Hi everyone
At long last I had the time to complete consolidating and cross checking the data to obtain a continuous rod leg and fly leg velocity history (along Y axis, slanted parallel to the cast) from the snap cast footage Graeme kindly provided.
Tracker data from individual marker runs down each leg were pieced together in Excel. At higher leg velocities, combined with the rather far apart 1m markers spacing, some small velocity data gaps occurred between marker velocity tracks, which I bridged in Excel with its ‘fill series’ function, set to ‘trend’.
Velocity data taken at 2 footage frames per step (may show more subtle detail) and another set taken at 3 footage frames per step (may show less noise) were integrated.
Acceleration data from Tracker had bigger gaps between legs’ marker tracks, so was calculated from the combined velocity data and spot checked against measured longish Tracker marker runs.
Loop propagation velocity can be pieced together from Tracker marker tracks with the loop travel track set as reference frame, but rather was calculated from the already pieced together leg velocities. Accuracy of the calculated loop propagation velocity is supported by compared calculated loop travel velocity vs. measured loop travel velocity (see graph below), which match well enough. Calculated loop propagation velocity was also spot checked against measured longish runs.
“Downward” and “upward”, unless otherwise stated, are along the parallel-to-the-cast slanted Y axis.
Time scaling of the footage, and resulting measured duration, velocity and acceleration, is not entirely certain. Graeme shared the footage as 240fps frame rate, but at that rate the rod leg’s free fall acceleration (this time along a Y-axis perpendicular to ground) right towards the end of the sequence measures at average -16.2m/s², which is higher than acceleration by gravity. At 180fps the same free fall section measures at average -9.1m/s² acceleration. This appears to be closer to reality, with air drag likely accounting for the difference with gravity’s 9.8m/s². So, the data presented here is based on a best guess frame rate of 180fps. In absence of a filmed marble drop or such like more solid reference though, values given here should still be taken with a slight pinch of salt.
Here is the plot of measured fly leg, rod leg and loop front travel velocities throughout the cast, with the calculated (as previously mentioned) loop propagation velocity:
- VELOCITIES
Fly leg velocity data, and therefore loop travel and loop propagation velocities, ends at the point where the last line marker (just before the leader butt) enters the loop.
Note, the rod leg’s velocity and calculated loop propagation velocity reach their highest values at the instance that rod leg acceleration (see below) reaches zero.
And here is the loop front travel measured vs calculated velocities, as check for the validity of loop front travel calculation used:
- LOOP TRAVEL VELOCITY - MEASURED VS. CALCULATED
continued...