Distance issues

[jpotas]

I found that the exact opposite is true. My club distances are right at where I would expect them to be based on my recent ShotScope purchase as well as a couple of years of experience with my Skytrak vs real life shots that I laser. The randomizer on the Skytrak range had been the ultimate practice experience for approach shots, letting me hone in club distances. This has correlated very closely to real life play.

How long have you had the Skytrak? Based on the almost unlimited amount of reviews between Skytrak and all the other launch monitors out there, they are all extremely close to each other. Usually a yard or two. If you are set up correctly it makes me think you have a defective Skytrak and should contact the company, or you don't swing the same indoors. Indoor Swing Syndrome is a real thing!

I did notice that your launch angles are low. ( of course maybe mine are really high???) My 5 iron launch angle is about 22 degrees, yours is under 13 and your 7 iron is only 16.7. The 4 degree difference between your 5 and 7 seems unlikely. Is the bottom of your Skytrak unit dead level with the hitting surface? The unit itself, not the case?

[Chmiller]

Today I tested the Skytrak against my PRGR launch monitor. I found that they agreed very closely on ball speed with a little more variance on club head speed and distance as might be expected since they measure different things in different ways. At this point it seems unreasonable to think that the Skytrak is not reading accurately. I got reasonable spin and launch angle results using a well marked ball. But the distances still don’t compare reasonably with real world averages. I was absolutely crushing the 6 iron and the longest balls of the lot were 150 yards. My on course average for the year 157 yards. Really good strikes on the course would easily be 165 yards. There’s just no way that those swings would have totaled only 150 yards outside. I don’t know what the discrepancy is, but I still find this really frustrating. It’s time to test this thing at the range where I can get accurate measurements of the ball flight to compare with what Skytrak is giving me. I’ll be shocked if they read the same distances. I was at the range just a couple of weeks ago and hit 8 irons up to 150 yards. This just can’t be right.

[preludesam]

No need to apologize. Regardless of what happens we want you to keep posting. I can’t speak for everyone else but my belief is the more people we bring into simulator golf and launch monitors the larger our market becomes. It means companies will want a piece of that pie and bring us better innovation at cheaper prices.

[tlrcash]

Please start approaching this discussion from the carry distance perspective. It is not effective to compare total distance on the course to total distance in any sim software.

[jpinkardvt]

That’s exactly what I was about to say. I find the carry distances to be spot on. Total distance has infinitely many variables, wind, lie, slope, firmness, etc. how many of those shots that you have tracked over the last year were in a zero wind, perfect flat condition?

Lower swing speeds result in a lower apex, which leads to more roll out in real life. The group I play with every week in real life includes my dad and his work friends. A shot that I carry 150 yards is going to back spin 3-4 yards, while shots they hit 150 yards carry 135 and roll up 15 yards. Their carry distances throughout the bag are much tighter together, and this is reflected in my sim.

[Ronsc1985]

The OP's. posted ball speed with a 5 iron is less then my 7 iron measured with a GC2 and I'm 84. If his stated distances are really much longer then the Skytrak then there are two possibilities:

1. His Skytrak has a malfunction where the time between the two ball pictures is not what the computation software assumes..

2 He has the Skytrak set at an angle significantly different then 90 degrees to what a straight shot would be. Remember all camera based LM's measure everything relative to the themselves. This causes a compression of the distance between the ball pictures in the composite image making the computed ball speed less i.e. speed =(distance traveled)/(time between the two ball pictures). Doing this also screws other calculations by making the second ball picture smaller then it should be.

BTW the way ball speed is computed is by measuring the distance between the centroids of the two ball pictures taken. The centroids are computed by the software drawing the outline of each ball picture and computing the center of gravity of each area enclosed.

[Morini]

Late to this, but it is 4.12 milliseconds between the pics, highly highly unlikely that it is off.

[Mirek_62]

... I use a Shotscope watch so I really know my distances. ...

Any advice would be appreciated.

How do you measure carry distance with a golf watch? Comparing total distances outdoors and indoors is a typical mistake of beginners with LM. NEVER compare total distance (even with the most expensive systems like Trackman). ALWAYS compare only the CARRY distance.

[Ronsc1985]

To calculate the carry distance, a quite complex equation is used, which is also verified by knowledge of aerodynamics and airflow. These calculations come from university professors and NASA personnel. They are by no means estimates or mere extrapolations.
Skytrak is a photometric system, and all it really needs to calculate is a short segment of ball flight where it takes two photo images and uses them to calculate everything needed to calculate carry distance (i.e. ball speed, launch angle and backspin).

