The Crane

This is the Crane.  It is designed to span the gap between two tables or other raised platforms.
It consists of two drive modules at the bottom with support beams going up to the lifting mechanism
at the top.  

The two drive modules are built the same way, but the left one has been modified so it can hold the
RCX.  They are powered by standard Mindstorms motors, which power wheels on the bottom.  The motors
have a half bush to medium pulley connection to both sides, then a 16-tooth to 16-tooth gearing on
each side simply gets the wheels lower down.  This drive system enables the Crane to drive any
distance to either side.  

The lifting mechanism at the top is powered by the Racers motors from the Hot Flame RC.  Two motors
were used to give greater power and speed.  Each motor is geared down 1:9 with two 8-tooth to 24-tooth
stages.  The lifting string is tied to a pulley on each side and wraps around the axles as the load is
raised.  The string is looped between the hook and upper support axle four times, giving a mechanical
advantage of four.  This enables heavier loads to be lifted.  The lifting mechanism has a lot of
friction, unfortunately, probably because one of the geared axles is also the axle that holds the
side and top beams together.  

The angle at the top is made by the four 4x6 angle beams at the four top corners.  The drive motors are
both connected to the same motor port, the far motor's wire being run over the top of the Crane.  The
lifting motors are connected two the other two ports.  The Crane does not use any sensors.

The heaviest weight I have lifted is the one in the pictures.  According to my precise laboratory
balance, it has a mass of 1045.25 grams.  In the earth's gravitational field, this can be converted to
pounds...one moment please...which comes to 2.29997 pounds.  (Is that precise enough?  :)  )  The total
motor run time for lifting, moving, and setting down the load is 33.0 seconds.  Since I put a wait of one
second in between each activity, it takes slightly longer actually.  The load is lifted one foot off the
ground, and the Crane drives over a foot to the side as required.  If I had enough room, the Crane could
obviously drive any distance to the side.