Box Beam Legs
I have designed a one-piece leg-ankle assembly built as a
structure. There's a clear center section down the middle of the leg to
route wiring between the body, battery boxes and feet. It's made from a
double layer of .125 styrene with an internal eggcrate construction
style box beam for strength. Not shown in any of
the 3d drawings is the wrap of .040 styrene that goes around the edge
of the legs. There are two layers on the curved top of the leg where it
gets the most abuse (and has the least support) and one layer
everywhere else for cosmetic reasons.
|This is the
beam leg (with only the edge skins missing)
image links to a 3d pdf file, click on it if you want to be able to
rotate the image around and examine it from other angles. (Note, the
3d.pdf file opens in a new window. If you have
problems with the 3d feature you may have to upgrade to the latest
version of Adobe Reader).
After 'activating' the 3d mode by clicking
on the display
select a part by left clicking on it (the part will be highlighted)
then right clicking brings up a window. Follow the sequence
-> part options -> part render mode -> transparent
to make the outer parts transparent and the inner
Or you can use the views below which also link to .pdf files.
version has the back removed to show
the Shoulder Hub Mounting Details
The Ankle Curved Section is built on the outer layer of the Ankle
Surface. Each of the images below links to a 3d
pdf file, click on it if you want to be able to
rotate the image around and examine it from other angles.
did the design for the Box Beam
Leg I made a mistake in understanding how the Shoulder Hub was supposed
to mount on the surface of the leg.
This is the way I designed the Shoulder Hub opening,
the Hub was supposed to be mounted on the surface of the leg.
I'm now aware that the Hub is supposed to mount flush
with the leg surface as is shown above.
There are several consequences to this design mistake.
1. The mounting
hole in the center of the leg is too small.
design drawings have been updated (now on version 4) to reflect the
changes in the parts. I have made a template, and
instructions, for my customers that purchased and assembled legs to
them make the necessary changes. The template marks a set of .125 holes
that are .03 inside the finished .385 diameter of the correct hole. Use
the template to mark the hole locations, drill the holes, remove the
excess plastic & slowly enlarge the hole to finished size. The
template is here.
An alternative to using the template, for those of you who have already
purchased Shoulder Hubs, would be to use the Shoulder hub as a
template, tracing around it's outside edge. Customers who had not yet
assembled their legs were given replacement parts. There are
instructions here on shortening the Fixed
Shoulder bolts. Finally there is information here
on the changes to the Shoulder Hub.
The risers (internal ribs) in the area of the mounting hole have to be
notched to provide a surface for the Shoulder Hub to sit on.
3. The bolts on the 3-Leg Fixed Shoulders (Or 2-Leg if you
have those) are too long and have to be trimmed.
4. The Shoulder Hub itself is too deep to fit into the space
and has to have part of it's bottom edge removed.
As with any design, there are limitations to
what can be reasonably accomplished by CNC machining. For example,
cutters are available for 30, 45 and 60 degree angles. If you could
find one for the 35 degree angle of the Ankle Curve section it would be
prohibitively expensive to use. You might have noticed the red lines in
the Ankle Curve with Skin drawing above. Those are the edges of the
ribs 'sticking' thru the skin. I had a choice. I could make them the
hight of the rings but then you'd only get support on the edge. Instead
I made them higher. They will have to be filed down to match the
contour of the rings. See the Assembly Instructions for the highlights
of what you'll have to do
drawings are available
as both Autocad .dwg files and Adobe .pdf files download drawing
files with the understanding that the
drawings are copyright to Media-Conversions and are not to be used
commercially. (That note also appears on each of the drawings). I've
also put together a set of assembly
instructions to help you
put the legs together.
Here's what a finished leg
From time to time
I've seen comments about how strong Styrene Parts
really are. The precise answer is "I don't know".
I went and set up one of my Box Beam Legs (the second one I built)
supported only on each end, and I stood on it, in the middle.
The long answer is that it will hold 160 Lbs! Might