Rapunzel Crane Project

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Abandoned Project
Rapunzel
A 2nd-floor crane for Joy Street.

Sequence of operation

People
Creator(s)User:Threespeed
Leader / P.I.
Collaborators
Status
Date startedMay 6, 2011
Date abandonedDecember 14, 2011
Reason abandonedNew facility does not have 2nd-floor door.
Website[ ]


Rapunzel is the name of a proposed crane to hoist things in and out of the side roll-up door at the Asylum. It will let a couple of people move objects up to 600 lbs between the Asylum floor and the ground outside in the driveway without bearing any of the load themselves.


This project never went further than being a proposal.

Contents

How it Works

Rapunzel is a boom on a pallet, which, coupled with the existing pallet jack, becomes a floor-based travelling crane. It picks up the load from a location on the floor inside of the door, conveys it outside so it hangs next to the building, and then lowers it to the ground with an electric hoist. The operation is reversible to bring a load into the second floor of the building. This picture shows the sequence of operations in cross section: the Asylum building cross-section is in gray, showing floor and the lintel over the roll-up door; Rapunzel is in green, load is black, and the hoist is red.
File:Rapunzel-seq.png

Proposed Design

The crane is designed to make the best use of available resources: namely, the pallet jack, a 600-lb electric winch generously offered on loan by Calvin, and the existing structure of the Asylum.

Operation

Referring to the figures above, here is the sequence of operations to get a load out of the Asyulum:

  1. Preparation: Get crane and load into initial position
    1. Open stargate and get it out of the way. Roll-up door may remain down.
    2. Position the load just inside the roll-up door, hoisting point over where the crane will pick it up (this will be marked on the floor)
    3. Insert pallet jack into the pallet and raise it just enough to move, less than 1"
    4. Position Rapunzel with tail wheel in track, hoist over the load pick-up point. This will be marked on the floor.
    5. Safety checks:
      • Tail wheel is in its track
      • Crane boom is aligned with track
      • Tether is attached to inboard end of crane boom (other end stays attached to truss).
  2. Pick up load:
    1. Attach the hoist and raise it enough for the load to be free of the floor.
  3. Move outside:
    1. Raise roll-up door
    2. Push the crane forward until load is hanging free outside the door.
  4. Lowering the Load:
    1. Lower the pallet jack so the pallet is resting on the floor.
    2. Activate the winch to lower the load to the ground.

Bringing a load up from the ground into the asylum is simply the exact reverse of these steps, starting with the crane extended and pallet resting on the floor.

Capacity

Its working load is limited by the hoist anyway to 440#, or 880# if the cable is doubled over. The pallet jack is rated for 5,000# so it is not the limiting factor. The crane structure is designed for a working load of 1,000 lbs.

The design has been analyzed by a qualified mechanical engineer, SCUL pilot Buckminister, who specifies that a beam of double 2x10's or triple 2x8's can carry this load.

Storage

When not in use, Rapunzel reverts to being a pallet with stuff on it. Can be dragged around by force or moved more easily with the pallet jack. It takes up a 4'x4' chunk of floorspace, and the boom can hang over existing piles of cruft. It should stay near the door and a regular asteroid belt of cruft seems to have taken up residence there.

Design Analysis

Beam Strength: (Bucky, please add load analysis of main beam here)

A-frame: The A-frame holding up the front of the beam (acting as a pivot) is appropriately overbuilt. It has 4 pieces of 2x6 dimensional lumber almost vertical. (Bucky, can you find an estimate for the load a 64" long piece of 2x6 can support vertially?)

Upward Force: When there is a load pulling down on the tip (outboard, or winch) end of the crane, something has to exert a downward force on the other (inboard) end of its beam. This is done by the track bolted to bottom of the roof trusses. The end of the beam has a straight, non-swivelling caster pointing up which rides along a 2x4 track, and the track has side rails to keep it confined. There is a stop at the end of the track to prevent the crane from rolling out of the door; in practice we will also add a tether rope from one of the trusses to the end of the beam as a backup.

  1. the back of the crane is pushing up, not down, so it's actually reducing the load on the trusses
  2. it spreads the upward load over two trusses
  3. the trusses are rectangular, not triangular, and are thus equally stiff pushing up and down. They support at least a 50 lbs/sq-ft load plus the dead weight of the roof
  4. the inboard (middle of building) end of each truss is welded to the top of the main spine girder, and the outboard end is embedded in the masonry wall, so even if you push up with a lot of force the truss isn't going to be lifted out of place.
  5. the numbers:
    • pulling down with 800# (limit of hoist) 3' from the pivot will push up with 266 lbs at the other end of the beam, 9' from the pivot.
    • divided between 2 trusses 5' apart, this applies 300 lbs over maybe 100 sf, probably more, that is 3 lb/sf upward load. This is 1/3 of the typical dead load of the roof deck and covering (at least 10 lb/sf).
    • Adding the dead weight of the trusses (by my estimate at least 200#), the dead weight alone is more than a factor of 3 of what the beam will ever push up.

Fasteners: The beam is supported by 2 short horizontal 2x6's bolted to the top of the A-frame, as well as notches in the A-frame members themselves. Each of the 3/8" bolts connecting the horizontal framing to the legs can support 1,600 lbs (the expected strength of ungraded mild steel carriage bolts), so all four of them can support over 6 times the expected load.

Cost Estimate

An early estimate of the cost to build it, assuming mostly new material, is $150. This breaks down into:

  • $80 lumber
  • $40 hardware and fasteners
  • $12 caster
  • $18 margin for tax, unforseen extras

This can be reduced if we can scrounge any of the lumber. It also assumes we get these for free or on loan:

  • Electric hoist from Calvin
  • Use of pallet jack
  • Pallets are free
  • Scrounge rope for restraint

Drawings

NOTE: These drawings are not entirely accurate since they were made before the beam analysis was done, although the beam shown is one of the acceptable configurations so it might even be what gets built.

Expected changes: makeup of the main beam, "padding" between beam and roller (depends on caster dimensions).

travelling assembly on pallet
track and roller detail
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