Shooters: What have you learned?

[Grim Tuesday]

I doubt that next year will be a shooter game, but I can guarantee that some years down the road, there will be another year where a shooter is the de facto method of scoring. I hope this thread will be useful to teams when that year does roll around!

So what less than (or more than) obvious facts have you learned about shooter design this year? What problems did you run into that you weren't expecting, and how did you fix them?

I'll start off: Make a single axle shooter if you want backspin. And if you make one with two axles, make an easy way to adjust the squish and make it easy to take apart. Because you'll be doing a lot of that.

[jblay]

Backspin is nice, try to have it.

Don't put used wheels on your shooter, it's a dumb move.

Prototype your idea thoroughly, don't just assume it will work because you see that every team has built a shooter prototype that works.

[jspatz1]

Originally Posted by jblay

Don't put used wheels on your shooter, it's a dumb move.

Ummmmm......maybe not so dumb.

[waialua359]

Originally Posted by jspatz1

Ummmmm......maybe not so dumb.

Darn, I guess we'll scrap ours as well.

[efoote868]

The theory I learned in Feedback System Analysis and Design actually works.

[jwfoss]

Consistent feed and positioning of the ball as it enters the shooter is absolutely critical. Our initial design allowed the ball to move left and right in the lift ~1/2" each way, after adding guides (and inducing a slight amount of lateral compression in the ball) we noticed a large increase in our accuracy.

For reference our shooter is a hooded shooter, 2 6"x1.5" colson wheels ~1.5" apart, and between 1"-1.5" in compression.

[CalTran]

Consistent feed and positioning of the ball as it enters the shooter is absolutely critical. Our initial design allowed the ball to move left and right in the lift ~1/2" each way, after adding guides (and inducing a slight amount of lateral compression in the ball) we noticed a large increase in our accuracy.

^Truest statement I've ever heard.

Some balls lose their squish...and other balls just don't like to be squished all that much.

If the game requires precision distance shooting, do us all a favor and get the design done so you can tune said design. Just ramping up the power does NOT equate to making a shot.

Oh, and if you're using heavy, custom fab wheels, make sure the motors you pick have enough power to make them go...

[Hawiian Cadder]

Consistency can be gained through LOTS of compression. We ran our competition robot with 4-5 inches of it in order to ensure precision.

[Bongle]

Don't solid-mount your gyro to your turret or other vibrating chassis components. Use a soft material that will damp vibrations. Note: we only learned this yesterday, when we took the time to do proper analysis on our gyro's heading over time. Makes it hard to auto-aim straight if your gyro starts drifting about 1deg/sec when the shooter turns on.

[LeelandS]

Since I'm looking to mentor new teams next season, these are the things I'll be bringing if a shooter game comes back up:

• Lighter wheels - With lighter wheels, the wheel will be back up to speed faster. This is especially necessary if you're using a motor with less torque and power to run the shooter wheel.
• More time on programming - Shooters are almost definitely the best way to score this year, but a lot of shooters aren't used to their full potential because the programming wasn't up to par. Spending more time on the target tracking algorithm can allow a shooter to be very succesful.
• Watch the weight distribution - Our robot this year is a bit top heavy. That's being worked on and resolved for champs, but it hurt us at FLR. When designing a shooter in the future, I'd like to make sure the shooter doesn't have an uneven weight distribution. This prevents disadvantages in game situations such as the bridge, and prevents the robot from rocking and potentially tipping as it moves.
• Responsive, consistent turret - Part of the key to succesful shooting is having a quick, responsive turret to shoot at the proper angle to meet your target. With a turret that has the proper hardware and coding, shooting can be made greatly effective.
• Make sure the ball enters the shooter quickly and consistently. We have a nasty habit of coming up with some unnecessarily complex storage-to-shooter designs. With some thought, I think there could be a quicker, more consistent way of getting the balls into the shooter.
• Don't let the balls enter the shooter at an angle - Without making sure of this, balls may enter (and come out) at an angle, or not get into the shooter at all.

These things aren't NEEDED for a good/great shooting robot, but they are things I'm going to greatly consider next time there is a shooting game.

[pfreivald]

Originally Posted by Leeland1126

[*]Lighter wheels - With lighter wheels, the wheel will be back up to speed faster. This is especially necessary if you're using a motor with less torque and power to run the shooter wheel.

