Since this video is all about learning, please reply to this comment if you have any insights on centrifugal force - including what we got right and/or wrong! 🧐
I think the wobble comes from the initial launch. The water in the cup ramps up to the speed and so the water is evenly pushed to the sides, but when throwing the disc, you are testing Newton's law of "an object at rest will stay at rest." The sand and the water are at rest, you yank the disc, and the water/sand push towards the back of the disc. Not sure how the rest of the flight works and if the centrifugal force pushes the sand/water out, but the wobble comes from the launch for sure.
Also I think the volume of water was insufficient to see a whole lot of difference, you need something denser like Mercury (Not suggesting this) to make a major change. either way you need heft with a low viscosity of gels are likely not a good answer.
I believe the disc with the hollow rim (the one you assumed to be very understable) demonstrated similar stability to its filled rim counterpart because even though the overall weight is less, the weight is more centralized to the disc body which gave it a lower inertia. This means the disc can spin quicker about it's axis. Think about a figure skater when they spin with their arms tucked in. They spin faster. Now with spinning objects such as a disc the faster they spin the more stability they will have. So to sum up, you reduced the weight, which tends to make the disc more understable, but also decreased it's inertia which increased the disc revolutions per second, which tends to make the disc more stable. Resulting in a net result of similar flight characteristics to it's original design.
I am inclined to believe that the sand was wobbling because at the launch of the disc-regardless of how you attempt to spread out the sand before-the sand gets pushed to one side of the disc from the sheer force you exert onto the disc through your pull. Then the sand attempts to level out evenly but struggles to do so perfectly because it is not a fluid(liquid or gas)-but acts similarly to one. TLDR: The sand would level out more and become more and more balanced, given that it had a longer flight time, whilst the water doesn’t need much time since it is not only a fluid but also had a high viscosity(ability to move around quickly). Love the videos; you’re making an amazing impact on growing the sport sustainably!!
The hollow disc being more overstable is exactly the opposite of what MVP does with their overmolds. The closer to the center of the disc the weight distribution, the faster a disc will lose its rotational speed and gyroscopic stability, causing it to fade faster. If you took the same disc, filled it with metal, and somehow threw it as fast as a hollow one, it would keep its rotational speed for a very long time. This in practice is used for things like a flywheel in a car. The reason you're not really seeing results with things like water or sand is in part the empty space will allow it to move around, which as you discovered becomes really complex when you add in the fact that the disc is flying while spinning. If you were able to have the disc at 100% capacity, it would keep the rotational forces more consistent and keep the disc spinning longer, but in theory also increases the initial energy needed upon release to get the disc spinning at the same rate. MVP has pretty much been working on this kind of technology since they started and it's the reason they have overmolds in the first place, it pushes the rotational inertia further away from the center of the disc.
There is one more variable in disc throwing and it is the fact that arm can only apply so much rotational energy to a disc which ofcourse isn't probably the same across different moment of inertia on varying discs it's still limited which results on lighter especially with lighter rim disc gettimg far more spin than a heavier disc. How fast it loses it I have no idea but the disc tends to keep the rotation going quite well usually comparing the airspeed slowing.
The phrase "pushes the rotational inertia further away from the center of the disc" should be changed to "increases the rotational inertia." Rotational inertia is a scalar quantity, so it doesn't have a "position" and doesn't move. A nitpick, but conceptually it matters.
THIS is the kind of science we need happening in disc golf. We know some scientific principles that make us lean towards this design being a poor idea, but we can learn so much by experiments like this. Keep it coming Jesse!
You need to get an engineer like Destin at Smarter Everyday to work with you on testing. He'll be able to explain why the discs fly the way they do, not just speculation, And could give you some better ideas for flight efficiency.
If 3D printed parts struggle to hold water, no way they are going to hold helium. I reckon It also wouldn't have been that big a difference from the air one anyway, since the difference in weight would be negligible.
Rotational precession and the shape of the rim will have a bigger impact on the stability verses just the weight. The weight will impact how fast you can throw it, but like Tyrus said below the change of how far the weight is from the center will impact the rotational momentum to maintain high spin rate.
I've wanted to make a fluid filled rim disc since 2006, very happy to see you this. I was thinking of using mercury as the fluid and having it 100% filled, no air.
