Are two shocks really better than one
My first attempt at making oversized Bush Plane landing gear was a solid success. The piggyback rock crawler shocks were the perfect addition to the custom designed arms. After destroying a few arms in the high-speed taxi tests, I learned the importance of print orientation. Small diameter pivot pins will rip right though PLA layers. This fix and others can be found in this blog post.
The one problem with the shocks was the vehicle sag when accelerating. When the tail raised up and all of the weight shifted to the main gear, the suspension would compress and the prop clearance would get way too close. I never had a prop strike but the pucker factor was high. I tried all the easy fixes like stiffer springs and heavier weight oil, but they weren’t enough.
I set out to make a better version with more clearance and DUAL SHOCKS. The only constraint was it had to have the same mounting holes as the first version, I already had holes in the plane and I didn’t really want to fly swiss cheese.
To get more clearance I lengthened the arms by 40mm. I knew this would put more load on the shocks, but with the addition of a second shock I was confident it would better. This was the begging of my demise. It was Archimedes who said
Give me a lever long enough and a fulcrum on which to place it, and I shall move the world
He was definitely right. The longer lever arm of the lower arm canceled out any extra spring from the second shock. The lower shock attachment was at the same place 50mm from the main pivot but the overall length grew by 50%. Ultimately the longer lever-arm won out over the second shock.
If I didn’t have to work with off-the-shelf components, I could calculate the spring constant I needed and use a much stiffer spring, but I don’t have that luxury so back to the drawing board.
If you like version 2, you can download the files from Thingiverse.
Check back soon for the next version.
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