So, with the absence of lifts this year, we will need to launch the balls into the goals.
What ideas have you come up with to do this? So far, I’ve heard and thought of ideas involving rubber band powered catapults, pneumatic catapults, and side wheel launchers, as well as combinations of these ideas. Are there any other ways that might be effective?
Also, it seems like another side roller intake year. Has anyone considered some variation of this, or something completely different?
cams and springs all the way. pnumatics would be great but you only get so many activations .
There are several options for long distance ball launchers:
Slingshots are easier to make but their left-right aim is very sensitive to the quality of the rubber bands on the left and right sides.
Catapults are good at maintaining aim in horizontal direction, but may be tricky to get a good vertical/distance aim accuracy.
Crossbows should be better at maintaining both aims, but you have to build the linear slider with the ball holder and, maybe, some sort of guide for the balls. It gets tricky fast.
All three of the above designs need to be rearmed by pulling rubber bands with motors or pneumatics before each ball (or pair or triplet of balls) are launched. You will also need a separate trigger gizmo.
This is the most high performance type of launcher. Unlike catapults, slingshots, or crossbows it doesn’t need to be reloaded before each shot and will spew a constant stream of balls.
However, it’s horizontal aim accuracy is very sensitive to the rotation speeds and local radius of the wheels. Beginner teams should, probably, link left and right axles with gears or chain to sync their speeds.
Advanced teams may actually shift the left-right aim by monitoring rotation speed and slightly adjusting motor power. Pros may even try to create a contraption with three launcher wheels. Then by varying rotation speeds they could control both horizontal and vertical aim.
In any case anybody who wants to do effective autonomous should start learning about calculating ballistic charts, otherwise you may just as well drive up to a goal and gently push the balls up to the net 
Flywheel, catapult, VEX U could 3D print a tube and attempt using the air pressure directly to launch balls depending on how squishy they are, any kind of elastics to just kind of hit the balls would work, etc.
I’m liking the flywheel myself. Working on how I could finely control the speed with only 127 speed adjustments, most of which will be too slow.
I’m thinking the motors powering the wheel need to be nearly full powered, with something else somehow varying the gear ratio ever so slightly which means some kind of continuous variable transmission.
Flywheels will need to be heavy (to accumulate enough momentum) and therefore will not change their rotational speed at once when you change the power level on the motors. It will take some time to rump up or down. Depending on the speed you need you can feed the ball just at the right time.
Relationship between power levels and the time to feed the ball will likely be non-linear, so you will need to experimentally build the charts, including battery voltage as one of the input variables.
If you want fine grained speed control you can try to use a differential with two motor inputs, where the output speed is the sum or difference of individual motor power, but I afraid there will be too much power loss due to friction and not sure if the added complexity is worth it. Guess, somebody have to try it.
An encoder + a decent PID loop with enough overhead in motor power to compensate for a match’s worth of power drain should keep the thing at a decently constant speed.
in reality it’s less, at about 90 or 100 the motor’s speed stops increasing, and that’s without load.
jpearman does some tests here:
So a good source to find ides would be to look at some of the best teams in FRC during the 2012 season. The game was strictly basketball and design concepts for it could easily work for the game this year. Also another idea to look at is, some high schools or students have made ping pong ball shooters with vex parts before. They use regular motors with intricate gear ratios and ive seen a few with loading mechanisms.
I’ve made those but they can’t shoot that far maybe 5 feet with 1 to 1 but the were with small intake wheels. Maybe try with 6 inch and 1:2 or 1:3.
And that’s why u make these gear ratios. Also instead of using two wheels, you could have one that the ball travels around and adjust the angle of the backing to choose distance.
That wow be cool the reason I didn’t do gear ratio because it was my first year.
If you can get enough power to launch the balls when close up at power that’s less than full, you could use an ultrasonic sensor to determine distance from the goal, then use that value to determine the power put into the wheels for the shot.
I would love to prototype this design, but since I’m not allowed to build anymore, since I’m a graduating senior at my high school. After worlds ends, anyone want to test out how far you can shoot one of these balls using a flywheel at a variety of powers and gear ratios?
Took me a while to find this, I had one of these as a kid.
well, the only issue with cams are that you only get a constant force when firing. flywheels seem to the best because of the variable RPM, especially in vexU when combined with a bunch of advanced sensors.
We are building a prototype flywheel right now, but we’ve hit an immediate problem: The pre-cut squares in our in our metal make the set up such that our wheels are a little too wide or a little too tight for the ball. This may not be a problem due to squishiness, but we don’t have a ball for testing. Does anyone know if these balls are squishy at all?
It turns out they are those soft squishy balls. Polyurethane. How fun it is going to be playing around with them!
Maybe instead of the ball traveling trough two wheels, it could pass around only one. You then can adjust how far the wheel is from the backing allowing for the perfect fit.
3D printing for the win.
Idk, I need some of those playing elements.
The balls need to also have spin on them, if you ever watch baseball, the pitchers always add a sort of spin to the ball to keep it going straight, that way, a light breeze won’t affect your robot as much.
The spin in baseball is actually to help it rise up. Because of physics I at one point learned, and then promptly forgot, if a ball is spinning backwards it gets a bit of lift, which helps it travel better. The stabilising spin you’re thinking of is the spin on (American) footballs as well as bullets which is explained here.
Note: I actually don’t really understand aerodynamics, so I could be horribly wrong. If I am, sorry, please correct me.