Sunday, June 5, 2016

D-Walker build part 1 - Design


Hi!  This is a breakdown of how I built D-Walker from Metal Gear Solid V.  It gets pretty detailed, especially as to the source of the materials - this is because almost everything used was left over from old projects.  I wanted to use up as much of my surplus material as possible before moving across the ocean next year.  In this respect, D-Walker is a culmination of most of my various projects over the past ten years and a fitting final project before I pack up my tools.

The history of the items is only really significant to me, but where I got them and how I used them might be interesting or useful to you.  From brainstorming sketches to final construction, everything was designed or improvised around a collection of random junk.  My goal was to keep the project as simple as possible while still having some cool, seemingly complex features.  I got a little carried away on some parts, but I would still describe the build as pretty basic and not requiring much in the way of special tools or skills.

This build will be broken up into sections going into the details of each major part.  There is a video showing final assembly and testing of the main components in the conclusion section, but in case you don't make it that far, here it is!

This is the design phase, in which I planned out the frame and major components.  I began on or around April 1st, 2016.


I started by designing a PVC skeleton that would be fitted with EVA foam panels and suspended from a belt.  The frame had to be able to support the head, arm, and weapon (I didn't end up building a weapon though), as well as extend between my legs to support the rider's fake pair of legs.  The inspiration for the fake legs gimmick comes from that sweet inflatable T-Rex rider costume.

I only had a little bit of scrap 3/4" PVC, so I had to buy most of the frame parts (~$50 worth).  The frame has plastic feet towards the front (integrated with the fog light housings) so that it could be set down on the ground without messing up the foam.  These plastic feet are motorcycle frame sliders that came with my bike, retired after taking too much damage.

The fog light housings are scratch built from Celtec and clear acrylic, with yellow vinyl for the tint.

At first I was just going to suspend the head in some super simple method, like tying a rubber band around a length of PVC.  This PVC "neck" would extend into the body cavity and could be moved by reaching my hand inside, or by attaching a weight to the bottom.  I had something similar in mind for the arm.  However, I was not really feeling this approach.  By digging through my bins of materials, I found inspiration to make slightly more complicated mechanics for the head and arm (which absolutely had to be articulated).

A scrap piece of aluminum C-channel from my old solar job became the solid base for the moving neck parts.  More scrap pieces were also used in the shoulder and neck articulation points.

Borrowing from my bike again - my supermoto came with an aftermarket throttle assembly, as well as the stock parts.  The stock parts sitting in my bin were too cool and too appropriate to ignore.  I ended up using the stock throttle grip in the arm mechanics, and I bought another set of controls for the head.  The throttle and clutch assembly came from an 06-ish Kawasaki Ninja 250, purchased for $50 from Sportbike Hawaii, a tiny local motorcycle shop (I over paid for these, but I like the guy and he has worked on my bike for free in the past.  Plus they were vital to the design).

Motorcycle controls work by moving a steel cable through a flexible but fixed rubber sheath.  The throttle has both a send and return cable, meaning either way you twist it, one cable is pulling in and the other is extending.  Even while installing the controls, I wasn't really sure how I was going to utilize them.  Eventually I decided the head would sit on a hinge, which sat atop a swivel, turned left and right by the dual throttle cables.   The clutch lever pulls a cable attached to the back of the head downwards, tilting the head up.

The green marks on the frame are the joints that are not glued.

The key to the pivot is the carriage bolt visible at the base of the neck.  The underside of carriage bolt head is squared, and this square fits into a square hole in the aluminum neck riser.  The bolt rotates freely within the neck base and frame, protruding down through the PVC.  An aluminum arm is threaded and secured to the bottom of the bolt, and the throttle cables are attached to either end of the arm.  Another aluminum bar clamps the round tabs at the end of the throttle cables in place while allowing them to rotate.

Blue Kevlar string keeps the clutch cable out of the way of the rotating neck parts.  The string was a rather random gift from my girlfriend that eventually proved invaluable because it does not stretch and is very durable.  

The arm would be on a pivot at the shoulder, actuated by pulling a lever.  The gif below demonstrates it better than I can explain.  The throttle grip used on the arm lever had the same potential to twist and pull cables as the head controls.  It would use a pulley system to extend the arm at the elbow (more on that later).

Almost all of the nuts, bolts and washers were sitting in my toolbox for such items, so sometimes the sizes or heads did not quite match up or bolts needed to be shortened.  The aluminum stock was either scavenged scrap or removed from a now obsolete rack made to transport my girlfriend's baked goods.  Unfortunately I didn't get anywhere close to using up my supply of aluminum C-channel and stainless hardware.


A key part of the "rider" type costume is that the D-Walker mech, while capable of autonomous operation, could also be piloted by a human.  While I could have made just the D-Walker and hidden my upper body inside, I knew the simple visual trick of swapping the pilot and mech legs at the waist would produce worthwhile results.  Plus I did not want to be hunched over inside a foam box for several hours.  I designed the frame angles so that I could sit down without taking any part of the costume apart.  I did not, however, explicitly plan for bathroom breaks.  I can't even walk through a regular sized door while in costume, so urinals and stalls were out of the question anyway.

Just some fake legs.  I ended up removing a lot of stuffing from the calves and all of it from the thighs.

I got lucky and found used U.S. Army coveralls at Goodwill for $8.  While the digital camo pattern is not in MGSV and is not time-period accurate, the fact that it was all a single piece would make suspending the fake pilot legs much easier.  I also found a black down coat (~$6) and grey denim jeans ($4) on the same trip to Goodwill.  The coat would be used to make the arm bands on the coveralls (which turned out to be a huge feathery mess and a lot of sewing trouble), and the jeans would be the base for the mech legs.  The jeans had to be denim because it wrinkles the least and it had to be sturdy enough to somehow attach foam panels to it.  The color palette of the coveralls is what dictated the paint job on D-Walker.

Looks like bullfrog road jerky.

The coveralls are cut open in the crotch so that I can wear the upper half while the stuffed legs dangle behind me.  A wide molle belt attaches to the pictured carabiner, which in turn clips onto the PVC frame.  The fake legs attach to the PVC footpegs - at first I wanted to go with magnets, but I ended up strapping them on with a a more secure quick-release paracord latch.  The bulk of the frame's weight rests on the belt, leaving my arms free enough to pitch the frame up and down and operate the controls.

The belt is a cheap eBay item I bought a few years ago to use as compound bow sling.  The boots are authentically weathered work boots purchased for me by my old company, and the "kneepads" (elbow pads) are from when I used to play airsoft in 2001.  Same with the pistol holster and pouches on the belt.  Save everything!  That's kind of the theme of this whole blog - save your junk in case you ever need to build a robot.

Update 1/8/17:

The total weight of D-Walker's body and attached components is 30 lbs.  The dummy legs + uniform are 8 lbs without shoes (13 with the large boots I used, which I do not recommend). The piston-shoes are 7 lbs a piece - cool to look at but not to wear.  They could be replaced with lightweight replicas.