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#1
11-24-2012, 04:10 PM
 iacas Double Eagle Member Join Date: Aug 2012 Location: Erie, PA Years Playing: 1.4 Courses Played: 28 Throwing Style: RHBH Posts: 1,376
Quick Thoughts on Basic Throwing Geometry (BH)

Apologies if the subject/title is poor...

Someone posted elsewhere about "throwing smarter" versus "throwing harder." I whipped up a quick post that may or may not help people understand the concepts of disc pivot, wrist extension (wrist "opening"), etc. This is from the perspective of a RHBH throw, but the physics apply to just about every kind of throw.

I agreed with the other poster that "throwing smarter" is a good thing. I said don't think anyone (unless you're in a long drive competition) should "throw hard" but everyone should "throw smart." Physics can be your friend.

In golf there's a concept called the endless belt. It actually applies a bit better to disc golf because there's more linear components to disc golf than in golf.

Here's an illustration. It's top-down, and the basket is to the right for an RHBH thrower.

Imagine that these are four conveyor belts. The top of each conveyor belt is moving towards the target, it hits a wheel or a gear or whatever you want to call the circle and loops around to go the other way. For an RHBH thrower with the basket to the right, we can ignore the bottom half of the diagram - it's simply there to show the "endless belt" going the other way (an LHBH thrower can use the bottom and ignore the top with the target to the left).

Both A and C have the same size "wheel," as do B and D.

Imagine that you're in a car riding along the top of the conveyor belt in A. As the car enters the turn at the wheel you begin to feel a force pushing you to the outside of the car because - even if you maintain the same linear speed - you're accelerating (angular acceleration). Consider B now, and imagine going the same speed (say 50 MPH) in the car and then hitting THAT turn. You'd feel much, much more force.

In both of these instances, you'd feel nothing while traveling along the straight line at a constant speed (I'm assuming you don't have a convertible and the windows are rolled up), and then you'd instantly feel force as you whip around the corner.

Now consider C and D. In these, traveling along the arcs at 50 MPH will feel some force with the gentle turn. These forces would gradually build, reaching a maximum at the point where the turn is the sharpest. We see designs like this in loops on roller coasters, and the tightest portion of the loop is at the top, because that's when gravity directly pulling riders out of their seats:

Because we've kept the linear speed constant at 50 MPH in all of these diagrams, which would impart more speed to the disc? The bigger wheels or the smaller wheels? The answer is the smaller wheels. The same way you're slammed against the door of the car more when the car makes a tight turn versus a wider turn.

And yes, A and C would experience the same amount of forces at the maximum, as would B and D. But disc speed is not why disc golfers are better off with a linear or straight-line delivery. A linear "delivery line" is preferred for accuracy. In a linear motion, the disc experiences no real forces (just linear acceleration, which we're ignoring because we'll consider it the same in all of these examples) while traveling straight, then instantly experiences tremendous forces when the disc enters the turn. The smaller the turn, the more forces, and if the wheel is small enough, the disc experiences enough force to be ripped from your hand consistently. Imagine you're gripping the disc with 800 units of strength, but the disc instantly goes from 0 to 1000 units of force. There's no need to time that - the disc will begin ripping from your hands at that instant.

Now consider that you're in a car going on the oval tracks in C and D, or a disc being thrown with a more rotational motion. Now timing becomes a bit messier. From the top of the loop onward the circular path is constantly tightening its radius and thus the forces are gradually increasing. Instead of going from 0 to 1000 in an instant, they're going from 0 to 1000 gradually. If your grip strength is 800 on average, the disc may slip early if you only grip it at 750 one time and you might grip lock it with a grip of 850 the next time. Once it reaches the threshold established by your grip, it will come out, but that threshold has to be the same every time, whereas in the linear delivery the threshold is instantly exceeded.

So that's why a linear delivery line is preferred. Why then a smaller circle?

Think back to the car analogy. In both A and B you're traveling linearly at 50 MPH just prior to entering the turn. Yet in B you'll be thrown inside the car with much more force than in A. A smaller has more torque and thus produces a bigger spike in instantaneous acceleration. In A it might go from 0 to 1000, and in B, from 0 to 1500.

But if the acceleration is truly instantaneous, and goes from some low number (again we're ignoring the linear acceleration and calling it 0) to 1000 (A) or 1500 (B), why do we need to grip firmer to throw farther? If we grip both at 800, they'll both rip out at the same instant, right? Well, it turns out of course that everyone's throwing motion has a bit of a rounding to it like we see in C and D. Nobody throws on a purely linear motion transitioning perfectly into a purely circular motion. Everyone has a bit of a "decreasing radius." Something like this:

So in this example (the right-side images), we still go from 0 to 1000 in A and 0 to 1500 in B, but we do so over a short span of time - a fraction of a second. But given the rotational rates, a fraction of a second is all you need to miss your line by 2°, 5°, or even 10°, either early (slipping) or late (grip lock). And that's why a stronger thrower needs more grip strength as well as consistent grip strength. They want to hold on to the last possible moment, translating the most speed into the disc, before it rips out. 1250 will rip out at 1250, 1450 will rip out at 1450. 1450 will not work if you're A and only generating 1000 (the disc will never come out), and 1550 will never work if you're A or B. By the same token 1450 will never work if you're B but only moving 40 MPH prior to entering the arc, either.

1. I believe there are actually two small arcs. One is formed by your wrist opening, and is the "primary" arc illustrated above. The second is the disc pivoting around your pinch point. These two arcs overlap but are not directly on top of each other - the sequencing is that your arm begins going forward, your shoulder and your elbow arc (fourth and third arcs, respectively, though their purpose is more linear in summation). When the shoulder/elbow is near its peak, the wrist will begin to open, and when the wrist is near its peak, the disc pivot will begin.

2. Neither of those latter two arcs occur instantly. When the threshold is met, your wrist will instantly start to open or the disc will instantly start coming out of your hand, but will not finish coming out until later. Because the disc is then in motion (and wants to stay in motion) and takes some time, you can actually release the disc AFTER your peak, though we're talking about a very, very small amount of time there, and conceptually you can ignore these small blocks of time so long as you realize that these times - paired with the overlapping series of arcs (particularly the wrist and the pivot arcs) occur sequentially - to explain why your wrist is not still on the outside of the disc or the front of the disc (closest to the target) when the disc actually comes out. This also explains why Blake feels he holds on until 4:00 or 4:30 - the disc pivot arc starts after the wrist pivot arc has started. This graph is kind of the "grand unified theory" of disc throwing:

P.S. Apologies if I've made any quickie typos. I'm relatively confident in the base science here, but if I typed 1500 where I meant 1000 or something, please forgive me. We're celebrating our Thanksgiving today and I've written this quickly and in between some cleaning chores and other such things as the wife demands. The graphics took five minutes to assemble, for example, so I doubt very much that the colored arcs vs. time are plotted exactly in the proper dimensions, magnitude, time, etc. But conceptually they should still be "okay."
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