24 February, 2024

Selecting precision motors for smart defence applications

12 February, 2024

Developing the latest smart munitions, today’s military contractors rely on specialist manufacturers to provide critical control and actuation. The motion solution is central to ensuring targeting accuracy, and while each specific smart defence application has its own unique challenges that demand an exacting approach, the design will essential attributes common across applications. Whether utilising a bespoke or customisable off-the-shelf (COTS) approach, this makes motion solution design a critical requirement for smart munitions. H&P reports.

Precise control for missiles and guided bombs, as well as for the seekers that maintain their path, is imperative. In these most critical situations, it is also essential that the motion control solution is reliable, as well as safely integrate with the avionics and electronics within the wider aircraft or launch system.

Actuation control in use

Vital to the position of control surfaces on a missile, a control actuation system makes high speed adjustments to the fins or canards based on the inputs from the missile guidance system. Similarly, the extension of a wing deployment system on a guided bomb is vital to achieve the desired range and targeting.

The priority in motion design for both of these systems is precise control to actuate the flight surfaces with speed and smoothness which is key to determining whether a missile or guided bomb will strike its intended target. This control must be achieved within an extreme temperature profile, ranging from a low of -55°C to an excess of 100°C, and the motion solution must also withstand high levels of shock and vibration during operation. This reliability must be maintained through a long storage period that could extend to more than 20 years. Working in a compact space and weight envelope, low mass and a small footprint of the motor are also compulsory.

The electro-optical or infrared systems in missile and guided bomb seeker heads (also used in vehicles and land-based guided munitions), demand similar characteristics. To achieve target accuracy, the azimuth, elevation, and zoom axis motors must precisely coordinate, and it is imperative that the system performs in the most demanding environmental situations. Here too, footprint, mass, and electromagnetic compatibility (EMC) compliance are imperative. Even if the overall duration of use is short, the limited onboard power budget requires a high-efficiency motor to minimise power draw from the vehicle power system.

Designing the motion solution

Typical motor choices for smart defence applications include brushed DC coreless designs, as well as brushless cylindrical and flat motors. The brushed DC coreless motor includes a coil arrangement rotor, free of iron laminations, and a stator with fixed magnets. Meanwhile, brushless DC (BLDC) cylindrical motors utilise a stationary coil with a rotating permanent magnet and coil windings as part of the stator, and these designs remove the need for brush commutation. In addition to the cylindrical designs, a BLDC slotted flat motor includes coils in lamination slots, but unlike their cylindrical counterparts, they incorporate an outer rotor in a flat architecture.

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