Ball Pitcher Hood Design

[BJC]

What are you saying no to, everything I said was true. You will not accelerate a ball to the shooter wheel's speed with a single point of contact. That is not to say that it won't work. Just that it won't be traveling through the air as fast as 1/2 the surface speed of the wheel.

Your experience is interesting. There are many reasons why the ball might not have gone as far. (too much or too little pinch comes most readily to mind) However, as a rule takes about 1/4-1/3 of the wheel curcumference to get the ball up to full speed (1/2 shooter speed) all the way up. So yes it will spin faster, however this is the result of the ball rotating faster as it travels faster. I can draw a diagram quickly if you want but basically with a single shooter the outside of the ball travels the shooter wheel's surface speed while the middle of the ball (what you care about) travels 1/2 the shooter wheel's surface speed.

[JellyMan]

I agree. It would seem to me that added backspin cannot come without added velocity of the ball.
Note that it also takes some energy to crush the ball. Our theory is that a flat plate hood (point contact) requires significant crush to pitch the ball. If the same heavy crush of the ball is used with a curved hood (longer travel), is it possible that this wastes enough energy to result in a shorter pitch?
We are hoping that a longer contact curved hood (with light ball crush) will still result in a long pitch.
Thanks for the discussion, we'll let you know how it goes on Monday.

[JellyMan]

Update:
We modified our prototype ball pitcher today by replacing the flat top plate with a curved hood. The hood starts vertical behind the pitching wheel, and extends through a 45 degree arc, so the ball leaves the wheel at a 45 degree angle.

I am happy to report that the ball velocity is at least as fast as with the flat plate the other day. It may even be a bit faster ... it was hard to tell because the elevation angle is now a little higher than before, and the ball hits the ceiling under maximum power (a good sign). We are working in a portable classroom with a low ceiling.

Stay tuned!
GO FALCON ROBOTICS / TEAM 3414!

[Mk.32]

Originally Posted by JellyMan

Update:
We modified our prototype ball pitcher today by replacing the flat top plate with a curved hood. The hood starts vertical behind the pitching wheel, and extends through a 45 degree arc, so the ball leaves the wheel at a 45 degree angle.

I am happy to report that the ball velocity is at least as fast as with the flat plate the other day. It may even be a bit faster ... it was hard to tell because the elevation angle is now a little higher than before, and the ball hits the ceiling under maximum power (a good sign). We are working in a portable classroom with a low ceiling.

Stay tuned!
GO FALCON ROBOTICS / TEAM 3414!

Video or it didn't happen.

[MrForbes]

Here's ours, which sounds like it's working about the same as theirs.

http://www.youtube.com/watch?v=jeLe2WWemWA

We never got around to trimming the top of the shooter, so the students are holding it at an angle. It's not quite 45 degrees. There is a Lexan flap behind the shooter, that is being held down over the top of the ball before inserting the ball into the shooter.

http://www.youtube.com/watch?v=jeLe2WWemWA

[falconmaster]

I feel bad about ours now...

[roborat]

Originally Posted by squirrel

Here's ours, which sounds like it's working about the same as theirs.

http://www.youtube.com/watch?v=jeLe2WWemWA

We never got around to trimming the top of the shooter, so the students are holding it at an angle. It's not quite 45 degrees. There is a Lexan flap behind the shooter, that is being held down over the top of the ball before inserting the ball into the shooter.

http://www.youtube.com/watch?v=jeLe2WWemWA

What motor are you using to spin the wheel, we used a single wheel when we had the shooter a few years ago and used a CIM. We are not for sure if we want to use two wheel or one, I like the one wheel because of the amount of space required

[Easton8]

for inspiration look at team 1717 and 217s shooters from 2009. Both had adjustable sheet metal hoods powered by window motors (i think) that could adjust their trajectory from about 75 to 150 degrees. while for this competition you would want something lower (maybe 40-80 degrees) the basic design would stay the same.

[MrForbes]

Originally Posted by roborat

What motor are you using to spin the wheel, we used a single wheel when we had the shooter a few years ago and used a CIM. We are not for sure if we want to use two wheel or one, I like the one wheel because of the amount of space required

We are using a 9015 Fisher Price motor, the spec sheet says it's not as powerful as this year's motor, but it's about the same as the AM 0912 motor that came in the kit. We have it connected to a custom gearbox from a previous robot, which uses FP gears to give us 3:5 reduction, then we have another 9:22 reduction from a chain/sprocket set.

We intend to make the departure angle adjustable, possibly similar to what 1717 did with their hood in 2009, although I think they used a small 385 series Banebots motor.

[greasemonkey]

my team intends to use a material called wacky wood which is basically a plywood with a layer of rubber in the center this makes it extremely flexible the only problem is that it is hard to find but if you live in New England than we found ours at Boulter Plywood in Somerville, Mass. they also have a website to

[TerryS]

This is our first experience making a shooter and we were struggling with our prototype until I came across this thread. Thanks to the advice given here we finally got a good proto running today. Made over 60% of our 3-point shots from the free throw line. Over 90% doing 2-point layups.

We ended up using two 8-inch AM FIRST wheels mounted side-by-side on a 1/2" shaft. The proto is powered by a CIM with a 1:1 chain drive. We plan to use two RS-550s with a CIM-U-LATOR gearbox on the robot. Not sure how much we'll gear it down yet. Today's proto used a flat plywood hood fixed at 60 degrees. Compressing the ball by 2-2.5" seems to work best. Range dropped when we backed off to 1.5". We're going to try a 70 degree hood next as the 60 degree trajectory looked a little flat. We could make a rotating hood, but today's testing showed that we can probably make shots consistently from up close to the top of the key with a fixed angle just by changing the wheel speed.

A big mahalo to all who contributed to this thread! We'd still be struggling without your coopertition! On to the next challenge!

[MrForbes]

Originally Posted by TerryS

We're going to try a 70 degree hood next as the 60 degree trajectory looked a little flat.

As far as I can tell, if you have a lot of backspin so the ball bounces down off the backboard into the basket, you WANT a flat trajectory...then you don't need to worry about how far away from the goal you are. One less thing to sense and control.

At least that's how we're planning to play the game.

[TerryS]

Originally Posted by squirrel

As far as I can tell, if you have a lot of backspin so the ball bounces down off the backboard into the basket, you WANT a flat trajectory...then you don't need to worry about how far away from the goal you are. One less thing to sense and control.

At least that's how we're planning to play the game.

Good observation. You're right a lot of our 3-point free throws were off the backboard. We'll still test at 70 and compare.

[gpetilli]

Originally Posted by squirrel

Here's ours, which sounds like it's working about the same as theirs.

http://www.youtube.com/watch?v=jeLe2WWemWA

We never got around to trimming the top of the shooter, so the students are holding it at an angle. It's not quite 45 degrees. There is a Lexan flap behind the shooter, that is being held down over the top of the ball before inserting the ball into the shooter.

http://www.youtube.com/watch?v=jeLe2WWemWA

It seems that the amount you compress the ball is a critical parameter. Too little and you get slip, too much and you waste energy. We are looking at about 1.5inch compression of the wheel on the ball. Can you share what you are using and how you calibrated it?

[MrForbes]

In the video, the ball is being compressed to about 6". We're working on modifying it so we can do more testing.