Actually the solution is an iterative process. The solution starts out with the initial conditions, ball speed, launch angle etc. and a initial distance traveled. It then computes the changes in the initial parameters, .i .e. ball speed and direction,spin etc. and makes new calculations for the next distance traveled. These iterations continue until the ball height is 0 i.e. it lands.. The number of iterations can be as many as the program writer desires. Obviously there is a point of diminishing returns for more and thus smaller iterations and time to complete the iterations.

The point of all this is the ball speed, direction and the spin are constantly changing throughout the ball flight so just plugging initial conditions into a single equation doesn't get the job done.with sufficient accuracy to be really useful.

Some low end LM's which really don't measure spin do use a single non iterative method. You can usually spot these systems because they have you specify what club you are using. The ball has no idea what club you are using. All it knows is it's velocity, spin and direction.

[Chmiller]

Thanks for all the posts since I last wrote. I can only use total distances from my Shotscope since it can’t measure carry. I hit the ball fairly high and it stops pretty short generally. I have friends who hit the low running shots you refer to and that’s not me. My long irons don’t fly as high because of my swing speed but I play on well watered courses where there is little roll out in general. The distances Shotscope yielded are from over 50 rounds of golf and unusually long and short shots are eliminated by their Performance Average stat. That’s the stat I’m using for my distances and I’m confident that they’re reasonable. The rollout distances I see in Skytrak seem reasonable compared to my real world experience.

I was finally able to go to a range where they have Trackman Range set up. It records carry and rollout as well as launch angles and directional information for every shot. I set up my Skytrak and compared shot by shot. It was impossible to make any conclusions based on individual shots. They varied wildly. By going over the data I worked out an average of well struck shots for each system. That is, I took maybe the best five or six shots that weren’t unusually long. This is my approximation of Shotscope’s Performance Average stat. These are the comparisons:

Pitching Wedge, Skytrak 116 - Trackman 106.
Eight Iron, Skytrak 140 - Trackman 129.
Six Iron, Skytrak 135 - Trackman 148.
Five Iron, Skytrak 150 - Trackman 160.

Puzzling numbers. Note the 6 and 8 iron numbers! How does Skytrak see the six iron being shorter than he eight iron by five yards where Trackman sees a much more reasonable increase in distance of 19 yards? Trackman’s numbers progress in a reasonable way from short to long. Skytrak’s numbers are not sensible. With the short irons Skytrak is reading long, with the long irons it reads short. At least on this one occasion.

Since then I’ve done quite a bit of looking at my Skytrak data for the last month to see if my perception of the distances I’ve been getting were reasonable. I wrote down what I’ll call my Performance Average for each club for each session over the last few weeks. Again, this is an average of well struck shots, leaving out any anomalies on the high side and all of my poorly struck shots (of which there are many). I hit more than enough shots in each session to have struck a number of shots as well as I can strike a ball. Here are the ranges I’ve gotten from one day to another over about three weeks

Pitching Wedge from 92 to 116 yards (many shots with indicated spins in the low 2000s)
9 Iron from 100 to 136 yards
8 Iron from 116 to 145 yards
7 Iron from 125 to 145 yards
6 Iron from 140 to 162 yards
5 Iron from 152 to 167 yards

Remember, these are not individual shots. Those are the “performance averages” for whole sessions with each club, typically 20 or more shots with each club in any given session. I hit more than enough balls to strike several absolutely pure shots and determine that I simply can’t hit it any farther on that day. I usually start with a pitching wedge and work my way up so the pitching wedge numbers could represent a lack of warm up in some cases but with the other clubs I should easily reach my peak for the day. The readings seem to generally be more consistent with the longer irons though the lower numbers in each are ridiculously short.

My conclusion from looking back is that my frustration is not unreasonable. How could you possibly draw any conclusions about your performance or your equipment from numbers like these? I believe my setup is careful and consistent. Can I guarantee that my alignment and the height of the unit are perfect? No, but my setup doesn’t vary from one session to another. There will be tiny differences in alignment over time but I don’t think it’s reasonable for a system to be so sensitive to tiny changes that a user can’t achieve reasonable results. I don’t see any issues with distances based on the direction I hit the ball. I get the expected long left/short right pattern. It doesn’t make sense to me that alignment of the unit is affecting my distances to such an extent.

I guess my next step will be to call Skytrak and inquire about an evaluation or repair of the unit. Given the randomness of my results I am skeptical that there is a mechanical issue. I actually doubt that it needs repair. I suspect that this is just the way the unit works. I’ll talk to someone about it. If it’s not unreasonably expensive and they think there’s any chance that it’s not working correctly then I’ll send it in.

