Curved shooter mysterious hook.

[lemiant]

Our shooter includes a 90 degree curve and a top to increase compression. We're shooting with a white high-traction wheel from the kit.
The problem is that when the frisbee exits the shooter the side nearest the wheel ends up higher than the side opposite the wheel. Making it hook. Has anyone experienced a similar problem?

[DanielCH]

Originally Posted by lemiant

Our shooter includes a 90 degree curve and a top to increase compression. We're shooting with a white high-traction wheel from the kit.
The problem is that when the frisbee exits the shooter the side nearest the wheel ends up higher than the side opposite the wheel. Making it hook. Has anyone experienced a similar problem?

How much compression are you using? That may be the problem, but it's hard to tell from your description.

[Ether]

Post a couple a pics of your shooter from different angles, including one looking "down the barrel" of the shooter.

[lemiant]

Almost 1/2" of compression.

[DanielCH]

Originally Posted by lemiant

Almost 1/2" of compression.

As an initial guess, that amount of compression may be too much, and the frisbee may be tilting due to the compression. That's just a guess though, pictures would definitely help.

[rlowe61]

Based on description and the proto-typing conducted at the beginning of the season, I would have to say too much compression.
First you'll get a hook from a slanted disk trajectory, and possibly a spring type action as the disk decompresses against the wall.
Though we are way too deep into the season to change anything drastically, if the disk is lifting due to compression, it's too much.
624, worked on many variables to include, but not limited to; wheel diameter and material type, compression between wall and wheels, radial vs linear shooter, type of oppossing wall material (aluminum, wood, different type plastics, foam), length of follow-on wall (after it leaves the wheels).

Good Luck. Maybe a quick fix would be the ablity to adjust the motor distance from the wall

[DELurker]

First, it sounds like you have way too much compression. The Hi-Grip wheels don't compress much, so you've got 1/2" of bow to the Frisbee, assuming your outer wall doesn't flex. We found that reducing the compression until the frisbee rode flat on our deck improved our shooting tremendously. Of course, taking the tools away from the guys who were continually trying random adjustments to the shooter wall helped tremendously, too ...

Is it hooking towards the wheel side or towards the wall side? Does your outer wall have some flex at the end or is there a bracket right there? Is the outer wall straight off the wheel? Does the outer wall extend past the tangent point of the wheel?

[Chris is me]

Originally Posted by lemiant

Our shooter includes a 90 degree curve and a top to increase compression. We're shooting with a white high-traction wheel from the kit.
The problem is that when the frisbee exits the shooter the side nearest the wheel ends up higher than the side opposite the wheel. Making it hook. Has anyone experienced a similar problem?

Yes. This problem seems to be inherent to any non-pneumatic wheeled shooter. Your compression numbers (1/2") sound right on. We ran 10.5" from the wall to the wheel tip (so 1/2") the entire season on Banebots wheels. Maybe you need a touch less for a different wheel, but that's what we use.

What you have to do now is constrain the frisbee. Physically prevent it from "popping" and then it won't anymore. The simple addition of some slippery plastic guides might be all you need.



Here's a picture of the ones we made for the WPI Regional. The simple addition of these guides removed the problem entirely, resulting in a very straight shot with dramatically more consistency. When we used to miss 1-2 frisbees per cycle, we now miss 1-2 frisbees per match, and that's probably user error.

The more you stop the frisbee from moving around, the better your accuracy will be.

[KrazyCarl92]

We are using about a 60* shooter with 8" gray kit wheels from previous years. We also had about a half inch of compression at first, then we've been adding/taking away compression with additional lexan strips so I dont know what our final compression was that worked well. I imagine its +/- 1/8" of 1/2".

We found three ways to mitigate the frisbee riding up issue during prototyping:
-contrain the discs vertically so it can't go up and down much. Our chute for the discs in our rotary shooter is just over 1 disc tall.
-adjust the height of the shooter wheel such that it pushes the discs into the surface it rides on due to contact, but not too much.
-add "lips" to the wall the disc is riding against so the disc also can't ride up the wall. The geometry on ours from a cross section view looks like this:
_________ceiling constraining discs______
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|||
||
|
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|____________disc sits on this surface___

If you can eliminate the disc riding up issues and ensure that your exit is level, you should achieve consistent and straight shots.

Out of curiosity, have you actually fired good shots with the high grip wheel from KOP? Those were the only wheels which did not yield a single satisfactory result in our testing this season.

[thefro526]

Something worth looking into is the compression surface as well. As a lot of others have said, 1/2" compression can be a lot, depending on the exact shooter configuration.

If you compare the Disc shooters to those of previous games like 2006, 2009, and 2012, you'll see that they need to work in the opposite of 'the norm'. When the game piece is able to be compressed, like a poof ball, orbit ball or gopher balls, everything else should be/needs to be as rigid as possible. In the case of the 2013 Discs, since they are 'rigid', something else needs to compress, whether that be the shooter wheel or the wall opposite the wheel.

