[SML] Detailed drawings for man-powered stage lift

[Kim Hartshorn]

There are several factors that will affect the design considerations so
providing detailed drawings may not be that useful.  I built one years ago
using a w(in)ch that had been donated from a touring production.  This was
a grooved drum winch, the grooved drum really makes winch powered mechanics
much easier to deal with since things like cable length and power ratios
stay consistent.

That being said:
1.  How much are you going to lift?  The one I made worked great in
testing, in actual use with the 250# actor we had to put a second handle on
the winch and use two people to crank.

2.  How fast does it have to move? this is crucial because the power ratios
for human powered devices favor slower movement.  As above you can gear the
device for greater speed if the actor you are lifting is lighter.

3.  Can the trap be self sealing?  In other words can the lift be stored in
the up position when not in use?  If not you will have to engineer a weight
bearing door into the trick.

4.  If you can engineer a counterweight into the system it will make things
easier.

5.  There should be a safety to prevent a run-away.  This may be the most
difficult element to engineer and was missing in the lift I made.  We did
have two people on two cranks which gave some safety and the lift used two
lift lines running to the drum so if one had parted I don't think the lift
would have dropped.  But also to be on the safe side as the lift rose above
3ft from the trap room floor I had a couple people with notched 2x4's
bracing the lift to the floor as it ascended.  Again this safety factor
became more critical as we worked with the actual weight of the actor.

6  The design itself was pretty simple.  The lift platform was a plywood
box that ran in 1x4 L girders.  The lift platform had some UHMD plastic
bearings to bear on the L girders.  The box was lifted by two 1/8" aircraft
cable liftlines rigged as a double purchase (sheaves were mounted on the
box, lines deadheaded to the beams above and returned back down to the
winch.

hope this helps

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Kim Hartshorn
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