Don't let the water-filled disc freeze! Regarding the stability of the hollow disc, it is known that weight is not directly related to stability. Take the blizzard-type discs: there are plenty of videos demonstrating that the lighter weight does not equate to understability. Stability is directly related to shape and spin. More spin results in more stability, not more overstability, but more stability in the neutral sense. If a disc has a lightweight rim compared to one of the exact same shape but heavier, you can get more spin on it. It will lose the spin faster though, because there is less angular momentum. Conversely, the heavier rim will yield less spin for the same power throw, but will maintain that spin longer. This is precisely the dynamic that MVP's Gyro technology plays with.
I mostly agree, but I'm quite certain that the spin does not slow down significantly during a flight (just look at a fidget spinner or a table top spinner where almost all resistance is through friction in the ball bearings and against the table). It is not the spin that makes a disc more stable, but the angular momentum, which is (simplified) the weight times the spin, so a heavier disc spinning slowly could have the same angular momentum as a light disc spinning fast. Do you have any tests showing that people actually get less spin on heavier discs? Of course this will be the case to some extent, but this is also down to human physiology and such, so it's possible most people get almost the same amount of spinn on both light and heavy discs (within reason). I don't feel that the weight of the disc is limiting my ability to put spin on a disc, but it would be interesting to see if this is actually the case.
A few ideas to throw out there. 1) When the disc spins and the water fills the outside of the hollow portion due to centrifugal/centripital forces, there isn't much difference between the water and a solid infill. It is mostly just the density of the water that is the difference. The forces on the water are the same as the forces on a solid except that the solid doesn't move. 2) The fact that the water moves means it creates friction. That friction will in fact slow the disc spin which I think we wouldn't want.
yup. I think all it does is add some wobble. The rotation momentum should still stay consistent even though the spin rate slows. but not helpful either way. Water is less dense than disc plastic so I wasn't sure how it was supposed to help
Lateral thinking ahead, congratulations! The idea of a fluid inside the rim could change moment of inertia of the disc during the flight like a motorbike variator could work if: - Difference between inner and outer diameter of internal chamber is big. - Fluid is dense enough ( mercury=16,6 g/ml vs water=1g/ml ) - Disc is always horizontal and, without rotation, liquid stays close to the center. - Centrifugal forces pushes liquid to the outer part of the inner chamber during flight. I guess that those are too many conditions… The other line of investigation could be: if inner chamber walls were smooth enough so that de disc turns at higher rpm than the fluid ( mercury again ), disc would have a lower moment of inertia with the same total weight. I guess that it wouldn’t be good because it would loose its rotation faster.
maybe a non-newtonian fluid that becomes liquid when force is applied? also, some baffles/honeycomb in the hollow part could be useful to further slow the liquid from reaching the rim and then delay its return to the center when the disc slows.
A 'dead blow' hammer is partially filled with grains of something like sand to kill the inertia of the object trying to make the hammer bounce backwards, which puts all the inertia of the hammer into whatever is being struck. Would partially filling the rim of a disc with sand or water do more to kill the spinning inertia than help it?
Yeah the water will slow the disc spin as the water slowly accelerates from stationary to matching the disc speed. But the rotational MOMENTUM should not be affected. so there should be minimal affect on the flight apart from the wobble
I could be completely off but my first thought was that you could get some way to spin the disc before it’s thrown. That would cause the sand/water to become evenly distributed using centrifugal force and then when you throw it I would think that distribution would stick through the whole flight. Maybe not but if it did that would be awesome lol
So, understability and overstability is measure by how the wind is distributed when going over/under the rim of the disc. The closer the top is to being flat and the rim being closer to the top of the disc the more overstable it will be, hence discs like the Tilt looking flat. The recent video by Latitude 64 explains this really well. You aren't changing the shape the disc at all by making it hollow, you're changing the weight. Changing the weight of a disc does two things: 1) makes it easier to throw higher speeds and 2) makes it so wind can push it around easier. Making the disc lighter so you can throw it faster will make it more flip up a little more than a max weight disc, but not as much as throwing a disc designed to be understable. Danny Lindahl from Dynamic Discs has a video about this.
Interesting concepts. In order to adjust for the shift in sand and water due to inertia, you could try evenly distributed cells filled with water or sand.
I want you and ezra alderhold to collaborate so bad. He is one of the hardest throwers and could make these discs fly to the absolute maximum potential. Pleaseeeee!!!!!
