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December 2016

Using gears in the military


Over the next decade, the UK will spend £178 billion on military equipment. This equipment may range from torches to high calibre weapons, but it all requires high quality manufacturing and the ability to adapt to a variety of conditions. Much of this equipment requires high precision gears, as Graham Mackrell, managing director of Harmonic Drive UK, explains. 

In the military, all equipment must be able to cope with a range of environmental challenges, including extreme fluctuations in temperature, high levels of rainfall and sandstorms. Reports show that British troops in Iraq were exposed to temperatures of over 60 degrees Celsius and at the other end of the scale, Indian troops have been given specialist gear to help them brave temperatures of up to minus 50 degrees Celsius. 

To combat this issue, products for military applications must be manufactured with extreme temperature variations in mind and be built using the right materials. For electromechanical equipment that includes moving parts, engineers must also choose the right lubrication to ensure that gearing systems remain functional under severe operating conditions. Take Harmonic Drive’s Flexolub M0 lubricant, for example.  It is effective at temperatures ranging from -70 degrees to 150 degrees Celsius. 

Because military equipment is often used outside, it must be resistant to all weather conditions such as heavy rain in the tropics. The parts must have corrosion protection, either through a paint coating or other finishing or they should be made out of non-corrosive materials. To protect them from weather conditions such as a sandstorm in the desert, gears should be adequately sealed and have a suitable level of ingress protection. Sand can cause pitting and corrosion on the surface of the equipment, so it is essential that gears and actuators are fully sealed to protect them against harsh weather environments. 

Another challenge for military equipment is that it often travels over rough terrain and is subject to high levels of shock and vibration especially on tracked vehicles and this needs to be managed through good design. Harmonic Drive gears and servo actuators have a rugged output bearing which is able to withstand high loads and  effects such as vibration. 

Military gears, and all military equipment must be reliable. Of course, in the heat of battle, operators need to trust that the equipment will work correctly. A study by Arthur J. Alexander found that improving reliability has a number of benefits. It has “direct effects on maintenance time and manpower, spare parts usage and investments, operational availability, logistics loads and life-cycle costs.” By using high precision gears with a low part count, military engineers can reduce the amount of maintenance required and increase reliability, bringing them the benefits as explained by Alexander. 

Bomb disposal robots use Harmonic Drive military gears for their high levels of accuracy and zero backlash. As the gears are lightweight and compact, engineers can easily fit them in a robot without dramatically increasing its size. They are used in the CUTLASS robot, which has eight axes on its 2.6m long arm. The length of the arm means that any errors, which come from the base of the robot are magnified when they reach the end of the arm. 

Accuracy and repeatability are vital in such military applications, where they can ensure the threat is safely managed and the robot’s operator is not under any danger. 

There are therefore a large number of factors to consider when choosing a gear or servo actuator to integrate into military equipment. While there is a high level of military spending, which offers many opportunities to companies looking to produce equipment for this sector, they must consider the high levels of reliability and accuracy that are required in often tough environments.