Clubhead & Ball Speeds Are Correct...but Yardages Are Hugely Inflated...

[Morini]

So how do we know if Swing Caddie is any good at REPORTING an item such as "backspin" if it is not actually measuring it...and is instead only predicting it based on the aforementioned algorithms? Becasue in head-to-head tests versus Flightscope and Trackman, Swing Caddie somehow mangaes to consistently come within 1.5-5% of the numbers that these much higher-end machines report. If you trust Trackman and Flightscope, then you can trust Swing Caddie to within a 1.5-5% margin of error...not on every individual shot mind you, but definitely on an averages over a number of shots.

Assumptions are made that fall apart during atypical situations. If you give an algorithm some data such as height, age, occupation and lifestyle it can probably guess your body weight with remarkable accuracy. Just assumptions based on correlations, not actually measuring your weight. Get an atypical person, way off. Just like your spin.

I give up at that his point. Take your Skytrak to your next TM session.

Skytrak is accurate on the vast majority of shots (80%), with about 15% minor and 5% major misreads. It is possible you have a bum unit, but unlikely because a bum unit wouldn't get reads. It is as mentioned really really hard to screw up spin photometrically. You compare rotation between two images with known interval time. It is just physics. The odd time an unclear image slips through and it misidentifies spin. But no chance that it would do it consistently. The camera doesn't lie.

[Morini]

The tee itself was offset to the right of the net center, so I angled the SkyTrak unit to the left a bit to compensate. Not sure if that had anything to do with the visual representation showing little draws every time, or if they impact the the side spin calculations.

Angled causes you to swing differently. Skytrak doesn't care where you are aiming, it reads side angle relative to unit. Visual representation is based on modeled ball flight. Modeled ball flight is based on ball data. Ball data had spin axis. Spin axis was caused by your swing, not setup.

They were not little draws.

[Morini]

Iphysical set up of the unit, .

Having unit at wrong height can lead to really messed up ball data, including spin. But it is obvious with random reads. Unlikely for mid trajectory in any case.

or the lighting,

Too much direct light can interfere and create no-reads and misreads. But there would be fluctuations and randomness. You cannot have too little light, it works in the dark.

or the position of the golf balls,

Balls at extremes of field of view can experience misreads and no reads. But unlikely for mid trajectory, and as above, would not be consistent

internal damage

Unlikely that internal damage would affect only one variable spin. So extremely unlikely.

or some other variable we have not covered

Anything is theoretically possible. Occam's Razor says that you have low spin in your home setup. I'd do the tee test again, and not at a weird angle. I'd also foot spray your club and use center strikes as your good strikes. I'd also align skytrak properly, place a target on the target line and only use shots with minimal side angle.

[Sixmudd]

Looks like this thread has run its course. OP says his set up is fine, he’s done all the leveling, using good balls, logo facing camera etc. OP then just needs to send the unit back to skytrak to see if they see any issues with it. Could be , or could not be. But as Morini suggested, take it with you to your next TM session. And if you’re still it happy after that, then sell it or return it.

[Morini]

OP says his set up is fine, he’s done all the leveling, using good balls, logo facing camera etc.

You are probably right. I am not going to totally second guess Rogala, but I am going to play devil's advocate in that I feel that he gets lost in the details, the wrong details, which drowns out systematic trouble shooting. It can be sent back sure, and he will be out of a unit while they look at it. And if I am correct, it will get sent back exactly the way it was. Or maybe a different unit, with the same result. Of course, I concede that I could be wrong. Rather than going without and going through all these hassles, I'd say either trouble shoot one more time ... very methodically. No detours. Or just take it to a place with TM4. Don't forget to bring a a board or two to get right height, depending on mat. Probably easiest out of the case.

[Rogala]

Assumptions are made that fall apart during atypical situations. If you give an algorithm some data such as height, age, occupation and lifestyle it can probably guess your body weight with remarkable accuracy. Just assumptions based on correlations, not actually measuring your weight. Get an atypical person, way off. Just like your spin.

