Motorised Bradshaw Buggy
The client is a bilateral above the knee amputee and uses one of the Bradshaw buggies owned by the Riverside Indoor Bowling Club (RIBC) in Winchester. He can just manoeuvre the chair using the wheel rings but isn’t strong enough to do it for an entire game. The wheels are low down and inboard of the seat so they chair can be used for its primary purpose of bowling. However it makes it tiring to propel manually.
The sponsor had asked if the chair could be fitted with electric propulsion. It was agreed that this would be the solution. However the Bradshaw chair is relatively compact and there wouldn’t be a lot of space to mount motors and batteries. The wide wheels of the chair also restricted access to fit pulleys or sprockets for any drive system.
The wide wheels did provide a large area for a friction drive system and this was the solution adopted. A pair of wheelchair or mobility scooter motors where obtained as used items, along with the joy stick controller, and most of the harness. A system was devised to mount the motors on pivots such that a 150mm (6”) diameter drive wheel would bear on the surface of the chair wheels.
The original wheels driven by the motors and gearbox where circa 8″ (200mm) dia and that scooter would have had a top speed of 4mph. Using 150 mm dia driving wheels reduced this to 3mph on the adapted buggy. This was considered sufficient for the application. The 3D printed plastic driving wheels bolts onto the original wheel centre hubs.
They are fitted with rubber sheet ‘tyres’ to drive against the smooth plastic main wheels. Contact is maintained by the use of elastic cords pulling the motor and drive wheels forward. This maintains good contact despite any eccentricity in either wheel. At the time of writing the system appears sufficient but will be monitored to ensure it withstands the rigours of use.
Another design aim was to not modify the existing buggy frame. This would ensure that the weight bearing capability of the frame was not compromise and would allow the modifications to be transferred to another Bradshaw buggy if necessary. This was largely achieved, however it was considered necessary to replace a couple of spring clips with bolted connections as they bore the weight of the batteries.
The controller is mounted on the left hand arm rest allowing the right hand side to be used for bowling. In common with other electric wheelchair controls the speed and direction are controlled by the movement of the joy stick. The advantage of using a complete mobility scooter drive system is that it immediately solved problems of control and connection for charging. These are inbuilt into the control unit fitted to the arm rest. Its operation is familiar to the client who has a ‘standard’ electric wheelchair, but in any case is intuitive.
The batteries are mounted to the foot rest with securing straps and terminal covers. This position is dictated by the limited space on the buggy, but has the advantage of balancing the weight of the motors at the rear. One important feature of the chair when used for bowling is that it pivots forward onto the front platform and stops the chair moving when the ‘wood’ is delivered by the bowler. Maintaining the balance was considered important.
The motor mounts where constructed from steel angle & tube welded together. Many parts where 3D printed in various grades of plastic, including the driving wheels, various retaining clamps and the battery terminal covers.
Finally a system is provided that completely disengage the drive to allow the chair to be wheeled manually when the control system is turned off. Without this the motors and hence main wheels are locked in place. This is a safety feature common to electric wheelchair drives.
The client is now able to bowl independently and more frequently as he will not be reliant on the availability of volunteers to push him up and down the arena. He is very happy with the additional freedom and the help in maintaining his independence.