Dan Baker`s R2 Manual.indd

SECTION
4.1
FOOT SHELLS
Foot Shells
The foot shell flatpack is cut in vinyl.
4.1
Templates are applied to .080” aluminum. THAT should
stand up to pretty well anything.
Now time for something cool. Please understand that out
of all the things I have done in my life, welding has never
been one of them. I’ve done soldering on circuits, and had
plans to try and do some brazing at some point, but never
got that far.
I had heard a few people say that one of their major
contact points between their droid and the public was the
feet. People come up to hug R2, and step right onto the
foot shell. That definitely made me want metal feet, so I
chose .080” aluminum for the shells.
I like JB Weld, but only trust it so far, so I began to look for
an aluminum welding method. That’s when I ran across
ALUMALOY! This stuff is not only so cool and molecularly
advanced, but it’s a LOT of fun!
Two full evenings of cutting mark the end of the foot shell
cutting. It’s slow going with such thick metal.
Alumaloy is a low-temperature, fluxless welding rod that,
when cooled, provides a bond stronger than the base
material. It even bonds to itself, so can be used to bridge
gaps and seal holes or fissures.
Foot Shells
4.1
Alumaloy’s melting point is 738°F, and its specific
magnesium content prevents it from producing the
blindness-inducing sparks of TIG/MIG welding.
The tools needed are: hand-held propane torch, stainless
steel wire brush, Alumaloy rod, safety goggles and thick
gloves.
I picked up this handy device at Harbor Freight. Anyone
familiar with soldering knows about the “Helping Hands”alligator clips on bendy wires to hold your components.
This is the same idea, but uses vice-grips and ball-jointed
arms. In a nutshell, it keeps the heat from being transferred
from the metal to your hand (or the table, setting it on fire
like I did), and it’ll configure to pretty well any angle.
First step is to clean the area to be welded with the stainless
steel brush. Then you have to position the pieces right up
to each other. The “Hands” took a bit of time to get exact,
but they sure made a difference compared to my trying to
hold previous pieces with pliers, wood, or metal tape.
Foot Shells
4.1
Now we preheat the metal. With Alumaloy, you heat the
metal, not the welding rod. If you just heat the rod, it’ll
crumble. Even though it was 85° in my workshop, you can
see the metal condensing like it had been sitting in the
freezer. I found that heating the entire piece helps, since it
prevents the heat from being shifted away from the weld.
After a few minutes of pre-heating, you test the metal by
scraping the Alumaloy rod against it. If nothing happens,
it’s not ready yet. Keep heating.
Just like solder, once the base material reaches the
desired temp, the rod instantly liquefies when you touch
it to the metal. It will flow down and fill any gaps, and you
can move back and forth perpendicular to the seam to
further bond the pieces over a larger area.
Be sure to keep the torch moving, as the aluminum tends
to cool rather quickly. If you need to go back and adjust
an area, just take the Alumaloy back up to 738°F, and all at
once it’ll become a shiny pool of liquid metal that you can
push around. Another solder-like property.
Foot Shells
4.1
The finished weld is a smooth, shiny finish. Once it cools,
you can literally grab the two pieces and wrench them
back and forth, but the weld will remain intact while the
aluminum bends!
The first weld on this foot is complete. It is slightly out of
square, but the weld is strong enough to accept a bit of
force to bring it back in.
The finished outer foot shell (minus the lower sections and
the curved panel).
It is very hard to weld together materials of different
thickness’, so the inner curved section will actually be a
piece of .020” aluminum that is JB Welded in place while
it’s held on by braces.
Foot Shells
4.1
NOTES:
1. Aluminum is a very efficient heat-transference material.
That is why it is used as heat-sinks for CPU processors.
Thicker aluminum is more difficult to thoroughly heat,
because it is dissipating almost as fast as you are
heating.
If you’re trying to weld two pieces of aluminum in a
configuration where one piece is laying flat on the table
and one is held upright, be aware: The standing piece
of metal will heat faster than the piece laying flat. It has
nowhere to send the energy it’s receiving. The other piece,
however, will be sending as much heat as it can to the
closest thing touching it- the table. I set three tables on
fire while learning this, but they were small fires, and I had
marshmallows on hand.
Here is the middle foot. The joint ends are filed down so
that they evenly match the front of the foot shell.
And finally, I’ve got three welded foot shells. The edges
still need to be filed down and the panels cut out, but here
they are. Now for the curved inside section of the outer
feet. This took a bit of trial and error, but I finally found the
right material...
