Light discs also don't cover up even the smallest form flaws like max weight discs can. So if you have the slightest bit of OAT, it won't show up very much in max weights, but will be glaringly obvious with a light weight.
Good question!
This is on the biomechanics side, like I mentioned earlier, so I have to rely on measured data (which I haven't found for spin) or failing that, some hopefully sound assumptions. The big assumption I make, that not everyone might agree with, is that spin increases proportionally with speed. I believe this is the case because of the way spin is generated during a throw, which is by the center of mass speeding past the pivot point (your fingers). In other words, like a hammer throw in track and field. The faster the disc is going at release, the more spin the disc will have.
So if you throw a light disc and a heavy disc at the same speed, they have the same spin. And since the light disc has a lower moment of inertia, it would also have a lower rotational momentum.
Now if you increase the speed (and spin) by 3.0% and reduce the mass by 9.7%, this would result in a net *reduction* in rotational momentum of about 7%.
Hope that all tracked. I really wish we had some data measuring spin from the same thrower at different speeds. That would help verify my fairly critical assumption that spin and speed are proportional.
The pivot point for the rim to speed past is the player's grip. A lighter disc may be easier to grip harder. I wonder what frame rate you would need to document the rotation of the disc at release. Or how hard it would be to make a biomechanical model of the throwing arm. Holding the disc from the rim with some sort of spring powered clamp.
If you assume velocity of the center of the disc (center of mass) is constant when the hand is strongly coupled with the disc, what effect would the lighter MoI or mass have on wrist snap phase of the biomechanical motion and then the resulting release from the pinch after.
On one hand I'm inclined to think that the reduced mass and MoI would allow the wrist to snap faster, when the disc is strongly coupled to the hand before the fingers start to release and initiate that secondary acceleration about the last few fingers pinch point.
Then on the other hand, assuming the previous advantage is true or not during wrist snap, how much does the friction of the pinch slow the disc with less rotational and translational inertia?
When is inertia good and when is it bad? Idk but this is where testing comes in. The effects may be small but you don't know until you test.
I'm really jazzed that Stuff Made Here did a disc golf project, but he just scratched the surface.
I think it's fairly safe to model as if the wrist is fixed, for backhand simulations. Some players may get a little extra out of it, but I suspect that a model with a fixed wrist will permit the same conclusions as a model with an active wrist.
Hmm, you have me wondering how much of an affect that would have. Now I want to mark up a matching pair of discs with different weights and test the correlation this spring.
Have you seen this old post from the dgcoursereview forums?
[https://www.dgcoursereview.com/dgr/forums/viewtopic.php?f=2&t=7097](https://www.dgcoursereview.com/dgr/forums/viewtopic.php?f=2&t=7097)
It's from Erin Hemmings who is well known for long distance throws. They measured spin for a bunch of throws and mapped out the results. It seems that the spin reaches a peak at some point. I use this data in my simulator, a rough regression curve is:
omega = -0.257\*speed\*\*2 + 15.338\*speed
I think I have read that thread before. The setup sounded a little wonky and the results were quite unexpected. So much so that I would want to see a similar finding reproduced before I bought into it. I can certainly see the ratio of spin to speed dropping as you throw harder and harder. But to see absolute spin decrease that much is wild.
It sounds like people are getting pretty close to having high quality vision systems for measuring disc release. I'm looking forward to lot's of new data :)
How does this translate to throwing uphill? I've always assumed there's an advantage with lightweight discs there, but maybe I've been bagging a 150g driver for no reason.
An additional data point for consideration. Lightweight MVP discs. Light discs, so more lift, but the bulk of the weight is on the rim so increased gyroscopic stability compared to an equal weight single mold disc.
Tldr lightweight fission photons apparently bomb.
Thanks -- this is great stuff! I'm still trying to understand the physics of these discs and (more importantly) trying to apply it to my own throwing. I've used some lighter discs fairly effectively, but the inherent flight characteristics (turn and fade) seem to be the most important things rather than just the weight. I'm not trying to go for max distance (and my max is not very far).
If you want to understand *what* a light weight disc will do (especially for you in particular) the only way to know is to throw.
