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Threaded pins are key on new all-terrain wheelchair

Threaded pins are key on new all-terrain wheelchair

Now in full production, the world's first all-terrain wheelchair relies on a clever fastening system to connect its unique drive levers to the drive train.

In their standard design format, wheelchairs are almost impossible to use on the majority of woodland and country paths. This means that many wheelchair users find themselves extremely frustrated by the limitations imposed on them by the mobility of their chair. Tim Morgan, managing director of Mountain Trike, recognised this problem and designed the world's first, truly all terrain wheelchair.

The basic blueprint for wheelchair design has remained relatively unchanged for the last 100 years (discounting updates in the materials used). Two larger wheels are located at the back - allowing the user to propel himself by pushing the wheel - and two smaller wheels are located at the front for stability. Whilst this creates a stable and comfortable ride on smooth surfaces, it makes it almost impossible to move the wheelchair across uneven, muddy or steep terrain. Even when pushed by a companion, the lack of suitable suspension and tyres means that the ride is extremely uncomfortable and the wheelchair is liable to suffer damage.

In recent years, attempts have been made to adapt the wheelchair design for use off-road. These designs usually incorporate the standard wheelchair platform but include mountain bike style tyres or suspension. This still makes self propulsion awkward as the wheel rims quickly become dirty and slippery. Steep hills are also hard to negotiate without tipping backwards due to a lack of rear stability. In contrast, the Mountain Trike has been completely re-designed from the ground up and resembles a high-end mountain bike as much as it does a traditional wheelchair. It employs a unique lever drive system that allows the user to power, steer and brake the Trike using two levers which are positioned in front of them. The levers are connected to the wheels using similar technology to that found on a mountain bike and power each wheel independently. A third wheel at the back stabilises the chair and can be steered using a joystick mechanism attached to one of the levers.

Morgan comments: "The Mountain Trike has been designed to be useable in the harshest conditions possible, including deep mud and steep downhill tracks. This has led to a radical redesign of the traditional wheelchair through the use of levers to drive the chair. These levers have to be able to withstand a great deal of force as they propel the Trike forward but also help to prevent roll back when climbing hills.

"However, in order to reverse the Trike, the levers have to quickly and reliably disengage. I had to source a pin component that users could quickly engage and disengage, even when extremely muddy, and that I could rely on to survive day after day for many years. I was aware that WDS has a vast range of standard parts and that the 3D CAD files are available to download from the website. This allowed me to source my parts quickly and check that they would be suitable prior to order."

Morgan specified M6 studs and handles which he uses as the locking pin for the drive levers. The handle features an ergonomic, Bakelite finish which is weather resistant while the thread insert is galvanised steel. The stud is manufactured in-house by WDS using high-tensile steel. The combined weight of the two components is 27g which is important for applications where weight needs to be kept to a minimum. The metal threads are extremely tough, meaning that they won't become stripped or shear during use.

Because WDS manufactures many of its products and keeps its warehouse stocked to maintain optimal stock it is able to satisfy 95% of orders for next day delivery. The company is also able to accept orders of any quantity without a small order surcharge. It's this level of availability and reliability that allows SME manufacturers such as Mountain Trike to place orders with WDS to suit their current schedule without fear of extortionate costs or late delivery.

Morgan adds: "The ordering process through WDS suits our business model down to the ground. We're turning around almost 100 Trikes a year which means we work our way through stock relatively slowly. Thanks to the flexibility of WDS we are able to order small batches as we need them rather than tying up capital in larger orders which can sit on the shelves for months."
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