Linear Path Shooter vs. Circular Path Shooter?

[ttldomination]

Originally Posted by billbo911

Different tread to reduce slippage.

Are you guys using roughtop here? If so, I don't think it'll actually reduce it, but it's just not audible anymore.

- Sunny G.

[DampRobot]

In regards to Ether's numbers, at those high speeds, don't trust that you'll get anywhere near no slippage. We ran our belts at a surface speed of about 60 miles per your last year, and it was an unmitigated disaster. Tons of slippage and lack of any speed sensing (or even compensation for voltage changes) led to a shooter that was completely inaccurate. Our two CIM shooter (given, at a large angle) could barely get shots for the key.

When you're designing a shooter, think about what your numbers say and what your testing demonstrates. I really appreciate 2073's testing, especially their result that indicates that lower speeds mean more consistency. But remember, what works for their team (or my team, or robot in three days, or anyone else) may not work for yours. We're prototyping using pneumatic wheels, and have had a lot more success with the straight shooter, for example.

[billbo911]

Originally Posted by ttldomination

Are you guys using roughtop here? If so, I don't think it'll actually reduce it, but it's just not audible anymore.

- Sunny G.

Yes, it's roughtop.

The audible indication of slippage is definitely reduced, no screeching at all.
Whether it is because of the compliance of the tread is gripping the Frisbee better or because it's dampening the sound out isn't really clear.
We can tell by a couple sections of the video that the slipping appears to be greatly reduced. That is part of why we added the mark on the small piece of pool noodle on the hub.
With the hard tread, we were actually transferring material from the Frisbee to the tread. The tread was becoming whiter with every pass. With the roughtop, we saw no transfer to the tread, and the tread has shown no signs of wear....yet.

[Bob Steele]

Originally Posted by billbo911

As Adam stated, there are many variables that need to be identified and worked out before any designs are made. The following video and the one posted yesterday are proof that prototyping works.

The three things that changed between yesterday and today are:
Larger wheel (6in to 8in).
Different tread to reduce slippage.
Much more solid backing to the wall.

The result is, we can run the wheel at a lower RPM and get much longer and repeatable flights. This will allow us to also have more headroom in the drive for faster spin up and shorter recovery time.
Can anyone say "Bang Bang" Speed Control"?

Yesterday's
http://www.youtube.com/watch?v=Wa6pc...ature=youtu.be


Today's
http://www.youtube.com/watch?v=_iqd_...ature=youtu.be

Did you also add something to the wall on the inside? The black material? Or is it just plastic? It seems you are increasing the spin rate of the frisbee as it leaves. Nice job and many thanks for sharing!,,

[billbo911]

Originally Posted by Bob Steele

Did you also add something to the wall on the inside? The black material? Or is it just plastic? It seems you are increasing the spin rate of the frisbee as it leaves. Nice job and many thanks for sharing!,,

Ah, good catch Bob.

That is basically just traction tape, or anti-slip safety tape. It has a rough, rubberized surface, with a texture much like sprayed in truck bed liner. It is pliable enough to not mar the Frisbee's surface and prevents it from sliding on the polycarbonate. We had applied it the previous night, but it was applied after we had stopped recording.
I'll edit the post to include it as a change.

[ayeckley]

Originally Posted by CalTran

"NIP point contact"? Can you elaborate on to what this means?

Basically how Jeffy interpreted it. Some folks might call it a "pinch point". A place where the object (your finger, a frisbee, etc.) passing thru the mechanism would get deformed, rather than the path itself deforming to accomodate the object.

[wireties]

Originally Posted by Robogineer1649

We built a prototype and it had two parallel wheels as you were saying you might try. I must add that it was in a linear fashion. But what i really want to tell you is that the frisbees go much further if one side is stationary compared to both sides spinning. Additionally our team has not tried to make a half circle shooter design only a linear so i can not take about that aspect of your question. What i can ask you is why would you use a half circle shooter that takes up much more space especially this year with smaller robots rather then building a linear shooter that works just as well?

Try spinning one wheel faster that the other to impart spin on the disc.

