LRA Motor
An LRA creates back-and-forth vibration for tactile feedback. The actuator's resonance, mounting and drive waveform affect what the user feels. A suitable haptic driver can manage resonance tracking and braking; these are not automatic properties of every actuator or driver.
Alternating current in a coil produces force on a spring-supported moving mass. Drive near the system's resonance can produce useful vibration efficiently. The stored mechanical energy can continue the motion after drive stops, so active braking can shorten the settling time. A closed-loop driver can monitor the actuator and adjust its drive, but exact startup, stop time and frequency range are design-specific.
In plain terms
Push a playground swing at the right moment and a small push builds a useful motion. An LRA similarly benefits from well-timed electrical drive, while braking applies force against the motion to help it settle.
Why designers use it
- Produce tactile effects whose intensity changes over time.
- Use suitable resonance tracking and braking to make adjacent effects feel distinct.
- Provide a physical cue when a visual or audible notification is not the preferred interface.
Best for
- Wearable tactile feedback
- Touch-interface feedback
- Haptic prototypes
Key specifications
- Resonance and bandwidth: Actuator-specific (Choose a driver and waveform compatible with the intended range.)
- Drive and duty cycle: Follow actuator and driver limits (Do not assume an arbitrary voltage or continuous-drive condition is safe.)
- Transient response: Includes mounting and braking (Startup and ring-down figures are not universal.)
- System integration: Actuator, driver and mechanical mounting (Test the tactile result in the assembled device.)
When not to use it
- When the required vibration frequencies lie outside the selected actuator's useful range.
- When the drive, duty cycle, mounting or temperature exceeds the selected actuator and driver's specifications.
Common mistakes
- Treating an LRA as a DC eccentric rotating-mass motor.
- Assuming every driver automatically tracks resonance or brakes the actuator.
- Using a quoted timing figure from one actuator as a guaranteed response for another.
- Claiming a particular phone's actuator material or driver IC without a supporting teardown or manufacturer reference.
Where you will find it
- In the TI-hosted article, Somatic Labs' co-founder describes using a DRV2605 to prototype tactile effects across four LRAs in the Moment wearable. This is the author's account of that project, not independent evidence about unrelated products.
- The article also shows an Adafruit DRV2605 breakout as a prototyping option. It demonstrates a documented driver/actuator workflow without identifying the internals of an iPhone, Pixel or MacBook.
A short history
A linear resonant actuator moves a spring-supported mass back and forth along one axis. Driving it near its mechanical resonance produces efficient vibration for tactile feedback. A suitable driver can track resonance and control braking, so the actuator responds to short effects rather than simply running continuously.
Good to know
- An actuator can keep vibrating after its electrical drive ends because the mass and spring store energy.
- An LRA is the mechanical actuator, not the haptic driver chip. The two need to be selected and configured together.