Brushed Pancake Motors

Pancake motors or printed armature motors and servodisc motors as they are also known, are employed for various industrial applications wherever rapid stop-start, zero cogging, low inductance, precise electronic motor control, a low thermal time constant or just a slim, axially flat packaging profile is needed.

PMW’s flat armature motors differ from conventional DC servomotors in their unique slotless disc armature design. This enables them to deliver a concentrated level of performance in both incremental motion and continuous speed that is not attainable with conventional iron-core motor designs.

Please note that we are using the terms “brushed pancake motor”, “printed motor”, “servodisc motor” and “flat armature motor”to mean the same thing.

Below is our range of brushed pancake motors. Please click below for our quick guide to our brushed pancake DC motor range.  The guide is intended as a help in specifying and building your motor:
Quick Guide to PMW’s Brushed Pancake DC Electric Motor Range

PMW are immensely proud of the brushed pancake motor range which constitutes an ongoing development effort spanning 50 years. PMW has recently reviewed and improved everything in the construction from replacing metal parts with high specification injection moulded engineering plastics to lengthy studies into graphite compositions to ensure product life is optimised.

Our complete brochure of our brushed DC pancake motor range is available here:
PMW Pancake Motor Range

GP Series Pancake Motors

The PMW GP series can provide a cost effective servo capability in low volumes. Using flat armature technology the motor is ideal for general purpose applications. Two magnet variants of each size are available: standard ferrite (GPM) and high-power neodymium magnets (GPN). There is also a choice of either a standard series wound armature or a higher speed but lower torque parallel wound armature that has a lower resistance (LR).

Armature sizes vary from 9cm to 16cm and higher on special request. Historically this motor has been popular in across general servo applications requiring smooth movement and high acceleration/deceleration. The GP series is often a straight drop-in replacement for older F-series and UF-series servo motors from PMI Kollmorgen.

GP series pancake motors in sizes 9, 12 and 16.

Below is a table with some examples from the GP series brushed DC pancake motor range:

In the UK some these motors have historically been sold through RS Online.

We are happy to supply these directly to customers and generally have these in stock ready for next day dispatch. Please email us to order.

GM Series Pancake Motors

The GM series (High Precision Compact Series) is an extremely accurate high power pancake motor range with possible high ambient temperature (150C, 302F) operation, for high performance industrial applications. The range is available in 9cm, 12cm and 16cm armature diameter sizes, with standard and high power AlNiCo magnet options. Additionally, through our special build scheme every motor in the GM series is available as a low resistance, i.e. parallel ‘winding’ (designated LR) motor perfectly suited for low voltage, battery or higher speed applications. Historically this motor has been popular across high-end servo applications requiring a compact motor with perfect control. The GM series is often a straight drop-in replacement for older U-series, S-series and Platinum series servo motors from PMI Kollmorgen.

GM series printed armature pancake motors in variants GM9, GM12 and GM16

GM16H pancake motor with 16:1 ratio gearbox and brake used in scientific tensile testing machine.

Below is a table with some examples from the GM series brushed DC pancake motor range:

GN Series Pancake Motors

The GN series (High Precision Slim Series) is an extremely accurate high power motor range but is one third the axial thickness of the GM range, making it our flattest motor ever. The additional benefits of using NdFeB (Rare Earth) magnets are that it is possible for the motor to operate in low ambient temperature (-20C, -4F), for high performance industrial applications. The range is available in 9cm, 12cm and 16cm armature diameter sizes. Additionally, through our special build scheme every motor in the GN series is available as a low resistance, i.e. parallel ‘winding’ (designated LR) motor perfectly suited for low voltage, battery or higher speed applications. Historically this motor has been used in extreme high-end servo applications requiring an ultra-compact motor with perfect control. The GN series is often a straight drop-in replacement for older N-series and KN-series servo motors from PMI Kollmorgen.

GN series printed armature pancake motors in variants GN9, GN12 and GN16.

