New video: ultra-power disc golf launcher (Patreon)

I'm equal parts excited and relieved to have wrapped up my ultra powerful disc golf gauntlet. I had to go through what felt like endless iterations on the design to get it really working, and for a while was worried I wouldn't be pull it off. It was a lot of fun though, and there's something deeply satisfying about designing mechanisms, especially when they finally work.

Even after cutting a lot of work and details from the video, it still wound up being one of my longest ever. As usual I'll be scheduling a patron only directors commentary livestream to watch through the video and share lots of extra details. I'll also answer whatever live questions you might have. I'll share details for that soon and I hope to see you there!

In the meantime let's talk about launching discs really far. Disclaimer: I really am a newb about all the science behind this and there's a high chance I'm wrong about small details, major points, or everything.

My research for this project convinced me that matching the disc golf distance record was highly unlikely. This is why I made breaking the speed record my primary goal. My reasoning was based on the flight behavior of high speed discs as well as the  exceptional environmental conditions during the world record throw.

NOTE: I did not invent this theory. It is derived from a variety of sources.

It pretty much all comes down to the fact that a disc is an airfoil, and acts very similarly to an airplane wing. As it travels through the air, it generates lift.

The lift is distributed across the disc, but you can think of the aggregate force of the lift pushing up on the disc at a specific point sometimes called the center of lift.

As far as I understand, the center of lift is almost always towards the front half of the disc. This is a problem because this is not stable and the disc will uncontrollably pitch and flip. This is because the lift force will rotate the front of the disc up, which generates even more lift due to the increased angle of attack. This leads to it lifting faster, and so on...

This is why spinning the disc is critical for flight. When the disc spins it acts like a gyroscope which will resist any motions that would change the plane of rotation. Here's a dramatic example:

This puts us in a situation where the the disc is attempting to flip from the lift, but it is resisted by the gyroscopic behavior of the spin. Clearly something has to give and what happens is pretty weird.

The really short explanation is that the spinning disc has angular momentum. When you apply a torque to something with angular momentum (such as trying to flip the disc upward), it changes the direction of the angular momentum. In the case of the disc, the torque from trying to lift the front will change the angular momentum of the spinning disc such that it makes the disc roll to the right.

Here's some historical footage of the first scientist to observe this behavior:

This is a non-intuitive phenomena called gyroscopic precession and is a staple of PHYS101 lab demonstrations. If you want to learn more, here's a good short video on the subject. My belief is that this interaction between the off-center lift force and disc spin creates a gyroscopic precession and always rolls the disc to the right. If this is true, it's not great news for me because lift force increases with speed. This would make the desire for the disc to roll worse as we go faster. 

This is why I think the environmental conditions for the distance record are so important. The distance record was thrown in the desert with a 40mph tailwind. This means that the relative air speed to the disc was 40mph slower than still air. This means a lot less tendency for the disc to roll.

The other major impact of a big tailwind is that it massively reduces drag  on the disc. Drag force grows with the square of speed. For an 80mph throw, a 40mph tail wind would reduce drag by roughly a factor of 4. Less drag means that the disc can go further for a given throw.

The drag and rolling behavior makes me think that the distance record is untouchable without one or more of the following conditions:

A huge tailwind

A custom disc designed for high speed flight†

Super human disc spin

I think I can accomplish one or more of those in a future iteration of the project. I've been thinking a lot on how I might do that. Diving deeper into these issues is something I'm quite interested in doing so watch out 👀.

Hope you all enjoyed the video. It's so great to be able to work on projects like this. Thank you all for the support!

-Shane

†This disc would have low lift and a center of lift close to the center of the disc to reduce the pitching torque.

P.S. A lot if people have reached out to recommend throwing the disc with a hyzer angle to solve the rolling problem. That is actually something that I tested and it had marginal impact on the throw. I think this is because an extra 30 degrees of hyzer angle doesn't help that much if the disc wants to roll a massive amount.