Quad Rotor High-Torque Motor Repair

At Motion Tronic, we don’t shy away from a challenge! This unique quad-rotor high-torque motor repair provided exactly that—it’s not something that comes into the workshop every day. When a customer recently needed it repaired, they knew that our team would be unmatched in overhauling the motor.

This motor is a true heavyweight, weighing in at 1.5 tons. Used for applications requiring high torque at low speeds, such as plastic extrusion, this particular motor can achieve 30,000 Nmof torque. Let’s just say you wouldn’t want to get your hand—let alone anything else—stuck in the gearing system of this motor!

Initial assessment

During our initial assessment, we found that while the motor was mechanically turning, there were significant electrical issues. Two of the four stators had direct shorts to earth caused by broken-down insulation on the windings.

To fix this, a rewind of the stator was required. For a specialized motor with four stators, we recommend rewinding all four to ensure the speed of each rotor is perfectly matched, preventing further damage once the unit is back in operation.

Stripping of the motor

To rewind and service this motor, a complete strip-down is necessary. We began at the non-drive end, removing the mounting bolts and cabling to expose the bearing housing, shafts, and bearings.

Once the non-drive end housing was removed, we gained access to each rotor shaft. We also noted the recesses between each stator, which house the gasket seals for the water-cooling jacket. Ensuring these are sealed properly is critical, as a leaking water jacket is a recipe for repeat failure.

We ordered new gasket kits directly from the motor manufacturer in Germany to ensure a proper seal in the water-cooling system when reassembling the motor. The next step of the repair was to remove the main block that holds the four stators of the motor. With the help of special lifting equipment, the stator block was rigged and removed from the motor, exposing all four rotors.

With the main stator block removed, the stators could now be worked on independently, and we could start the process of rewinding all four stators of the motor. While the rewinding of the stators was taking place, the rest of the motor needed to be stripped. Each rotor was removed from the gearbox, and new bearings were installed to ensure that each rotor was mechanically serviced.

Up next was the gearbox located on the front of the motor. We needed to change the bearings and seals on the gearbox to ensure a full mechanical service. Stripping a gearbox can be a very intricate job and generally requires full attention and documentation throughout the process.

By the time the gearbox had been stripped and serviced, the stators had been rewound with new thermal sensors installed into each stator. It was time to run each sequence in reverse and reassemble the motor.

Assembly

Once the stators were rewound and the gearbox serviced, we began reassembly. Each rotor had now been serviced with new bearings and, one by one, re-installed into the gearbox. Happy with the assembly of the rotors, we moved on to installing the new gasket kits from Germany on the drive-end housing. The housing was cleaned thoroughly to ensure a completely smooth and non-contaminated surface before laying the seals in their positions. Once this was completed, the main stator block was lowered back onto the motor, navigating each rotor to ensure they were properly located into each stator.

Once the main stator block had been lowered into position, it was secured firmly with the large mounting bolts that connected the stator block to the gearbox, confirming each seal was compressed and forming a water-tight seal. The cables from each stator were then directed through the last non-drive end housing before we lowered it down onto the stator block to complete the main assembly.

The same process of ensuring the housing was completely smooth and non-contaminated was repeated so we could provide the best seal possible on the non-drive end housing, too.

The non-drive end housing was then firmly secured by the mounting bolts that located into the main stator block. At this point, we needed to test the water jacket under pressure to ensure there were no leaks and that the water jacket could hold. The water jacket was filled with water, and we proceeded to pressurize the water jacket chamber up to 8 bar to ensure it held pressure. Once under pressure, the water jacket was left under pressure for a prolonged period to ensure the force did not drop, not even due to the smallest leaks.

We didn’t experience any issues and could complete the assembly of the motor and wire each stator into the terminal block and all the stator thermal sensors. Once completed, the motor was moved to our painting bay, sprayed with a primer, and given its final look with a brand-new coat of paint.

Completion

With assembly now complete, we could fill the gearbox with the correct grade of gearbox oil and perform a run test. The motor was connected to our test VSD stand, and the motor parameters were programmed into our VSD. An autotune was then performed on the VSD to calculate the winding characteristics of the motor, and we were ready to run!

The motor was successfully brought up to full speed, with everything sounding smooth. It was left to run for a while before we were satisfied that the repair was complete, and it was now ready to go back into production for the customer.

As a team, we were delighted with the result of this repair; it is always very rewarding when we overcome a challenge and come out on top!

If you have any servo motor repair requirements, please get in touch with us so we can discuss how we can assist you.