I give up at that his point. Take your Skytrak to your next TM session.

Skytrak is accurate on the vast majority of shots (80%), with about 15% minor and 5% major misreads. It is possible you have a bum unit, but unlikely because a bum unit wouldn't get reads. It is as mentioned really really hard to screw up spin photometrically. You compare rotation between two images with known interval time. It is just physics. The odd time an unclear image slips through and it misidentifies spin. But no chance that it would do it consistently. The camera doesn't lie.

So, how do you explain the unit providing backspin rates 1,500-2,000 RPM lower than I have seen over the past 8 years (on boih the mat and off a short tee) ??

Likewise, how do you explain away some of the other threads which also discussed lower than expected backspin RPM reporting ??

P.S. We know that a height difference equal to the thickness of the feet on the metal case (plus a few threads extra) was enough to cause a 2K RPM reading difference between my very first 7-iron swings which inspired this thread, and the last two days of testing. I think I am going to go back and try some more fine tuning with height based on that effect.

The odd thing is that somehow the overall carry numbers are still making sense...its not like the RPM difference is producing the type of carry differences one might expect.

[Rogala]

You are probably right. I am not going to totally second guess Rogala, but I am going to play devil's advocate in that I feel that he gets lost in the details, the wrong details, which drowns out systematic trouble shooting. It can be sent back sure, and he will be out of a unit while they look at it. And if I am correct, it will get sent back exactly the way it was. Or maybe a different unit, with the same result. Of course, I concede that I could be wrong. Rather than going without and going through all these hassles, I'd say either trouble shoot one more time ... very methodically. No detours. Or just take it to a place with TM4. Don't forget to bring a a board or two to get right height, depending on mat. Probably easiest out of the case.

I might be focussing on the details....no denying that as I am a total newbie on this system...but I am not "lost" in the details, as backspin is not a minor detail. RPM helps define trajectory, and in my expereince, trajectory in golf is everything. If you can control trajectory, you can really start golfing your ball.

BTW, I am not "unhappy" with the unit. I am actually very impressed with it...just interested in getting to the bottom of the RPM and height numbers.

[Morini]

I know when to call it quits, lol.

[Rogala]

I know when to call it quits, lol.

LOL...I like to call it quits when ALL the data makes sense...not just some of it. I guess that I prefer dealing with uncomfortable truths vs. comforting reassurances. ;-)

To that end, I got up early this AM and watched a whole series of videos which show various pros doing head-to-head comparisons of TM vs. SkyTrak to see if any interesting RPM and/or apex differences were noted. I also watched one video of the SkyTrak vs. the GC Quad...which also proved to be super intriguing.

1) First the SkyTrak vs. TM - I had really only watched two "comparison videos" of TM vs. SkyTrak before I decided to pull the trigger on SkyTrak, and I will freely admit that I focussed more on carry distance and what I will call "overall shot shape" (meaning draws or cuts from a purely Left-to-Right perspective...not necessarily launch angle, apex or descent angle) when I watched these two "comparison videos". I had been assuming that the RPM numbers on Skytrak (since they were measured and not calculated) would theoretically be better than radar-based units.

In the compasion videos which I had previosuly watched, SkyTrak did a very good job in indoor sessions vs. TM on these two metrics...holding its own very well on shot shape and carry numbers. It also did a good job on those same metrics in most of the videos which I watched this AM when they featured average-type swing and ball speeds (although not as well with elite player swing and ball speeds).

This positively reinforces my pre-purchase belief that SkyTrak is a very reasonable, low cost choice for an indoor LM to power a golf sim for both my kids and me, as none of us are elite swing speed players. So far so good.

