Vibration motor (ERM core)

01

Set the vibration strength and motor type

Precision Microdrives' Application Bulletin AB-004 describes the ERM, or pager motor, as a DC motor with an offset mass on its shaft whose rotating, unbalanced centripetal force displaces the motor repeatedly, felt as vibration. It models the motor in its product as driven harmonic vibration — a mass, spring and damper excited by a force F₀ = m·r·ω², where m is the eccentric mass, r its distance from the shaft and ω the angular speed — so vibration strength depends on the eccentric mass, its radius and the speed, and on the stiffness, damping and mass of whatever the motor is built into. The maker therefore quotes nominal vibration in G (acceleration relative to 9.8 m/s²) on a 100 g mass as a practical comparison. [1]

Its ERM product page says its small range suits handheld equipment of about 25–200 g, is based on motors up to about 6 mm diameter with 1.5–3 V rated voltage for single or double battery cells, uses brushed coreless designs with NdFeB magnets, says connections are "most commonly made with flying leads", and that coin motors are also ERMs with the eccentric mass inside a low-profile case. [3]

Bulletin AB-003 explains that a linear resonant actuator (LRA) moves a magnet and mass on a spring with a voice coil, so it needs an AC drive signal at its resonant frequency, with output falling off sharply away from it; its C10-100 example resonates at 175 Hz with little amplitude above 220 Hz, and an ERM cannot be swapped for an LRA without changing the drive. [2]

Editorial calculation: an eccentric mass of an assumed 0.5 g at 1 mm radius spinning at 12,000 rpm (ω ≈ 1,257 rad/s) gives F₀ ≈ 0.0005 × 0.001 × 1,257² ≈ 0.79 N; raising the speed by 20% raises the force by about 44% (1.2²). Measure the actual vibration in your housing, as the bulletin notes the product's mass and mounting change it. [1]

Give the supplier the required vibration amplitude (G, and on what test mass or in your housing) and frequency, motor type (cylinder ERM, coin ERM, LRA), maximum size, supply voltage range and battery type, rated and start voltage, allowed current, lead length and connector, mounting (bracket, adhesive, overmould), duty cycle and life, noise limit, sealing or ingress needs, and quantities.

02

Set voltage, current and drive circuit

AB-004 explains that an ERM driven from a constant DC voltage at its rated voltage runs at constant speed, frequency and amplitude; it works over a voltage range but the maker quotes a start voltage that must be met for the motor to start every time. Raising voltage raises frequency proportionally and force with the square of speed. Back EMF is proportional to speed (V = R·I + K_E·ω) and current to torque, so a loosely held motor, which loses more vibration energy, draws more current than one clamped tightly. Drives range from a single transistor or dedicated driver IC to an H-bridge that reverses polarity for active braking, shortening stop time for haptic effects. [1]

Editorial note: ask for the speed, current and vibration against voltage curves at your battery's full and low voltage, and check start-up at the lowest voltage and temperature the product will see.

03

Read a coin-motor selection table: size, speed, current and G

Vybronics' coin vibration motor page tabulates brush-type ERM coin motors and explains when to choose other types: brush coin motors suit low-cost products with simple alerts at light to moderate duty, brushless (BLDC) coin motors suit very long life and high MTBF at higher cost, and LRAs suit crisp haptic feedback with fast rise and fall times. Its table lists, for example, the VC0625B001L at 6.0 mm diameter and 2.5 mm thick, rated 2.5 V (2.0–3.5 V), 100 mA maximum and 42 mA in the column Vybronics labels “typical”, at least 10,000 rpm (167 Hz) and 0.30 Grms measured on a 50 g mass; the VC0834B011F at 8.0 × 3.4 mm, 3.0 V (2.7–3.3 V), 85 mA maximum and 61 mA (Vybronics “typical”), 13,500 rpm (225 Hz) and 0.70 Grms; and the VC1020B111F at 10.0 × 2.1 mm with the same 3 V, 13,500 rpm and 0.70 Grms. The table gives maximum response times of 90 ms to rise and 50 ms to fall to 50% of power for these brush motors. Motors can be supplied with connectors, spring contacts, FPC or bare pads, and with foam pads or adhesive tape. [4]

Editorial calculation: the vibration frequency is speed ÷ 60, so 13,500 rpm gives 225 Hz and 10,000 rpm 167 Hz, as the table shows; at 3.0 V and the 61 mA Vybronics lists as “typical”, the 8 mm motor draws about 0.18 W. A 90 ms rise time means a 100 ms pulse barely reaches half power, which is why short haptic clicks are given to LRAs. Ask for the G value with its test mass, since the 6 mm motor is rated on 50 g and others on 100 g. [4] [1] [2]

04

Two coin-motor makers: one with LRA and SMD types, one with 8–10 mm 3 V parts

One listed maker shows coin ERMs next to LRA, coreless and SMD types; the other lists 8–10 mm, 3 V flat motors with start voltage, speed and current, the same columns as the Vybronics table above. [4]

05

Winding, NdFeB magnet, eccentric mass, coin housing and driver

06

Motor type, G on a stated test mass, start voltage and current for a vibration motor order

A G figure means little without the test mass it was measured on (Vybronics rates its 6 mm motor on 50 g, Precision Microdrives quotes on 100 g), so the vibration row asks for both. [4] [1]

07

Send the vibration, size and electrical data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Vibration: [amplitude; frequency; test mass]
Type: [cylinder; coin; LRA]
Size: [diameter; length; mounting]
Electrical: [voltage range; start voltage; current]
Drive: [transistor; driver IC; H-bridge; AC]
Supply: [leads; connector; life; quantity]

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