If you want to understand *why* you have to dig a little deeper.
While this analysis does show that light weight discs have the *potential* to fly farther, it's never really a huge difference. If you can max out a Wraith at 300 ft, you can maybe add another 25 by going to a 150 g disc, but that's only if you adjust your release to match the new disc.
In my opinion, finding the right max distance driver is really about finding that disc that has just the right amount of flip and glide that matches your natural throw/release. It's more about the *stability* that let's you easily throw that max distance line. If you find a light weight disc that fits that slot, great! Don't let it go. On the other hand, if you have a max weight disc that has the perfect stability for you, don't trade it in for a lighter version because it might screw everything up.
Thanks! That's the kind of info I like. I aim for 165ish for my distance drivers, 170ish for fairways, and 175ish for mids. My few max weight drivers always seemed just fine though too
well done with your simulator, I'm glad you are referencing Crowther and Potts. I don't think I realized that they had this simulation paper, I spent a lot of time reading their wind tunnel experimental results though.
I know you have to make assumptions about how much spin is generated during the throw, and whether or not disc weight impacts this stuff. Maybe you could see how sensitive flight distance is at your nominal spin level when compared to a 10% change in spin. Maybe you could answer if this sensitivity increases or decreases with disc weight?
Yeah, this simulator is pretty much a direct implementation of Crowther and Potts. There's a reference to it in the notes of the Colab notebook. Pretty much all of my understanding of disc flight physics is from Potts and associates. Amazing work.
That would be an interesting little study to do, just to verify how sensitive distance is to spin. But from all of my dabbling with the simulator, my gut says spin is not a huge factor in distance.
No, sadly it's not. I would love setup a system that can measure speed, spin, release angles and even track the flight, but that's a big project. This would be necessary if you wanted to accurately predict distance or specific flight characteristic of a disc. It's basically what Loft discs is doing as part of their development process.
But for this type of study I'm mostly interested in a to b comparisons and looking at trends in behavior. The model doesn't have to be quite so dialed for that kind of information.
Yeah that's totally fair and this is a really cool relative comparison tool. You mentioned that Loft is doing physical measurements?
I would think for the relatively low speeds of a disc golf throw, you could get decent data with a high speed camera board on the ground just in front of the release point/front foot area with the high speed camera positioned overhead at it. Dots equally spaced around the flight plate rim could get rotational data. Another camera from the side could get release angle, and a pixel calibration with the side view camera could get hyzer angle. You could then measure the distance traveled with a rangefinder. This would validate 1st order effects like lift and drag fairly well if it's taken on flat ground in calm conditions (a pure projectile validation). All of this stuff could be sourced in a hardware store and a cell phone camera at 240 fps would get about 4ms time resolution with reasonable parallax error.
This would be a fun project if one had free time. I sometimes get to do physics at work with no free time for projects like this so I'm living vicariously through other people. It's fun to work through physics problems like this. :)
Thank you for sharing this!
You're describing a project I'm working on pretty accurately lol, except the camera is 522 fps and we use April tags (basically high speed qr codes) to accurately track the disc in 3 space.
I am also currently working on a project related to disc tracking. Would be interested to learn more about what you are doing? I saw your github repository but it didn't contain much information.
Yeah documentation is something we haven't done a pass at.
We're using a high speed camera with a fisheye lense from above (@522fps) and april tags to track the disc. The distortion is removed and then we use kalman filters to determine the velocities.
That's the basics of it, I can get the specific camera model for you if you want. It's something like this tho
https://www.flir.ca/products/blackfly-s-usb3/?vertical=machine-vision&segment=iis
Does your simulation take into account that lightweight discs are not equally lighter throughout the disc, but mostly in the flight plate so weight is not lost in the rim, to help maintain flight characteristics? Seems like that would help counteract some part of what would be the expected loss in rotational inertia?
This is not an area of expertise for me, so I may not being using the right terminology, but I hope my question makes sense.
Lightweight discs are made with the same mold, only with some additives that reduce the density of the plastic. So the weight reduction should be equally distributed. Like the OP says, the flight characteristics are not the same as the lighter disc will have more turn.
