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Zippermast – tape measure meets zip

The remote-controlled caterpillar vehicle stops just in front of the head-high wall. Then, a mast extends upwards from its interior on top of which a small camera is mounted. A few moments later, it has an unhindered view of the events behind the wall. The Bavarian company progenoX supplies the vehicle for unmanned exploration, and a highlight is the extremely compact Zippermast which consists of three interlocked steel tapes following the zipper principle. A motor from Faulhaber provides the unique design with reliable retraction and extension.

“Everyone who sees the Zippermast for the first time is amazed at how high it can be extended,” says Frank Woodcock, general manager of progenoX. Thats because the housing where the mast is hidden is very small: the smallest model, the ZM4, is just 15 centimetres high and the standard model, the ZM8, is 25 centimetres. How far the mast can be extended can be seen from the model number – it corresponds to the height in feet. In the case of ZM8, which is easy to carry with its weight of seven kilograms, the mast extends to around two and a half metres. The mast of the ZM40 reaches a height of more than 12 metres.

Inspired by the tape measure

The trigger for the development of the innovative telescope technology was a request from the American armed forces. They were searching for a particularly compact and robust system which can be used on unmanned vehicles. For the design of the Zippermast, its developer, George Woodruff, was inspired by the metal tape measure which is under tension due to its curvature and can therefore be extended without kinking. Woodruff used three steel tapes and interlinked them when extending according to the zipper principle. In this way, the flexible tapes become a stable mast.

The three tapes made out of spring-tempered stainless steel are wrapped around coils and arranged in relation to each other at angles of 120 degrees. A guiding spindle, which is in the middle of this tri-angle, grips the tapes in the bevelled slots provided. The tapes are rolled upwards by the rotation of the guiding spindle. Their jagged outer edges interlock with each other. The Zippermast can be extended to any position in-between. No additional locking mechanism is required to hold this position: the weight of the tapes and the load rest on the guiding spindle’s thread which can only be moved by rotation, like the nut on a screw.

“When I saw the Zippermast for the first time, I was immediately excited by the design principle”, recollects Woodcock. He acquired the technology in the USA in 2012 and brought it to Germany. He reworked the telescopic mast with his team from progenoX and got it ready for series production.

Customers are mainly the so-called blue-light organisations such as the fire service, emergency service, disaster control, civil defence and the police. They mostly deploy the masts for monitoring and surveillance purposes – hence in the area for which it was originally designed. But the Zippermast has also proven itself to be useful at other tasks, such as inspecting pipes and shafts. Thus, it is used in nuclear power plants in order to search the ventilation systems for cracks and foreign objects.

Space-saving and stable

Thanks to the coiled tapes, the Zippermast only requires a very small housing. Another advantage of this design is that the diameter of the Zippermasts remains constant in any position across its entire length – unlike telescopic masts which consist of components nested into each other. Thus, enough space in the interior of the masts remains to lead the cable through the guiding spindle to the head and be protected from outside influences.

Furthermore, its design principle makes the Zippermast extremely stable. This sturdiness is increased further by heat treatment of the steel tapes. To do this, coiled tapes are heated on the coils and subsequently cooled again. The crystal structure of the steel adapts itself to this position and seeks to adopt it. Tension is therefore generated by rolling up the tapes which further stabilises the mast. Thanks to its stability, the Zippermast can also extend horizontally and be loaded. progenoX has done a lot to make the Zippermast fit for everyday use. The steel tapes are coated with a special surface coating in order to minimise wear. The guiding spindle is hardened in a heating process, the electronics moulded. Furthermore, the originally used spindle motor has been replaced. “When selecting the optimal drive, we received outstanding technical support from Faulhaber,” emphasises Woodcock.

As the Zippermast is often used under the most severe conditions, it must have a particularly robust and long-lasting motor. Furthermore, it was important to achieve very high performance at low volumes. “The motor which drives the guiding spindle had to be housed in the space between two of the three coiled steel tapes and could only have at most a diameter of 32mm,” recollects Andreas Eiler, who supervised the project at Faulhaber.

Nevertheless, the DC-micromotor had to deliver high output torque in order to extend the mast quickly even when loaded. They therefore jointly decided to use a Faulhaber DC-micromotor. This provides a rated torque of 120mNm with its powerful rare-earth magnets. The Zippermast also requires a very powerful drive. Here, the choice fell on a Faulhaber planetary gearhead. “They are made solely from steel components,” emphasises Eiler.

With this, the motor can also work reliably under the most adverse conditions and it has an extremely robust housing made from highly-resistant plastic. The DC-micromotor thereby fulfils the requirements for protection class IP68, keeps both dust as well as water away and is resistant to chemicals, UV and infra-red radiation. The Faulhaber DC-micromotor also drives the sea-water resistant variants of the Zippermast which can be integrated, for example, in a buoy in the sea. Woodcock even believes application in space is conceivable, and he has already applied to participate on two projects.

“The Zippermast can be used as a boom for small and medium-sized satellite antennas or optical devices, for example,” he says. “In addition, we are working together with the company ODG- Argo who supply robot vehicles to the NASA and CSA space agencies. We have just installed the Zippermast on one of the Argo robots which may be used for a planned Mars mission. I figure we have a good chance to be involved in one of these space projects.”

Faulhaber motors and gearheads are available in the UK from EMS.

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