Motors

Motors are servo actuators, which, in their simplest form, comprise a permanent magnet field, and a wound armature designed to convert electrical power into mechanical power. The inherent characteristic of a Motor, with its response and ability to operate accurately over a range of speeds, makes it ideal for use in torque, positioning and controlled speed systems.

As well as offering Motors in brushed or brushless form, Muirhead can also provide a range of tachometer generators and limited angle motors. Models may be supplied housed or unhoused with a choice of permanent magnets materials. We also specialise in the design of motor packages to suit individual customer requirements. These can include motors combined with encoders, Resolvers, tachos, gearboxes and brakes.

Hyperlinks to types of motors:

DC Motors

What is a Brushless Motor?

A brushless motor consists of a permanent magnet rotor spinning in a laminated stator that contains the winding. The rotor is magnetised to give one or more pairs of poles with 2 and 3 phases being the most common winding configurations. By switching the energisation of the phases in the appropriate sequence the rotor follows in step mode the stator magnetic field (DC brushless). By modulating the phase currents in sinusoidal mode the rotor follows the stator field in continuous mode (AC brushless).

Applications

Hydraulic Oil Immersed

This motor drives a pump, which supplies the hydraulic supply to a local backup system for the A380 spoiler actuation system. The motor is designed to contain system hydraulic fluid (Skydrol) under a maximum pressure of 350 bar. The motor provides approximately 9 kW of power from a relatively small package size of 130 mm diam x 235 mm long with a maximum driven speed of 12,000 rpm.

Weight is reduced to 9kg by use of high strength aerospace materials.

For our Engine Control sub assemblies’ typical applications can include

• After Burner Control
• Fuel Flow Regulation
• Nozzle Area Control
• Pilots Lever Demand
• Guide Vane Actuation and Control
• Thrust Reversal

High Accuracy Motors          

This motor is used in conjunction with a reduction gearbox and an intelligent controller in the throttle actuator on wide-bodied aircraft. The whole packaged system is called “a smart actuator” which can take off or land the aircraft without the pilot’s intervention once the AUTO Command is received from the onboard computer.

In an emergency the pilot can override auto actuation and knows the throttle lever position through a feedback signal. The Hall-effect sensors are configured highly accurately to give an encoder type output in addition to commutation.

High Speed Motors

Muirhead has developed three, 3-phase DC brushless motors using Hall-effect computation to run between 60,000-90,000 rpm. This requires the motors to be robust and be able to withstand harsh environments.

Compressor Drive

Muirhead Aerospace supply a brushless DC motor & gearhead assembly for use in a proprietary High Pressure Pure Air Generator system. HiPPAG™ is a compact, electrically powered, pure air compressor and filtration system designed as an onboard source of pure air for cooling infrared seekers in air-to-air missiles. The Muirhead motor and gearbox assembly drives the compressor and therefore is an integral part of the system.

DC Torque Motors operate on the same principles as conventional DC motors but the magnetic circuit design and consequent mechanical configuration is designed for maximum torque output rather than the usual low torque / high speed characteristic. Low speed Torque Motors are beneficial for direct drive applications. Position and velocity feedback can be achieved via additions of DC Tachos, Resolvers or Optical Encoders. The unhoused motors described below can be offered in custom designed housings for specific applications.

Brushed DC Torque Motors

A range of unhoused units which are supplied as three separate components, a permanent magnet field assembly, a wound armature with precision bore for mounting and a brush ring assembly or brush segments.

Brushless DC Torque Motors

These unhoused units are generally supplied with a wound stator and a rotating permanent magnet rotor assembly. Brushless Motors require external commutation in conjunction with a suitable switching device and models are typically supplied complete with Hall-effect sensors.

Applications

High Torque Motors

Muirhead has developed a specialised permanent magnet motor, with an integral Resolver, to meet the stringent requirements of the semi-conductor processing industry. The application involves the provision of a drive motor and integral position sensor to index and then accelerate a wheel carrying silicon wafers, so that they can be implanted with ions. This custom-design was developed to replace a motor, a drive belt with jockey wheel, a complex machined housing and support structure, plus an absolute encoder, which were previously in use by the customer.

The new design is direct drive. The Resolver is mounted onto the motor shaft and is contained within the motor housing. Water-cooling is used in order to minimise the package size. This subsystem is easily mounted, requires no adjustment and provides superior performance. Absolute position information is available from the Resolver, which is also used to provide rotor position information for a sinusoidal drive.

This type of motor is specifically designed for operation over a limited angle, which is dependent upon its particular application, whilst providing a constant torque. In valve control systems, for example, these motors can be switched in forward and reverse modes, whilst exhibiting no cogging.

Applications

Seeker Head Gimbal Motors

Muirhead Aerospace are the chosen manufacturer of many Aerospace and Defence companies who need equipment that can be depended upon to work first time after a long storage or to work through demanding duty cycles. Limited Angle Torque Motors are ideal for use in seeker head gimbals.

The two Limited Angle Torque Motors illustrated are used to provide two axes of rotation to the seeker head assembly. Operating in the final phase of flight, these units endure a long storage life and a harsh thermal and mechanical environment. Both motors consist of a housed stator with a high density winding around a steel core connected to an EMI screened cable. The rotor is built from high-grade samarium cobalt magnets on a stainless steel core.

A digitally driven DC motor providing positive angular positioning without the need for feedback.

Permanent Magnet Stepping Motors

The Permanent Magnet (PM) Stepping Motor consists of a cylindrical permanent magnet rotor rotating in a laminated, slotted stator, which contains the windings. The rotor is magnetised along a diameter and may have one or more pairs of poles. The stator winding can be considered a two-phase winding. In operation, the rotor lines up with the stator magnetic field produced by applying DC voltages to the stator windings. By switching the polarity of the DC voltages in a particular sequence, the stator field is made to rotate in steps either clockwise or counter clockwise.

Variable Reluctance Stepping Motors

The Variable Reluctance Stepping Motor has a soft iron multi-toothed rotor with a wound stator. The number of teeth on the rotor and stator, together with the winding configuration and excitation, determines the step angle. The two most common have three or four phases. The motors can have single or multiple stacks. The multi-stack motor can achieve a much higher torque than a comparable single stack unit.

Hybrid Stepping Motors

The Hybrid Stepping Motor is a combination of variable reluctance and permanent magnet stepping motors. The stator has eight salient poles, the tips of these having a number of smaller teeth. The stator is wound with a 2-phase bifilar winding which gives, what is commonly termed, a 4-phase winding. This type of winding simplifies the electronics because the polarity does not have to change. The rotor consists of a cylindrical magnet axially magnetised and two rotor poles with uniform teeth on the periphery. The rotor poles are displaced a half tooth pitch relative to each other. The step angle depends on the number of small teeth on the stator and rotor and the excitation sequence of the winding.

Muirhead has developed three 3-phase hybrid stepping motors that are used in a defence application. The motors position a mirror, in azimuth and elevation, which reflects RF radiation generated within a decoy towards an incoming missile. These units were specifically designed for maximum output torque per unit volume, in order to achieve high agility for the RF reflector.