Ever since the first vibrating console controllers came into the hands of gamers, we’ve been able to literally feel the world on the other side of the screen. Linear actuators are the latest evolution of this immersive technology.
How the traditional Rumble works
The vibration effect that we all know and love uses a simple yet ingenious method of creating vibrations on the controller. There are usually two electric motors, one on each grip, which spin an unbalanced weight. They are known as eccentric rotors and the principle is the same as having an unbalanced washing machine. As the unbalanced weight spins around it, it wobbles and the controller vibrates. By varying the speed of the motor, the intensity and frequency of vibration can be varied.
In modern controllers that use this design, such as the Xbox One controller shown below, the two vibration motors have weights of different sizes.
This allows for a greater variety of rumor types and the mixing of rumor types. The motors themselves have also gotten much stronger and more precise over the years, so the haptic experience of a modern controller like Xbox Series controllers feels much more refined and powerful than, say, a PlayStation 2 DualShock controller.
However, VR controllers, PlayStation 5 DualSense, and Nintendo Switch Joy-Cons do not have these vibration motors. Instead, they use a device known as a linear actuator, also known as a linear resonant actuator, or sometimes a “voice coil motor.”
How Linear Resonant Actuators Work
A linear actuator gets its name from how it moves its mass. Where the traditional vibration motor rotates its mass, a linear actuator moves its mass back and forth along an axis. Linear actuators are usually labeled according to the axis they are aligned to. They are commonly used in smartphones for haptic feedback.
Linear actuators use a voice coil that is the same as that found in a loudspeaker. A voice coil is essentially an electromagnet. In a loudspeaker, the voice coil drives the speaker cone using magnetism. By altering the frequency at which the voice coil drives the cone, sound can be reproduced in air.
In a linear actuator, the voice coil drives a spring that has a resonant frequency. When driven at its resonant frequency, the spring moves a mass inside the actuator with maximum force. The further away from that resonant frequency the coil is driven, the less efficient it becomes. Linear actuators can only be driven within a specific frequency range centered around that optimum spring resonant frequency. Going too far out of that range means the vibration needs too much power to be usable.
Within that frequency range, linear actuators can recreate vibrations with amazing levels of detail. In fact, Nintendo Switch game developers literally convert audio files into rumble files for the console’s HD Rumble feature.
On the PlayStation 5 DualSense controller, the built-in speaker can be used to boost the linear actuators at the edges of their frequency ranges. Therefore, the loudspeaker is used both to increase haptic vibration and to produce audible sound.
Why linear actuators are the new gold standard in haptics
It seems that linear actuators are becoming the most popular choice for haptic feedback. Among the current generation consoles, Microsoft’s Xbox Series consoles are the only systems that remain with eccentric motors. In the world of virtual reality, all current generation controllers use linear actuators, and in mobile devices they are the only practical option thanks to their compact size and low power requirements.
More than anything, we believe the drive for linear actuators is due to more than just their cost advantages, power, and refined details. Since the software we use has become so detailed and sophisticated, a new generation of haptic technology is needed.
As electronics become increasingly solid state, with fewer moving parts or mechanical components, linear actuators are the logical choice for thin and light systems. While they can’t quite match the sheer power of traditional rumble motors, there’s nothing like feeling your hand “bump” into something in VR, feeling raindrops falling across your controller, or being able to see the texture of the path to through your hands when racing in a simulation.