I'm a programmer working on a project where we will be controlling a crane's boom for motion control. We are currently a year out from having the actual crane in house, but are doing the software ahead of time as we can 3d simulate a lot of it. I thought it would be a fun idea to make a little miniature version to play with (and it would be a fun toy for the office). Our crane boom consists of 4 segments and to scale it down somewhat proportionally each square tube will be 1.5 feet long and the first extension will be 2 inch outer diameter, with each inner tube getting 1/4 smaller. Making a little mechanism to pan and tilt the boom is simple, but I'm not sure how to go about controlling the extension with a motor.

enter image description here

Ideally I'd like to control the extension with just one motor I can mount at the base of the boom. My question is, is there a mechanism that can create this collapsible column with just one motor?

I realize the easy solution is probably 4 separate motors that use a rack and pinion to extend each segment, but I don't think Ill have the space for the motors at this scale.

Another option I've pondered is using a spring and then having the motor just wind up a string that pulls to compress the spring but I feel acquiring a spring of the right diameter, length and strength would prove challenging as at full extension this will be about 4 feet, though I'd like to make it as small as possible.

Hydraulics and pneumatics are completely out of my ability.

In this, each segment should move the same amount as the boom extends. I feel like there has to be some sort of mechanism for this but I can't think of anything else. I think our actual crane uses a bunch of pulleys but I'm not sure how that works. My boss is designing the crane, but I'd like to do this as a surprise for him so I don't want to ask him for his input.

  • $\begingroup$ Have you looked at the big heavy wreckers aka Rotators - they have full remote control... $\endgroup$
    – Solar Mike
    May 31, 2019 at 8:44

1 Answer 1


Many moons ago, I was involved in a process which required a transportable antenna tower. The assembly was similar to your requirements. Tilt the tower module vertical and crank a winch handle to cause each of the "telescoping" segments to elevate. One crank, many pulleys and a strong wire cable.

extensible crank assembly

The drawing above is not to scale and placement of the pulleys are not critical. The individual segments to be extended would require guiding mechanisms as the segments are offset from the centerline. In the case of the antenna tower, the guiding mechanisms were a combination of low-friction plastic guide blocks and boat trailer rollers.

A series of nylon or teflon buttons would likely serve your requirements for guidance.


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