Introduction: Build Your Own Steampunk Chicken-walker Mech

I have a long history of biting off more than I can chew when it comes to Halloween costumes. It's in that tradition that, when my friends suggested Star Wars as a theme for costumes this year, my first idea was to go as an AT-ST, the 2-man chicken-walker mech that the Ewoks beat up on in Return of the Jedi. After several design iterations I had left the Star Wars Universe behind in favor of a steampunk flavor, and thus was born the Steam Walker.

The idea is to make it looks like I'm sitting in a chair riding atop a steam-powered mech that walks on two robotic legs. In reality my seated legs are false, and my real legs power the robot's legs. This is basically a variant on the age-old circus-clown costume where someone looks like they're riding a horse, and is also inspired by Ben Hallert's APU costume and the paintball mech costume called Steel Dawn.

While not fast enough to keep up with 6-year-old trick-or-treaters as they went from house to house, I was still able to walk down the street and show off to passers by. The most common reaction was along the lines of "Wow! That's the coolest costume I've ever seen -- what the heck are you?!? I also got little kids (and some older kids, who really should know better) asking me how the thing was powered, several adults admitting they couldn't figure out how the thing worked, and at least one little girl bursting into tears as she saw me ambling towards her. All in all, I'd say it was a big success :).

Step 1: Build the Frame

I started with an external-frame military backpack, and stripped off the the canvas. Drilling out the plastic plugs in the bottom of the main backpack-frame pipes revealed two pipes with a 1" inner diameter, with a convenient hole and cotter pin at the end.

Next I built a box frame out of six lengths of ½"-inner-diameter PVC pipe, two 'T' joints, two 90° elbow joints and four 3-way corner joints. Connected to the 'T' joints in back
are two short lengths of ½" PVC, which fit inside the backpack-frame pipe. My first prototype was just as wide as the backpack frame itself, but that was a little too tight a squeeze so I widened the frame by adding a couple of 120° angle joints to each side. Once everything was tested I used PVC cement to secure all the joints, except for the front cross-pipe which I left free to turn. That pipe needed to remain free to turn so I could fold up the leg-holder for easy storage. I made the PVC box frame the right length for a chair such that my knee would
come to the far end (about 21" for my leg-length).

I then drilled a hole through each of the back PVC connectors to match the holes in the backpack frame, so when the backpack was connected to the PVC frame I could use the existing cotter pins to secure them to each other.

Step 2: Mech Feet

To get the extra height I bought some boots off of eBay that had a 2" platform and 5" heel. I then hid the shoes inside of the mech's feet / lower legs, which are made out of foam core poster board. I designed it so the mech foot would extend in front of the boot by several inches to help the reverse-knee illusion. I also went with a tapered look in front to make the foot look less boxy. The bottom three holes are for short lengths of ½" PVC -- the front pipe is just to add structural support, the middle pipe goes across the top of the toe of my platform boot, and the rear pipe goes under the heel of my boot. The top holes are for attaching the upper-leg pistons with 1" PVC pipe, which bind around the front and back of my leg. I originally thought I'd use
three pistons instead of two, thus the extra hole up top, which I later ignored completely.

I used fiberglass resin to strengthen the feet so they could withstand the pressures from walking. If you've never worked with it before, fiberglass resin is basically the daemon-spawn older brother of paper-mache, only instead of paste you use a resin that sticks to everything and has toxic, explosive fumes. And instead of newspaper you use a fiberglass cloth that feathers into these long thin strands that always float into whatever you don't want them to stick to. And since they're fiberglass, they give you nasty little splinters. And then once the resin
dries around them they become sharp little needles poking out of your piece that you need to sand down. It's pretty nasty stuff, but it did protect the feet well. I found the best technique was to essentially upholster my foam-core shell with the fiberglass cloth using a stapler, then paint the resin over the cloth. Use as few pieces as possible to avoid feathering.

Step 3: Pistons / Mech Upper Leg

Since I wanted a backwards-facing knee the mech's upper legs needed to connect between the front of my box frame and the back of the mech feet. The tricky part was that they also needed enough degrees of freedom that they could track wherever my own forward-facing knees moved the feet. In the end I went with a piston design with a screw joint (rotation) at each end.

The piston is a piece of 1"-inner-diameter PVC pipe with a piece of ½" PVC inside. The inner pipe still leaves some wiggle room, so I wrapped duct tape around the end about eight turns to make a snug fit that would still slide in and out. To the inner pipe I added an elbow joint that was threaded at the other end, which gave me rotation where the piston connects to the frame. To that I attached a snap "saddle joint" which could snap onto the frame itself and yet still be disconnected for easy storage. On the lower end I added an elbow joint which attached to a
length of 1" PVC pipe that went through the top holes in the mech feet. Since the mech feet are tapered, the lower cross pipe for the rear two pistons will be longer than for the two that go in the front.