Below is a table with some examples from the GN series brushed DC pancake motor range:

GR Series Pancake Motors

The GR series (Ruggedised Series) is a high power pancake motor range but with a heavily ruggedised motor casing. The range is available in 12cm, 16cm and 19cm armature diameter sizes, with standard and high power AlNiCo magnet options. Historically this motor has been popular in the food industry. The GR series is often a straight drop-in replacement for older JR series servo motors from PMI Kollmorgen.

Ruggedised GR12, GR16 and GR19 pancake servo disc motors.

Below is a table with some examples from the GR series brushed DC pancake motor range:

GPG Series Pancake Motor

The GPG9 and GPG12 series combine the GP series with a fully integrated slim gearbox (G) to make a compact, lightweight and durable motor gearbox combination.  The GPG series provides a high quality, low cost solution to suit a vast array of applications. To provide maximum selection flexibility, the GPG9 is available with 2 gear ratios while the GPG12 is available with 8 alternative gear ratios from 206:1 to 10:1 each with 4 motor models to suit voltages from zero V to a maximum of 60V. An optional encoder or brake can also be externally fitted to the rear of the motor to provide a feedback control loop or simple safety feature.

GPG series pancake motors with integrated gearboxes side by side: GPG9 and GPG12 designs B and A.

The following data sheets are available for the GPG series pancake motors:

GPG9 Series Printed Motor Overview

GPG12 Series Printed Motor Overview

Sample Applications

* Welder conductor feeds
* Small rewinders
* Wire drawers
* Rolling shutter doors
* Outdoor rotating advertising displays
* Medical equipment
* Industrial machines

Drives for Pancake Motors

We can offer high frequency (40Khz) drives (both programmable and simple amplifiers) for our entire range of printed motors. The high frequency ensures maximum smoothness from the printed motor, however 20Khz would be acceptable for most applications. Most of the drives we supply for our pancake motor range are from Copley Controls.

Tachos, Encoders, Resolvers, Brakes and Gearboxes for Pancake Motors

We can also offer cost effective low inertia dc tachometers, encoders, resolvers, brakes and gearboxes that can be coupled directly to our pancake motors.

Custom Brushed Pancake Motors

Custom motor design: double printed armature motor for ultra high temperature fan (with ATEX approval).

Custom motor design: flat high-power yaw roll motor with brake for use in wind tunnel.

PMW has extensive application knowledge and experience in adapting our standard pancake motors to suit customer’s specific requirements. This includes incorporating ancillaries, providing special features such as alternative mounting plates, motor housings and shafts. Our mechanical and electronic engineers will be happy to work with you. If printed armature technology is the first choice for your application, but you can’t find the right power, speed or torque please call or e-mail us with your requirements as we may be able to offer an armature or twin armature design that could suit your needs.  Examples of this are the 24cm and 27cm armature designs that are not listed in our standard product offering.

All of our brushed pancake motors can be made available as an open motor without a front plate. This motor kit can then be built directly into the customer sub-assembly which will house the bearings and shaft.

Unique Features of Brushed Pancake Motors

Brushed pancake motors, or printed motors and Scheibenläufermotoren as they are known in Germany, have a number of unique features that make them stand out from other electric motors:

Size
The motor is much smaller and thinner than normal iron-core motors

Rapid acceleration and deceleration
The armature is very thin giving low-inertia and exceptional torque ratios. The result is extreme acceleration with a typical pancake motor able to accelerate from 0 to 3000 rpm in only 60 degrees of rotation. To achieve rapid acceleration and deceleration printed motors can handle a peak current of up to 10 times the continuous rating which would be impossible for iron-core motors without demagnetising

Zero-cogging
Printed armature motors are the only electric motor variant in the world with no torque ripple. A conventional motor has a tendency to prefer certain positions where the magnetic alignment is best. This is called cogging and creates torque disturbances. The flat armature motor is ironless and is thus intrinsically non-cogging. This gives perfectly smooth rotation at any speed with no ripple effect. Click here for a graph that explains this

Long brush life
Because brushed pancake motors have no iron core there is minimal inductance. The result is no arcing, because there is no stored energy in the armature to be dissipated during commutation. In an iron-core motor a lot of energy is stored in the magnetic field of each coil. When this field collapses, the energy tends to be discharged by arcing to the brushes and this wears them out.  Depending on the application, the brushes in our printed motors tend to last as long as the bearings.