This morning, I focussed a lot more closely on the RPM data in the multiple videos which I watched. On most of the iron shots I saw on "comparison videos" this AM, the reported backspin numbers between TM and SkyTrak were actuaslly only 200-400 RPMs apart for most shots. I did notice one consistent exception, however, and that was on mid-iron shots hit with significant draws. On that shot shape, SkyTrak often reported these shots as having 1,500 to 1,700 fewer RPMs (25-50%) than did TM. 7-iron spin rates were being reported that looked more like 4 or 5-iron spin rates.

Note: That 25-50% is a significant number...and right in line with the 30% differences I am seeing/expecting on my own 7-iron RPM rates. I will also note that I did not see the same spreads on wedge or 9-iron shots in these videos. In fact SkyTrak seemed to be particulalry solid at reading wedge and 9-iron RPM rates vs. TM.

Despite that large 25-50% RPM difference on mid-iron shots, however, I noticed (oddly enough?) that the Skytrak "carry distance" numbers were still fairly close to the TM carry distance numbers (2-4 yards) for those clubs, and that they were only inflating the total distance by 6-8 yards vs. TM (depending on the club, and presumably due to more roll being predicted by SkyTrak).

Note: On drawn driver shots in these "comparison videos", Skytrak seems to report about 500 to 700 (20-25%) fewer RPMs than TM...with the effect of inflating both driver carry and total distances about 3-4%.


2) A video which compares the SkyTrak to the (also optical-based) GC Quad was something I had never watched before today, and this video was, in its own way, every bit as interesting as the comparison videos versus TM. The video points out some clear differences, but winds up being a mostly positive review of the SkyTrak when it comes to home-based monitoring for the average golfer. It does highlight one well-documented issue regarding higher swing speed players.

I am assuming that some of you "old hands" have seen this video before...but just in case, here is some commentary and a link:

In a nutshell, this video (which featured an elite swing speed golfer) shows the GC Quad reporting about the same backspin RPM numbers as the SkyTrak for wedge shots, but consistently reporting much higher RPM numbers than the SkyTrak for 7-iron shots, whether drawn or straight.

For a series of 7-iron shots, the SkyTrak reported an average of 4,232 RPMs and the GC Quad reported an average of 5,914 RPMs in back-to-back sessions by the same golfer hitting the same exact 7-iron off the same exact same mat. Another significant difference was that peak ball height (apex) as reported by the SkyTrak averaged 105 feet, while the GC Quad reported an average peak ball height of 125 feet...no doubt related to the RPM numbers.

The RPM difference is specifically cited by the pros in the video at around the 10:50 thru 11:35 minute marks. They actually say that: "..really fundamentally, the two issues we have with [the Skytrak reporting of the] 7-iron is that it carried too far and spun far too little...25% too low..."

HOWEVER...

When the elite swing speed player purposely slowed down his swing to produce a 7-iron shot which carried only 150-160 yards, the backspin numbers reported by SkyTrak averaged only 200-300 RPMs lower than the GC Quad (about 5% lower) and there was even some overlap on individual shots.

The reason given for this difference between elite vs. average ball speeds given in the video was that the GC Quad's 4 cameras produce images taken over an 18" ball flight path, while the SkyTrak's flight window is much shorter....meaning that higher ball speed players get less accurate results due to fewer images being available for analysis. Makes logical sense to me...

Note: Becasue the units could not both be physically positioned to measure the same exact shots at the same time, the golfer in this video hit a series of shots with each unit, and then compared the two data sets. In other words it was not a theoretically perfect test, but it was as close as one could ever do given the physical realities of the situation and a human golfer. I do suppose it could only have been a better test had it been performed by a robotic Iron-Byron type machine instead of a human. The golfer who made the swings, however, is an elite player, with what is shown to be highly consistent ball striking.

Here is a link to this video: https://www.youtube.com/watch?v=17ICvO80dFQ

BTW, in the driver launch comparison portion of the video, SkyTrak reported the elite player's RPM numbers to be consistently HIGHER than the GC Quad by 25-30%....which may or may not exactly fit with the video's previous explanation regarding why the spin numbers for a 7-iron appear LOWER on the SkyTrak vs the GC Quad...but that will have to be a topic for another day.

