I thought of a design for a 4 wheel launching mechanism. It will have a wheel on the top, bottom, left and right. The idea is that if you decrease one of the wheels, for example the left wheel, then it will be angled towards the left. My only concern is the speed of each motor. Each one has to go very fast. Also I was planning on making the buttons on the controller control the speed of each motor. Any advice?
It’s an interesting idea but my advice would be to start with something simpler. First, build a two-wheel launcher and get really good at aiming the ball by making the wheels turn at different speeds, side to side, then rotate the whole thing and try up and down. If you can accomplish that, then move forward with your idea, if you think it’s necessary.
[ATTACH]9335[/ATTACH]
works in baseball.
prototype it!
I’ve built a prototype and it works ok. I just need to increase the RPM of the motors. Which gear ratio would work best? Also here are one of my sketches.
[ATTACH]9362[/ATTACH]
With 4 wheels you could have halved the RPM requirement. Start with a 7:1 ratio to make the build easier and see what happens.
Is that the case for a 4 wheeled launcher? I understand that a ball in a single wheeled launcher has to roll twice as far as a two wheeled launcher assuming a no-slip condition, but what changes from a two wheel launcher to a four wheel?
it is the same speed requirements as a 2 wheel launcher. a good and simple ratio to start with would be a turbo motor to a 7:1 (speed) with 5" large wheels. it might not be perfect, but it should be able kick the ball pretty far. (theoretical 1680 RPM).
Well, if all wheels contact the same, each wheel contributes more kinetic energy to the ball.
But from the picture, it seems only two wheels will be touching the ball. :D:eek:
From an energy standpoint, that’s true. But from a geometric standpoint, it wouldn’t matter if you had 2 flywheels or 4: you would still need those flywheels to impart the same final tangential velocity to the ball because the final tangential velocity of the flywheel (= ball velocity) is what gets the ball to the target.
A single flywheel must impart a tangential velocity of twice the speed of the 2 flywheel configuration because of the geometric constraints. Of course, you have to think about kinetic energy when aiming for that final tangential velocity.
I guess the confusion stems from “At what speed must I run my flywheels before launching the ball?” vs. “At what speed must my flywheels be running when the ball is finally leaving the launcher?” Those will be two different values because the ball sucks up energy as it passes through the flywheels, so the flywheels slow down as they accelerate the ball.
So there are two major constraints to consider: the kinetic energy constraint (“How do I store enough kinetic energy in the flywheels to make the ball fly?”), and the geometric constraint (“How do I get the ball up to the speed it needs so it makes it to the target?”)
To illustrate how those are two different questions: theoretically you could have two flywheels that each weigh 100 tons and are 10 feet in diameter rotating with a tangential velocity of 3 centimeters/second. Those flywheels would have plenty of kinetic energy to provide to the ball, but their tangential velocity could never get a ball to fly very far.
On the other extreme: you could have two thin styrofoam flywheels spinning furiously with a tangential velocity well above what a ball needs to fly across the field, but the styrofoam flywheels, because of their low mass, won’t be able to store enough kinetic energy to provide to the ball, so the ball would just stall the flywheels and sit there (maybe with its skin on fire).
I hope all my babbling helps rather than confuses people even more. :o
Yep, those are the kinds of tests we plan to run.
Measure the velocity drop as the ball goes through as well as recovery time for different velocities and different size/weight flywheels. This will get to the best flywheel configuration.
However anyone have any ideas on measuring the actual initial velocity of the ball?
High speed camera mode of the iphone against a backdrop of measured lines was one idea and vex light sensors as a speed trap was another. Vex limit switches would slow the ball down.
My kids made some iPhone slow-mo videos of their two-flywheel launcher. It was cool to watch. I was most impressed by how much their frame flexed when the ball passed through. They had tape on their flywheels but even with the slow motion, the wheels were nothing but a blur at their top speed. As the ball was fed into the flywheels, it was somewhat like “now you see it, now you don’t”. The ball just disappeared in a greenish blur. Maybe from a distance and/or with more intense lighting it might be easier to actually see the ball. They were using just regular room lighting at night, I think.
But would it be safe to assume that the initial flight velocity of the ball is going to be whatever the tangential velocity of the flywheels equals at the moment the ball is launched? In other words, if you can measure the flywheel speed, and you see in the data that the speed suddenly dips down to some value, couldn’t you use that speed dip to determine what the ball velocity probably was? These flywheels seem to have a fairly good grip on the balls, so I’m not sure they are slipping terribly much. I do see some scuff marks here and there, but I’m not even sure those are being caused by the flywheels. So can we assume a no-slip condition between the ball and the flywheel and simply get the initial ball velocity from that???
Not sure if it as good of a transfer as we might think. Hence why I want to measure it to prove it so.
A timing strobe light will be the tool of choice for the flywheel direct measurement. Have to remember how to use one of them though…
For the balls, you could also try the old-fashioned strobe with long-exposure photograph.
I’m not sure how easily that could be adapted to the flywheel, but it might work for that, too, maybe if you put a piece of white tape on the wheel and add a spinning color wheel in front of the camera lens so the tape will appear to change color with respect to time.
If you can take some measurements (range, initial height, launcher angle, final height, estimated spin) I could estimate the initial velocity from the aerodynamic model I have been working on. We could see how closely that agreed with the tangential velocity of the wheels and maybe we could get an idea of how good the no slip assumption is. Worst case they disagree heavily and that lets me know something may be wrong with my model 
I was rushing when I made that sketch. Each wheel will be the same distance apart from the center.