When testing wheelchairs, manufacturers play it safe for understandable reasons. That three budding mechanical engineers took no chances when they developed a drop test construction for wheelchairs on behalf of the renowned German company MEYRA test construction for wheelchairs on behalf of the renowned German company MEYRA.
To protect the inner workings of their construction, they relied on miniature shock absorbers from ACE construction.

Arne Hankemeier, Julian Raimann and Tobias Ridder recently completed their training as
state-certified technicians specializing in mechanical engineering at the Felix-Fechenbach-Berufskolleg vocational college in Detmold. Volker Geise, who is responsible for education management there, notes that the proportion of practice-oriented work is very
important in the mechanical engineering department of the vocational college. He therefore welcomed the fact from the outset that his three graduates wanted to work closely with the nearby company MEYRA GmbH as part of their final thesis.

As a member of the internationally active MEYRA Group from Kalldorf, the company is one of the leading manufacturers of high-quality wheelchairs and has also made a name for itself as a provider of rehabilitation equipment. In line with its claim "We move people", MEYRA supports and motivates many people with disabilities around the world to achieve greater mobility and independence. The constant exchange with those affected as well as with medical professionals and those from therapy and care also enables MEYRA to develop practice-oriented products, not least in close cooperation with the specialist medical supply trade. This holistic, hands-on approach suited the study group at the German university very well, although there was another connection: Tobias Ridder, one of the three young talents, was already working as a designer for custom-made products at MEYRA when he decided, together with Arne Hankemeier and Julian Raimann, to develop a professional drop test device for wheelchairs as his final thesis at the university. With the full support of his employer, they set about building a structure that would primarily be used to test the load-bearing capacity of MEYRA's new wheelchair models.

Requirement: high load capacity

The test facility is designed in such a way that each wheelchair is first loaded with the maximum permissible weight and then driven into the structure. Each model is then latched onto a gripper and pneumatically lifted and dropped from a predefined height after latching. In order to dampen the force of the lifting device's impact plate and protect their entire construction, the three technicians considered installing shock absorbers. The aim behind this plan was not only to prove the stability of the wheelchairs, but also to ensure that the test device itself was as stable as possible and did not have to be repaired after just a few cycles of use.

In an interview, the students said that they were aware of one of the main advantages of hydraulic damping elements, namely that they work without rebound effects due to their linear characteristics. "Thanks to a presentation by ACE Stoßdämpfer GmbH, which we were able to attend as part of the class, we knew that certain shock absorbers can not only better solve the tasks of deceleration in terms of their damping properties, but also help to reduce the risk of damage.but also help to make the tests quieter than before, especially when you compare the damping tasks with the performance of steel springs or rubber buffers," recalls Arne Hankemeier.
As ACE offers dimensioning tools on its homepage:         www.acecontrols.co.uk/uk/sizing.html and many other helpful services accompany the products, the students contacted ACE's European headquarters in Langenfeld. To their delight, the sales engineers not only confirmed the young engineers' design data over the phone, but also provided them with samples of four miniature shock absorbers free of charge. This support for young engineers has been a practice at ACE for years, as the company has found that supporting young academics and technical schools often leads to innovative solutions and even new product series.

Problem solver: Hydraulic damping elements

Once the team had received the four MC25EUM miniature shock absorbers from ACE, everything
went very quickly: thanks to their compact design, the hydraulic components are predestined to be integrated quickly, even into existing designs. Available in versions with and without diaphragm seal technology, the shock absorbers optimize a wide range of machines by braking masses quickly and non-destructively. Customers can choose between adjustable and self-compensating versions. The latter were used in this case. The outer bodies of the miniature shock absorbers are made from a solid piece of steel and filled with temperature-stable special fluids. These hydraulic machine elements have integrated fixed stops and are maintenance-free. They have been developed and perfected by ACE, the technology and market leader for industrial shock absorbers
for more than 60 years. The models used in this application have a stroke of 6mm and are suitable for an energy absorption of 2.8 Nm per cycle.

The teamwork of the three university graduates worked perfectly throughout the entire
project. Tobias Ridder was responsible for the design, while Arne Hankemeier and Julian Raimann were responsible for the construction and documentation. Ultimately, the integration of the four components sponsored by ACE was a small exercise, says Arne Hankemeier and draws this positive conclusion: "We were able to make the adjustment precisely using the continuous
thread of the components and reliably hold them in the preset positions with the supplied lock nuts. These dampers absorb the permissible load really reliably, quietly and quickly and fulfill their purpose to the full extent. In our test series, we were also very pleased to find that a wide variety of large masses can be braked almost silently and safely without rebound in the small installation space of our design.