Skytrak’s Side spin

[DannyMRICS]

According to Trackman’s blogs, for a 150y shot, each 1* of spin axis = 1.1y offline. So, for my attached shot, it should be 8y offline, but SkyTrak calculates it as being 12y offline! Add to that that SkyTrak virtually never measures a horizontal launch angle between 0.1 - 1.3 (it seems to be either zero or over 1.4), trying to hit a baby draw on the pin is pretty difficult!

[keither5150]

Side spin is something that drives me crazy as there is no such thing. There is spin and spin axis. What gives your shot shape is when the club path differs from the face angle or relative face angle. When these two things differ, the ball spins on an axis or tilt. If you hit a shot with 4 degrees inside out path but have a 6 degree closed face. You will 2 degrees SA or a slight draw. But your shot will start off to the right due to the club path To hit a draw, you have to close your face more than the path. Most of my straight shots still have a 4 degree inside out path but also have 4 degree closed face. HA launch angle doesn't play a part in whether a shot draws. However a draw will generally start right ( for right handers) and come back left. The ball starts right because of the path. When you face angle is closed and exceeds the path either way, you will have shape on the ball.

[Morini]

The subject line says side spin, but the rest of the post uses the term spin axis, and shows clear understanding of the concept. Not sure where you are going with this.

[jut111]

spin decay - skytrak's algorithm doesn't take it into account. And it's a 2k dollar piece of equipment vs a 30k piece of equipment, you can't expect tolerances to be as precise.

[DannyMRICS]

Thanks Jut11,

Think you’re probably right.

I’ve been crunching some numbers with three other flight algorithms, and they all seem to take spin decay into account. I would have thought it would be pretty easy to allow for spin decay (?) and its pretty important for a launch monitor. It just adds a cumulative effect to slight inaccuracies - 2 degrees HA out, 3 degrees spin axis out in the same direction, then add no spin decay on top of that, just seems an easy way to make to SkyTrak more accurate.

Dan.

[triplebogeysrbetter]

I would account for some limitations of the hardware as well.

Without knowing what’s under the hood. It might be like comparing VM for workstations vs VM on cluster of top of the line servers.

You might not ever get the same compute power.

[Morini]

Yes, I would go with lack of spin decay in ST algorithm. I have a spin decay formula somewhere and will see what it gives for your numbers. If it is around 4 yards, problem solved. I believe Seth has stated that they are considering updating the algorithm to take it into account.

[DannyMRICS]

Thanks Morini,

That would be interesting.

[Morini]

I am out and about and don't have time to dust off my old calculus text books, but spin decays roughly 4% per second of ball flight.

[jrz]

The ball starts right because of the path.

I believe that face angle determines which direction the ball starts. Path relative to face is what causes side spin.

[keither5150]

You are correct. Old school thinking was that initial direction came from path.

[Morini]

Path does have influence, but not much. Something like 15% for driver and then up for every higher lofted club from then on.

[keither5150]

Path relative to face gives the ball it's spin axis..... that is correct. But I have been taught that it's the path that dictates which direction that the ball starts. Maybe my buddy that showed me how to shape my shots is incorrect.??? Update!! Turns out that you are more correct than I am. I did some checking and the consensus is that 85% of path comes from face angle. Here is some light reading. http://perfectgolfswingreview.net/ballflight.htm

In my buddy's defense..... he is pretty old.

[A_little_thin]

I remember hearing this and it keeps it straight for me "face sends it....path bends it" Face determines start direction, and face to path relationship dictates the curve/bend.

Most beginners are wanting a "push draw". Draw being a shot that starts right of target and bends back to target. Hook would be starting right and curving PAST target or really anything ending left of target that started right of target line. A draw is getting closer to the target, a hook is a draw that is curved too much. Same with fade/slice.

[Morini]

As per trackman, it will curve roughly 3.5% for every 6 degrees of spin axis

[DannyMRICS]

Morni,

yes, so that would be 6-7y on a 150y shot with 7* spin axis, not the 12y shown by SkyTrak.

[wbond]

But how many yards off line did it roll. I would assume the numbers above from trackman would be for carry only.

[DannyMRICS]

Fair point.

It did roll 3y, so I suppose it could have rolled an additional 1y offline.

[rjd1975]

I love this discussion and although I may not use the correct terms, it has seemed as though my ball flight is straighter in real life than on the SkyTrak. But I would rather that be the case than the opposite.

[taeho]

Side spin is something that drives me crazy as there is no such thing. There is spin and spin axis. What gives your shot shape is when the club path differs from the face angle or relative face angle. When these two things differ, the ball spins on an axis or tilt. If you hit a shot with 4 degrees inside out path but have a 6 degree closed face. You will 2 degrees SA or a slight draw. But your shot will start off to the right due to the club path To hit a draw, you have to close your face more than the path. Most of my straight shots still have a 4 degree inside out path but also have 4 degree closed face. HA launch angle doesn't play a part in whether a shot draws. However a draw will generally start right ( for right handers) and come back left. The ball starts right because of the path. When you face angle is closed and exceeds the path either way, you will have shape on the ball.

my skytrack too. problem of side spin..all my shot go left.with side spin..thats real big problem..

[Morini]

my skytrack too. problem of side spin..all my shot go left.with side spin..thats real big problem..

I think you missed keither's point. He does not have a side spin issue with his skytrak. He just mentions that he doesn't like the term "side spin" and prefers the spin axis/total spin setting to side spin/back spin.

It is rare for Skytrak to have false spin axis, so most likely that is your actual shot shape. A million reasons that could happen, but one test would be to hit a few off a short tee to rule out mat grabbing and twisting face shut. Second, if offset, move target line because aiming at an angle to screen tends to lead to draws and hooks. Ultimately, probably best to take it to the range. Use white ball as yellow can give weird readings.