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Taking wheelchairs off road

Taking wheelchairs off road

A linear position sensor is being put to full use by the innovative all-terrain electric wheelchair manufacturer Molten Rock.


With a distinctive and ergonomic design that allows users easy access and straight-forward operation, the electrically powered Boma7 off-road wheelchair from Molten Rock enables simple outdoor activities such as walking a dog or visiting a local park, but is equally at home as an all-terrain wheelchair for use in more challenging landscapes. Harsh weather environments and steep gradients with mud, rain and ice mean that the chassis, suspension and especially the steering mechanism are subjected to high levels of shock and vibration.

When looking for a steering position feedback sensor to form part of the servo control system for the joystick operated version of the wheelchair, Molten Rock turned to Variohm EuroSensor. Molten Rock's designers chose Variohm's ELPM linear position sensor to match the high demands of the steering system specification which includes a robust Linak linear actuator and a Dynamic Controls joystick control system. The ELPM's pedigree as a compact solution for motorsports position measurement for ride height, suspension and steering angle measurement helped the company decide on putting the slimline miniature sensor through its paces with impressive results.

Molten Rock company director Chris Swift explains: "We have been producing the joystick version of the Boma7 since 2010 and from development through to full field use the sensor has been thoroughly tested on the wheelchair and has performed very well under a range of conditions."

As a heavy-duty and competitively priced motorsports position sensor, which also suits applications in harsh environment industrial, agricultural and construction equipment, Variohm EuroSensor's ELPM is available in measurement ranges from 12.5mm to 150mm with independent linearity to ±0.5%. ELP potentiometric series sensors feature a conductive plastic resistance element built up by the application of several layers of specialised printed inks combined with a wiper assembly with an elastomer damped multi-fingered precious metal brush arrangement. This patented measurement technology ensures smooth and uninterrupted contact with low electrical noise under the most demanding physical and environmental conditions.

The sensors also include an improved felt seal and O-ring sealing arrangement providing the ELPM with an IP67 protection, a 150ºC upper temperature rating (175ºC short term), and a serviceable rated life of more than 25 million operations. The lightweight miniature slimline sensor features self-aligning spherical bearing mounts and impressively compact retracted mounting distance for straightforward installation. An optional quick release version (ELPM-Pop) includes snap on fittings for very fast replacement.

Molten Rock Equipment was formed in 2004 by a group of wheelchair users who were frustrated with the limited capabilities of assistive equipment that did not reflect their lifestyle interests in adventurous outdoor sports.
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