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Old 08-29-2021, 06:55 PM
dremu dremu is offline
Join Date: Aug 2019
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Default Re: 1:10ish Alvis Stalwart 6x6 high mobility carrier, wrongest of the wrong

The next engineering challenge was slipshafts at each wheelstation. I needed a really short driveshaft (CV joint, whatever you wanna call it) with just a bit of slip, but of course the RC driveshafts are all waaaay too long. I briefly considered printing the parts, but even at high infill, they're just too small to do in plastic with enough strength, so I had to mix off-the-shelf parts with printed and fabricated to make it all fly. Err, roll.

U-joints are available in a bazillion sizes, but I needed something into which I could fit a collapsible shape which could still transmit rotational force. That is, something like square tube, in matching sizes so that the outside of the one fits just into the inside of the other and it telescopes.

Finally, there is NO extra space whatsoever in there, so the U-joint had to fit *inside* a bearing on each end. There wasn't enough length to have the bearing at the end of each U-joint.

Took forever, but eventually found U-joints that are big enough to fit the slip mechanism inside, AND matching bearings. Curiously, the U-joints are metric and the bearings are inch, but it works. Left side has a bevel gear to come off the drive shaft, right side is a 12mm hex for the wheel drive. See what I mean about short? There's all of ~2mm of slip, just enough that I couldn't have used a solid shaft or it woulda broken over time

The slip shafts have printed bushings with a hole through for the setscrew to hold down the square tube. The outer ends are sized to fit one of those brass threadserts, filed on one side for the set screw:

Fiddly to get the threadsert flat enough that the setscrew would hold it, but still leave room for the bolt to the thread into it. Also had to find fairly short setscrews so that whole thing could fit inside the bearing.

Then, in testing, discovered that the U-joints like to shift back and forth a bit in the bearing. Didn't want to glue them in, too permanent, so opted for another solution. Cleaned the chrome-ish stuff off the surface, then soldered a ring around them to prevent slipping through the bearing.

Not my prettiest work -- I'm used to electronic soldering -- but they're structurally sound.

Then onto assembling the suspension. Sooo many fasteners, so much lather, rinse, repeat:

I mean, how hard can it be?

Last edited by dremu; 08-30-2021 at 12:56 PM.
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