• aditya mehrotra.

chip3 updates: coaxial cable drive? [updates]

Today we took a look at chip's leg design and realized we were happy with the lower leg, but the upper leg is really kinda bulky and awkward.

So what if, instead of using the same exact mechanism in each of the joints we try something new. The problem with this is that big "L" shaped thing we need for the AB/AD joint, we want to see if we can make this better. So we started sketching some concepts.

We call this coaxial cable drive or axial cable drive or something. We need to do much more to figure out how this will work but it's essentially a replacement for a planetary gearbox, like if we were to create a planetary gearbox that worked on cable drive this would be what we were thinking. That allows for no weird looking brackets and we can mount directly to the leg! Let's try some CAD. The tradeoff with the above would be the following:

  • The torque produced would likely not be the same depending on the joint position, it would vary since the angle is changing.

  • The range of motion is no where near a planetary since a planetary can spin 360deg, this has physical hard stops (but it could work for some applications)!

Preliminary CAD design suggests that the drive will work for ranges of -90deg to 90deg but let's keep going.

This is what the system is starting to look like, we still need to pick a bearing for the font part and we still need to design the unit in the center but it looks like the beginnings of something cool. We might want to rethink the design a little more too, but this is kinda a prototype here. It was done fairly quickly and can definitely be improved. This design was also built for water jetting but could be made better if we create a CNC-case for it and use that.

So we want to try making one of these for fun, we'll see how we go about the whole thing. The first thing we want to do likely is make just the lower and upper portions of the leg w/o the AB/AD joint and test the torque capabilities and force capabilities of that system with the cable drive! Once we do that we can move to making this or a similar version of this for the shoulder joint and AB/AD!

#update #omgrobots

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