like it would be a more easily used system for general airsoft games, more of an augmentation of the support gunner role than a full on load bearing exoskeleton, as cool as that is.

 

Yeah, the FORTIS is really smart. I think the idea you have described is pretty much what I was thinking, just with more details actually worked out than "it would be cool if" ;-)

 

If you wanted to both arms supporting "one" weapon, you could always just double up the MG42. Seems like double guns are all the rage at the moment anyway.

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The suit is tentatively complete and I tried out a better lighting setup. The ISO on my camera was all wrong so it didn't come out as well as I'd hoped- lessons learned. After reviewing the photos I intend to move the hip joints rearwards, which I think will solve the current awkwardness of kneeling and certain other movements. But other than that, it's done.

 

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Looks good!

I see what you mean with the hip joints - from the side profile it looks like the knee joints could come forwards a bit too.

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Looks good!

 

I see what you mean with the hip joints - from the side profile it looks like the knee joints could come forwards a bit too.

 

Well, because the support brace runs along the back of the suit leg, bringing the knee joint fully inline with my knee may not be practical, although it is worth experimenting with. I might be able to make it work with a spacer of some sort.

 

Just to see what would happen, I drilled a new set of mounting holes to shift the hip bars two inches backwards, and reversed the lower leg piece. The result actually seems pretty good:

 

5gyYbLz.jpg

 

While the knee joint is still behind my knee, which still causes the same geometric issues involved in kneeling, now both the hip connection and the boot connection are more inline with my actual joints. However, this has shifted the 'knee' point just a little too far forward, and it's a little bit uncomfortable to stand fully upright. As well, the useful element of the rearward slant to the leg on the previous configuration was that it provided very stable lockup to support the weight of the suit, so now it's a little less stable.

 

I think I might try this new hip position combined with the original lower leg orientation, which will both reintroduce a slight rearward slant and move the knee joint just a touch back.

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