Build log: Digi stilts

This describes my recent build of digitigrade stilts for my Kerapac costume and future costumes. Check out my feed on my social media pages, or the front page of my website to see them in motion!
They’ve gotten a couple QoL updates based on my first experiences, they’re either noted throughout the document, and again described at the end.

For these stilts I used the following specialty tools:

Power drill with M4 and M5 metal drills (HSS)
Tap and die set (tap size M5)
Jig saw (for the ABS plastic sheet)
Metal handsaw (i couldnt order everything to size)

I used the following hardware:
2x Aluminum 2040 profile 450mm (45 degree corner on one end each)
4x Aluminum 2020 profile 180mm
4x Aluminum joining plate 90 degree
4x 250mm Aluminium slats 20mm wide and 5mm thick
4x large 100mm stainless steel chair corners
6mm ABS sheet

I used the following bolts and bits:

~40x 25mm M5 bolt
~20x M5 locknuts
Bunch of wide washers that fit M5 
8x 60mm M5 bolts for the foot plate
5mm thick bungee cord

For the straps I made my own using:
25mm wide nylon webbing
50mm wide nylon webbing
20mm wide velcro
50mm wide velcro
12x rectangle D rings for 25mm
2x rectangle D rings for 50mm

I started on the base. I didn’t get the 2040 profiles cut to size, so I sawed 2x 45cm 2040 profiles from one piece of 90cm painstakingly by hand with one side 45 degree corner (the 45 degree corner is so I had no extra space to drill a hole in the flat corner otherwise).
I got the 2020 profiles cut to size (4x 150mm, later 4x 180mm) from the same webshop.

Using the holes in the joint plate I marked the holes where i need to drill. Used a centerpoint (not sure about the english term) I hammered a hole and then I drilled them with my power drill and M4. Then I tapped the holes using an M5 tap and die set which leaves the holes threaded and then I could use my M5 bolts to bolt everything together. 

The foot angle in the end is 45 degrees so i’m using the 90 degree joint plate the wrong side. Due to this assembly, the smaller profiles don’t fit on the inside, I mounted the smaller side profiles on the outside which made the point of contact much wider and more stable too.
I had to take off the joint plate to mount the bolts to the inside, then screwed them on again.

Once the base was put together I tried to figure out the joints for the eventual shin support. I decided to add the shin support since it helps divide the forces all over your legs rather than just your feet. Since the stilts are quite angled and pretty far up it’s definitely recommended. It basically acts as a backup achilles heel.

I bought some steel ‘chair’ corners from the construction store that seemed big and sturdy enough, then with some effort I bent them using pliers and a table vise
(note they bent with walking, later i switched to stainless steel and had to mount them without bending since it’s too strong).

I mounted the steel chair corners using M4 drilled holes then tapping them with M5 and bolted them to the main aluminium profile using 25mm M5 bolts. 

I added 25cm long 5mm thick aluminum slats. I had to cut these to size by hand and I bought 1 meter so in the end i would have picked a little longer (maybe 30cm) to provide more support farther up the leg, especially if youre taller.

I drilled both ends using M5 drill (no need to thread them they need to rotate) and mounted them to my steel corners with my M5 bolts and locknuts to prevent the nuts from falling off.

I drilled two holes for my bungee cord on the core 2040 profiles, and looped the bungee cord through the end, ziptied it in the middle. The ends of the bungee cord were then looped around the bolt to the top of the aluminum slats, tightening the loop again with a ziptie.

That’s pretty much the base frame complete, and then last I added the straps and plates for my legs to sit in. I sewed my own straps from some nylon webbing, velcro and D rings I had left over. I doubled the nylon straps up for comfort and strength.

I used a jigsaw to saw some foot rest plates from 6mm abs sheet, ABS is really strong so I knew I could not break them by standing on them or tilting or whatever.
I drilled 4 holes through the foot rest plates, and through the frame using an M5 drill, and used very long (60mm i think) bolts to bolt the foot plate and the straps along the bottom of the frame all at the same time. I used some of the wide washers so the nylon straps would not pull off the bolts.

FEEDBACK ADJUSTMENT: Later I decided to modify the foot rest plates to add extra pieces to the sides of my foot (heatformed with a heatgun along the top of the foot), to provide a stiffer foot rest. I also added a piece of plastic to the heel so the foot would not slide backwards out the straps.

The last steps were to add extra straps to the lower leg plates. I sawed out some more ABS plastic sheet shapes to support my calves on one side, and then straps on the other side. The pieces were heated to shape with a strong heatgun (took forever to make them mallable but abs will eventually be very flexible when hot). And then bolted into place with the straps inbetween the aluminum slats and the plastic pieces. I then tightened the bungee cord between the washers and zipped up the zipties for the final strength according to my preference.

FEEDBACK ADJUSTMENT: The ABS plates for my calves were later inverted to be used on my shins instead. The forces on your shin are quite strong and as such the straps were cutting into my shin. Dividing that force over the plates using a bit of upholstery foam was a much more comfortable solution.

Changes that were made after initial tests and extensive use:
I added 180mm side 2020 aluminium profiles to the ‘toes’ and used all three available bolt slots on the joint corner plate, using an extra long 60mm bolt to bolt both the side profiles and the main 2040 profile. I noticed some bolts and threading may wear out quickly due to the force exerted on that toe area. I also opted for stainless steel bolts instead of galvanised steel bolts in the toe area.

Due to some missed steps on a long day of intensive use of these stilts, the ankle joints (the steel chair corners) were bent. I switched them out for the exact same 100mm chair corners, but in stainless steel. I had to mount them on top of the 2040 plate since you can barely bend them, requiring to add some spacing between 2040 profile and the foot rest plates, which was simply done with another layer of ABS plastic.

I added an extra layer of abs on top of the foot support plate, with space drilled out for the bolts. This way the bolts didn’t poke through my shoes hurting my soles. The extra plate of abs also got extra side ‘wings’ that were shaped over the top of my foot to provide more support.