It might not have been necessary, but just to make sure the piston didn't jam as I was walking I threaded an elastic band down the middle of the inner pipe. At the larger elbow I threaded the elastic through a cork (which fits inside the joint but is too long to go around the turn) and then doubled it back up to the snap saddle, where I tied it off. This made the pistons naturally snap closed, which also made storage easier.

Step 4: Side Walls, Back Wall and Seat

The side walls are just foam-core poster board with a 2"-wide front and top edge attached. (I didn't bother using resin on these, though it probably would've protected them from the dings and scrapes they got.) I cut two rectangles in each, both near the front and just big enough for the snap-saddle of the upper-leg piston to fit through. I spaced these about 5.5" apart apart, the same distance as between the larger holes in the top of the mech feet.

Since I wanted these to be detachable for easy storage, I used a glue-gun to attach a wooden dowel to the back, making sure to leave the ends of the dowel glue-free so I could slip a zip tie behind each end. This way I could attach th dowel to the upper pipe on the main frame with a
zip-tie loop, and simply slide the loops off when I wanted to detach the sides.

At the top of each side wall I added a hole for my side railing (though in retrospect I should have put them further forward, as my arms were a little cramped as it was). These railings just consisted of a couple pipes connected by several right-angle joints.

The back wall is simply another pieced of poster-board, cut to fit the bottom back of the frame area. For decoration I cut the heads off of two slotted-spoon cooking utensils, leaving a little bit of handle remaining. After everything was painted I stabbed the handle stub through
the foam core and hot-glued both spoon-heads in place to look like exhaust vents.

The seat is just the lid from a cardboard banker's box cut to fit over the front half of the main box frame (the back half is where my body fit). I just zip-tied this to the frame bottom on both sides.

Step 5: (Fake) Foot Supports

I wanted the foot supports (for my fake legs) to stick out like a recliner chair so the mech feet wouldn't kick the boots. Along the front cross pipe I drilled four holes and inserted dowels. At the bottom of the dowels I attached another four dowels, spaced such that the false-leg boots fit
snugly between dowels 1 & 2 and dowels 3 & 4. To get the correct angle I pushed the top dowels such that they stuck out the other side of the PVC pipe, and then tied down another dowel such that it lay across the exposed ends. That way I could just remove the top dowel and fold the whole foot-support rack under the main frame for easy transport.

Step 6: False Legs

The thing that makes legs look real is having bone structure in the right places, particularly the knee and pelvis bones. That's what makes the difference between a real-looking leg and a scarecrow leg stuffed with straw. Each leg consists of two dowels (representing the upper and lower leg bones) that are plugged into holes in a tennis ball (representing the knee cap). Since I wanted the feet to stick out at an angle I connected the dowels at a 120° angle to each other. I filled in the fleshy parts by wrapping the lower-leg dowel with a towel and padding the upper-leg dowel with a large bag of cotton balls, and tied both off with rubber-bands. Then
I stuffed the entire package into a white nylon stocking.

For the pelvis, I just used a piece of packing foam that had roughly the right shape, bent it a bit with a strategically-placed rubber band, and inserted the dowels into it. (Men may wish to augment the foam as vanity dictates.) I stuffed the entire thing into a pair of white pants that I had split down the back seam, starting at the belt line and stopping just before the crotch. I recommend picking a pair of pants with a slightly larger waist than your own, since you'll want the belt to be able to go around both the false hip and your own hips.

Wrap a rubber band around the bottom of the pants and stuff them into boots. The boots then get rubber-banded in place with the heel hooked over the PVC pipe at the bottom of the foot supports.

Step 7: Random Gauges

The random gauges on either side of the mech are just clear DAT-tape cases with some paper in the back and black foam covered in electrical tape. The foam covers a yellow LED that's been electrical-taped to a button-cell battery to give the meter that steam-punk look.

Step 8: Putting It Together

Getting into the mech takes a few minutes and is best done with some help. First I pin the backpack onto the main PVC frame and attach the side panels. Then I put on the platform boots, insert them into the mech feet such that the heel hooks over the back cross-beam PVC pipe, and slide the middle cross-beam pipe over the toe of the boot, locking it in place. Then I slide the 1" PVC end of the pistons through the mech feet, the shorter one just in front of my shin and the longer one just behind my calf.

I then get someone to help me put the main frame over my head, placing my arms through the backpack straps as it comes down. I then tighten my belt while my assistant pushes the saddle clips at the top of the pistons through the holes in the side panels and snaps them to the upper of the two side pipes in the PVC frame. After that my assistant puts the false legs onto the seat and rubber-bands the boots into place while I thread my own pants belt through the two sides of the false-leg pants and buckle it in front. (Be sure to stretch the fabric around your own hips as much as possible so they extend below where the side panel shields you from view.) Hook the side-rails over the top of the backpack frame and into the top hole in each side panel and you're good to go!

I found it was pretty easy to walk on level ground with this contraption, but much harder on broken sidewalk and certainly impossible to keep up with 6-year-old trick-or-treaters running from house to house. All in all it was great fun and I loved the reactions — but next year I plan to listen to that little voice that tells me "no really, you should have started this project earlier than October first!".