"OAT"

[Doofenshmirtz]

I have heard various explanations for what is described by "Off Axis Torque." Aside from the fact that "torque" has an axis and that I suspect what is meant is "Off Intended Axis Torque," I have read descriptions that describe it as the force that results in wobble and/or that imparts a rotational momentum on the horizontal axis that is parallel to the direction of travel, i.e., a momentum that makes the spinning disc roll to the right, after leaving the thrower's hand (which would also mean that the free spinning disc has two axes of rotation at once for a brief period).

So which is it: 1) an unclean release or other force that results in wobble; 2) a fancy word for unintended anhyzer; 3) an impartation of some sort of "rotational momentum on the horizontal axis" that gives the disc two, simultaneous axes of rotation and ignores the laws of physics; or, 4) a meaningless code word for people to use to make them feel like they are "in the know" about all things disc golf?

 

[garublador]

I have heard various explanations for what is described by "Off Axis Torque." Aside from the fact that "torque" has an axis and that I suspect what is meant is "Off Intended Axis Torque," I have read descriptions that describe it as the force that results in wobble and/or that imparts a rotational momentum on the horizontal axis that is parallel to the direction of travel, i.e., a momentum that makes the spinning disc roll to the right, after leaving the thrower's hand (which would also mean that the free spinning disc has two axes of rotation at once for a brief period).

So which is it: 1) an unclean release or other force that results in wobble; 2) a fancy word for unintended anhyzer; 3) an impartation of some sort of "rotational momentum on the horizontal axis" that gives the disc two, simultaneous axes of rotation and ignores the laws of physics; or, 4) a meaningless code word for people to use to make them feel like they are "in the know" about all things disc golf?

It's 1 and 3, which are the same. I don't know why you think having a torque component on two or three axes ignores the laws of physics. You can have a disc that's spinning in the traditional sense and tumbling "head over heels" at the same time. There's nothing in physics that prevents that.

How many axes you have torque about depends heavily on how you define your axes, too. If you have a disc that's spinning in the traditional sense, but define one axis to not be orthogonal or parallel to the flight plate, you'll have torque about multiple axes.

 

[Pwingles]

@Garu

So, the center of the rotation for a hopefully wobble free spin, is the center of the disc, yes? Not taking into account release angle and its affect on flight.

 

[Timeetyo]

Here is my understanding:

- A perfect "clean" throw would rotate perfectly on the axis of the black line.
- On a throw with OAT, when releasing the torque from your release imparts a force on the green axis. The disc tries to rotate around the green axis, which makes it wobble. Eventually, the centripetal force from the spin will smooth out the wobble....during this time the instability from the wobble often causes the disc to turn over.

 

[garublador]

@Garu

So, the center of the rotation for a hopefully wobble free spin, is the center of the disc, yes? Not taking into account release angle and its affect on flight.

Yeah, for wobble free spin all of the torque is about the axis orthogonal to and through the center of the flight plate.

If you're familiar with the aeronautical terms, pitch, roll and yaw, spin is about the yaw axis. OAT can be about the pitch (nose up or down) and/or roll (hyzer or anhyzer) axis, but when people say "OAT" they're almost always talking about a torque about the roll axis.

 

[PMantle]

3) an impartation of some sort of "rotational momentum on the horizontal axis" that gives the disc two, simultaneous axes of rotation and ignores the laws of physics;

You need to revisit these laws.

 

[garublador]

Here is my understanding:

- A perfect "clean" throw would rotate perfectly on the axis of the black line.
- On a throw with OAT, when releasing the torque from your release imparts a force on the green axis. The disc tries to rotate around the green axis, which makes it wobble. Eventually, the centripetal force from the spin will smooth out the wobble....during this time the instability from the wobble often causes the disc to turn over.

I'm not sure I understand that picture. In "normal" Cartesian coordinates (x, y and z axes) all of the axes are perpendicular to each other. The green line is already off axis.