The easiest way to try this is to get a strip of some compressible material like rubber or urethane (we use urethane) and line the outside wall of the shooter's path with it. What you'll see is that the disc will compress that strip as it travels through the shooter and it's shape and path will remain a bit more stable.

All of that being said, another thing to look at, in addition to adding a compressible material to either the wheel or the shooter wall is to add some sort of 'ceiling' to the shooter that constrains the disc path further. If you look at a disc as it compresses, you'll see that the center of the discs likes to move up as it's compressed, essentially making it a leaf spring of sorts. Once the disc leaves the shooter, it will spring back into shape and do all sorts of weird things. Adding something in the shooter to keep the disc 'down' when it springs back into shape will help normalize your shots. From what I've seen, this simple part can do wonders for weird trajectories and increase overall range by a noticeable amount.

[lemiant]

Originally Posted by KrazyCarl92

We are using about a 60* shooter with 8" gray kit wheels from previous years. We also had about a half inch of compression at first, then we've been adding/taking away compression with additional lexan strips so I dont know what our final compression was that worked well. I imagine its +/- 1/8" of 1/2".

We found three ways to mitigate the frisbee riding up issue during prototyping:
-contrain the discs vertically so it can't go up and down much. Our chute for the discs in our rotary shooter is just over 1 disc tall.
-adjust the height of the shooter wheel such that it pushes the discs into the surface it rides on due to contact, but not too much.
-add "lips" to the wall the disc is riding against so the disc also can't ride up the wall. The geometry on ours from a cross section view looks like this:

|||
|||
||
|
|
|____________disc sits on this surface___

If you can eliminate the disc riding up issues and ensure that your exit is level, you should achieve consistent and straight shots.

Out of curiosity, have you actually fired good shots with the high grip wheel from KOP? Those were the only wheels which did not yield a single satisfactory result in our testing this season.

Thanks for the advice. And in answer to your question, yes, our earliest prototypes with that tire greatly outdistanced our other wheels while maintaining accuracy. Odd that different people's prototyping works out so differently.

[stryker0603]

I'm not sure its the compression that is the problem. My team has a curved shooter with almost an inch of compression using pneumatic wheels for shooting. It might be that pneumatic wheels are needed for that much compression though.

[Ether]

Originally Posted by stryker0603

I'm not sure its the compression that is the problem. My team has a curved shooter with almost an inch of compression using pneumatic wheels for shooting.

You may be comparing apples to oranges.

It might be that pneumatic wheels are needed for that much compression though.

With a low-pressure pneumatic tire, you don't get an accurate measurement of the compression of the frisbee by simply measuring the gap between the tire and the fence, especially if the frisbee is passing slightly underneath the tire (as it does in many pneumatic-tire designs)

[team4384]

In the past discussions everyone has been talking about compression how much is too much etc. Last year the basket ball was more compress-able than the hard plastic frisbees. Thus it was more forgiving. If you compress the frisbee 1/2" or more, does it not buckle/bend upward? If you don't have guides, the compressed frisbee will ride up. It was recommmended by others to provide support from the top to prevent frisbee from poping up. Guess what, in addition to wasting energy in compressing you are adding more friction, slowing down the frisbee. Every frisbee is not alike,some have little more flexibility than the other (even if the frisbee is molded to 99% accuracy), one frisbee will not shoot out as the other one. When the frisbee exits, these anomalies add up to your frustration.

Many teams are using 8" pneumatich wheels, if you do so, make sure its not fully inflated, you should be able to press with your thumb to make about 1/4" deep dimple. If your thumb goes in more, the wheel is under-inflated. Since pneumatic wheel has rubber sidings, the wheel will get compressed more than the frisbee, hence firsbee will not lose its shape. Also the rubber wheel will give enough traction to push the frisbee out. If you add velcro or fiction tape on the guide rails (other side where frisbee contacts), it will increase the traction on that side, causing frisbee to spin. The spining frisbee will fly relatively straight (horizontally) and will be more consistent. This you need to expriment and find out the best combination, combination of wheel pressure, this distance between the wheel and the guide rail.

If you are using 8" pneumatic wheels, make sure they are balanced and do not wobble. If they do, try to add counter weight (typically opposite to the brass inflating valve), again you have to expriment this, unless you have access to balancing machines (not the one in Belle Tire). Anyways, balancing is required for anything that spins at high speed.

Since you are using the solid wheel from KOP, my recommendation is to tape the velcro (soft side) to the wheel, it gives you enough compression and adjust the distance between wheel and the guide rails so you get about 1/8" compression. without any support from the top, if you can turn the wheel with your hand and frisbee does not ride up, you should be good. Try with different frisbees.

[RB73]

We actually had a similar issue when we were building out shooter. We didnt have a roof and the disks were raising out of the shooter rather than going out the end. We ended up raising our shooter wheels about a quarter of an inch. This put the wheels slightly above the frisbee and acted as a top. This, when paired with a lip on the opposite wall, stopped the disks from riding up out of the shooter.

In other words, compression wasnt an issue in the disk coming out tilted.