KerbalX

Taking BendyTech to the Extreme

Recently, there’s been an odd revival in stock mechanics, allowing single-craft stock mechanisms in a way that was only possible before in the buggiest versions of the game - bending parts of your craft out of alignment.

I, along with HB_Stratos have been pushing this tech as far as we can, and my contribution is this magnificent beast - a fully functioning excavator, without relying on any mods or DLC.

User Manual

INSTRUCTIONS FOR USE:

AG 1 - Step Waist Rotation 22.5 Degrees
AG 2 - Reverse Waist Rotation Direction

H/N - Shoulder Rotation Out/Back
J/L - Elbow Rotation Out/Back (touchy)
I/K - Wrist Out/Back (slow, low motion)

It’s very easy to hypoextend the elbow,
be careful when retracting it
GEAR to decouple the support structure

Statistics

Part Count: 480
Waist Rotation: Unlimited, bidirectional
Shoulder Rotation: 60 degrees
Elbow Rotation: 120 degrees
Wrist Rotation: 40 degrees

Under The Hood

For the basics of Bendy Tech, I recommend first reading this forum primer

Waist Rotation

Originally, when I was first conceptualizing uses of BendyTech, I didn’t imagine that it would be possible to exceed the rotation range of a single part, much less be able to create controlled 360 degree rotation. But, through a clever arrangement of elevons and choreographed toggling of Same Vessel Interaction, each RCS ball can be passed forwards to the next elevon in the ladder, allowing 22.5 degree actuation precision.

Adding a second set of RCS balls strengthens the hinge and locks it into a single position, instead of flopping across the 22.5 degree range.

Interestingly, this drive abuses the way that KSP’s physics engine calculates bending to allow for unlimited rotation with a finite spring. The core theory of computational structural analysis is Strain Energy Minimization, which tries to find the arrangement of parts which are the least stretched. Once the craft has rotated 360 degrees, there are two possible arrangements for the spring: rotated 360 degrees, and rotated 0 degrees. Because the game doesn’t have code to account for people bending something 360 degrees without breaking it, the physics engine simply takes the less stretched position, and the parts snap into place, ready for another rotation. I wish I could say that I planned for this to happen, but it was just a lucky accident.

Shoulder/Wrist Rotation

Each of these joints is the simplest form of bendy tech, using elevons to push smaller parts, similar to what is shown to the right. Each is strengthened by a thermometer hinge, which helps redirect the motion into rotation.

Elbow Joint

Another very basic BendyTech technique here, albeit one that abuses a current bug in 1.8/9 where adjusting the Airbrake deploy angle using axis groups can extend it far past the intended limits, in both directions. It’s a cheap, dirty, way to get a large rotation angle in a small package.

This element takes full advantage of the single-craft nature of BendyTech, since the best way I found for the airbrake to be set up was attached to the rotating element. Just another way that BendyTech represents a major upgrade over classic stock tech.

Cheers, and Happy Flying Constructing!