kjorn wrote:9m jump isn't massive, sounds more like a lucky gust.
We regularly put the Woo, PIQ, and xsensr on the same board and get similar results.
Why do some of you think its so hard to calibrate the Woo? These guys are engineers, I bet they have a million ways to calibrate and check each woo... put it in a machine that flings it up 5m, 100 times, does it read 100 5m jumps? Do the same for 5.1m, then 5.2m, etc until you get to 50m job done. Why do you thin that they have not done this? Have you never met an engineer before?
yep 9m is not massive but it was the highest achieved (by woo measure) at conditions they had that moment at Öland. Normal summer in Baltics winds are under 10m/s or 20kn. Maybe once a summer we get >10m/s wind. That's why I think woo's global stats are insane. Why should I at Scandinavia 6m/s wind "compete" against guys jumping at Cape Town in 20m/s winds because there is no competition?
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About accelerometer and height measurement and calibration.
- Accelerometer reports acceleration (usually) as a 16-bit number (65536 values) from given resolution (±1g, ±4g, ±12g, ±24g etc).
- Acceleration is digitized (ADC) so it has quantization noise. ADC-value is not integrated between two samples but derivate (short integral actually how ADCs work) at certain time. Remember ADC is a comparator where it compares ADC's internal electical voltage against measured voltage. If internal is less, ADC will add voltage and re-compare as long as required. And at the same time input signal voltage is constantly changing as time goes on.
- Feel free to download different 6/9 axis IMU specification sheets for study.
- Accelerometer (and magnetometer & gyroscope) output needs to be analyzed what is most obvious orientation of Earth's coordinates aka gravity field
- Matrix needs to be done with estimated rotation values to calculate acceleration on earth's coordinates. Keyword: Quaternions or Euler angles.
- Most accurate output would be via Kalman filtering but woo does not have additional sensors to increase prediction accuracy of Kalman(?)
- Board is shaking/rotating all the time
- Now at jump you need to determine threshold amount of acceleration upwards in earths gravity field. (minimum value to determine it was a jump)
- Then you need to use some algorithm to backtrack to release-point (freefall sports like snowboarding is easy because it is time when freefall begins)
- Kicker - acceleration changes upwards and upward speed on wave bottom. But jump begins when you are airborne, not at wave bottom.
- From that point you must begin integrate acceleration to speed
- Re-integrate speed to position (= height)
So actually the IMU algorithm for kite sports is not that simple as you Kjorn want to imagine it to be. That is why Woo ver1 and Woo ver2 gives out different readings. Different hardware, different software etc.
