One wheelchair for all situations

Test driver Raffael smiles. He is the first person with a walking disability that gets to drive up a flight of stairs with the Scalevo wheelchair – in reverse on two caterpillars. That is almost like floating. At the top, the journey continues on two wheels; the system is self-balancing. The wheelchair is a prototype of ETH Zurich and is currently not on the market yet – unfortunately. For many persons with walking disabilities, everyday life is filled with barriers. They usually have to circumvent curbs and stairs. Ten Swiss students want to change that. In the future, no obstacle should prevent the freedom of movement of wheel-chair users. The budding engineers developed a new type of wheelchair, within just a year. A masterpiece that took up practically every free minute of the students’ time. It was worth it. The first feedback received from persons with walking disabilities all over the world is positive “and many want to purchase our wheelchair already,” says machine engineer Carlos Gomes.

It starts

Actually, Gomes and his colleagues only wanted to build a robot that can climb stairs. But their professor encouraged them to go a step further. That is how the eight engineers of ETH Zurich started with the development of a stair-climbing wheelchair in the summer of 2014. It had to be very maneuverable, easy to operate – and, above all, safe. Additionally it should look good. The team recruited reinforcement: two industrial design students from the Zurich University of the Arts. And then they got started. The basic principle was found quickly. During normal operation, the wheelchair should drive on two wheels, like a Seg-way. They planned to overcome the stairs with caterpillars that can be extended and retracted. The wheelchair is called Scalevo and unites two motion principles in one: a hybrid chair, so to speak.

The practical test

Finally, this is what it looks like: The wheelchair user approaches stairs and selects the appropriate function on the touch screen. With sensors and cameras, the chair measures the incline of the stairs and automatically drives up to them in reverse. The caterpillars lower. They start to turn and move the wheelchair up the stairs. Speed: one step per sec-ond. The driver stays in a straight position the entire time. As soon as the sensors detect the end of the stairs, stabilising wheels move into position. Thus the wheelchair cannot tilt over. Then the caterpillars lift up and the wheelchair continues the journey on two wheels.

The wheels and the caterpillars are equipped with two maxon electric motors that act as drives. Brushless DC motors are used in combination with ceramic gearheads. Ceramic is always a good choice when high forces act on the components, yet the gearhead has to be very durable. Carlos Gomes and his team are enthusiastic about the drives that maxon provided to them: “The motor-gearhead combination is strong, precise, quiet and, at 3.2 kilograms, relatively light. The maxon engineers gave us expert advice and the support was excellent.”

The key to success

The students are very satisfied with their work. “Good teamwork was the key to our suc-cess,” says Gomes. Additionally, they implemented the suggestions of many persons with walking disabilities, like adding a belt or inclining the seat backward slightly, so that the wheelchair user does not slip forward. “We would never have thought of such details ourselves.”

Time to face the competition

It is not the end yet. Even though the project could be considered finished. In the autumn of 2016, the engineers compete in the Cybathlon in Zurich with their Scalevo wheelchair. This is a competition where people with disabilities compete against each other.

Technical aids are not only permitted but actually encouraged. After all, the intention of this event is to motivate researchers and engineers to invent better and more affordable wheelchairs, prosthetics and other aids.

A vision for the future

The Scalevo team is sure: They want to win the Cybathlon in the wheelchair category. Some modifications to their device are necessary. The suspension of the caterpillars has to be made stiffer, the operation more intuitive, the reliability has to be increased. Then everything is possible. Perhaps the young inventors will found a start-up, who knows? The idea is in place. If they do, the new wheelchair with its integrated caterpillar might be avail-able on the market soon. Astonished glances? That’ll be a thing of the past when it be-comes normal that wheelchair users cruise up and down stairs as if it is the most natural thing in the world.

 © maxon motor ag