17
7
The pedestal can be easily manoeuvred around the studio. The steering ring
is used to turn the
pedestal wheels and the steering mechanism provides two modes of operation - crab, where all three wheels
turn together, and steer, where two wheels are locked in the straight-ahead position and the third wheel steers
independently.
8
The main assemblies of the pedestal are described in more detail below.
Base
9
The base consists of a robust tubular steel fabrication which forms the nitrogen storage tank and is the
frame on which the pedestal is built. On the upper face of the tank there is a machined and tapped flange
which provides the mounting face for the fixed tube and on the outer shell are three pairs of equally spaced
mountings to which the wheel assemblies are attached.
10
Each wheel unit consists of an alloy housing supporting a twin-wheel axle assembly. The wheel pivot is
supported in a pair of ballraces and the upper end of the pivot shaft terminates in a sprocket assembly for the
steering mechanism which links all the wheels together by an endless chain. The wheels are rotatable
through 360 degrees by means of the steering ring and both the crab and steer modes of movement are
controlled by the steering ring, with changeover effected by foot-operated buttons mounted on the base.
11
The wheels are of cast alloy running on ballraces and each is fitted with a low friction, squeal-free tyre.
12
The base unit components are enclosed by contoured covers and side plates. Optional lifting handles
may be installed on the covers.
13
A continuous cable guard
surrounds the base and is adjustable for height.
Column
14
is located in a fixed tube secured to the welded pressure tank and consists
of three concentric column sections and a two-stage ram.
15
The fixed tube is a static unit bolted rigidly to the base. Four pairs of roller bearings are dispersed
around this section at 90 degree intervals, with each pair arranged one at the top and one at the bottom of the
column. Two pairs of the bearings are fixed and two pairs are adjustable. The adjustable bearings differ from
the fixed units in that they have an eccentric shaft with an adjuster, a clamping arrangement on the bearing
housing and a screw to close the clamping arrangement onto the eccentric shaft.
16
The adjustable roller bearings are positioned diametrically opposite the fixed roller bearings and are
used to take up any clearance across their individual planes of support thus eliminating any sideplay in the
column. The outer and centre tubes of the telescopic column are fitted with the same arrangement.
17
The tubes of the column are linked together by a system of chains and sprockets and cords and pulleys
which ensure that, during extension and retraction, the telescopic action is equally distributed between the
moving sections. All three stages have hardened steel bearing tracks on the outer surfaces, which correspond
with the roller bearings on the inner face of the next lower stage to form the motion guides.
18
The balancing force for the column is provided by a two-stage ram. The movements of the ram stages
in relation to each other are controlled by the movements of the outer and middle stages of the column. The
ram is connected to the pressure tank via a manifold.