That was a great video. Way to push the limits of the pdga :p I wonder if the lighter disc is more stable because it doesn't have enough spin force to flip it because there isn't enough weight on the rim? Just like when you throw an under stable disc with low speed/spin it can be stable. (I know nothing of the science but figured it was worth a stab). Also way to represent the Kerr jar club.
If you want to increase your rate of spin I would make a few models of the prototype that are solid on one section of the rim and 20-30% infill on the rest, I would try three designs, 15 degrees of arc, 30 and 60. this will be like the Aerobie epic but fit the technical standards and not be like a 15 speed. Your printer will have to work with slicer setting to get this to work out it not really straight forward and might be easier on an SLA printer over an FDM.
This is what I was thinking too. Experiment with imbalance and possibly try and use imbalance mitigation techniques (glass beads in motorcycle tires for example).
Why did you do this? The drag of water inside the disc will cause the disc to de-spin the instant you let it go. On top of that, water is less dense than TPU! We know this because discs sink in water. It's like taking the best idea in disc golf (adding mass to the rim with special weighting agents in an overmold) and making it the worst idea by putting the wrong stuff in the rim. The best thing you could ever embed in the rim of a disc is depleted uranium , as it is the densest substance available. Not too sure about the long term consequences. You might want a lead-lined bag for that disc. :P One important point to note here, is that MVP midrange discs have by far the greatest moment of leverage of all discs. Because the diameter is slightly larger, and the blunt leading edge allows more mass closer to the edge of the disc, whereas a smaller diameter driver with it's bevelled edge necessarily moves more mass further inwards. I've always wondered why MVP don't produce a 241mm diameter disc like the amazing Innova Condor (legal up to 200 grams!) as it would have by far the highest gyroscopic stability of any disc ever made.
What about removable flight plates? You could make a locking clasp system and then change the rims depending on need. Then you wouldn't need to replace a whole disc just because the rim is worn out. As an aside - what do you think about microplastics in the environment coming from disc wear? All that beating in of discs removes material which is going into the soil - just wanted to hear your thoughts on this.
My theory on why the hallow disc is still overstable has to do with moment of inertia. The more weight distributed from the axis of rotation the higher the moment of inertia, in our case our disk has a lower moment of inertia because the weight is more distributed towards the axis of rotation. The lower the moment of inertia means less resistance to a change in motion. From here we can suggest that it's easier to stop the disc from spinning hence it fades sooner.
I am quite certain of that the rotation of a disc slows only slows down an insignificant amount during a flight since there is very little air resistance acting on the rotation (as opposed to the forwards flight, where there obviously is significant air resistance). Just imagine a fidget spinner or a table top spinner where the vast majority of resistance is due to friction in the ball bearings or against the table. Here's a video of a spinner with only airresistance: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-hu1jEWLZVug.html which seems to be able to spin a lot longer than the duration of a disc flight. Instead I think fading happens when a disc slows down in its forwards flight and starts to fall. So a lighter disc might still fade sooner, since it will slow down through the air sooner. There is also a second effect in that a lighter disc will have less inertia from the angular momentum and thus once it starts to fade it will fall over quicker. However this second effect will also make understable discs turn quicker since there is also less inertia to resist the turn. So this explains why some people have witnessed lighter discs as more understable. Basically a discs over/understable characteristics are inherent to their shape, but light discs will accentuate any turn/fade and make these characteristics more extreme and noticeable.
I would like to see one with vegetable oil and one with bb’s. Try 3 of each with varying amounts inside to see which is better or maybe not. Fun video, thanks for sharing!