2. Usually, one piece will reach the target temp before the
other one. It is tempting to start welding at that point, but
WAIT for BOTH the pieces to reach 738°F, or the Alumaloy
will not bond with the cooler piece, resulting in a weak
weld that will break off the first time it’s stressed.
3. It took me about a week and three wasted rods to
really get the hang of Alumaloy. Remember, I have never
welded before this! It was very encouraging to see such
fine results so quickly.
Using a super-thin piece of .020” aluminum, I secured
it to a piece of cardboard tube that was about the right
diameter. I slowly hand-rolled the piece until enough of
the sheet was curved to fit. I just used a squared-off piece
of aluminum. It’ll have to be trimmed, but it gives me one
less thing to worry about when I’m trying to fit these things
together.
Foot Shells
4.1
The new curved section is placed inside the foot shell for
fitting, adjusted, then tightly secured with electrical tape.
I like using vinyl electrical tape because it’s stretchy and
strong, but won’t distort the piece I’m holding down.
Tipped on its side, the new joint is given a generous
amount of JB Weld and left to sit overnight.
Since it was curved by hand, I needed to straighten the
flat bottom portion after I ‘Welded the sides. It’s held in
place and JB Welded too.
Once they’re cured, the excess aluminum is cut away with
the Dremel.
Foot Shells
4.1
The underside of the completed foot shell.
Now, the edges are filed down smooth with the thicker
sections of the frame.
*Sniff* It’s a beautiful thing. The curve is perfect, thanks
to the rigidity of the metal, and the entire foot shell is
aluminum!
All three foot shells are lightly filed and puttied.
Foot Shells
4.1
The corners are filed to match, then sanded smoothly
together with the electric sander.
Decals of the outer foot panel are re-applied to the foot
shells. The basic shape was cut out before using a vinyl
template, but if the vinyl was left on when the piece was
being welded, the aluminum would transfer the heat
to the vinyl, and it would burst into flames. Hence, the
reapplication of vinyl.
Two evenings and about 30 cutting wheels later, the outer
foot panels are removed.
Once the panels were cut out, the edges of the opening
and the panel are cut, filed and sanded smooth down to
the edge of the vinyl templates.
Foot Shells
4.1
A piece of .080” styrene is cut to fit inside the outer wall
of the foot shell and taped into place. Because of the
variegated edge created by the welds, I chose styrene
to use here, since I could trim it to fit the contours very
easily.
This shot from the inside of the foot shell shows the
styrene being clamped into place to keep it tight, and JB
Weld was drizzled into the corner and gap.
Once the JB Weld dried, the opening was again cut out
of the styrene. This allows access to the motors and drive
system, and creates the recess between the foot shell and
the panel.
For the skirts on the foot shells, the vnyl patterns was
transferred to some .125” styrene.
Foot Shells
4.1
The recesses were cut out with the Dremel, then handfiled smooth.
A piece of .020” styrene was glued to the back of the
skirts, then each glued-together section was cut apart on
the bandsaw.
The corners were hand-beveled on a Dremel grinding
wheel. I didn’t bother beveling the top of the pieces.
The skirts are ready to be installed.
Foot Shells
4.1
I began by taping a single section in place, then the one
next to it. Using a thin piece of tape, I taped their corners
together, then worked my way around the other corners.
The corners of the styrene skirts were first filled with model
cement to melt them together, then JB Weld was drizzled
into the new joint where the skirts meet the foot all the way
around.
One the JB Weld set, the outside joint is fulled with putty
and sanded to a nice corner.
The finished outer foot shell, with the side detail in place.
Foot Shells
4.1
Because I found that cutting the side gaps on the outer
feet took foreer with the .080” aluminum, I cheated on the
middle foot. I cut the panel gap out from a piece of .080”
styrene, then glued one to each side.
The excess was left to compensate for the extra thickness
of the shell due to the addition of the styrene sides, but
was trimmed down after gluing, then sanded and puttied
in the gaps.
The side panels for the center foot are also cut from .080”
styrene.
The styrene skirts for the center foot were added and
puttied the same way as the other feet.
Foot Shells
Then they were sanded down and primed.
Here’s the completed outer foot with details installed.
4.1
After test fitting the foot shell over the motor holder, a small
section of the inner curve was removed to make room for
the scooter motor. This will be covered up by the battery
box.