Servo motor

In the high-stakes world of industrial manufacturing, a failed servo motor isn’t just a broken part—it’s a production bottleneck costing hundreds of dollars per hour. At 24cnc.com, we specialize in supplying high-performance AC and DC servo motors for critical machine tool applications. Whether you are retrofitting a legacy 3-axis mill or maintaining a high-speed robotics cell, our inventory is curated to get you back online fast.

We stock thousands of hard-to-find, refurbished, and new surplus units from the world’s leading OEMs. Every motor that leaves our facility undergoes rigorous static and dynamic testing on dedicated test stands to ensure it meets original factory specifications for torque, speed, and encoder feedback accuracy.

Leading Servo Motor Manufacturers We Stock

Compatibility is non-negotiable in CNC systems. A servo motor must communicate perfectly with its specific servo amplifier and CNC controller. We specialize in the “Big Three” of the CNC world, along with other major brands.

Fanuc Servo Motors (The Industry Standard)

Fanuc motors are the heartbeat of the global manufacturing industry. Known for their legendary reliability and “Red Cap” / “Yellow Cap” distinction, they cover a vast range of applications.

• Alpha i Series (αi): High-acceleration motors designed for modern, high-speed machining centers. These utilize advanced Pulsecoders (up to 32,000,000 pulses/rev) for nano-interpolation precision.
• Beta i Series (βi): A cost-effective solution offering high performance for auxiliary axes and standard machine tools, balancing inertia and torque density.
• Legacy DC Motors: We actively stock the older yellow-cap DC servo motors found in machines from the 1980s and 90s, helping you extend the life of valuable legacy equipment without a costly control retrofit.

Mitsubishi Electric Melservo

Mitsubishi Electric’s servo systems are renowned for their compact size and high torque density. We support a wide generation of Melservo motors:

• HA & HC Series: Low-inertia motors ideal for high-frequency positioning applications like chip mounters and robotics.
• HF & HG Series: The modern standard for general industrial machinery, featuring high-resolution absolute encoders that eliminate the need for homing routines after power loss.

Siemens Simotics

For complex motion control involving synchronization and heavy loads, Siemens motors are unmatched. Our inventory includes:

• 1FK7 & 1FT6/7: Permanent magnet synchronous motors known for high dynamic performance.
• Drive-CLiQ Interface: Many of our Siemens units feature the intelligent Drive-CLiQ interface, which simplifies commissioning by automatically uploading motor data to the drive system.

Understanding Servo Technology: What You Are Buying

A servo motor is more than just a motor; it is part of a closed-loop system. Unlike a standard induction motor, a servo relies on a continuous feedback loop to correct errors in position and velocity.

The Feedback Loop: Encoders vs. Resolvers

The most critical component of your servo motor is the feedback device. If your machine is faulting out with “Position Error” or “Excess Lag,” the issue is often the feedback device, not the windings.

• Optical Encoders: Used in most Fanuc and Mitsubishi motors. They use a glass or metal disc with fine gratings to generate pulses. They are incredibly precise but sensitive to vibration and oil contamination. (See our Rotary Encoders section for replacements).
• Resolvers: Used in harsh environments (often changing temperature or high vibration). They are essentially rotary transformers and are more durable than optical encoders, though typically less precise.

Brake vs. Non-Brake Motors

When selecting a replacement, you must verify if your original unit has a Holding Brake. This is crucial for Z-axis (vertical) applications or any axis affected by gravity.

Warning: Installing a non-brake motor on a vertical axis will cause the head to drop when power is cut, potentially damaging the tool, the part, and the machine table.

Before You Buy: Is Your Motor Actually Dead?

Servo motors are robust. Before ordering a replacement, check these common failure points to ensure the motor is the root cause:

1. Megohmmeter Test (Megger): Test the insulation resistance between the power phases (U, V, W) and the Ground. A reading below 10 Megohms suggests winding insulation breakdown or fluid ingress (coolant/oil) inside the motor.
2. Phase-to-Phase Resistance: Use a multimeter to measure resistance between U-V, V-W, and W-U. The values should be balanced (identical). If one phase is open (infinite resistance) or shorted (near zero), the windings are burnt.
3. Cable Inspection: High-flex cables in cable chains (drag chains) often break internally. A “Motor Overcurrent” alarm can sometimes be caused by a shorted Power Cable rather than the motor itself.
4. Encoder Alarms: If the drive displays a “Pulse Coder Disconnect” or “Communication Error,” check the feedback cable connectors for oxidation or loose pins before condemning the motor.

AC vs. DC vs. Stepper: Technical Comparison

Understanding the architecture of your motor helps in maintenance and expectations. Here is how modern servos compare to other technologies.

Repair or Replace? A Guide for Maintenance Managers

When a line goes down, the pressure is on. Should you send the motor out for repair or buy a replacement unit from 24cnc.com?

Option A: Repairing (2-4 Weeks)
Sending a motor for rewind or encoder repair is cost-effective for very large motors (15kW+) where shipping weight is high and replacement stock is non-existent. However, the lead time is often unacceptable for production environments.

Option B: Buying Surplus/Refurbished (1-3 Days)
This is usually the superior option for standard frame sizes (Fanuc Alpha 2 through Alpha 40, etc.). By purchasing a unit from our stock, you can have the machine running in 24-48 hours. Furthermore, keeping your old “bad” motor gives you a core that can be repaired later and kept as a spare shelf unit, breaking the cycle of downtime.

Frequently Asked Questions (FAQ)