I was never intending to make the foot so early on in construction, but as there were issues to sort out with the drive setup, the foot was needed to get them right. It was no good making a drive setup that wonít fit in a finished foot, so work was started.
The first thing was to print off the plans and where they needed it scale them to full size. As mentioned before this makes construction far easier when you can lay full size pieces on full size plans for comparison.
As this will be made in carbon fibre when done, the prototype was constructed out of 2mm styrene sheet as itís quick and easy to work with. All the bits were cut to size and laid out on my bench, and a quick assembly using masking tape to hold it together was done to check it was correct prior to gluing, then when happy the bits were glued together.
One of the advantages of styrene sheet is very quick prototype development.
Next I made the inner layer of the skirt. As I need this more for drive dimensions, I havenít put the pattern round the skirt yet, Iíll get to that later.
Then using masking tape, I attached the skirt onto the foot so it could be placed over my tracked drive system. I needed to see how much room I had to spare, and also where the motor will go, and this could only be done with the completed foot.
I then added some more of the foot outer wall bits at the top to make it a bit more solid and also see clearance for the ankle pivot point.
With what I needed done for my drive checks, I set about adding the detail to the foot itself. This is really just cosmetic, but nether the less care should be taken to make sure it looks right. I wanted to keep nice clean sharp edges so the detail would look clean and defined when a cast was made.
Next came the half circled angled bit on the outside. First of all using two lengths of plastic, I glued and pre-curved them into shape so when the glued dried they would stay curved. I then glued them to a flat section I had cut out, and added strengthening bits to the edge to make sure it all stayed in place. When it was dry, I cut and sanded it to the correct angle, then added the outer slightly angled bit with slots in.
I then cut out of styrene sheet the detailed bits that go along with the half curve bit and stuck them all to the foot. I still have a couple of side bits to add where the ankle will pivot, but as I am still working on the pivot mechanism, they will stay off till itís done.
With the detail bits stuck on, I set about adding filler to the edges. Things you have to bear in mind when making stuff out of either carbon fibre or fibreglass, is sharp edges are air traps, and can also be a sore point to remove from the mould. It doesnít matter how much mould release you use, sometimes the cast is just wedged into the mould and the only way it comes out is with leaving a very thin edge section behind. Normally if this happens itís a tiny bit, but still a bit. Therefore using something with a small curve to just apply filler to remove the sharp inner curve saves a huge amount of time later. If you look at fibreglass moulding, there are never any really sharp edges on them, itís just slightly rounded to the feel.
So with the foot ready to be moulded, I turned my attention to the hose fixing that is on the front of each foot. Normally I make stuff like this from a rod of resin, but because knurling doesn't take to resin to well, as itís a bit soft, I made this bit from a rod of alloy.
Itís made to the plans as are all bits, so the first job is to size the rod down a bit to the correct diameter. When this is done, the knurling is added, and then the slightly rounded lip put on what will be the r outer face.
Now this is where I deviate from the plans as it says to cut a thread into a longer shaft than I added, but as this will go mainly in my feet, which are fibreglass a short thread less stud will be fine as it will be glued in place.
So with my adjusted plans for the shorter unthreaded end section, I machined the end down to under that of the width of the knurled section.
With the bit now just about finished, it was just time to drill the half inch hole through the middle as per the plans. While I altered the method of fixing, everything else needs to stay as it should be. Now all that is left to do is make a silicon mould or two and cast a few copies.
With the mould made, now the easy part. The mould has to be well polished prior to adding any resin or it will stick like you know what does to your shoe. Once polished, several coats of white gelcoat are applied and let to cure between coats. when that is done, CSM is cut to shape to fit the sides and top, then laid into the mould while the gelcoat is still tacky, and resin applied to wet out.
Several layers are added in varying orders to make sure each bit overlaps the other, creating a nice strong cast. I experimented with several thicknesses, and settled for this one, after testing a foot by standing and jumping on it. Primitive, but a good way to test how durable it is.
Once the whole thing has cured, itís time to remove it from the mould and cleaned it up. Spending more time making sure the mould is in enough parts to get of easily, and also joins together well, means clean up is at a minimum.
By putting the mould case joins on the edges, means with only light sanding the joins are gone and the corners are nicely rounded. The surface is semi shiny from the mould, so its given a light sanding using fine grade wet and dry sandpaper, prior to being buffed on a buffing wheel. This removes the fine scratches left by the sandpaper, and brings the surface to a nice shine. Another part done, but still lots to go.