[RAH5]

Interesting stuff Rogala, thanks. I recall those videos before purchasing Skytrak and the explanations make sense to me. I’m fine with it as the price point is a fraction of the more expensive units so I knew it wouldn’t be perfect. To me it’s strikingly close enough for my needs. Others may disagree and I don’t criticize anyone’s approach to this.

I really appreciate your and other’s efforts here, though, so people who are looking to purchase or refine are able to get the best information possible.

[Sixmudd]

You’re comparing a 2k launch monitor vs $20k launch monitor. For most of us, skytrak works for what we’re using it for, assuming it is set up correctly If you want trsckman or gc quad results, then buy yourself a trackman or quad. But for the average golfer like 99 percent of us on this board, skytrak is just fine.

[Rogala]

You’re comparing a 2k launch monitor vs $20k launch monitor. For most of us, skytrak works for what we’re using it for, assuming it is set up correctly If you want trsckman or gc quad results, then buy yourself a trackman or quad. But for the average golfer like 99 percent of us on this board, skytrak is just fine.

1) You are mistaken about my reasons for starting and developing this thread...and if you look at the ENTIRE thread, you will see that.

2) This is not a "LM comparison thread" at all...and any comparisons to data from other LMs is cited to shed light on what may (or may not) be some valid questions regarding the RPM numbers as reported by SkyTrak vs. IRL results.

3) The thread exists because I was simply trying to determine if my SkyTrak set-up practices were good ones...not to discuss the overall merits of SkyTrak vs. any other system. As I wrote earlier, I am actually quite impressed by my new SkyTrak unit...especially with regard to carry distances and overall shot shape, considering the relatively low price.

4) The initial impulse that lead to this thread was that on "Day 1" out of the box, my SkyTrak was reporting that I was carrying my 7-iron 176 yards with a total distance of 194. These numbers made zero sense to me, as IRL experience shows that I carry my best 7-irons (with 34* loft) only about 155-160 yards and get about 5 yards roll-out under normal wind and turf conditions. I also have launch monitor data from multiple professional club and ball fittings over the past 8 years, as well as about 10 months experience with an inexpensive home doppler-radar system. All of these data points made me 100% confident that something was wonky with my initial SkyTrak numbers.

As I dug into the Skytrak data on the inflated 7-iron carry numbers, my best clue as to what was going on looked to be the backspin numbers reported by SkyTrak...which appeared to me to be about 4K too low based on other data I had seen over the past 8 years.

Based on the recommendation of several helpful users on this site, it seemed that a) my SkyTrak unit height was an issue, as I had the unit in a metal case on a mat which was the same exact height as my actual hitting mat and right next to it, and b) I wasn't aiming the ball logo at the camera.

So, I simply removed the metal feet from the case of my SkyTrak unit (lowering it about 1-2" to 11/16") and retested with the ball logo aimed right at the camera. This brought the RPM numbers up approx. 2,000 RPMs (!) thereby lowering SkyTrak's carry and overall yardage distance numbers to the point where they made some logically reasonable sense for my 7-irons.

So far, so good.

I still noticed, however, that, even with the suggested tweaks, SkyTrak's RPM numbers still remained 1,500 to 2,000 RPM lower than I was used to seeing based on 8 years worth of previous LM data. That is a big % difference, and so I mused: "Just how accurate the RPM measurements are on SkyTrak?". I freely admit, that this was just not some "minor detail" to me, as I had bought the SkyTrak, in part, because I have historically really keyed-in on controlling RPMs and spin axis as being the keys to overall trajectory control. Before purchase, I had thought that SkyTrak would be far, far superior to my cheap doppler unit in reporting these metrics.

