Launching the ball

[Christopher149]

Originally Posted by JCharlton

In previous years our team has used quick exhaust valves, but I believe that those are not longer permitted. Instead the return air has to pass out the solenoid valve. Haven't read the rules in that detail yet. Pity, we used it on our 2008 catapult.

It's been a while since our team has used pneumatics, but there seems to be very little in the rules dictating how to setup the system past the last regulator.

[cmrnpizzo14]

Originally Posted by LH Machinist

The pneumatic trick is called blocking the cylinder. You essentially use two pistons, one large and one small whereas the smaller cylinder acts as a release mechanism. The larger cylinder is activated, but it cannot move because the smaller cylinder is blocking its movement. When the smaller cylinder is moved it unblocks the large cylinder. The resultant force of the large cylinder is tremendous.

I think that our team used this in 2010. We didn't use the smaller cylinder to directly block the larger one but we had a latch that would hold our kicker back until that smaller cylinder released it. We would activate the solenoid to let air flow into the larger piston but it wouldn't extend due to the latch. Then releasing it we got a fairly good kick since the air was already through the solenoid.

Forgive me if I have the system wrong, it was my (and the team's) rookie year. I definitely didn't understand what was going on yet.

[carol95]

Hello, my name is Caroline Santos. I am the President for team 5023 (rookie team) from Capuchino High School. I was wondering if you could give us some tips as to how to design the robot for the FRC 2014 season. Please reply back. Thank you.

P.S: This is only our first season. Therefore, we need some help with designs.

Caroline Santos

[RRLedford]

Those here to gain insights as to how to make the best shooter should be aware of some factors influencing your choice for type of shooter and how you design/build it..
Most teams will use either a swing arm (catapult), a ram punching the ball, or spinning pinch wheels (or belts) to launch their balls.

1) Since at 2.75 LBS, the balls are fairly light, this means that a catapult arm style launcher does not require the arm to have very much structural mass, making it easier to accelerate the COMBINED mass of both catapult arm and the ball to a higher velocity with less force applied.

2) With the 60" height and 20" protrusion beyond the 112" circumference frame limits, the length of a swing arm design is rather constrained.

3) A set of spinning wheels (or belts) launcher is fairly compact, but needs to grip ball without damaging it from high slippage/friction/heat/melting.

4) Both ram and swing arm can be powered pneumatically or via winch stretched surgical tubing (or bungee cords).

5) All methods of launching need energy stored and ready to be delivered by a triggering method.

6) Best game performance requires launcher that fires at a wide range of speeds and angles.

7) High goal accurate shooting favors launcher designs that reach higher ball velocities, but it also favors launcher designs where their accuracy does not require a consistent level of ball inflation pressure, which the ram and pinch wheels designs do require for accuracy.

8) Missing high goal shots in auto is to be seriously avoided, since no assist points can accrue until all missed shot auto balls are retrieved and scored, which could easily take the whole rest of the match if defenders are good.

9) Catapult swing arms launchers are potentially highest accuracy and more consistent for handling ball pressure variation, of the three types, but they are less capable for reaching higher ball velocities.

10) Variable shooting speed & angle combined with shot triggering and trigger resetting is not a trivial design task.

11) Winch designs that retract an energy storing element (metal spring, air spring, bungee, latex rubber tubing, etc.) to store a variable level of launch energy are tricky to design, especially the triggering and trigger resetting mechanisms. However, they do favor better precision control of amount of energy delivered per shot.

12) Slow turning winch designs where the launch trigger system releases drum to free spin as ball launches have issues. Care must be taken to avoid too much slack of an unwinding cord/cable, which must be prevented from snagging, and cord/cable must also then be fully rewound before next shot is ready for launch. In addition, much of the stored energy can be wasted on accelerating the free spinning winch drum instead of delivering launch energy to the ball. Consider nylon winch drums.

13) Ram designs require that the ram velocity be absorbed by the robot frame after launched ball separates from the ram. A well optimized ball-to-ram mass ratio and a well tuned peak velocity ram acceleration allows ram rebound off the ball to help limit the ram speed at the limit of travel stopping point.

14) Swing arms also have end of stroke arm travel concerns, but if air cylinder power is used, pneumatic pressure can be used for an end of travel cushion.

15) Ram launchers only impart energy to ball while ram maintains contact with the ball. Inadequate ram speed and travel can give too little ball penetration/compression by the ram end. compressed ball acts like a spring and extends time/distance that ram stays in contact with ball.

I am sure others can add more thoughts to this list.

-Dick Ledford

[MrForbes]

Good stuff, thanks!

Originally Posted by RRLedford

6) Best game performance requires launcher that fires at a wide range of speeds and angles.

That's debatable....if the variable speed/angle require complex control that can't be accomplished by your team, then a well designed single speed/angle shooter that can be easily aimed and scores consistently might be the way to go. We did that last year, and it worked great.

[RRLedford]

Originally Posted by MrForbes

Good stuff, thanks!




That's debatable....if the variable speed/angle require complex control that can't be accomplished by your team, then a well designed single speed/angle shooter that can be easily aimed and scores consistently might be the way to go. We did that last year, and it worked great.

It is always best to design & build within the capabilities of your team to accomplish the goals it sets.

However, this does not ensure that meeting those goals will produce the same level of best performance that the more elite teams can & will accomplish.

I was only suggesting that variable launch speed and elevation angle will be what most elite teams will end up having.
Good results can still be accomplished with well executed simpler designs as well, as you point out.

-Dick Ledford