This is probably the best way to do it. You could potentially do a theoretical calculation, but you would have to know the moment of inertia of the launch wheels and how fast the ball is moving after the launch. By the way, your calculation would have to use angular momentum instead of kinetic energy. Energy will be lost to heat and deformation of the ball during the launching, whereas momentum is always conserved within a system.
This is exactly why the 5" wheel is great for flywheels. It has a lot of mass, mostly far away from its center. Unless teams want to somehow make a custom flywheel out of VEX parts that is better for the job, I think the 5" wheel will be the dominant flywheel.
Iām no expert, and itās been a long time since Iāve dabbled in these kinds of analyses, but I think it would be best to model this from a kinetic energy standpoint and not from a momentum standpoint.
While itās true that momentum is always conserved, as I understand it, linear momentum is conserved as linear momentum and angular momentum is conserved as angular momentum. They are two different concepts. You canāt convert linear momentum into angular momentum or vice versa. If Iām not mistaken, the apparent disappearance/conversion of momentum can usually be explained as momentum transferred into the earth.
On the other hand, kinetic energy can be converted from one form into another, including being converted into other forms of energy, such as heat. So the kinetic energy of your flywheels can be calculated, and the measured loss in their kinetic energy will be roughly equal to the kinetic energy gained by the ball plus whatever was lost in compressing the ball, skin friction, etc. The amount of kinetic energy pumped into the flywheel by the electric motors during the fraction of a second the flywheels interact with the ball will probably be very small. Keep in mind that the kinetic energy of your flywheel also includes the kinetic energy of the entire gear train, including whatever is whizzing around inside the motor.
So if my calculations are correct, with at 3.25 inch wheel, you would need 33 revolutions per second. Add 30-50% for the load of the ball slowing the wheels, slippage etc. and looks like to shoot for 3000 rpms. ā¦
What is the chance that VEX determines that their components are not designed/safe at these speed and restricts this design?
I feel like this was probably something that was thought about by the GDC when designing the game, but you could lower the rpm needed by increasing the size of the wheels you use for the launcher.
I think what mathman was saying is this: if you use a larger diameter launcher wheel (larger than, say, 3.25 inches), then the wheelās circumference is larger. Because its circumference is larger, it would not need to spin as many revolutions per second to provide the same (tangential) velocity at its circumference. So by using a larger wheel, you could reduce your rpm and still get the desired ball velocity.
This thread is focused on the physics of the flywheel design, hence the name. If youāre interested in pneumatic launching concepts I would recommend looking for a different thread pertaining to that idea, or start your own.
Couldnāt the possibility of differentiating angular velocities between the two wheels be negligible by mechanically syncing the wheels via sprockets/gears? I know our team will.
Also, any thoughts on doubling up the wheels on each side?
I would assume that doubling the wheels, since there is no increase in diameter, would only affect the flight of the ball by increasing the contact area between the ball and the wheel. I am not entirely certain of what the effect would be. I do know however that doubling the wheels would increase the moment of inertia (inertia for spinning). So when a ball is shot, some energy from the fly wheel ( KE=.5* Iw^2) would transfer to the ball (KE = .5m*v^2). Since the moment of inertia(I) cannot decrease, the wheels will have to slow down. With a larger moment of inertia though, the amount that the wheels slow down is smaller. This would be good for several quick shots. The downside is, that for a fixed power input, it will take longer to spin up the launcher.
The most important characteristic of the launcher is predictability. It doesnāt matter if ball leaves launcher at an angle or straight. The goal is to have exactly the same trajectory for each motor speed as read by quad encoder.
I agree with TheFIVE_Keck that mechanically linking both sides of the launcher is, probably, the best way to do it. Unless somebody builds a launcher with independent motors and shows that it has better success rate.
Also, you donāt have to run both sides of the launcher at the same speed. If you think it is better to have some spin to the ball - then one side may be differently geared, but still be linked to the same motors.
That is a good point. More surface contact area sounds better. When I get my hands on a NbN ball my first prototype will be a double 4" high traction wheels to see if balls will not slip too much against that surface. The bigger 5" wheels have studs and may give some extra unpredictability, but I will test them as well.
Before you have the real balls it is too early to say which design is better. We know by now most of the forces that could affect the ball, but donāt know how much each of them will affect trajectory. I would suggest everyone to build a number of designs and see how repeatable the results with be.
So putting spin on the ball decreases the distance the ball travels because some energy went into making it spin. But if there is no spin on the ball will that produce a knuckleball effect? Or will that kind of effect be a non factor with the nbn balls and the relatively short distances they are being launched?
So, our team has got a flywheel system that is getting 1,990 RPMās out of non-high speed motors (we are working on a double-motor design with high speed motors, updated numbers will follow), and are launching a foam practice softball (same dimensions as NbN balls) an average of 2.5 meters. The softball weighs 7.25 oz. An actual NbN ball weighs 1.76 oz. Can anyone help us out with what we should expect from the competition balls? Thanks.
