July 17, 2012 Volume 08 Issue 27

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Micro-motion solutions:
Microdrives excel in hazardous terrain

The timely tracking down and disarming of bombs, IEDs, booby traps, and other dangerous munitions from the extremist arsenal is most definitely a job for the professionals. Conducting thorough reconnaissance to avoid calling in the specialists unnecessarily and to ensure a confirmed threat is handled as safely as possible is an essential element of this process. In this scenario, special remotely operated devices can drastically reduce the risk to the human beings involved in such activities, with high-precision micro motors replacing manpower to undertake the necessary hazardous operations at the bomb scene.

AB Precision (Poole) Ltd., a U.K. company based in Dorset, has been supplying the British Ministry of Defense since the mid-1960s. To respond to the currently heightened risks in tracing and defusing explosive devices, the experts from Dorset developed the latest generation of their Guardian MROV (Miniature Remotely Operated Vehicles). The modular miniature vehicle is designed to carry additional equipment as required. Universal deployment capability also means that it has to cope with any terrain - which includes not only grass, gravel, and dirt, but inside airplanes, trains, and buildings.

Compact design in demand
Equally important is the compact design, so that it can be maneuvered in narrow passages (e.g., in trains, aircraft, or underground rail carriages/subway cars). With a view to accommodating as many different functions as possible in a slim-line design, including a powerful four-wheel-drive transmission, ABP's security experts collaborated with microdrive specialist Faulhaber.

In the basic Guardian module, 15 different microdrives accurately execute the control commands. The entire procedure is managed from a control station in a carrying case. A 17-in. LCD monitor shows the images captured by the cameras, while a 10.5-in. touch screen with soft buttons and 3D imaging of the vehicle offers intuitive control of the device and any additional modules installed. The command center is rounded off by two joysticks for the drive and manipulator arm. As reconnaissance often has to be performed in confined spaces, a compact design is essential.

The dimensions of the vehicle - 417 mm (tracks), maximum length 1,280 mm (extended), and height 504 mm - are designed to facilitate navigation in narrow passages. In addition, the reconnaissance radius has to be as large as possible. Therefore, a telescopic arm extends the reach of the pan-and-tilt head up to 2.10 m. At the same time, the head can also be lowered so that it can inspect vehicle underbodies. A low center of gravity and sturdy caterpillar tracks provide a stable base for sharp, shudder-free images as well as accurate manipulation using the cantilever head. Depending on the terrain involved, the chassis can also be fitted with wheels, allowing it to move faster on solid ground to enhance mobility.

Highly flexible thanks to modular design
The complete vehicle can be quickly assembled at a safe distance from readily portable modules. This makes it easier to transport and allows the experts to deploy the right tool for each individual situation by choosing a particular module. Apart from the four on-board cameras providing color images, there are numerous other modules available, such as various hardware devices (e.g. lock-pick gun, x-ray unit, water jet, and many more). Additional equipment can be transported in an optional trailer.

Customized solutions from the modular drive set
The drives used in this system are just as diverse as the range of applications. However, all of them must meet certain general requirements such as absolute reliability, compact design, and high performance combined with high-precision handling and the greatest degree of efficiency for long battery life. In a nutshell, the product philosophies of the Guardian and the Faulhaber drive motors are very similar. Both rely on a modular product to ensure the widest possible range of applications.

This similarity is also reflected in the deployment of the 15 drives. Motors and gearheads are selected depending on the task at hand and combined to meet the required performance. For example, each of the four drive modules is powered by a 38-mm-diameter motor with matching diameter planetary gear. With over 200 W and around 150 mNm at the motor shaft, the combined motor output of 1 metric HP is more than sufficient to move the vehicle and its equipment through terrain or over inclines. Two structurally identical motors with different reduction ratios are also responsible for raising and lowering the telescopic arm. The wide range of gear ratios allows the ideal output torque and speed to be selected for both operations. Smaller 32-mm motors with an output of around 80 W extend and retract the telescopic arm. To keep the weight of the head low, light 26-mm diameter, 44-W drives perform the turn-and-tilt function. The camera and optional weapons, on the other hand, are actuated by two identical drives 23 mm in diameter and with around 20-W output. Depending on the function required, the manipulator works with a 23-mm and 26-mm drive. All motors come in rugged, DC brush design and are therefore capable of starting even at very low voltages. The comparatively simple yet robust drive control system using pulse-width modulation is also ideal for this application.

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Published July 2012

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