What about a ball bearing and a magnet? Wouldn't that move around in a uniform manner especially if you mold a pattern for it to sit within? Magnets are powerful
I’m sure there’s other people saying this but about lightweight discs: in general, when manufacturers, make something lighter, they have less dense plastic in the same mold. So it lowers the parting line height and makes the disc less stable. But it’s not simply because of the lighter weight, it’s because of a changed mold. The 3D printed disc makes the same exact mold at just a lighter weight. But it has the same shape and should fly the same
Most lightweight discs do fly less stable. But there is some Prodigy where the lightweight stuff is more overstable than max weight because that’s how the plastic cooled. I have a very overstable 139g P Model S
Awesome video! Your content just keeps getting better and better. I've been really curious to see how an oblong disc would fly. My guess is that it would be extremely overstable . I assume that because it's oblong one edge will be moving faster than the other edge similar to how a boomerang flies. I hope you try it out! 🤙🏽
Over/Under stability is caused by the profile of the disc, not the weight distribution. A profile that causes the incoming air to push the nose down causes a gyroscopic correction to the right (for rhbh), which is where understability comes from. A profile that pushes the nose up will cause a gyroscopic correction to the left (again, rhbh). This is also why all discs fade left (rhbh) at the end of the flight: the disc is dropping, which pushes up on the nose, which causes a leftward gyroscopic correction. The weight distribution of the rim is going to determine how long the gyroscopic effect can last, extending the full-speed flight characteristics of the disc. You kind of saw that in the video - the prototype had a normal disc flight, the hollow empty disc had a normal but slightly truncated flight (you did throw hyzer so it's hard to tell how much, but it didn't hold the line quite like the proto did), sand was wonky, but the water had a slightly extended period of stable flight, similar to the prototype.
Very odd how the hollow rim wasn't under-stable, it seems that the rim weight has less effect on the stability, I could be wrong. Love the vids keep it up.
Basically a discs over/understable characteristics are inherent to their shape and not weight, but light discs will accentuate any turn/fade and make these characteristics more extreme and noticeable. So an lighter understable disc will behave more understable than a heavier understable disc, but a lighter overstable disc will also behave more overstable than a heavier overstable disc. Making a disc ligher/heavier in many ways has the same affect as throwing them with less/more spin. There are some other affects, such as a heavy disc retaining its forwards speed for longer and fading later than a light weight disc as well as not being as affected by gusts of wind.
The higher the center of mass the more overstable I think. If you hollowed out below the top of the disc you just shift the center of mass up. You can see on rims of overstable vs under stable discs how they are angled
My theory on why the hollow wing is overstable is because it moves the center of gravity higher. Since the center of gravity is higher, this creates a larger moment of inertia in the vertical direction. This moment of inertia opposes the torque created by the different in lift between the left and right side of the disc, caused by spin. Since the lift difference is the same, you have the same torque but less resistance to that torque, which means more change in angle (turn) of the disc
For the hollow rim, try evenly spaced hollow segments that you'd individually fill with water/sand etc. Would help with the balance issue. Though a ton more work Maybe some thicker gels and other substances like BBs? Bonus points if you name it " The BattleRattle"
Interesting...I was thinking about printing some discs and comparing different infills instead of just being hollow. On the centrifugal force side...some interesting comments I see in the comments section. But I'm a little surprised no one brought up, what I learned when I was still a physics major, that centrifugal force isn't really a force. Technically it is centripetal acceleration.
@@scottconner4100 It's surprising how many places get this wrong that are science related sites. Wikipedia screws this up even further by calling Centripetal Acceleration as Centripetal Force. For those of you wondering what Scott I are talking about...a "force" can only move in 1 direction by definition. When you change direction it becomes a change in force with is an acceleration. Since going around an arc is constantly changing the direction of force it now becomes an acceleration.
Awesome video. Just really fun! Interesting application. Would be neat to host someone that could talk about the physics. I imagine most of this has been tried, but with all the money flowing into the sport, I guess there is a possibility that disc tech could take another leap. You are doing good things. Keep it up!
I can flip a Innova base plastic Leopard to a roller with no problem. The MVP signal, though technically a flipper disc, takes me considerable more effort to flip to a roller.
When you say the helium disc "didn't work," what do you mean? What did it do? Did the helium just not stay in the disc? Or was that a joke in the first place because you can't put helium in the disc?
I was not able to read every comment, but if no one else suggested it, you need to design it with baffles or cell chambers every cm or so, rather than a single large chamber. It will keep the fluid or fluidic soid from gathering at one side during launch. If you put in helium, it needs to be in the flight plate, not the rim (a la MVP migobubbles lessening the weight of the flight plate in comparison to the rim. Which, with a domed flight plate with a flat or convex underside, may introduce other fascinating flight charageristics.
