disc spin measured

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disc spin measured

Postby twisted discer » Tue May 13, 2008 12:25 pm

I am posting this on behalf of Erin Hemmings, at his request. Erin is a distance thrower and recently had the longest throw at big D 8 last month, 748 feet. Erin is very interested in acquiring data on golf disc flight dynamics.

Disc Spin Test Results

I have designed and tested a method for measuring the RPM's of a thrown disc. This design utilizes an on board LCD readout taken from a Powerball
Gyroscope. This small computer counts the revolutions of a revolving magnet. It can keep track of total RPM's, as well as a maximum
RPM which is conveniently held in memory until either exceeded or manually reset. I then constructed a lightweight vertical tail/boom and fastened it
to a pin in the discs center. I then attached a doughnut shaped magnet to the boom. This magnet is set to pass directly over the computer sensor.
When the disc is the thrown the tail tracks in a straight back position, while the sensor and disc spin.

My initial prediction was that when thrown, a disc would essentially be rolling out of your hand. For an example a golf disc rolling along the ground at 60 mph would be
spinning at 2325 RPM, and I thought the same RPM would happen with a disc is thrown through the air at 60 mph.

My test plan was to use my radar gun in conjunction with the RPM disc to get an accurate range of data.The results can be seen in the graph below.
I was definitely surprised by the variance in spin. I made an effort to throw each test shot with the same form and technique.
As a disc is thrown harder, say over 70 mph the
spin of the disc can actually drop below what it was at 50 mph. I can throw 80 mph at my max and the spin at this speed is right around 2000 rpm.
A theory is that the wrist can't keep up with really fast arm speeds, and can't supply an ever increasing amount of spin.
As an example I never broke 2330 RPM during my tests, and that spin was with a 54 mph throw!

I also tested half a dozen sidearm throws. I have a "no wobble" side arm that uses allot of wrist snap. The results were conclusive that sidearm has 25%
less inherent spin than a backhand throw. I assume that is why so many peoples sidearm throws wobble.
It is also possible to increase or decrease spin purposefully, although I found this to be impractical and awkward. A disc with extra spin does seem to resist
low speed fade better than a disc with less spin. Strangely, when I tried to spin the hell out of a disc it would sometimes show less rpm's than a normal throw?!

I realize that individual form and technique might show very different results. My friend Jim tried the RPM disc and seemed to have a noticeably higher spin-to-speed
ratio than me. He really cocks his wrist, while I keep mine tight like a spring. I hope you guys find these results interesting!

-Erin Hemmings

note: Erin is currently building a disc launching machine, which spins the disc up at a chosen rpm and then launches it. This device has adjustable hyzer angle, and adjustable vertical angle of release. It has been tested ejecting a disc @109 mph into a radar gun, then net. (historically, the fastest recorded disc throw was 85 mph). This device will then make it possible to find the correlation between spin and distance. It will also allow any disc to be measured for distance and any desired flight characteristics during calm conditions and in a precise and repeatable way. It's cool. Will post pics and results in the near future.

click on thumbnails:

[img][img]http://img373.imageshack.us/img373/552/img8213ht2.th.jpg[/img]
[/img]Image[/img]
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Re: disc spin measured

Postby JR » Tue May 13, 2008 1:46 pm

I applaud Erin's idea and work and his long throw prowess. Thanks for posting this for him.
Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.
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Postby cmrichar » Tue May 13, 2008 2:03 pm

Wow, that is pretty sweet. Please be sure to post some pics/videos of that disc thrower if/when completed. Sounds awesome!

I remember seeing this youtube video that has a nice little disc thrower. Its quite accurate too. I think it was posted here before, don't remember where.

http://youtube.com/watch?v=9_68EfBfwY0
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Postby Aaron_D » Tue May 13, 2008 2:29 pm

This is very interesting. Keep us posted!
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Postby twisted discer » Tue May 13, 2008 4:45 pm

In the youtube video you're speaking of, a spinning wheel is used to fling the disc. The problem is that spin and ejection speed are linked and can't be adjusted independently. The accuracy was good, but the discs (ultimate) would just fly a short distance. Erin's launcher uses a long rail and a "traveling car" powered by large o.d. surgical tubing. (upgraded since the 109mph max test). Huge amounts of power are now available, it also has adjustable spin rates. :roll:
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Postby CJ1998 » Tue May 13, 2008 6:06 pm

That's friggin sweet!

I'd love to be around when this thing is being tested.
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Postby Eric O » Tue May 13, 2008 6:07 pm

Awesome! Keep us posted on further testing.
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Postby Barbikes » Tue May 13, 2008 8:40 pm

Hey, I agree with what others have said. This is great data! Keep it coming!
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Postby schla104 » Sat May 17, 2008 2:31 pm

I'd recommend using a heavier disc. A 150g Eagle is kind of light. It's interesting data but I think it would be more interesting if it was a heavier disc that many people throw. Just a thought. I don't know why but I feel like I can't snap light discs as well as I can heavy ones.
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Postby black udder » Sat May 17, 2008 2:42 pm

schla104 wrote:I'd recommend using a heavier disc. A 150g Eagle is kind of light. It's interesting data but I think it would be more interesting if it was a heavier disc that many people throw. Just a thought. I don't know why but I feel like I can't snap light discs as well as I can heavy ones.


You can snap them just as much, you just don't feel it as much :)
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Postby Fritz » Sat May 17, 2008 7:14 pm

Awesome, keep up the research. I can't wait to see more results.
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Postby twisted discer » Sat May 17, 2008 8:01 pm

A 150 disc was used because the weight of the tail, the bearing, the magnet and the reader brought the weight up near 170 grams. All part of the plan... :idea:
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Postby mahr » Fri Aug 15, 2008 2:58 pm

Very nice research. I've been wondering for a while what exactly causes the right turn on a hard thrown RHBH. It seems to me that there are a couple of possibilities:

1. A nose down orientation will cause an upward force on the left side of the disc. As the disc slows, the disc will nose up which will then cause it to come back to the left.

2. There's a magnus force which acts on spinning discs with a forward velocity. This is the force that causes baseballs to curve. For a RHBH, this force acts to the right. Most of the research on flying discs discounts this force because ultimate discs aren't thrown fast enough for this force to matter.

3. When throwing a disc with a lot of power, there may be an off axis force which causes the disc to roll to the right. I tend to discount this idea as when thrown with the correct amount of hyzer, the disc will slowly come up to level which would suggest a smaller force acting over a longer period of time.


I believe that 1 and 2 are critical to the proper flight of a hyzer-flip. I'd be really interested to find out how much the spin of the disc contributes to the flipping of the disc. This might be a hard experiment to do scientifically, but I think it'd be really interesting to throw a bunch of discs with a constant velocity and varying spin speeds. You could then eyeball how much right drift is achieved for each throw. I've always wondered what would happen if I threw the disc really fast but with very little spin. Unfortunately, I don't have that much control over my shots yet :)
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Postby J-Man » Fri Aug 15, 2008 6:21 pm

Oh you gotta be shooting some footage of this, can't wait to see it.
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Postby JR » Sun Aug 17, 2008 1:52 am

mahr, welocme. I'm waiting in hope that Erin publishes his data. So much easier to achieve than doing parallel research :-)
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