Reliable at high speed
Brushed pancake Motors do not suffer from arcing as thus can perform reliably at very high speeds

Instant torque delivery
Another benefit of minimal inductance is that the current flows into the armature extremely quickly (in less than one millisecond). This delivers instant torque

Flat torque curve
The ironless disc motor has a perfectly flat torque curve up to very high speeds whereas iron-core motors tend to fade at high speeds. Thus a small pancake motor may be sufficient where you would have to select a much larger iron-core motor to achieve the same torque at high speed

Easy to cool
Because the armature of a pancake motor is ironless it also has a low thermal time constant which makes it easy to cool either with air or water

Excellent EMC characteristics
Printed motors have excellent electromagnetic compatibility characteristics to minimise interference with any nearby electronic components such as communications systems or displays

Choice of magnets
Printed armature motors are available with standard Ferrite, AlNiCo and NeFeB (Rare Earth) magnet types. Each type offers different performance advantages with regard to speed, torque and temperature stability

Wide variety of design options
PMW can offer special shafts, dual armature configurations, integrated tachos, encoder mounting adaptors or motors complete with encoders, a variety of armature configurations and diameters, gearboxes, pulleys and solutions for cooling and electromagnetic compatibility

History of Brushed Pancake Motors

The history of brushed pancake motors and PMW Dynamics stretches back to the 1950′s with the invention of the disc shaped laminated armature made from printed circuit board. The technology was licensed to PMW Dynamics’ predecessor, PML, which started up in Aldershot in 1963.  PMW Dynamics is thus the original European manufacturer of brushed pancake motors. The original US manufacturing arm established in the same year was PMI Motion Technologies which later became part of Kollmorgen, now part of Danaher Motion.

The printed motor design was quickly adapted so that it could be made from laminated copper discs and was applied extensively as magnetic and paper tape capstan drive servos. The printed motor, or slotted disc servo motor as it was also known, was chosen to run analogue magnetic tape drives because of its very precise speed control as well as wide range of speeds. The motor was then combined with digital optical or magnetic tachometers.

Printed motors running analogue magnetic tape drives.

However, thanks to its very fast acceleration capability resulting from a high pulse torque to inertia ratio and the absence of cogging the pancake motor was very quickly identified for a number of other uses in energy, aerospace, automotive, life sciences, medical and general industrial automation applications. The iron-free flat armature motor provides some significant performance advantages especially for motion control applications.

How Brushed Pancake Motors Work

The brushed pancake motor or flat armature motor is an evolution of the original printed armature concept where the armature was made out of layers of printed circuit board, which is why it is still commonly known as the ‘printed’ motor. Today however, the flat armature is an ironless disc with coils punched from sheet copper instead of printed circuit board. The disc made from punched sheets of copper replaces the wound coils made of copper thread in a conventional electric motor. The sheets of copper are formed onto a non-magnetic disc insulation material similar to a lacquer.

As the disc spins the brushes are in direct contact with the copper conductors. Ingeniously, this removes the need for a separate commutator. At the same time, it creates in excess of 100 commutations per revolution. The disc rotates within an axial field magnetic field produced by high-coercivity permanent magnets mounted in either the rear end-plate, or both front- and rear end-plates, enabling the lines of flux to pass and return through the armature coils.

With no magnetic material present in the disc, undesirable ‘cogging’ is completely eliminated. This produces perfectly smooth low speed operation and continuous torque down to zero RPM. Torque output in the flat armature motor is not limited by saturation and instead directly proportional to current. At the same time, speed is directly proportional to voltage.

The inherent low inductance of the flat armature disc provides exceptionally long brush life due to the absence of sparking. Normally this enables the pancake motor to exceed the life of the equipment it drives. The absence of sparking also ensures excellent electromagnetic characteristics.