Project Description

DC Servo Motor Repair

DC servo motors are also known as brushed motors, DC brush type motors, brushed DC servo motors and DC motors. They are the earliest forms of servo motors. More and more manufacturers are doing away with their DC brush type servo motor lines in favor of the newer AC servo motors.

Brushed servo motors, are commutated mechanically and use different forms of feedback to relay speed and position. Tachometers are used for speed, resolvers and encoder for position. In some cases a combination of two or all three forms of feedback can be used. In other cases, none are used in favor of some other form of external feedback that is not integral to the motor.

Our goal is to give you the option of  that has been refurbished back to like new condition, rather than being forced into buying new. Our repair procedure follows these steps:

Servo Motor Down?
Get Immediate Assistance.

Call 866-807-3786 for technical support or 

Click to request a quote

Expert DC Servo Motor Repair

Servotech is experienced in the repair of a DC servo motors – from commonly-used manufacturers to unique motors. Our facility and technicians have the equipment and understanding to service these highly-specialized motors. We offer special expertise in conditioning the windings, the commutator, the brush rigging and the bearings of DC servos, as well as tuning the motor. Even simple tachometers are carefully installed in brushed DC servo motors, to be sure that the output voltage in both directions is congruent.

Servotech has a proven track record of returning DC servo motors to “like new” condition for customers around the world. We are an Authorized Baldor Warranty Center and Yaskawa Center as well as an Authorized SEM Service Agent. Servotech is proud of our distinction in DC servo motor repair as it reflects in our capabilities and the quality of our work.

DC Servo Motor

Servotech Repairs Pancake DC Servo Motors
& Yaskawa Cup Series DC Motors

Pancake motors are low-inertia servo motors that have very thin armatures and are incredibly challenging to work on. Kollmorgen produces a high volume of DC pancake servo motors. Servotech can also refurbish Yaskawa Cup series DC motors, unique in and of themselves, but low inertia just like pancakes. Read more on our pancake servo motor repairs.

We Repair DC Servo Motors From the Following Manufacturers:

ABB General Electric Peerless-Winsmith
AEG Getty’s Porter-Peerless
Giddings and Lewis Powertron
Glentek Reliance
Baumuller Goulds SEM
BBC Indramat Siemens
Bosch Inland Sinano
Bridgeport Kollmorgen Tamagawa
Cincinnati Milacron Matsushita Toshiba
Cleveland Motor Yaskawa
Fanuc Peerless

Our DC Servo Motor Refurbishing Process

Refurbishment, means re-magnetizing field frames and Tach fields – because over time the vibration and heat from operation degrades magnetism. Repaired motors have degraded magnets – refurbished ones have saturated magnetism.

Refurbishment means turning and undercutting commutators. Brushes will wear ridges into commutators, creating an uneven surface that can even create side wear – a very bad situation because changes in the geometry of the brush and can cause extreme high current. Repaired and refurbished servo motors get new brushes, and are turned in a lathe to create a new even surface for brushes to ride on. Then each commutator bar is cleaned out with a special tool that removes dirt and mica. All armatures are then balanced to make sure the newly refinished surface will wear evenly.

Refurbishment means setting neutral. Repaired motors go back together and they “run”, but refurbished DC brush motors also need to undergo a process called “setting neutral”. An important effort requires an oscilloscope and very accurate power supplies, as neutral determines the smoothness of operation. At Servotech, brushed servo motors are meticulously tuned to ensure proper operation, acceleration and torque. Refurbishment means understanding bearing pre-load. Repaired servo motors have new bearings installed, however new bearings do no account for worn fits or bearing journals, nor do they fix broken or worn bearing shims and wave washers. A brushed servo motor depends on proper bearing pre-load. A motor must run smoothly both cold and when it has reached full operational temperature. Small mechanical inconsistencies will become exacerbated by heat expansion unless the pre-load is set properly.

Refurbishment takes feedback tuning. Some companies will say that if a servo motor encoder produces signals both before and after servo motor rebuild, than the motor is repaired. At Servotech we know an encoder should produce pristine square waves, with proper output voltage levels, phase symmetry, and reliability at high speed. Encoder repairs are often outside the realm of expertise for some repair shops. At Servotech, we are committed to excellence in all aspects of servo motor refurbishment. Any servo encoder that cannot be tuned back to “like new” condition is replaced with a brand new encoder. Lack of a direct replacement does not constitute a lack of ability to replace a feedback device. Our servo refurbishment process includes a strong, new feedback device that will last for thousands of continuous operation hours without a loss of accuracy or reliability.

Refurbishment includes protection. Cutting fluid, coolant, and water can all be present in a servo motor’s operational environment. While a repaired motor may simply be cleaned, a refurbished servo motor is disassembled, washed, baked, rebuilt, sealed, and painted with a two part epoxy coating – the same coating used by the U.S. Navy on submarines. This ensures that a clean environment inside the motor, and that it can remain contaminant free throughout the lifetime of the servo.

The Importance of DC Servo Motor Refurbishing

Brushed DC servo motors are extremely delicate. Brushes, made of carbon, wear down with every hour of operation. After a few years the build up of carbon can be so immense that even if the motor is in good shape, the carbon residue can be enough to cause a short in the windings, or between commutator bars. A botched rebuild can land a brush rigging out of place. Improperly shimmed and tensioned bearings can force brushes to hit the commutator unevenly. Even just bolting an end bell on in the wrong orientation can result in a motor that does not run in the proper direction.

Brushed DC servo motors are employed in harsh environments. In every hour of operation the servo motor is exposed to vibration, heat, electrical noise and contaminants. Even running by itself on a bench, a DC servo motor creates heat and a certain amount of vibration. All of these variables will degrade a motor’s ability to perform. Magnetism, electrical integrity, mechanical structures, shims, gaskets, greases and fits will all wear down given a long enough amount of time.

Each system that is not refurbished back up to “like new” will only continue to degrade, and do so more quickly. Not undercutting a servo motor commutator means changing the brushes much more often. Not repairing servo encoders means missed counts, lost accuracy or perhaps even a complete failure of the feedback device resulting in a downed machine. At Servotech, refurbishment means breathing life back into a motor – and returning that motor “like new”.

At Servotech, we are committed to the highest quality standards when refurbishing servo motors. Contact us today and request a free quote for your brushless servo motor.