Don't let the title fool you, I'm not talking about a reduction in alternatives, but
about alternatives in reduction - gear and pulley reduction that is.
You see them everywhere and on almost every type of device from laboratory
equipment to production machinery. With the power of today's personal computers, many
are constructing automated systems that were unheard of just a few short years ago. With
low-cost, PC-based automation and high price/performance ratio systems becoming
commonplace, reducers (Gear and otherwise) are being seen in more and more places. A reducer can be used
with almost any type of positioning system to increase resolution and torque. Reducers
can also improve acceleration in many applications due to better inertial matching of the
motor and load.
Well-designed reducers mount easily between the motor and the application in order to
provide the desired mechanical effect. Reducers are normally constructed with a
machined housing that contains bearings, shafts, and a gear set. Common gear sets
include worm, spur, and planetary types. The housing contains the features necessary to
mount the motor and to attach the reducer to the mechanical system. Most reducers
provide an over-sized output shaft to transfer the torque produced in high-ratio models.
This non-standard shaft complicates installation and often requires custom machining to
achieve a correct fit.
While several companies offer high-precision, high-cost gear reducers, many
applications simply don't require everything they provide. Designers are often forced to
use a high-priced gear reducer on a system that doesn't need the precision offered by such
a unit. It's not uncommon for one of these gear reducers to cost more than the motor and
drive electronics combined.
When automation builders search for alternatives to solve their reduction needs they
may discover pulley reducers. Pulley-based units provide much more than just a
mechanical reduction, they also provide the impressive cost reduction needed for today's
Like other reducers, pulley reducers mount between the motor and the driven device
using standard hole patterns like those found on a NEMA #23 step motor. Unlike many
gear-based reducers, the output shaft is the same diameter as the motor eliminating the
need for modifications and custom machining. This is due mainly to the fact that pulley-
based reducers normally have smaller ratios such as 4 to 1 or 2 to 1. This results in less
torque multiplication and reduces the strength requirements of the output shaft. Usage of
such a unit is as simple as removing the motor, attaching it to the reducer, then mounting
the entire unit back on to the mechanical system.
An open, sandwich-frame construction has several advantages such as making it
easier to replace bearings, belts, or pulleys. Users can actually see what's going on inside
these units to eliminating "unknowns" during system troubleshooting. This ease of access
also allows the changing of ratios by simply replacing pulleys and belts. The entire unit
disassembles with only four screws. Belt tension is easily adjusted using the slotted motor
mounting holes. The output shaft can exit either side of the frame to provide additional
mounting options. By swapping the input and output pulleys, an increaser can be created.
Increasers are used for applications requiring a multiplication in speed instead of an
increase in torque.
Overall, the pulley reducer offers a simplified, low-cost alternative to traditional gear
reducers where very high precision is not required. Other features of an open-frame
design make the pulley reducer a powerful alternative to gear-based units. Keep a watch
out for these ever-increasing reduction alternatives.
Roger Arrick is President of Arrick Robotics which manufacturers PC-based motion
control products including step motor systems, positioning tables, and accessories such
as pulley reducers. Send E-mail to firstname.lastname@example.org. The Web address is
Learn more about the PR23 Pulley Reducer