Ball flight lies

[birlyshirly]

Jul 14, 2012 1:00:54 GMT -5 teeace said:

Jul 13, 2012 18:13:36 GMT -5 birlyshirly said:

Anyone understand why he says that the direction of the divot doesn't reflect clubpath?

Because you take the divot after the impact so it' doesn't show how you arrive to the impact. FS tells I'm coming mainly 2deg in to the ball but my divots are all the time to the left as they should be.

But the really interesting case is how those devices find that 2 degrees out or in or even smaller differences.

Thanks. That makes sense, although I can't help but feel that the video feels almost deliberately obscure. Call me pedantic, but "divot doesn't show path" isn't quite the same as "divot shows path, but not the bit of the path you need to worry about".

Got it now, I think.

Cheers

[jeffy]

Jul 2, 2012 17:51:38 GMT -5 gmbtempe said:

Pretty interesting video, I think I am going to get some impact tape to see where I am hitting the ball.

I need a poor man's trackman.

I watched this video and have some questions for the Trackman experts.

My understanding is that the bulge built into drivers should more or less offset the gear effect that arises from an off-center hit, no matter where the ball is struck on the face. As a consequence, similar swings (i.e., swings with similar paths and face angles) should produce reasonably similar results, no matter where on the face impact occurs. In fact, that was the basis of the patent for bulge granted to Spalding in the 1940s. You can download the patent application here which includes a summary of the mechanical testing which showed this to be true in practice.

www.freepatentsonline.com/2395837.html


Physicist Dave Tutleman does the math here:


www.tutelman.com/golf/ballflight/gearEffect1.php



So, unless there are serious errors in the Spalding testing or Tutleman's math, or something seriously wrong with Graham's driver, there is something wrong with the Trackman numbers. Both drives should end up in the same general direction.

We know Trackman can't "see" what is going on at impact (face angle in particular) and deduces that information somehow, presumably from path information pre-impact and ball flight information post-impact. However, I can't find anything on-line that describes any kind of testing or verification of the reliability of these calculations by Trackman/Flightscope. Richie or Trackman owners, do you know what testing has been done?

Hell, I can't even find any verification of the D-plane from "live" testing. Is everyone just relying on an unproven theory and assertions???



Jeff

[tba]

Go to Wishons site there is a tech forum there and lots of info, you could ask Tom about that.

[jeffy]

Sept 6, 2012 21:11:04 GMT -5 @tba said:

Go to Wishons site there is a tech forum there and lots of info, you could ask Tom about that.

Thanks. Checked it out, didn't see anything on point.



Jeff

[dcell]

My understanding is that the bulge built into drivers should more or less offset the gear effect that arises from an off-center hit, no matter where the ball is struck on the face. As a consequence, similar swings (i.e., swings with similar paths and face angles) should produce reasonably similar results, no matter where on the face impact occurs. In fact, that was the basis of the patent for bulge granted to Spalding in the 1940s. You can download the patent application here which includes a summary of the mechanical testing which showed this to be true in practice.

My guess is that Trackman is not really measuring the face angle. It would need to use the radar measure from above or from some angle ahead to "see" the face surface.

From Trackman's blog:

"TrackMan measures the 3 dimensional direction and speed of the clubhead at impact, in addition the 3 dimensional ball launch direction, speed and spinrate are measured by TrackMan.

By measuring these parameters and applying the law of physics this provides the orientation of the clubface at the point of impact on the clubface. This orientation of the clubface is 3 dimensional and are reflected in the data parameters “face angle” and “dynamic loft”. Even though that “face angle” and “dynamic loft” are derived numbers from direct measurements and a collision model, numerous robotic test has proven that this is indeed a very accurate calculation of “face angle” and “dynamic loft”."

So with off hit shots, the math model is probably guessing the face angle with more error. I don't think face bulge has any standard radius, so each club is going to give a different starting line, and Trackman is going to estimate face angle, and the other clubhead related parameters. In the end, Trackman is a tracking doppler radar, and it tracks a ball accurately, not the club. Trackman is getting the spin, trajectory, et al correct, it just has to compute some things because the radar is located behind the action.

[jeffy]

dcell-

Yes, that sounds reasonable. As I think about it, the bulge on John's driver would cause Trackman to calculate the face angle on the toe hit as more open than a center hit on an identical path. I'm not sure John took that into account when he compared the two sets of numbers. Lots of moving parts to keep track of!


Jeff