Fully articulated Catapult battlemech

Discussion in 'Science Fiction & Fantasy' started by Millenniumfalsehood, Nov 13, 2011.

  1. Millenniumfalsehood

    Millenniumfalsehood Active Member

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    Let me begin by saying that I usually build something once, and then never build another model of that subject again, unless it's in a different scale or a better kit comes along. This leads me to try my best when I model something to build it with something special about it, especially if it's my favorite subject of a particular genre.

    For the Catapult, it's my all-time favorite battlemech. I love the support role; sitting on top of a ridge, raining LRM-flavored destruction on the enemy to draw his attention away from my lance-mates is my idea of a good time, provided they don't get too close (the ol' Cat is a good 'mech with respectable speed, but it's no Flea, and the only backup weapons are a quartet of medium pulse lasers).

    Anyway, I decided to build up the 40mm scale Catapult from Shiftdel's Mediafire page (I think), and do it with a fully articulated undercarriage. That means hip and ankle joints that can move not only forward and backward, but from side to side. Not a particularly challenging thing to design, but building it so that it can withstand repeated repositions and still maintain integrity is no mean feat, especially since it has to be compact enough to fit the smallish profiles of the ankles and hips.

    But I never let a little thing like a challenge keep me from starting a build.

    I only did one leg, so I could see if the ideas work. This way, if the ideas were not sound, I only had to scrap one leg instead of two. For orientation, left-to-right is the X-axis and front-to-back is the Y-axis.

    First of all I constructed the cockpit and missile battery. I weighted the missile pods with 6 grams of metal to increase the inertia of the upper body so it wouldn't have as much of a tendency to tip over after completion. Six grams, because I felt any more would make the body weigh so much that the legs couldn't support it.

    After that I began work on the legs. I decided to start with something easy, so I constructed the knee joints. They're simple cylinder-inside-a-cylinder joints, but with strong tubes made from thickly rolled cardstock, with strips of card around the inner tube to concentrate the torque acting on the joint on specific points.

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    The next thing was to construct the hip joint. This was done by first creating a cylinder-inside-a-cylinder joint for the X-axis joint, then taking the outer tube and drilling two opposing holes in it. Once those were done I enlarged them till they snugly fit a Q-tip shaft, which I then wrapped in paper to create an axle for the joint's Y-axis rotation. These wrappings were then cut from the Q-tip shaft and glued to the outer tube, making sure they didn't poke into the interior at all. I gave this setup twenty minutes to dry, speeding the process with a hair dryer and some superglue, then I set it aside to work on the mounting plates. These I made from 5-ply cardstock stacks glued and compressed to laminate it. I used a circle template to mark the correct inside diameter, then cut out the circle and trimmed it to fit tightly on the Y-axis axle. Then I glued the frames to a couple of 5-ply rectangles of cardstock to form cross-bracing, then I glued the entire assembly to a piece of card and trimmed it to fit. This I glued to the hip area, then I glued the inner tube to the thigh (or drumstick, if you prefer. :wink: )

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    Here is a demonstration of how much freedom of movement this joint now possesses:

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    After that was done I took a break, then I went to work on the foot. I wanted the toes to articulate, but if I simply jointed them at the bottom of the foot there would be a big hole in the foot. Another thing I needed to address was the feet needed to have weight so the Mech would be stable. I first assembled the toes, leaving a large flap of card with which to attach the toe to the foot. After they were dry I cut some lead weights and used Mighty Putty to attach them to the bottom panel of the foot. Finally, I scratched some inner plates which slide in and out of the foot as the toes articulate.

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    Finally, I proceeded to construct the ankle. This was a bit more complicated because 1) it had to support the weight of the entire 'mech and hold it's position, and 2) it had to articulate fully in all directions. The second one was the hardest, but I finally settled on a modification on the universal coupler design they use on truck transmission lines. I first took a section of a cardstock straw I got from, I think, Montana Mike's (I took six or seven of these things; they've been quite handy), and drilled a hole in either side for a Q-tip shaft. The tube would be the X-axis joint, because it had to be much stiffer than the Y-axis joint, and it has more contact area, thus producing more friction to hold the joint in place. I then took an 8-ply lamination of cardstock and cut a hole in it with a circle template to fit the tube. This I cut into a keyhole shape to allow the joint to move in the Y-axis, then I jammed it over the tube. After that was done I laminated a strip of card about ten times and glued the resulting cardstock block to the inner surfaces of the plate for strength, then I glued this assembly to the foot.