5) In response to my RPM accuracy questions, numerous people stated (quite unequivocally) that "..SkyTrak is accurate...it's probably your set up of the unit or your golf swing that is the issue" (paraphrased).

I will accept this premise coming from experienced users, as I am a definite NEWBIE of the first order when it comes to SkyTrak (although not LM technology in general). I will continue to accept it pending further investigation, and that is simply where we still are now....with me investigating all avenues and trying to figure out what I can change in my set-up to optimize the RPM numbers reported by SkyTrak. I plan to post whatever I find, on the thought that others might find it helpful. For example:

6) Several people commented that lower RPM numbers might be caused by my hitting mat...so I re-tested by hitting shots off a low tee, and then posted the raw SkyTrak data showing that it was NOT my hitting mat. Other people suggested I checkout several excellent set-up threads and online guides, and I did that. The numbers still look low.

Then several people threw up their hands and said "I give up...it works well enough for me...so it must be your swing". OK, if some people feel that way, that's fine with me...but I've not given up quite yet on the idea that the lower RPM numbers might be due to the way I set up SkyTrak in my hitting space....and I will be discussing it on the phone with a SkyTech tech later today.

7) In the mean time, I also decided to see what online reviewers were saying about SkyTrak's RPM numbers....and that is where the comparison videos came in. There does seem to be some genuine questioning about SkyTrak's ability to report accurate RPM numbers versus high end doppler and higher end optical systems for a) ELITE SWING SPEEDS and b) on shots with significant draw spin.

I do not fit into category a), but I do fall into category b)...meaning I hit trap draws with my irons....so maybe there is a problem with my swing in that sense...although other LM data seems to who my 7-iron RPM at 5,800 to 6,300 RPMs.

So, for now at least, my search into RPM numbers continues...feel free to utterly ignore this thread if it offends you in any way at all. I won't squawk.

P.S. Oh, and I continue to be impressed by my SkyTrak and have zero plans to send it back at this time.

[Rogala]

Interesting stuff Rogala, thanks. I recall those videos before purchasing Skytrak and the explanations make sense to me. I’m fine with it as the price point is a fraction of the more expensive units so I knew it wouldn’t be perfect. To me it’s strikingly close enough for my needs. Others may disagree and I don’t criticize anyone’s approach to this.

I really appreciate your and other’s efforts here, though, so people who are looking to purchase or refine are able to get the best information possible.

Thanks...I appreciate your comments.

They counter-balance my growing suspicion / sense that a subset of readers seem to hate my guts for even raising these questions...let alone investigating them and posting publicly about them. ;-)

I am supposed to be talking to a SkyTrak tech later today, and will report back.

I did take hitting data last night with 5, 6, 7, 8, and 9 iron shots off my mat...and will post that data too at some point. As a preview, I can tell you that the 8 and 9 iron shots had very little draw bias (neutral spin axis) and all started very near the target line, and the RPMs were quite a bit higher on those shots. On the 5, 6 and 7 iron shots...almost all of which all had a negative spin axis and a launch with started right of target...the numbers remain lower than I expected.

My working hypothesis (or at least my target area of interest) centers around how this shape shot (significant draws) are interpreted by SkyTrak's RPM algorithms based on its camera data.

[Rogala]

Success....I think...

I spent 30 minutes on the phone with a great SkyTrak technician today, and went through a number of set-up and alignment points with them after I told them that I thought my spin RPMs were reading low for my mid-irons. The tech told me that my set up sounded good, and that I should email them some photos of one or two aspects of the unit placement.

The key moment, however, was when the tech asked me where I was placing my golf ball relative to the laser dot. I answered: "Right on the dot or a fraction behind it."

The tech then asked me if I had a low, a medium or a high launch with my mid irons (5 to 7 iron), and if I generally drew or faded those shots. "I said low-to-medium launch and typically with a draw".