In that picture, a clean throw would rotate only about the vertical black line. Assuming the disc is flying left to right (i.e. we're looking at it from the side) then OAT would be about the horizontal black line (i.e. doing a barrel roll).

 

[Karl]

Your number 4.
They're really just referring to a disc's 'wobble' but wish to sound cool.

 

[BogeyNoMore]

Your number 4.
They're really just referring to a disc's 'wobble' but wish to sound cool.

Discs thrown with OAT don't always wobble, but wobble is typically indicative of OAT on a given throw.

 

[garublador]

Your number 4.
They're really just referring to a disc's 'wobble' but wish to sound cool.

FWIW, here's an article where Dave Dunipace wishes to make people think he's "in the know."

https://www.dgcoursereview.com/dgr/resources/articles/distancesecrets.shtml

 

[Doofenshmirtz]

Here is my understanding:

- A perfect "clean" throw would rotate perfectly on the axis of the black line.
- On a throw with OAT, when releasing the torque from your release imparts a force on the green axis. The disc tries to rotate around the green axis, which makes it wobble. Eventually, the centripetal force from the spin will smooth out the wobble....during this time the instability from the wobble often causes the disc to turn over.

It doesn't have two axes of rotation, in the case of wobble, the axis of spin is not perpendicular to the flight plate, but the axis is still vertical, not where your image puts it. This divergence of the spin axis from prependicular to the flight plate eventually resolves, resulting in wobble-free spin. There is a very good visual demonstration of this principle here, although some of the other descriptions on that page are inaccurate.

 

[Doofenshmirtz]

It's 1 and 3, which are the same. I don't know why you think having a torque component on two or three axes ignores the laws of physics. You can have a disc that's spinning in the traditional sense and tumbling "head over heels" at the same time. There's nothing in physics that prevents that.

It's not the "torque component" that is the problem. Torque is rotational force. You can apply torque on as many axes as you want. However, once the disc leaves your hand, it is free spinning and cannot have multiple axes of rotation without continued torque. So, if there were to remain some sort of "torque inertia" on the axis parallel to the direction of flight, precession would cause the disc to either nose up or down, not roll right or left.

As noted above, and demonstrated at the noted link, a wobbling disc only has one axis of rotation.

How many axes you have torque about depends heavily on how you define your axes, too. If you have a disc that's spinning in the traditional sense, but define one axis to not be orthogonal or parallel to the flight plate, you'll have torque about multiple axes.

And where is this Torque coming from after the disc leaves the throwers hand?

 

[rocthecourse]

Discs thrown with OAT don't always wobble, but wobble is typically indicative of OAT on a given throw.

Yup.

 

[garublador]

It's not the "torque component" that is the problem. Torque is rotational force. You can apply torque on as many axes as you want. However, once the disc leaves your hand, it is free spinning and cannot have multiple axes of rotation without continued torque. So, if there were to remain some sort of "torque inertia" on the axis parallel to the direction of flight, precession would cause the disc to either nose up or down, not roll right or left.

There is rotational inertia, just like there's rotational inertia that keep the disc spinning. If you spin a disc about the axis parallel the disc flight (the "roll" axis) the disc will barrel roll. If it barrel rolls in the anhyzer direction the disc will act more understable than normal.

As noted above, and demonstrated at the noted link, a wobbling disc only has one axis of rotation.

How can that be? If it's wobbling and spinning then its rotating about two different axes.

And where is this Torque coming from after the disc leaves the throwers hand?

In this case, nowhere, just like there's no additional torque that keep the disc spinning. The OAT can be thought of as a perfectly "clean" throw, but with someone pushing down on the rim at a point right when you release. The force doesn't continue, but the disc will "spin" about the roll axis, even if it's much slower than the spin about the yaw axis.

 

[Doofenshmirtz]

There is rotational inertia, just like there's rotational inertia that keep the disc spinning. If you spin a disc about the axis parallel the disc flight (the "roll" axis) the disc will barrel roll. If it barrel rolls in the anhyzer direction the disc will act more understable than normal.

