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Timing Is Everything

Precision watchwinder mimics human wrist action

The Watchwinder from Orbita Corporation, Wilmington, NC, uses a spur-type gearmotor to provide motion to keep watches wound when they're not being worn. Automatic, "self-winding" mechanical watches have pendulums or rotors that wind the watches through random wrist activity -- if unworn for more than 48 hours, the watch ceases to operate.

When designing the first Watchwinder, some of the major concerns included noise, AC or DC operation, and the potential for use with various watch bands. Component selection needed to keep within the parameters of affordability, weight, ease of use, durability, and extended life of the unit. The major component was the gearmotor supporting the mandrel. It had to be the correct torque, size, and weight, have clockwise and counterclockwise rotation and low noise. Designers chose a spur-type gearmotor from Micro Mo Electronics, Clearwater, FL, for the application.

Each Watchwinder uses one or more mandrels containing a 22B spur gearhead incorporated within a Model 2230 coreless DC motor. Less expensive than comparably sized planetary gearheads, the 22B is available in either stainless steel or brass to ensure a long life free from corrosion.

The gearhead itself uses non-integer gear ratios, which distributes the wear uniformly among all gear teeth. It allows for reduced noise and extended service life. The 2230 motor is an ironless core design; the rotating member of the electric motor is self-supporting copper coil rather than the usual iron rotor and copper. This design results in smoother operation and higher operating efficiencies than iron core designs, which makes the motors more suitable for use in battery operated devices.

For the most part, the Watchwinder is friendly to the watch and the device's internal electrical components. The operating speed is a slow 500 to 950 turns per day. Although torque requirements are low, Micro Mo's spur type gearhead has a maximum continuous torque of 14.2 oz-in. It can also be driven in either clockwise or counterclockwise directions with equal performance, thus accommodating a key specification that the mandrel rotate bi-directionally. As frequent reversal of rotational direction can often shorten gearhead life, an optional slip clutch may be used to prevent gearhead damage when the mandrel comes to a stop.

-- KC

For more information:

Circle 550 - Micro Mo Electronics

(800-403-1772)

Circle 551 - Orbita Corporation