How does Velo Bling-Bling work?
Mode of Operation
Thanks to the stroboscopic effect, the impression arises, that the image is motionless. The LEDs have to be turned on and off in time with the wheel rotation. One full wheel rotation takes about 750 ms at 10 km/h velocity, at 100 km/h it takes only 75 ms (supposed circumference is about 2.1 m for a 28" wheel). The radial distance between two LEDs is 2" (5.12 mm), the supposed tangential distance is the same for the same tangential and radial resolution. At maximum velocity the switch on period for a LED is 270 μs. There have to be 96 LEDs (32 LEDs times 3 colors) switched in this period. That means there is only 3 μs time for single LED.

circumference for 28" race wheel
C = 2.105 m

vmax = 100 km/h = 27.8 m/s
tmin = C ⁄ vmax = 75.8 ms

Tangential distance between 2 LEDs
dradial = dtangential = 5.12 mm

rLED = 0.23 m
CLED = 2 • π • rLED = 1.445 m

tswitch = tmin ⁄ (CLED ⁄ dtangential) = 269 μs

Stroboscopic Effect
The stroboscopic effect is a visual phenomenon caused by aliasing that occurs when continuous motion is represented by a series of short or instantaneous samples. It occurs when the view of a moving object is represented by a series of short samples as distinct from a continuous view, and the moving object is in rotational or other cyclic motion at a rate close to the sampling rate. It also accounts for the "wagon-wheel effect", so-called because in video or film, spoked wheels on horse-drawn wagons sometimes appear to be turning backwards.

Depending on the frequency of flash, the element appears motionless or rotating in reverse direction.
Strobe_2.gif

(Source https://en.wikipedia.org/wiki/Stroboscopic_effect)

-- Peter Schmid - 2014-11-04

Creative Commons License
Velo Bling-Bling by Peter Schmid is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

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