Slalom Ski (Handle) Path Physics part 3

[lundberg]

This is an update for my effort to understand what is going on while I ski. 

It started in the winter with a parameterized matlab model of the handle path based on a swing profile.

part 1-

https://ballofspray.com/forums/topic/51107-slalom-ski-path-physics-matlab-model/#comment-846939

followed by a simple setup to measure the actual swing profile with rope tracking camera mount and phone app to record the gyroscope data

part 2-

https://ballofspray.com/forums/topic/51660-slalom-ski-handle-path-physics-part-2/#comment-850767

 

A couple of weeks ago I took a trip to StellaBlue and had a chance to collect some data in the course and have a great time skiing!  (Side note - I improve my PB almost a full pass, running 15off/34.2 (7 times), getting around 4 ball at 22off/34.2mph and around 3 ball @ 28off/32.3mph) 

Here are a couple of fun pictures from the trip (you should go to StellaBlue if get a chance)

 

So here is the data.  There is lots of info here, but I think it would be most useful for those who are trying to make a change and see / measure the impact.  Whether it is location in the course for gates, speed dynamics (think "fast vs slow" ski), differences between onside and offside, or "what is another skier actually doing differently than I am"....its all here.  If you collect some as I described in part 2 I'd be happy to "process" it for you.

(The plots are not to scale (x vs y).  I'll put one at the end for reference.)

@MarcusBrown

@AdamCord

 

 

 

[lundberg]

@TFIN @Chris Rossi

I just finished listening to the latest spray makers podcast on gates, and loved the talk about "handle path". I wonder if you'd be up for collecting some data to see how it aligns with your thinking?

[Adam Caldwell]

@Lundberg....I think you lost them at Matlab.....

@AdamCords college buddy Tom Pollock did this with us via dual strain gage on pylon at Trophy. 

See if you can head to Hilltop with Cord this weekend and get some data through 41 with your setup.   I'd say come here, but thats a long as flight.

[ski6jones]

Your plots show min speed just before the bouy.  Seems to me you must continue to slow down through the turn until the boat picks you up and you start accelerating again.  This would mean your min speed would occur after the bouy.  How is speed measured (or calculated)?  Do you have an explanation for this?

[Kroeks]

I agree, but unless I'm reading his graphs wrong, I believe they do show the min speed being just after the bouy.  The entrance gates are at the bottom, no?

[lundberg]

@ski6jones

@Kroeks has it right, the plots show the course starting at the bottom and running to the top. As you round the ball you slow down as the swing goes away from the boat and you are just starting to accelerate. The pink mark shows where the peak swing speed happens and the green where max speed over the water happens.   In the last plot you can see that my peak swing speed is just before centerline and the peak speed happens sometime later as your direction becomes more in line with the boat.  You can see how I'm getting later and later by how close the max speed is to the ball. You can also see how I pulled long to 6 and my peak swing speed was after centerline.

[lundberg]

On 7/21/2023 at 5:27 PM, adamhcaldwell said:

@Lundberg....I think you lost them at Matlab.....

@AdamCords college buddy Tom Pollock did this with us via dual strain gage on pylon at Trophy. 

See if you can head to Hilltop with Cord this weekend and get some data through 41 with your setup.   I'd say come here, but thats a long as flight.

@adamhcaldwell thanks for the encouragement! I reached out to Cord and could not make this weekend happen,  but I'll try again. 

[lundberg]

Big thank you to @pkulio for being the first to collect and send me data!  He has a nice set up running standard phone video at the same time he was capturing gyro and gps data using a ski doc orbit mount.  He was skiing 36mph running passes at 28 and 32 off.  The "handle path" at the bouy gets less accurate as the rope gets shorter as it begins to arc as the skier gets higher and more free of the boat.  It should still be accurate when the rope is tight behind the boat showing location in the course as well as cross course angle, directional speed and peak swing speed.

 

Edited January 8 by lundberg
improve image resolution (take 3)

[lundberg]

@Horton is there a way to improve the resolution of the images in a post?  Looks great on my PC but once it get's up loaded to the tread you can't see any detail.  

[skialex]

I was going to say that top speed looks like a little late and closer to the buoy than expected, but then saw the shorter line data and looked more where top speed should be at…

[Horton]

@lundberg I may not get time to set it up today but your stuff could go in the downloads section. That way files could be as big as you want - within reason. I will set it up when I get a chance.

[lundberg]

Thanks again to @pkulio! His data is great and is making me think about what sort of trends I can find.  Here is a look at a comparison of angle, speed and location in the course at centerline (gate, 1 to 2, 2 to 3.....).  If you pair this data with video you might be able to correlate small details with the impact on angle and speed, what the actual difference between an "easy" pass and a "hard" pass. 

Here is one of my 15off 34.2mph passes (at a minimum you can see that Paul runs and earlier line).

[pkulio]

Amazing work!  Just keeps getting better and better!  Down course percentage is exactly what I've been trying to eyeball for years and it's so cool to just see it laid out in a chart.  I nominate @lundberg for the Nobel prize in waterskiing

[lundberg]

On 1/8/2024 at 10:54 AM, Horton said:

@lundberg I may not get time to set it up today but your stuff could go in the downloads section. That way files could be as big as you want - within reason. I will set it up when I get a chance.

@Horton I was able to use the "downloads" approach to increase the resolution of an image, thanks!

[Horton]

@lundberg

You could have used the Gallery section but since your plots are so big I think using downloads is the right solution. Any feedback?