SkyTrak review from Mr Short Game, with testing on driving range

[RAB_74]

I've been watching some of his stuff on youtube lately and as a SkyTrak user myself (for almost a year) I thought it was interesting to see how he liked it and rated it,
especially when they test full shots on a driving range, I haven't tried that myself yet.
Apparently there will be a couple more videos coming with more in-depth review of the different features and play-modes.

https://www.youtube.com/watch?v=PF-5tRDxyxQ

[TrueGolferNorth]

It’s a great video! Thanks for sharing.

[GungHoGolf]

Good video. The exaggerated side-spin effect is on full display with a few of those driver shots on the range - really hope SkyTrak addresses this soon SkyTrak_Seth .

[TrueGolferNorth]

Good video. The exaggerated side-spin effect is on full display with a few of those driver shots on the range - really hope SkyTrak addresses this soon SkyTrak_Seth .

For the purpose of game improvement this exaggeration actually provides the benefit of promoting tighter dispersion at practice....this is if SkyTrak does not exaggerate in the opposite direction.

[GungHoGolf]

True, it does force you to neutralize your path if you want to keep 'em on target. I've never seen it miss the spin axis direction - just the exaggerated ball flight and off-line distance.

[pcascio]

I've watched a number of Mr. Shortgame's videos. He's got a unique style, which I enjoy. He makes a good point about knowing where ST thinks the "center" or what I would call the Aim Point. Making sure Skytrak is aligned perfectly parallel to your target line is really important. If the angle is off even slightly, the ball path is effected,

[RAB_74]

I've watched a number of Mr. Shortgame's videos. He's got a unique style, which I enjoy. He makes a good point about knowing where ST thinks the "center" or what I would call the Aim Point. Making sure Skytrak is aligned perfectly parallel to your target line is really important. If the angle is off even slightly, the ball path is effected,

Yes, like he says at the end, he discovered after a while on the range that the unit's centre was a few yards left of where they were aiming so what he saw as an exaggerated side spin a couple of times might not have been too far off. I haven't thought about this much before as I'm a 30 handicapper and my shots are too inconsistent anyway and I don't have enough experience with golf or feel for what is a 'right' trajectory based on my contact when hitting into a net in the garden.

But when you think about it, if the Skytrak is just a couple of degrees off line from where you think is centre it will have a big impact on long driver shots. Say it's just 2 degrees offline to the left from where you are aiming, which will be difficult to notice on your mat by just eyeballing, that turns into more than 8 yards left of your aim at 250 yards, so if you then hit a driver that starts a degree to the right of your aim and it fades slightly 8-10 yards off line, and you can carry that long, it will end up looking like a slice around 20-25 yards off line.

Not saying Skytrak don't exaggerate side spin and trajectories, just that in some cases it could look more extreme because the user's aim line doesn't
match the unit's line 100%.

Good video. The exaggerated side-spin effect is on full display with a few of those driver shots on the range - really hope SkyTrak addresses this soon SkyTrak_Seth .

Have Skytrak confirmed this and are working on a fix? How 'big' is the effect and does the effect increase with increased side spin?
Has anyone ever tested it on a range in optimal conditions, perfectly aligned, in still weather, no direct sunlight etc. to see how close it was to reality?

[frodaddy00]

I calibrate my SkyTrak whenever it is moved by hitting shots directly at center line, then left and right, and move the unit until shots are lined up properly. After doing so I consistently see exaggerated draw spin. I think the topic of spin decay has been brought up ad nauseum and I 100% believe its an issue. For me this rules out any alignment issue contributing to exaggerated side spin.

I've accepted some of the SkyTrak shortcomings given its outstanding price point and opening up the sim market to the masses. I finally pulled the trigger on a special edition GC2 but I will miss the SkyTrak software.

[wbond]

Easily the most missed thing moving to a GC2 is their software. Not sure why some people complain about it so much, i thought it was really good and worth the annual price when they added all the features.

I finally pulled the trigger on a special edition GC2 but I will miss the SkyTrak software.

[Wizard of Coz]

I still get some withdrawal symptoms. I enjoyed the skytrak range. However I couldn'tgo back now and i don't miss the annual gip fee to use software i own. That didn't make sense to me. The fr1 helps me through my lows but it isn't the skytrak range.

[FaultyClubs]

...After doing so I consistently see exaggerated draw spin. I think the topic of spin decay has been brought up ad nauseum and I 100% believe its an issue...

Spin decay has been blown wildly out of proportion. It has a very small effect. Too small to be seen in a video of a ball flight.

Besides spin decay also affects apex, landing angle, distance and rollout but people who magically can see spin decay never talk about that.

I'd look elsewhere for the answer to overcooked draws/fades.

[trumb1mj]

The initial spin measurement seems to be quite accurate. The lack of a spin decay algorithm means that your ball will spin as fast from the moment it's hit until the moment it hits the ground. That could cause big issues with the accuracy of your ball flight model as well as the reaction once the ball hits the ground.

[FaultyClubs]

Andy is correct, the Skytrak spec is +/- 250 rpm on side-spin. Errors are statistical, real life Trackman comparisons show a significant number of shots disagree by more than 250 rpm on side-spin. Compared to spin decay, these errors are significant.

There are a boatload of parameters/assumptions that affect curvature more than spin decay. If there is indeed an issue with Skytrak's flight algorithm only they will be able to figure out what parameters need to be tweaked.