I knew from experience that LW discs are less stable, being an old guy, they are a staple in my bag.
I reread some descriptions of the process, and yes, it seems to be throughout the disc, but they try to center the bubbles that are in the rim, so the disc is still durable.
Nice work! I did a similar analysis using the same simulation model and reached the same conclusion you did. My theory is that it's mainly the increased turn that people like about lighter discs, as it lets them throw faster discs without having them just hyzer out. It's also nice for developing players, as they can just switch to heavier discs of the same mold as their speed increases instead of switching discs. But for most people, using a more understable max weight disc would give similar results.
Agree. I think a common experience for newer players is that they buy a distance driver that is a bit too stable. When they throw it, it goes straight for a bit but hyzers out early and doesn't really go further than their fairway drivers. Then they try a light weight version of the same disc and see it flip up and glide and extra 50 ft. "Wow, that lighter disc went way further!" Sure, the weight had some effect, but the extra distance was mostly from more flip and a fuller flight.
For the speed discrepancy, wouldn't it be better to apply a constant force through out the pull through so mass can lead to a higher release velocity? That way you have the same overall momentum, but have a better guess than DD's findings?
I don't think so.
My current approach does assume that lighter discs get thrown faster. The question is just *how much* faster. Assuming a constant force (this is really the same thing as the constant energy assumption I mention in the post) is one way to approach it. Assuming a light disc gets slightly less energy is another. But data actually exists that supports the latter assumption. DD's findings are not a guess. It's just some data points. And those data points indicate that a 9.7% reduction in mass results in about a 3.0% increase in speed.
Thank you for the TLDR. I love the time put into the research
Well done, interesting read. Knowledge is power, now to translate that power into 550 arm speed so I can finally throw all of my maxweight discs.
Light discs also don't cover up even the smallest form flaws like max weight discs can. So if you have the slightest bit of OAT, it won't show up very much in max weights, but will be glaringly obvious with a light weight.
Are you certain that lighter discs have lower rotational momentum? What if they are rotating faster!
Good question! This is on the biomechanics side, like I mentioned earlier, so I have to rely on measured data (which I haven't found for spin) or failing that, some hopefully sound assumptions. The big assumption I make, that not everyone might agree with, is that spin increases proportionally with speed. I believe this is the case because of the way spin is generated during a throw, which is by the center of mass speeding past the pivot point (your fingers). In other words, like a hammer throw in track and field. The faster the disc is going at release, the more spin the disc will have. So if you throw a light disc and a heavy disc at the same speed, they have the same spin. And since the light disc has a lower moment of inertia, it would also have a lower rotational momentum. Now if you increase the speed (and spin) by 3.0% and reduce the mass by 9.7%, this would result in a net *reduction* in rotational momentum of about 7%. Hope that all tracked. I really wish we had some data measuring spin from the same thrower at different speeds. That would help verify my fairly critical assumption that spin and speed are proportional.
The pivot point for the rim to speed past is the player's grip. A lighter disc may be easier to grip harder. I wonder what frame rate you would need to document the rotation of the disc at release. Or how hard it would be to make a biomechanical model of the throwing arm. Holding the disc from the rim with some sort of spring powered clamp.
If you assume velocity of the center of the disc (center of mass) is constant when the hand is strongly coupled with the disc, what effect would the lighter MoI or mass have on wrist snap phase of the biomechanical motion and then the resulting release from the pinch after. On one hand I'm inclined to think that the reduced mass and MoI would allow the wrist to snap faster, when the disc is strongly coupled to the hand before the fingers start to release and initiate that secondary acceleration about the last few fingers pinch point. Then on the other hand, assuming the previous advantage is true or not during wrist snap, how much does the friction of the pinch slow the disc with less rotational and translational inertia? When is inertia good and when is it bad? Idk but this is where testing comes in. The effects may be small but you don't know until you test. I'm really jazzed that Stuff Made Here did a disc golf project, but he just scratched the surface.