The tech then told me to place my golf ball 1" behind the dot and hit some 7-iron shots with them on the phone. So I went out to my garage, and I tried a few 7-iron shots like this, and, lo and behold, my RPMs went up a bit.

The tech then told me to try placing the ball 2" behind the dot, and the RPMs went up a bit more.

The tech then told me to try placing the ball a full 3" behind the dot, and...BINGO !!!! SkyTrak spit out what looked to be more normal RPM numbers for my 7-iron based on my past LM history...maybe 300-400 RPMs low, but much better than anything I had yet seen. The yardage numbers also looked to be more spot on than ever based on my IRL game.

I tried the same thing with the 5 and the 6 irons, and got the similar positive results.

The tech said the 8, 9 and wedges might require a different ball placement, and that I should feel free to experiment...maybe even trying the lofted wedges from a spot in FRONT of the dot. I played around with this, but eventually decided that a bit behind the dot was still the best ball placement even with higher lofted irons. In doing so, I collected some excellent data.

Here is some typical RPM data with the ball placed on the dot, then well behind the laser dot:

5-iron = was 3,500 RPM, now 4,100 RPM
6-iron = was 3,800 RPM, now 4,500 RPM
7-iron = was 4,500 RPM, now 5,800 RPM
8-iron = was 6,000 RPM, now 6,400 RPM
9-iron = was 6,500 RPM, now 7,200 RPM
PW = no previous data, now 7,500 RPM

Now, I actually had seen a number of comments over the past few days which suggested teeing up the DRIVER about 1" behind the dot, but I had not seen any tips about placing mid-irons up to 3" behind the dot. Is this some sort of well known "tip / fix", about which I was just clueless ??

BTW, can anyone tell me definitively what's going on from a technical POV and why this tip worked?? Is it as simple as the idea that, by placing the ball a bit further back, I am (maybe) giving the unit an extra fraction of a second to capture more images??

Anyway, despite this "fix" providing a bit more evidence regarding just how sensitive the SkyTrak optical system can potentially be in both unit set-up and ball placement, I am now growing ever more comfortable with my SkyTrak purchase as it related to RPM numbers...and I am definitely feeling positive in terms of the tech support as well.

[RAH5]

Interesting. This is similar to what people say to do with your driver to allow the cameras a tiny bit more to react. I’m surprised you’d need to do it with a mid- to low-range iron though.

Anyway glad you got it figured out!

[wbond]

It takes two images. The entire ball needs to be in both captured images to get the best results, so there is a window where these pictures are taken. With driver it’s typically the lowest launching club which is why you move the ball back and opposite for wedges. It still sounds like the bottom of the skytrak itself is higher than the mat you are hitting off of. Are you placing the unit directly on the same surface you are hitting from, if so that can cause issues as well.

[Rogala]

I was told by several people to NOT put the unit on the hitting mat, as the force of a club can jostle and reposition the unit. I was told to put it on a separate mat of the same height right next to the hitting mat, and with a tiny bit of separation front the hitting mat to prevent jostling.

The only height difference right now is the thickness of the metal plate which forms the bottom of the metal protection box.

[3on3putt]

Glad you got it figured out. I always place the ball slightly in front of the dot for wedges. Maybe a half inch for a full wedge shot and a full inch for a flop shot.

For driver I tee it up a good 4-5 inches behind the dot.

3-woods and hybrids off the deck are maybe an inch behind.

I have not heard of the concept of doing the same with mid/short irons.

As far as the technical standpoint ..... if a high lofted shot like a wedge is placed too far back, I think it just flies up over the top of the camera and the camera never sees it. So placing it in front of the dot keeps it in the field of view upon its launch.

For shots played from behind the dot .... I'm really not sure, but possibly the opposite effect. A lower launching shot like a 4-iron might not get high enough quick enough for the camera to get a good look if it's launching from the dot. But placing it behind the dot gives it a little extra time to get up high enough for the camera to pick it up. That's just entirely a guess though.