Tuesday, 18 June 2013

Counterbalance arm

The counterbalance arm has now been completed.  This is bolted to the central triangular frame by means of 10mm stainless steel bolts, since the angles which upper and lower chords make with the vertical are not 90° (and are different in each case). This would make a joint with multiple 4mm bolts very difficult unless one drilled a lot of non-standard holes (I reckoned a single non-standard bolt was better than this).  These 10 mm bolts fix into deeply embedded straps on either side (the two units being joined, that is).

At the far end of the counterbalance arm the two winding drums can be seen.

Each drum is driven by two window winder motors meshing directly onto the drum’s 8", 99 (large) tooth gear wheel as seen.  These drums are now motorised and revolve at about 7 rpm.  Also visible in the photograph is a servicing crane for the winding drum area, motorised by three meccano 6 volt motors, one each for slewing, elevation and hook position.

Servicing crane for the winding drum area

Workshop/store building
Just behind the triangular frame is a large workshop/store building 5 foot by 18½" by 7½". The floor of this structure is formed from 2 large plates (which were once the sides of an old electric stove which I scrapped!).  The side are largely flexible plate made from recycled spray paint cans.  It is therefore quite light, but pretty rigid.

Note the extensive use of compound girders in the mainframe structure. These are slightly heavier than those used in the bucket-wheel arm (some 1" flat girders being replaced by 1½" ones).  This follows the prototype.  The reason is that distances between main joint knuckles are quite a bit larger than in the bucket-wheel case and, according to Euler’s theory of buckling, the tendency to buckle goes up with the square of this distance.

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