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    Then I took more 7-ply card laminates and drilled holes for the Q-tip axle, cut them to shape, then glued them on the ends of the Q-tip axle. I then glued a plate of 7-ply card in between the plates, then glued this assembly to the leg.

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    I'll add coverings for the joint once I come up with a good solution for them that will maintain freedom of movement.

    My Catapult can now actually stand on one leg. How many chicken-walker style Mechs in *your* collection can do that? :twisted::mrgreen:

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    I'll post the rest of the build when I finish the other leg, which I should be done with tomorrow evening.
  2. ThunderChild

    ThunderChild Active Member

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    Looks great so far!
  3. Zathros

    Zathros Guest

    Nice job! Really nice! When you can zoom up that close to something it it still looks that good that's excellent!:thumb:
  4. ARMORMAN

    ARMORMAN FOUNDATION CORNERSTONE

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    love the joints. :D
  5. blaar

    blaar Member

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    That is really great work. You Catapult is standing on one leg, where as mine had the tendency to tip forward. Having joints really help to balance these things. I must admit, when building the models, one can quickly see where the real life flaws would have been if it was possible to actually construct a mech, one being balance and the other being some mechs feet are really close to each other, I could easily see a mech falling over its own feet.

    PS : The Catapult is shiftdel's. Maybe you got it from one of his sharing links. It is not available from my page.
  6. Millenniumfalsehood

    Millenniumfalsehood Active Member

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    Ah, sorry 'bout that, Blaar. :oops:

    I'll correct my post.

    BTW, I know what you mean about some mechs having a strong tendency to tip forward or backward. Your Crab is an excellent example. But we do what we can, right? :cool: Something that helps is weighting the feet. If they're more massive than the body, it won't be as apt to tip (depending on torque of course).

    Thanks for the compliment, too. :thumb:
  7. blaar

    blaar Member

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    LoL, the Crab is Yogsolthan's :)
  8. Millenniumfalsehood

    Millenniumfalsehood Active Member

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  9. ekuth

    ekuth Guest

    Awesome work, Millenium.
  10. MTK

    MTK Active Member

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    Agreed.
  11. Millenniumfalsehood

    Millenniumfalsehood Active Member

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    Thank you for all the compliments, guys! It really makes me glad that people appreciate my work. :cool:

    Does anyone want a sheet with parts to make joints like these for their own mechs? Blaar mentioned earlier that they would help get the balance right, and they would open up new possibilities for dynamic poses. They'd at least be great conversation pieces. :wink:
  12. ARMORMAN

    ARMORMAN FOUNDATION CORNERSTONE

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    post them. I'm sure I will add them to my projects along the way.
  13. MTK

    MTK Active Member

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    While I was looking for models for MF, I ran across an old copy of Mech-Warriors II. anyone need anything from that?
  14. Millenniumfalsehood

    Millenniumfalsehood Active Member

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    Awesome! I'll get to work on them right away, in several sizes and designs so you can have a variety of torque ratings and sizes for various classes of battlemech.

    Right now I'm working on adapting my designs to the Flea so that it can articulate as well.
  15. Millenniumfalsehood

    Millenniumfalsehood Active Member

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    Well, it's finally finished!

    I put in a lot of extra work into this build, and I think the extra effort to make the joints work was worth it.

    Here's the result of all that hard work:

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    The next one will be a Flea. I am adding leg articulation to that one too, and it's so small and simple that it should be done in a few days.

    After that, I'm making a short stop-motion animation of a fight between these two mechs.
  16. ARMORMAN

    ARMORMAN FOUNDATION CORNERSTONE

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    You did a very nice job. You should be proud.
  17. Vortex_4200

    Vortex_4200 Member

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    Awsome work, you were talking about the mechs sometime tipping forward an opposite example I can think of is the stone rhino which tips backwards, I finally had to build a hex base and glue it on to that, so agreed it can be frustrating at times when real world physics and scifi physics just cannot be found on the same page!
  18. Zathros

    Zathros Guest

    That is so Frakkin' COOL!!! You brought this thing to life!! I think someday you might be engineering one of these for real and it wouldn't surprise me at all! :)
  19. ThunderChild

    ThunderChild Active Member

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    Amazing build MF, the pose really does wonders for the model!
  20. Zathros

    Zathros Guest

    I can't wait the the movie!!!