Failing that, I guess I’ll keep using the unit. The Bushnell unit looks like it would be the least expensive alternative that might work better but I just can’t see spending the extra money and absorbing the high subscription fees. With the Skytrak I do get the benefit of at least seeing ball flight and getting relative distances on any given shot. The ball flights I am seeing are consistent with the strikes I am making. In fact, I can generally predict the direction and distance of each strike before the Skytrak begins to show the shot. I can set up a green and practice hitting it pretty easily. I just have to accept that on any given day I will likely have to set the green up for a really short distance. It’s not easy to accept the numbers I’m seeing but I guess I may have to. What I can’t do is draw any conclusions about equipment or yardages.

Anyway, thanks for bearing with my long-winded discussion of this. I don’t know what other people are finding in their practice. Are most of you satisfied that you get consistent and meaningful results from your Skytrak units?

[Mirek_62]

I'll reiterate what I've already written. Carry distance affects ball speed, launch angle and backspin.
If you compared to Trackman, what were the differences between the above parameters?
Another thing that could have influenced the different distance on the range is environmental conditions. Did you have the Skytrak set to the correct outside temperature and altitude and wind strength and direction?
Trackman measures flight distance all the time when used outdoors, while Skytrak uses preset environmental data in the carry distance calculation.

[Chmiller]

I haven't compared every parameter on each shot. I will try looking at the parameters for some shots to see where they differ. Trackman Range doesn't measure spin but does measure ball speed and launch. A difference in temperature or altitude or even wind would not account for the bizarre disparities between distances. What condition would cause a 6 iron to fly shorter than an 8 iron when Trackman is measuring a much longer distance? And parameters don't explain the bizarre randomness of distances I see indoors.

[tlrcash]

That is frustrating. What ball are you using when you hit a pitching wedge 90 yards but only generate 2k - 3k spin? I have hit thousands of wedges and I’ve never produced those launch conditions a single time.

[Chmiller]

I don't believe the spin is really that low. I find that one ball may be read at 2300 rpm and a different ball will be read at 9000 in the same session. I experiment with different balls and markings on the balls.

[Chmiller]

This may be hard to see but I compared a sample of shots between trackman and skytrak. I noted carry, ball speed, and launch angle. Trackman numbers followed by / followed by Skytrak numbers. You will see they vary wildly from shot to shot in every parameter.

[tlrcash]

Ball speed shouldn’t be that different between Trackman and SkyTrak. I believe it is the easiest metric to measure. I’m stumped.

[Chmiller]

Does anyone have experience with Skytrak repairs? Any ideas of what they can do or what it might cost?

[Chmiller]

One more interesting bit of info today. I practiced this morning and set up both the Skytrak and my little PRGR launch monitor. It records only club head speed, ball speed and distance. I’ve used it to look at swing speed while using the Skytrak but hadn’t paid much attention to ball speed or distance. Today I did. With a 9 iron the ball speed and carry were similar between the Skytrak and PRGR. With a 7 iron, the ball speeds were usually within one or two mph but the distances were ten to fifteen yards shorter on the Skytrak than the PRGR. With a 5 iron, the ball speeds were again consistent but now the distances were over 20 yards short. The distances from the little PRGR monitor were about what I hit on the course. Definitely something wrong with the Skytrak. I called support and they are sending an email with some tests to do. They also want pictures of my setup. They believe they can fix the problem by changing setup. I sincerely doubt that but I’ll go through the process. At least now I’m hopeful that there may be a fix in the offing. I sure would like to get more accurate numbers than I’ve been getting.

[Mirek_62]

Both LMs do not measure the distance but calculate it. I have repeatedly told you that you have to not look at the calculated Carry distance to "detect a fault" with Skytrak, but compare 3 basic values - ball speed, launch angle and backspin.

[Mirek_62]

I'm not sure the skytrak is broken, if the ball speed matches (with an acceptable variance) on both LMs (Skytrak and PRGR), the difference will probably be in launch angle and backspin (which is related to incorrect Skytrak setup in most cases). If these measurements are significantly different from the PRGR presets, then the resulting Carry will be significantly different as well.
Using the Flightscope Trajectory Optimizer, I simulated how carry distance varies for the same ball speed and different stance angles and backspin. You can see that at 16 degrees and 6000 RPM, the difference in carry distance is 8.4 yards compared to 18 degrees and 2500 RPM.

[bubbtubbs]

I also experimented with optimizer then gave up once I realized that we have no given spin metrics for the OP. With ball speed that low, I wasn't confident estimating how much spin they'd impart but the launch angle is pretty low for that speed.

If OP could post actual screenshots from the sessions, it would be far easier to assist.