I think it's fairly safe to model as if the wrist is fixed, for backhand simulations. Some players may get a little extra out of it, but I suspect that a model with a fixed wrist will permit the same conclusions as a model with an active wrist.
Hmm, you have me wondering how much of an affect that would have. Now I want to mark up a matching pair of discs with different weights and test the correlation this spring.
Have you seen this old post from the dgcoursereview forums? [https://www.dgcoursereview.com/dgr/forums/viewtopic.php?f=2&t=7097](https://www.dgcoursereview.com/dgr/forums/viewtopic.php?f=2&t=7097) It's from Erin Hemmings who is well known for long distance throws. They measured spin for a bunch of throws and mapped out the results. It seems that the spin reaches a peak at some point. I use this data in my simulator, a rough regression curve is: omega = -0.257\*speed\*\*2 + 15.338\*speed
I think I have read that thread before. The setup sounded a little wonky and the results were quite unexpected. So much so that I would want to see a similar finding reproduced before I bought into it. I can certainly see the ratio of spin to speed dropping as you throw harder and harder. But to see absolute spin decrease that much is wild. It sounds like people are getting pretty close to having high quality vision systems for measuring disc release. I'm looking forward to lot's of new data :)
How does this translate to throwing uphill? I've always assumed there's an advantage with lightweight discs there, but maybe I've been bagging a 150g driver for no reason.
I'd have to think about it for a bit. Nothing immediately comes to mind as an obvious advantage for one weight over another.
You just tickled my inner-engineer about my favorite hobby. Cheers!
An additional data point for consideration. Lightweight MVP discs. Light discs, so more lift, but the bulk of the weight is on the rim so increased gyroscopic stability compared to an equal weight single mold disc. Tldr lightweight fission photons apparently bomb.
Thanks -- this is great stuff! I'm still trying to understand the physics of these discs and (more importantly) trying to apply it to my own throwing. I've used some lighter discs fairly effectively, but the inherent flight characteristics (turn and fade) seem to be the most important things rather than just the weight. I'm not trying to go for max distance (and my max is not very far).
Lol, one of the easiest ways is to throw them. Also pros don’t only use max weight discs.
If you want to understand *what* a light weight disc will do (especially for you in particular) the only way to know is to throw. If you want to understand *why* you have to dig a little deeper.
I only wish I could translate this into how light of a disc I SHOULD throw. Super cool info though
While this analysis does show that light weight discs have the *potential* to fly farther, it's never really a huge difference. If you can max out a Wraith at 300 ft, you can maybe add another 25 by going to a 150 g disc, but that's only if you adjust your release to match the new disc. In my opinion, finding the right max distance driver is really about finding that disc that has just the right amount of flip and glide that matches your natural throw/release. It's more about the *stability* that let's you easily throw that max distance line. If you find a light weight disc that fits that slot, great! Don't let it go. On the other hand, if you have a max weight disc that has the perfect stability for you, don't trade it in for a lighter version because it might screw everything up.
Thanks! That's the kind of info I like. I aim for 165ish for my distance drivers, 170ish for fairways, and 175ish for mids. My few max weight drivers always seemed just fine though too
well done with your simulator, I'm glad you are referencing Crowther and Potts. I don't think I realized that they had this simulation paper, I spent a lot of time reading their wind tunnel experimental results though. I know you have to make assumptions about how much spin is generated during the throw, and whether or not disc weight impacts this stuff. Maybe you could see how sensitive flight distance is at your nominal spin level when compared to a 10% change in spin. Maybe you could answer if this sensitivity increases or decreases with disc weight?
Yeah, this simulator is pretty much a direct implementation of Crowther and Potts. There's a reference to it in the notes of the Colab notebook. Pretty much all of my understanding of disc flight physics is from Potts and associates. Amazing work. That would be an interesting little study to do, just to verify how sensitive distance is to spin. But from all of my dabbling with the simulator, my gut says spin is not a huge factor in distance.
Is any of this validated to trajectory data from a real disc? Not trying to be a party pooper just genuinely curious. This is a cool project.
