The stairs to be negotiated have one 90-degree bend at the top landing and a sufficiently spacious lower landing. The ceiling height exceeds 2.3m (7ft 6in). This lends itself to constructing a rectilinear suspension track to transport the individual in the hoisting sling between two wheelchairs, one positioned at the lower landing and the other wheeled onto a simple platform at the top.
The support structure consists of five gantries attached to the floors and the stairwell (Figure 1). A winch provides both hoisting from and to the chairs and translation along the track (Figure 2 left-hand side). The critical components permitting to realise this solution with just off-the-shelf parts and wood are the trucks and wheels of a skateboard. A carriage, very much like an upside-down skateboard, runs on an L-shaped track suspended from the gantries (Figure 2 right-hand side).
The design philosophy hinged on three principles:
- Components choice and dimensioning were based on the mechanical properties demonstrated in other applications, eg skateboard trucks are designed to withstand shock forces far exceeding our requirements.
- A simple design with a minimum of components kept the system transparent and the manufacturing effort low. The design method was heuristic with many details being worked out during manufacturing.
- The validation approach was empirical, meaning that parts and assemblies were tested during construction with twice the expected service load (equivalent to 125 kg).
Note that a fourth critical principle is being applied: Since the device has been in service it is closely monitored and regularly inspected.
Thus the lift could be built on a 450GBP materials budget and in short time using only DIY hand tools (hand saw, jig saw, hacksaw, drill, drill press, files, wood chisel, hammer, screw driver, level and measuring tape).