Vibration Motor Used for Panoramic iPhone App
List this as interesting or fun, but not exactly an app you would find in the “Productivity” section. That is unless you’re in the business of taking 360° videos!
The Cycloramic App uses the vibration motor in the iPhone 5 to rotate the phone whilst recording video. It also helps explain the direction of vibration forces in eccentric rotating mass vibration motors.
The app will only work with the iPhone 5. The previous iPhone 4S uses a linear resonant actuator, whilst the latest release reverted to a cylindrical ERM. Importantly, the ERM is located in the top left (facing the screen) and is positioned horizontally with the shaft pointing towards the right.
With the ERM rotating anti-clockwise, we can see that the centrifugal force would lift the side of the iPhone up and then push it forward towards the screen. As this pushes the left-hand side forward, it causes the phone to start rotating anti-clockwise (looking down from above). The app then simply records video and uses the internal compass to detect when it has rotated a full 360°.
The key is the force created in the vertical axis. It helps lift the side of the phone a tiny amount, but enough to reduce the friction between the phone and the table. Now when the force changes direction to the horizontal axis the phone moves a given distance. As the ERM continues its rotation and starts to produce a downwards force the friction is not reduced, and when producing a backwards force the horizontal direction of the phone does not move (or not as much as when moving forward).
Over time this unbalanced movement on one side of the iPhone causes it to rotate. This would not work with the LRA because it only vibrates on one axis, and therefore would lack the vertical force that reduces the friction. This means that the forward and backward force in the horizontal axis would move the phone an equal distance each way, leading to no rotation. The developers clearly state it is only compatible with the iPhone 5, alerting 4S owners it won’t work (as it uses an LRA).
Interested in how vibration directions and motor orientation can affect your design? Check out Application Bulletin 014: Mechanical Layout of Vibration Motors for Typical User Interfaces.
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