The Death of the Battery: Why Mechanical n Inductive Encoders are the New Standard for Stepper and Servo Motors

For years, the motion control industry has been stuck with a "necessary evil": the encoder battery. Whether it was a high-end Japanese servo or a customized closed-loop stepper, if you wanted Absolute Multi-Turn capability (the ability to know exactly where your machine is and how many times it has turned after a power-off), you usually had to strap a lithium battery to the driver.
But batteries leak, they die at the worst possible times, and they make international shipping a logistical nightmare.
A new era of Battery-Free Absolute Encoders is here. By combining Mechanical Gear Trains with Inductive Sensing, we are seeing a shift toward encoders that are "Fit and Forget."
The Three Generations of Multi-Turn Technology
To understand why the Mechanical + Inductive approach is winning, we have to look at what came before it.
Technology How it counts turns The Downside
Battery-Backed (Magnetic) A tiny RAM chip stays "awake" on battery power to count pulses. High Maintenance. If the battery dies while the power is off, you lose your "Home" position.
Wiegand Effect (Magnetic) Uses a special wire to harvest energy from rotation to power the counter. Patent Locks. Mostly controlled by one or two companies (like Fraba), making them expensive and hard to source.
Mechanical + Inductive Uses a physical gear set (like an odometer) and inductive coils for position. None. No batteries, no patent bottlenecks, and immune to magnetic interference.

How it Works: The "Odometer" Principle
The "Mechanical Multi-Turn" encoder doesn't "remember" the position in a chip; it stores it in space.
Inside the encoder, the main shaft is connected to a series of microscopic, high-precision gears. When the motor turns, these gears rotate at different ratios (e.g., 1:16, 1:64).
The Gears: Act as a physical memory of the total rotations.
Inductive Sensing: Instead of fragile glass disks (optical) or interference-prone magnets (magnetic), Inductive Coils on the PCB detect the exact angle of each gear.
The Result: Even if you move the motor while it's unplugged, the gears move too. When you flip the power back on, the inductive sensors "read" the gear positions and instantly tell the controller exactly where it is. No homing sequence required.

Why this is a Game Changer for Stepper & BLDC Motors
1. Zero Maintenance
In a factory with 50 robots, replacing 50 batteries every two years is a massive hidden cost. With mechanical encoders, the lifespan is limited only by the high-quality bearings and gears, often outlasting the motor itself.
2. Immunity to Magnetic Interference (EMC)
Standard magnetic encoders can "skip" or jitter if they are too close to a magnetic brake or if the motor's own EMF is too strong. Inductive technology uses eddy currents, which are unaffected by static magnetic fields. This makes them significantly more reliable for high-power BLDC and Servo applications.
3. Shipping & Compliance
Shipping products with lithium batteries requires "Dangerous Goods" certification (UN38.3). By going battery-free, you can ship your CNC machines or 3D printers globally without extra paperwork or fire-safety restrictions.
4. Robustness in Harsh Environments
Optical encoders hate dust and oil. Magnetic encoders hate interference. The Inductive + Mechanical hybrid is the "Goldilocks" solution—it’s rugged enough for a dusty CNC wood router but precise enough for a medical robot.
Applications in the RobotDigg Ecosystem
Closed-Loop Steppers: Upgrade your NEMA 17 or 23 motors to "True Absolute" status. No more homing to a limit switch every time you turn on your 3D printer or laser cutter.
Robot Joints (BLDC): For Scara or 6-axis arms, knowing the position of every joint immediately upon startup is critical for safety and speed.
AGVs and Cobots: Where vibration is high and downtime for battery swaps is unacceptable.

Conclusion
The collaboration between manufacturers like Reagle and technical powerhouses like Shanghai Jiao Tong University has finally brought this high-end industrial tech to a wider market. By choosing a mechanical-plus-inductive solution, you are choosing a future where "Homing..." is a thing of the past.