42097 base with centralized legs control

 


In my version with motorized legs, the inner & outer legs have to be operated separately to avoid collision, and I couldn't find a way around that. But I had a feeling it could be done, and there it is: in this new -manual- version, a single crank controls the deployment, lowering & extension of the 4 legs simultaneously, replacing all 12 knobs.

It took me a very long time to think of a solution, but in the end it's startlingly simple, and the key lies in exploiting the properties of a differential.

The legs will go through the following sequence:

  1. when deploying, the outer legs will first move out of the way, then halt until the inner legs have completely deployed, then finish deploying themselves.
  2. When retracting, at first all four legs will move until they're not under tension anymore. Then the outer legs will halt until the inner legs have completely retracted, then finish retracting themselves.

And this seemingly complex behavior is achieved through such a simple idea that it may not be obvious to see how it works just by building the model :)

Like previously, there are also a number of other smaller modifications:

  • secured the gears operating the leg turntables. In the original design nothing holds them vertically and they would tend to pop out over time.
  • improved support of the legs' platforms (weak in the original design).
  • added stoppers for the legs so that they stop turning in & out at fixed positions instead of pushing against random elements.
  • secured the large turntable's toggle joint. In the original design it's just floating, which hinders the operation of the heavy crane.
  • increased the torque of the knob operating the crane, which isn't enough in the original design considering the crane's weight.
  • modified the crane support bracket so that when stowed, the crane cannot move left or right (since nothing prevents that in the original design).

The instructions are for the base & legs only. You'll have to build the crane part using the official 42097 instructions.

Note that the build is sometimes challenging, since it adds a lot of functionality into an already compact model. Also for everything to work flawlessly, both side have to behave exactly symmetrically, which might require single-tooth gear adjustments.

The idea to use linkages instead of worm gears to extend the outriggers is from Ngoc Nguyen.

UPDATE
after rebuilding it (in blue!), I realized that if it is built with little friction on the gears (so in fact, better built), then the trick doesn't work so well, because the torque difference between both side becomes too small. I found a simple fix to this problem and updated the instructions.


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