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Step 3Pistons / Mech Upper Leg
Since I wanted a backwards-facing knee the mech's upper legs needed to connect between the front of my box frame and the back of the mech feet. The tricky part was that they also needed enough degrees of freedom that they could track wherever my own forward-facing knees moved the feet. In the end I went with a piston design with a screw joint (rotation) at each end.
The piston is a piece of 1"-inner-diameter PVC pipe with a piece of ½" PVC inside. The inner pipe still leaves some wiggle room, so I wrapped duct tape around the end about eight turns to make a snug fit that would still slide in and out. To the inner pipe I added an elbow joint that was threaded at the other end, which gave me rotation where the piston connects to the frame. To that I attached a snap "saddle joint" which could snap onto the frame itself and yet still be disconnected for easy storage. On the lower end I added an elbow joint which attached to a
length of 1" PVC pipe that went through the top holes in the mech feet. Since the mech feet are tapered, the lower cross pipe for the rear two pistons will be longer than for the two that go in the front.
It might not have been necessary, but just to make sure the piston didn't jam as I was walking I threaded an elastic band down the middle of the inner pipe. At the larger elbow I threaded the elastic through a cork (which fits inside the joint but is too long to go around the turn) and then doubled it back up to the snap saddle, where I tied it off. This made the pistons naturally snap closed, which also made storage easier.
The piston is a piece of 1"-inner-diameter PVC pipe with a piece of ½" PVC inside. The inner pipe still leaves some wiggle room, so I wrapped duct tape around the end about eight turns to make a snug fit that would still slide in and out. To the inner pipe I added an elbow joint that was threaded at the other end, which gave me rotation where the piston connects to the frame. To that I attached a snap "saddle joint" which could snap onto the frame itself and yet still be disconnected for easy storage. On the lower end I added an elbow joint which attached to a
length of 1" PVC pipe that went through the top holes in the mech feet. Since the mech feet are tapered, the lower cross pipe for the rear two pistons will be longer than for the two that go in the front.
It might not have been necessary, but just to make sure the piston didn't jam as I was walking I threaded an elastic band down the middle of the inner pipe. At the larger elbow I threaded the elastic through a cork (which fits inside the joint but is too long to go around the turn) and then doubled it back up to the snap saddle, where I tied it off. This made the pistons naturally snap closed, which also made storage easier.
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