HTH

[Justin m]

Isn't it possible to have several wheels along a path, imparting speed and spin along a linear pathway? I apologize if this has been restating a previous post

[vikesrock777]

Originally Posted by Justin m

Isn't it possible to have several wheels along a path, imparting speed and spin along a linear pathway? I apologize if this has been restating a previous post

Yes, it certainly is possible. It can be seen in this prototype:
http://www.youtube.com/watch?v=GT88v...SDSA& index=9
that was then utilized in this final design, illustrating moderate consistency and power:
http://www.youtube.com/watch?v=Bfyzb...SDSA& index=1

[billbo911]

Here is a link to a bit more video from last night.

http://youtu.be/gWvWDQKd-8k

It is a bit long, but I will try to summarize the details we took away from it.

1) The traction tape is preventing any slippage between the Frisbee and the outer wall.
2) As we increase the voltage to the motor, the exit velocity of the Frisbee increases until we get to around 10 vdc. At that point the exit velocity begins to slowly fall off. This, along with basic observation of the images confirms that the wheel is slipping on the disk.
3) We can comfortably shoot a Frisbee 45+ ft. at waist level. We also verified we can easily hit the top goal from the bottom of the Pyramid, and the Pyramid goal from the base of the Alliance wall.
4) A top plate will be needed at least around the wheel contact area and possibly along the wall contact area to allow inverted Frisbee's to be feed through. A single piece plate is also an option.

Even if we go with this current design, we feel we have a competitive solution. Although, we plan to try to improve on the findings in #2. Possible options include: a pneumatic wheel, over wrapping or replacing the tread with the same traction tape applied to the wall.

Feel free to watch the video when you have a few minutes. It is educational, and sometimes entertaining.

[Ether]

Originally Posted by billbo911

1) The traction tape is preventing any slippage between the Frisbee and the outer wall.

2) As we increase the voltage to the motor, the exit velocity of the Frisbee increases until we get to around 10 vdc. At that point the exit velocity begins to slowly fall off. This, along with basic observation of the images confirms that the wheel is slipping on the disk.

These are useful observations. Thanks for sharing them!



[edit] Just watched the video:

1) There's a lot of wobble in the shooter wheel. Is that due to the motor mounting, or the wheel itself?

2) One camera angle seemed to show the frisbee "climbing up" the curved chute as it was exiting.

[billbo911]

Originally Posted by Ether

These are useful observations. Thanks for sharing them!



[edit] Just watched the video:

1) There's a lot of wobble in the shooter wheel. Is that due to the motor mounting, or the wheel itself?

2) One camera angle seemed to show the frisbee "climbing up" the curved chute as it was exiting.

The wheel is only attached to the motor shaft via a hub. The motor is mounted to a plywood sheet with a couple if screws and a stack of washers is used to fine tune the height of the wheel. This is not a really solid mounting method, thus it allows a small amount of wobble. Additionally, there is some silver "Sharpie" markings around the rim of the wheel that add to the appearance of the wobbling.

We did see the climb up on the shot you mentioned.

We will be testing to see if that occurs regularly, or just by not inserting the Frisbee to the shooter correctly.
This is also one of the reasons we are looking into a top plate(s).

[waialua359]

If making a "wide" bot, I'd assume one would make a circular path shooter vs. a linear one OR vice versa.
Online videos have shown both to be effective and consistent.

The choice to do either becomes how you acquire the pieces and load them into the shooter themselves.

[rdmarsh]

robotinthreedays wasn't really using a nip contact - they were using pneumatic tires, with a couple inches of contact per wheel thanks to compression. You can really see it in http://www.youtube.com/watch?v=GT88vWTYgj0 when they're feeding the frisbee through by hand. 2009 and 2012 both had flexible game pieces, so the contact patches got extended by squeezing the balls through a cannon, but this year that give needs to be on the tire instead.

[scaryone]

Looks like a Plexi table/base material? We started with plywood (we always use wood), tried plexi and found remarkable loss of distance. Try sliding a Bee across plexiglass vs plywood by hand and you can feel the difference. Nice jig by the way.