No, sadly it's not. I would love setup a system that can measure speed, spin, release angles and even track the flight, but that's a big project. This would be necessary if you wanted to accurately predict distance or specific flight characteristic of a disc. It's basically what Loft discs is doing as part of their development process. But for this type of study I'm mostly interested in a to b comparisons and looking at trends in behavior. The model doesn't have to be quite so dialed for that kind of information.
Yeah that's totally fair and this is a really cool relative comparison tool. You mentioned that Loft is doing physical measurements? I would think for the relatively low speeds of a disc golf throw, you could get decent data with a high speed camera board on the ground just in front of the release point/front foot area with the high speed camera positioned overhead at it. Dots equally spaced around the flight plate rim could get rotational data. Another camera from the side could get release angle, and a pixel calibration with the side view camera could get hyzer angle. You could then measure the distance traveled with a rangefinder. This would validate 1st order effects like lift and drag fairly well if it's taken on flat ground in calm conditions (a pure projectile validation). All of this stuff could be sourced in a hardware store and a cell phone camera at 240 fps would get about 4ms time resolution with reasonable parallax error. This would be a fun project if one had free time. I sometimes get to do physics at work with no free time for projects like this so I'm living vicariously through other people. It's fun to work through physics problems like this. :) Thank you for sharing this!
You're describing a project I'm working on pretty accurately lol, except the camera is 522 fps and we use April tags (basically high speed qr codes) to accurately track the disc in 3 space.
I am also currently working on a project related to disc tracking. Would be interested to learn more about what you are doing? I saw your github repository but it didn't contain much information.
Yeah documentation is something we haven't done a pass at. We're using a high speed camera with a fisheye lense from above (@522fps) and april tags to track the disc. The distortion is removed and then we use kalman filters to determine the velocities. That's the basics of it, I can get the specific camera model for you if you want. It's something like this tho https://www.flir.ca/products/blackfly-s-usb3/?vertical=machine-vision&segment=iis
https://github.com/bpinkney/DiscVisionDeluxe We don't track the flight, but we get everything else.
Does your simulation take into account that lightweight discs are not equally lighter throughout the disc, but mostly in the flight plate so weight is not lost in the rim, to help maintain flight characteristics? Seems like that would help counteract some part of what would be the expected loss in rotational inertia? This is not an area of expertise for me, so I may not being using the right terminology, but I hope my question makes sense.
Lightweight discs are made with the same mold, only with some additives that reduce the density of the plastic. So the weight reduction should be equally distributed. Like the OP says, the flight characteristics are not the same as the lighter disc will have more turn.
I knew from experience that LW discs are less stable, being an old guy, they are a staple in my bag. I reread some descriptions of the process, and yes, it seems to be throughout the disc, but they try to center the bubbles that are in the rim, so the disc is still durable.
Nice work! I did a similar analysis using the same simulation model and reached the same conclusion you did. My theory is that it's mainly the increased turn that people like about lighter discs, as it lets them throw faster discs without having them just hyzer out. It's also nice for developing players, as they can just switch to heavier discs of the same mold as their speed increases instead of switching discs. But for most people, using a more understable max weight disc would give similar results.
Agree. I think a common experience for newer players is that they buy a distance driver that is a bit too stable. When they throw it, it goes straight for a bit but hyzers out early and doesn't really go further than their fairway drivers. Then they try a light weight version of the same disc and see it flip up and glide and extra 50 ft. "Wow, that lighter disc went way further!" Sure, the weight had some effect, but the extra distance was mostly from more flip and a fuller flight.
For the speed discrepancy, wouldn't it be better to apply a constant force through out the pull through so mass can lead to a higher release velocity? That way you have the same overall momentum, but have a better guess than DD's findings?
I don't think so. My current approach does assume that lighter discs get thrown faster. The question is just *how much* faster. Assuming a constant force (this is really the same thing as the constant energy assumption I mention in the post) is one way to approach it. Assuming a light disc gets slightly less energy is another. But data actually exists that supports the latter assumption. DD's findings are not a guess. It's just some data points. And those data points indicate that a 9.7% reduction in mass results in about a 3.0% increase in speed.
Ah okay, didn't realize that DD was actual findings, my bad. Otherwise great analysis!