No, it will wobble. The disc has inertia, not the yaw axis. Because the disc is free and spinning about the yaw axis, it will convert, through precession, any torque on the roll axis to a change in the pitch axis. Your claim of "rotational inertia," unaffected by precession and resulting in two axes of rotation for a free spinning disc is the problem.

How can that be? If it's wobbling and spinning then its rotating about two different axes.

No, it only has one axis of rotation and that is clearly demonstrated at the noted link. To do this yourself, poke a stick through the center of a disc (the stick will be the yaw axis). Using the stick, spin the disc like a top to get smooth, clean spin. Then, tilt the disc on the stick so that the stick or yaw axis is no longer perpendicular to the flight plate. Then spin the stick and watch closely, the disc will wobble even though it is clearly spinning around the stick which represents a single axis of rotation. Crucially, the stick does not have to change movement in order to allow the wobble.

In this case, nowhere, just like there's no additional torque that keep the disc spinning. The OAT can be thought of as a perfectly "clean" throw, but with someone pushing down on the rim at a point right when you release. The force doesn't continue, but the disc will "spin" about the roll axis, even if it's much slower than the spin about the yaw axis

If "someone pushes down on the rim at a point right when you release," the result will be wobble because the disc has now been tilted with respect to its spin axis. If some force were to contine to "press down on one side of the flight plate, after release, precession would convert that torque to rotation on the pitch axis causing the disc to either nose up or down.

Rotation on any one axis affects any attempt to rotate the disc on any other axis. If this were not true and a disc could rotate about multiple axes at once, gyroscopes would not work.

 

[araytx]

see this vid.

 

[Pwingles]

@Garu

So, just in the way we hold a disc, for arguments sake your pinchpoint is at 12 o'clock, and its rotating from there. Its already off of that axis.

The throw starts out with a slight wobble (precession?) and usually corrects itself.
Would this be correct? (Assuming its not overly torqued on to the point it will roll)

 

[Doofenshmirtz]

@Garu
(Assuming its not overly torqued on to the point it will roll)

No amount of torque, applied by your hand, is going to make the disc continue to roll (rotation around the roll axis) once it leaves your hand unless you throw it without spin (rotation around the yaw axis). The "off axis torque" of which you are speaking will simply result in wobble.

 

[Pwingles]

I meant the less sciency, more literal for DG term 'roll'

Like a wheel

 

[garublador]

Rotation on any one axis affects any attempt to rotate the disc on any other axis. If this were not true and a disc could rotate about multiple axes at once, gyroscopes would not work.

I had a longer response typed out, but we lost power and I don't feel like typing it again.

The tl;dr version is that the link you gave, and what you appear to be talking about assumes that the "axis" is the one about which the disc is rotation, no matter what. We're assuming the "on axis" is always perpendicular to the flight plate. So in my version, there can be torque components in different axes and in your version there can't. Defining the axes differently doesn't change what's happening. The link you gave supports everything I'm saying. It's just that the context is different because lids act way different than disc golf drivers because of the difference in amount of mass near the rim.

No amount of torque, applied by your hand, is going to make the disc continue to roll (rotation around the roll axis) once it leaves your hand unless you throw it without spin (rotation around the yaw axis). The "off axis torque" of which you are speaking will simply result in wobble.

That's just not true. Nearly everyone who's thrown with OAT has observed that happening and the link you gave described the same thing.

With lids you get wobble real easy compared to disc golf drivers because of how different the mass is distributed in the disc. Lids require the cleanest throw in the tri-state area to be thrown with lots of power. With drivers there's a ton of mass at the rim (way more angular momentum) so they resist wobble really well. Players learn to throw these discs with lots of OAT (a lid would wobble a ton and crash almost immediately) to get them to fly straight. They only see the disc turn more than it should (but as much as the flight ratings describe) rather than the wobble you see with a lid.