output devices. Because of their large size and high cost, they are normally used in large controllers that are integrated into equipment that requires highly reliable components, where failure and downtime come at an extraordinarily high cost. Cranes used in metal-producing mills and container-handling terminals are examples of applications using these devices. Strain gauge-type joysticks are generally relegated to use as small force-type joysticks.
This leaves joysticks using pots, induction coil or Hall effect as the most-commonly preferred controllers. Of these three types, the joystick using a potentiometer as a primary output device is predominant.
Pot joysticks using conductive plastic pots have published life spans in excess of 10 million cycles. In applications that don't have severe vibration, this duty cycle results in a very respectable lifetime for the joystick, if it is operated and maintained properly. Because pots are small devices, they can be included as components on both large and small joysticks. This allows flexibility in the design of machine control because the joysticks can be placed almost anywhere.
Electronically, the pot output can be used directly, producing a variable DC voltage, or that signal can be processed further through circuitry to produce a pulse width modulated (PWM) signal, a digital serial stream (RS232, etc.) or other variants of analog and digital signals. Potentiometers also are relatively immune to electrical emissions from outside sources. This makes their operation predictable around high voltage power transmission lines or in any application where the joystick may come in close proximity to a strong electric field.
As the most-widely used type of joystick, pots are found controlling the movements of excavators, agricultural equipment, aerial work platforms, scissor lifts, skid steer loaders, pavers, compactors and a wide variety of other construction equipment.
The disadvantage of using a potentiometer in a joystick is realized only if the application involves very high duty cycle or vibration. A potentiometer is a variable resistive device using a delicate wiper contacting a resistive element. Although the joystick may be in neutral (center) position for much of the time a machine is active, vibration from the machine can continuously dither the pot wiper on the element and produce heavy wear in the center region. Devices using contacts are always subject to wear and potential failure, but the use of non-contacting technology is a way to avoid this.