Interesting... If our shop wasn't getting knocked down next week (and rebuilt hopefully by September) we were going to add a bunch of weight flywheel-style to our shooter to see if that increases accuracy!

Also, this is just an anecdotal observation, but single-axle hood shooters seem to be much more reliable than double-axle shooters.

[CalTran]

Originally Posted by Hawiian Cadder

Consistency can be gained through LOTS of compression. We ran our competition robot with 4-5 inches of it in order to ensure precision.

Really? We did about the same thing with our original shooter, and we found DRASTIC variation between shots because of its explosive exit as it uncompressed...

[Jeffy]

Originally Posted by CalTran

Really? We did about the same thing with our original shooter, and we found DRASTIC variation between shots because of its explosive exit as it uncompressed...

Conveniently knowing both systems well allow me to answer.

Our shooter does not shoot the ball with a very high velocity (compared to most). The ball is compressed between a roller and a flat piece of poly carbonate. This allows the ball to be decompressed over a fairly large distance (~5 inches). So, it's not exactly an "explosive" exit like it is from a shooter with dual wheels spinning much faster than ours.

Morale of the story:
Allow the ball to compress and decompress over a distance rather than "instantly".

[CalTran]

Originally Posted by Jeffy

So, it's not exactly an "explosive" exit like it is from a shooter with dual wheels spinning much faster than ours.

Er, yeah? I don't recall comparing the exits from the two shooters...

[Kellen Hill]

In designing a shooter, you must design around the ball you will be shooting and what you will be shooting it into. In 2006, I think the Poof balls were much more consistent in their squishy-ness or it was just a lot easier to shoot at a 30inch diameter near vertical goal. Either way, shooters that year did not require as much work due to a more consistent game piece and/or a large goal to shoot at.

This year however, we are playing with a game piece that changes quite a bit throughout the regional and is not consistent in squishy-ness to start with, along with a much more difficult goal to shoot at (18 inches and horizontal). With these factors, creating a shooter that would make every shot without adjustment took a little more time and effort.

From what I have found, the top three options for having a consistent shot are:

1. Catapult (16 is the best that I've seen: http://www.chiefdelphi.com/forums/sh...d.php?t=103876)
This approach removes ball squishy-ness from the picture. While it's harder to get significant backspin, you can land the ball in the same spot every time if you do it right. The trick is the getting the thing lined up and the right distance away from the hoop.

2. Extended acceleration period (2949 using belts: http://www.chiefdelphi.com/forums/sh...highlight=2949)
With lower compression and extended acceleration, each ball will exit the shooter at a consistent speed regardless of squish. Backspin is tweakable based on your setup. 2949 had a good setup with their shooter on a turret and their laser targeting system.

3. Shoot it hard with a lot of backspin (341 and I believe many others: http://www.chiefdelphi.com/forums/sh...d.php?t=103579)
For this setup, you need a decent amount of compression for this years ball and I think it helps a significant amount to be a tall robot. I will definitely be inspecting 341's shooter at champs to see just how they did it. As long as you can hit the backboard in this case, the backspin should put the ball right into the hoop as long as you are lined up correctly.


As to what we (525) did this season, we had to find another way to do it. We didn't wind up having enough height (we are about 3 ft tall) or enough compression on our shooter to easily do what 341 did. We thought about speeding up the last stage of our feeding mechanism to do more of what 2949 did. And obviously a catapult would have been quite a drastic change from what we had to work with. Our shooter used a 6inch Colson with one FP 0801-0673 with just short of 2 inches of compression on the ball and an adjustable hood. We decided we had to adjust our shooter speed/hood angle on a per ball basis in order to have a consistent shot. To do this we added a compression load cell (http://search.digikey.com/us/en/prod...6948-ND/809394) to measure each balls squish factor. You can find more information about our setup for the load cell here: http://www.chiefdelphi.com/forums/sh...d.php?t=105394. This setup got us to the point where we hit 9/10 balls in tele-op for one of our finals matches at 10,000 Lakes, hopefully something we can carry on to champs.

I'm sure there are other options for having a consistent shot, bot these are the three designs that have stuck out to me.

I hope this is helpful and I hope I remember all of this for the next game involving shooting a ball.

Kellen Hill