The London Eye
Built by Alan Wenbourne in September 2008
Read an in-depth article about this model.
A ‘Mini-Version’ London Eye
This model is called a ‘mini version’ because its elements are not proportional. The wheel is to a scale of 1:120 and the capsules are 1:45 scale. This enabled the degree of detail that I wanted to produce in the capsules, on a wheel size that fitted into my car!
The London Eye has 32 capsules on a wheel with 64 inner spokes and 16 outer spokes. My model has 12 capsules on a wheel with 24 inner and 6 outer spokes. The ratio of the scales is 45:120 (3:8), as is the number of capsules at 12:32.
The capsules are 3½” diameter which rotate on four ½” Pulleys each end, rolling inside two 2¼" x 3½” Circular Strips that attach to the capsule mounting frames on the wheel periphery. Bent and curved Narrow Strips replicate the glazing. A 3½” Gear Ring forms part of the capsule levelling system. Four capsules are geared to a stationary central Gear Ring mounted at the wheel hub; from each of these a peripheral drive is taken to the leading and following capsules. 24 Universal Couplings are used in the capsule levelling drives. All the capsules are readily demountable for transportation.
The wheel is constructed from 64 one-metre lengths of Ø4mm stainless steel rod cut to size. The outer wheel rim is a circular truss of triangular cross section 34” diameter. There are 72 structural nodes formed by Three Hole Collars, secured to the three main hoops. Each node is the junction of up to six structural members using Rod & Strip Connectors, of which 600 were used altogether.
The two outer hoops are constrained by 24 axial rods attached by Short Couplings each end. The wheel hub is formed from Boiler Centres, Wheel Flanges, 12-hole Face Plates and Large Axle Bush Wheels strengthened by four Screwed Rods connecting each side.
Wheel assembly was assisted by a full size layout, drawn on an MDF board, onto which MDF brackets located the three main hoops in true position whilst fitting the interconnecting structural members. The finished wheel runs true to within +/- half a rod thickness.
Additional hoops each side of the rim forms the drive track for wheel rotation.
Twelve capsule mounting frames attached to the wheel’s outer structure replicate the original arrangement, providing four mounting points per capsule and a Bevel Gear/Pinion drive for capsule levelling. The overall diameter of wheel and capsules is 48”.
The supporting structure is an A frame inclined at 65° to the horizontal, made of cruciform Angle Girders encased in Cylinders of various lengths. These sit on small towers at their lower ends and are strengthened with Flanged Sector Plates at the top. The wheel spindle housing carries a Large Axle Rod and is hinge mounted to the top of the A frame. Unfortunately, the Large Axle Rod bends under the 40lb weight of the wheel and capsules, so I had to concede to using an outboard prop to keep the wheel axis level.
The four main restraining cables are replicated using 3.2mm nylon cord, but sheave strung, rather than separate strands, to maintain equal tension in each. The two restraining cables from the tail of the spindle housing are similarly reproduced, all six being anchored within a protective housing at ground level, that also incorporates Screwed Rod tensioning arrangements. The remaining four cables from the rear of the spindle to the lower A frame legs, for leveling the spindle, are represented but not active due to the prop serving this purpose.
The machinery towers and curved decks carry the 16 drive wheels (8 each side) on the north end of the wheel. Each set of four drive wheels is driven from a single 37 RPM geared motor, driving through 4:1 Meccano gearing to each (double) drive wheel via four ½” Pinions, allowing the drive wheels to oscillate to compensate for any drive rim irregularities.
I used double ½” Pulleys with Tyres to provide better tracking of the rod forming the drive rim. Each pair of drive wheels (upper and lower) is manually retractable by a ratcheted lever, so as to facilitate removal of the machinery for demounting the main wheel and for transportation of the separate modules. Between the drive wheels are a set of six retractable and spring loaded guide wheels. These are hydraulically applied on the London Eye to control transverse movement due to wind loading (and hence alarm to the riding, boarding and departing passengers!).
The tower on the south-west (river) side of the London Eye carries duplicate electrical pick-up equipment which feeds a five way bus bar around the outside of the wheel to provide electrical power for lighting, air-conditioning and capsule levelling motors etc. I have modelled this equipment for authenticity only, as I am not intending to feed electrical power to the model wheel. Both the London Eye south towers have the stabilizing guide wheel sets, which are reflected in the model.
The boarding platform is curved to match the path of the capsule footsteps and incorporates the ramped entrance and exit aisles of the actual architecture.
The London Eye makes one revolution in 30 minutes; the model rotation is once every 4.5 minutes, this complies with the physics of scale which state that time in the model world is equal to real time divided by the square root of the scale, i.e. :
t = 30/√45 = 4.5 mins
The model is mounted onto a 54in x 36in MDF board which incorporates wooden supporting features for laying the ‘A’ frame and wheel flat for transportation.