To counteract all of the sand/water being bunched on one side of the disc you could make separate "chambers" in the rim. For example, a disc with hollow rim would have just the one chamber, but if you put up some walls making 4 or so different chambers then you'd have better distribution
I'm at 4 mins, before I watch further I'm gonna leave my prediction - water filled disc will resist the spin and it's gonna fly terrible, sand will behave similar but a little less terrible. Despite that, I can't express how much I enjoy this vid and can't wait to see the results! Trying this kind of ideas is literal gold, even if they fly bad we can learn a ton by actually trying it out :D Now let's see what happens xD
Ok, they flew 100 times better than I expexted, I thought the water will stop the motion of the disc like when you try to throw a bottle filled to like 20% and try making double or triple spin with it. What the hell is going on there? xD I guess plastic bottle is just too light compared to the water inside and that's why you can't really spin it and disc is heavy enough to spin despite that... ? Damn this is interesting.
As you are filling the disc with water… I couldn’t help but think about how a more dense liquid in comparison to water would react. Although very improbable and possibly unsafe something like Bromide or Mercury would be very intriguing to test out!
MVP uses different plastic on the edge what if making the disc heavy on the edge can add distance. So in the hallow part add a heavy solid substance moving the weight to the edges.
Soft edge on the inside of the rim is something I am curious about. This might make it a bit strange to throw, but I always wanted to know if it would make a difference in distance, my thought is that is would displace air with less interference, but I have no idea
Since I saw the Løft-disc with the rounded grip, I've wondered if it would be even more aerodynamic if the underside of the disc was flat and the grip was just carved as a ring. Making the center hollow might make it possible to keep most of the weight in the rim.
Love your videos ! I don't have any physics that I can add, but I really dig the shirt you have on, midway through the video. The one with the 3 baskets. I went to your website in hopes you are selling them. Any help would be great. Would love to have one.
So this is a complex set of questions. I agree with quite a few answers already posted about the disc being filled with water and sand. The materials reacted as a human does in a motor vehicle that accelerates quickly, so they never evened out in the disc. Now on the other question, why the hollow disc is stable, as a structural engineer I believe many people are viewing the concept too simple for the true scenario at hand. While the interior of the disc would act one way the hollow rim will act a separate way. And the moment created by the material that is in the rim will mathematically have a larger effect on the disc than normal, and per your throws more effect than the interior of the disc. Since the rim is hollow the outer material now has a greater moment, or greater force on the disc. Since it effects the disc more, it has more determination on the flight characteristics. Since it is the furthest point from center it travels the slowest compared to other parts of the disc. Based on math, dynamic disc videos, and observation the faster a disc is thrown, and consequentially the faster a disc spins the less stable the disc acts. This makes sense when comparing the same disc in the hands of a pro compared to a novice. So since the most influential portion of the hollow disc is towards the outside of the disc it would require a faster throw than a none hollow disc to produce the same rpm at the most important part of the disc. Assuming you were throwing at roughly the same speed the disc would be spinning at the same speed, but the controlling point of each disc would be different. Causing different flight characteristics. There is more complexity to these situations and comparisons but this is a decent quick overview of why some of the things are happening.
My guess is that you are counting on the fact that centrifugal force is at its optimum spin. What you were not counting is the inertia necessary to spin the disk fast enough for that Apex ratio to occur, immediately upon release. My point is, once you start rotating the disc on snap, the sand remains at rest and will slowly try to catch up to the rest of the disc. Due to the friction inside the hollow chamber, my guess is it slowing the rotation down, making it more stable I thought about doing the same thing with my 3-D printer but realized it’s a lost cause. You would need to spin up your disc before release to have the desired impact that you are seeking.
This was really cool! Lighter weight rim has lower moment of inertia and spins faster. More spin = more resistant to precession or turn/fade. The sand flies like a car tire that is not balanced = wobble. The water flies like a hammer or Aerobie Epic, the water should get focused into the nose end at release and kind stay there and rotates around the center of mass which has moved closer to the nose. The water won't spread out evenly into the rim unless it's rotating on it's center.
"Lighter weight rim has lower moment of inertia and spins faster." ok yes if muscle power was limiting spin "More spin = more resistant to precession or turn/fade." not really. More rotation momentum will do this which = spin x moment of inertia. so the lighter rim disk cancels that out.
@@seabas22 yup that was a big assumption that normally pairs with strong head winds Personally I think any small differences in peceived stability could easily be due to 3d printing with a hollow rim. The geometry could have warped into a more over stable shape
As for the water or sand idea why don't you try compartmentalizing the rim of the disc into smaller sections so that way there is less likely for the sand to shift to one side or the other and allow it to distribute evenly across the rim. Like a down jacket.
