Tuesday, 15 November 2016

Project: Proteus Delta Part 4

Rod arms and Effector installed
   Well, it's time to cover the last of the major mechanical assembly for the Proteus, building and installing the rod arms. Most deltas use carbon fiber tubing, Traxxas 5347 joints, and M4x20mm set screws for building the rod arms, but since carbon fiber tubing is a bit tricky to find locally, I'm using some 3/8" cold rolled steel that I got at the local hardware store instead. I've also designed some 3D printed end caps to allow using regular M4x20mm cap screws for mounting the traxxas joints onto the shafts.

Traxxas 5347 assembly tool and end cap cross section
     For assembling the Traxxas joints, I used the delightful tool pictured above, it's a fairly quick print, 30 minutes and it's ready for use after adding a M3x30mm or longer screw. As for the end caps, the STL is here, I'd recommend printing them on their side since the length of the lower point is fairly critical to getting the final arm length correct. After assembling the joints, the next step was tapping both the end caps and traxxas joints with a M4x0.7 tap to make installing the screws easier.

Threading the endcaps with a M4x0.7 tap

Completed end cap assembly
     After tapping, the actual assembly is fairly quick if you use a power drill to provide the rotational power, I've got it clamped in an old bench vise to make it easier to keep things aligned, but you can easily assemble things freehand with just a hand screwdriver. For the shafts, I used the same technique that I used for cutting the Mostly Printed CNC's tubing to length to cut 6 327mm sections and printed a jig for final assembly.

Steel shafts cut to length on jig for length checking
     Once the jig was printed and screwed down to an old 2x8, flattest surface I had on hand, it was simply a matter of mixing some 5-minute epoxy, applying some to the ends and pushing on the end cap assemblies, then placing it in the jig and letting things slide until it fits perfectly.

Fully assembled rod arms jigged and drying
    After everything was assembled and settled, I left the arms overnight to dry, and printed a customized version of this delta effector generator to use for the outer part of the effector platform. Measuring and averaging the final lengths of all 6 arms gives a center-to-center length of 396.34mm, one of the numbers needed for calibrating the Proteus when it's finished. Finally installing the arms on the rest of the frame was straight forward, just needed 12 m3x20mm screws.
Rod arms half installed
    Now all that's left is to redo the printbed support and install the electronics, but that's a topic for next time.
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