How much offline error are you guys talking about? I searched the forums and couldn't find anything. Couldn't find where Seth even agreed there was a flight problem for that matter. Has someone compared the Skytrak range with Optimal Flight? Maybe it's just a presentation issue, or as Andy said, a measurement issue.

[AndyF]

Regarding spin decay here is a PM that I sent to Seth back in October 2017...

I have a formula that I've used in my own flight model that seems to give results that are consistent with a number of other models that are out there.

Now unfortunately I can't remember where I got the original equations from however they are as follows:

Spin reduction (dw/dt) = -0.00004 * (v²/R²) * S

where the spin reduction is given in rad/s = (rpm * 2 * PI) / 60

v = overall ball velocity in metres per second
R = ball radius in metres
S = (ball radius (in metres) * spin (in rad/s)) / velocity (in m/s)

I use this to calculate a spin reduction for each specific time point in my spreadsheet (which is set to 0.01 seconds) and apply this reduction to the overall ball spin rate before then splitting it into it's appropriate x, y and z vectors

As an example, if I've got initial launch conditions of a regulation golf ball (with a radius of 0.02134 metres) an initial velocity of 150mph (66.67m/s) and an initial spin rate of 2500rpm then first I calculate my spin rate in rads / second

Spin rate = (2500 * 2 * PI) / 60 = 261.80 rads/s

I then calculate the S factor

S = (0.02134 * 261.8) / 66.67 = 0.0838

And then I use these numbers to determine the spin decay over my time factor

dw/dt = -0.000004 * (66.67² / 0.02134²) * 0.0838 = -3.272 rads/s

So over my time period of 0.01 seconds I know that the spin reduces by 0.03272 rad/s and then I recalculate again for my next time period based on a new spin rate of 261.77 rad/s

I don't know if this will help or not but hopefully you can get something useful out of it.

Many thanks for your continual improvement of a really great product and long may it continue.

Best regards,

Andy


SkyTrak_Seth 10-30-2017, 03:41 PM
Thank you, Andy! This will certainly help get the ball rolling!


AndyF 10-30-2017, 09:59 PM
No worries ,
In total I think it works out approx 2% in spin reduction which is slightly less than the 4% or so that you see on trackman but hopefully it will give you a starting point from which you can work forward.
You can modify the global 0.000004 correction factor to suit whatever results you wish to get.
It's worth noting that as it's a %ge reduction then you will see a bigger reduction in higher spinning shots although they are generally airborne for less time unless you hit high spinning driver shots which will probably show an increase in distance.
It also obviously effects the distance offline that shots travel which I think is what caused the question to arise on the forum.

Hope it helps and if you need any more info then just let me know

Andy

[AndyF]

Here is the original spin decay thread for those that are interested...

https://golfsimulatorforum.com/forum/skytrak/128281-spin-decay-for-st/page2

Andy

[FaultyClubs]

Again, what is the offline error in Skytrak'a existing flight model? No-one seems to have documented there is a problem with their modeling let alone the culprit being spin decay.

I'm a proponent of modeling spin decay as you can see from the original thread Andy linked. 2%-4% seems reasonable. But the actual effect is small and nonlinear. It may not be significant depending on other factors in the system.

I don't have a Skytrak so can't do it but someone badly needs to take a bunch of shots with each club on the Skytrak range and compare the offline error with what Optimal Flight predicts. Document that and go from there.

[AndyF]

I've done some playing about with my flight model to give people a rough idea as to what sort of distances we are talking about in terms of spin decay being this so called big factor in the perceived offline error..

I'm using the following parameters

Ball speed: 150mph
VLA: 12.5°
HLA: 0
Back spin: 2,500rpm
Side spin: 500rpm
Zero wind and air temp of 20°C with 0% humidity

The results are as follows:

Using my original model values that gave an approx spin reduction of 2% per second of ball flight

Without spin reduction:
Carry: 225.53 meters (246.6 yards)
Offline: 29.07 meters (31.8 yards)

With spin reduction
Carry: 225.23 meters (246.3 yards)
Offline: 28.48 meters (31.15 yards)

I then changed the figures to model the spin reduction of 4% per second of ball flight as suggested by Trackman etc and got the following results

Without spin reduction is obviously the same figures

With spin reduction (4%)
Carry: 223.99 meters (244.96 yards)
Offline: 26.91 meters (29.43 yards)

So in the case of a 4% per second spin reduction on a 'typical' driver shot you are looking at a change in offline distance of 2.4 yards. Hardly a massive figure and I agree with Faulty that if there is an issue then I don't see it being related to the fact that spin decay isn't modeled.

I would suggest it is more a case of an incorrect reading of the spin axis resulting in applying too much sidespin to the flight model.

As an example, using the above reference case but increasing the side spin to 750rpm from 500rpm then I get the following figures:

With spin reduction (4%)
Offline: 41.23 meters (45.09 yards)

So the spin reduction effect gives a change of 2.4 yards when modeled at 4% reduction per second.
A 'mis-read' of the side spin by 250rpm gives a change of 13.3 yards

Andy

[wbond]

Wow, that is a huge difference with just 250rpm change on the side spin.

[andygg1986]

I wonder if the 250rpm tolerance is dependent on the total spin. I always think in terms of spin axis and 250rpm on a 2500rpm driver shot is a much larger axis change than 250rpm on a 10k rpm wedge shot. Just intuitively it seems like the wedge shot would be the one with the largest error in terms of rpm but I have no concrete reason for saying so.