B The physics of flywheel launchers (like tennis ball shooters)

[cardboard_box]

Yes, you will be able.


Yes, that is the principle of a flywheel.
Your flywheel is solidly connected to a motor that can't be just pop out of existence.
The flywheel will rotate a little slower after shooting the ball, it will try to slowdown the motor, which will react applying a torque to speed up the flywheel until reaching the motor nominal rpm's.


The case is similar to a car trying to reach a high speed in first gear: the wheels receive lots of torque, but are unable to spin faster.
If we increase the mass of the wheel instead of velocity, our machine will be able to shoot heavier balls at the same velocity.


If no connected to a source of energy (the electrical motor in this case), the flywheel will have less momentum after giving some of it away to each launched ball.
As the mass of the flywheel can't be reduced, a reduction in rotational velocity will be the result of a free spinning flywheel launching several balls successively.


Yes.
Please, see:
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#rlin

http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/rotq.html

http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#am

I already know some of these variables, but I am not fully sure I get every effect of them and I still don't understand the importance of RPM.

about the wheel imagine instead I spin it up and then disengage it so that it is spinning freely without any resistance but isn't accelerating and applying a force anymore.

since you use a car metaphor I'll try to use one too: imagine we lift a car up in the air and accelerate it, and a certain point we just disengage the engine so it isn't powering the car anymore, while the wheels still roll we let the car down on the ground. at this point the car should start moving, but the question is why, how does the RPM of the car determine how fast it moves (how much force it applies on the ground)

 

[Baluncore]

For an arbitrary set of launch conditions, the plot of force against time, is unpredictable, and will be different for every launch under those conditions. Yet, the integral of that plot, and so the ball final velocity, will be the same. You really don't need to go into the detail of the sliding friction, and chaotic capture of the ball. That may be fascinating, but it is not a tractable problem.

The KE of wheels before launch = KE of wheels after launch + KE of flying ball.
The velocity of the ball will be equal to the circumferential velocity of the wheels after the launch. You can compute that, it is a tractable problem.

I would compute the launched ball velocity in the easiest way.
1. Design your flywheel and evaluate its Moment of Inertia.
2. Evaluate the MoI of the mass of the ball, if spread thinly, on the periphery of the flywheel.
3. Work out the initial KE of the flywheel, when spinning at the specified RPM.
4. Add the MoI of the ball to the MoI of the wheel.
5. Back compute from initial energy, to the lower final RPM using the increased MoI. You now know the reduction in wheel RPM due to the launch.
6. The velocity of the launched ball will be the same as the final velocity of the flywheel periphery.

 

[cardboard_box]

For an arbitrary set of launch conditions, the plot of force against time, is unpredictable, and will be different for every launch under those conditions. Yet, the integral of that plot, and so the ball final velocity, will be the same. You really don't need to go into the detail of the sliding friction, and chaotic capture of the ball. That may be fascinating, but it is not a tractable problem.

The KE of wheels before launch = KE of wheels after launch + KE of flying ball.
The velocity of the ball will be equal to the circumferential velocity of the wheels after the launch. You can compute that, it is a tractable problem.

I would compute the launched ball velocity in the easiest way.
1. Design your flywheel and evaluate its Moment of Inertia.
2. Evaluate the MoI of the mass of the ball, if spread thinly, on the periphery of the flywheel.
3. Work out the initial KE of the flywheel, when spinning at the specified RPM.
4. Add the MoI of the ball to the MoI of the wheel.
5. Back compute from initial energy, to the lower final RPM using the increased MoI. You now know the reduction in wheel RPM due to the launch.
6. The velocity of the launched ball will be the same as the final velocity of the flywheel periphery.

the problem is that I am trying to understand how to determine how I design the flywheel. So get the data on what how I need to projectiles to behave and work back from that what mass and velocity and so on the flywheel should be.

I think I am just not wording this well enough and not really explaining what specific problems I am having to understand. Thank you for trying to help and I maybe can just use your calculations, but for now I think I'll just open a different thread with a more coherent and generalized set of questions then "how to calculate flywheel".

take care.

 

[Baluncore]

"how to calculate flywheel".

Why ask when you can read all about it.
https://en.wikipedia.org/wiki/Flywheel#Design
https://en.wikipedia.org/wiki/List_of_moments_of_inertia

 

[cardboard_box]

sadly this is more about flywheels as a tool for conserving energy, while I'm mainly interested in using them to shoot out a projectile.

 

[renormalize]

the problem is that I am trying to understand how to determine how I design the flywheel. So get the data on what how I need to projectiles to behave and work back from that what mass and velocity and so on the flywheel should be.

Why are you trying to reinvent the (fly)wheel? Just use an existing calculator like this one: https://calculator.frc4322.com/shooting-mechanism.

 

[cardboard_box]

Why are you trying to reinvent the (fly)wheel? Just use an existing calculator like this one: https://calculator.frc4322.com/shooting-mechanism.

somehow I did not stumble upon this calculator, very useful indeed. I still want to learn how it works though, since without fully understanding it feels kinda empty.

I can not stretch this enough though but this calculator seems incredible, and now I got more of a focus on variables to study.

is a bit sub optimal to use this calculator since you input the variables for the result instead of the other way around, as well as variables that I (at least at the moment) do not understand how you could possibly know.
but again, a great help so thanks. any chance you know if I can view the way the calculator itself works by any chance?

 

[renormalize]

but again, a great help so thanks. any chance you know if I can view the way the calculator itself works by any chance?

This calculator is provided by a California robotics team. You should contact them for more info: https://frc4322.com/contact/.

 

[cardboard_box]

This calculator is provided by a California robotics team. You should contact them for more info: https://frc4322.com/contact/.

thank you.

 

[A.T.]

any chance you know if I can view the way the calculator itself works by any chance?

You cloud look at its source code:
https://calculator.frc4322.com/main.582e45e1ffceb5fd.js
But first use some tool to reformat it by inserting line breaks and indentation again.

 

[russ_watters]

I already know some of these variables, but I am not fully sure I get every effect of them and I still don't understand the importance of RPM.

so for example, if you are given a projectile which you know everything you want about, and are told to fire it at this and this velocity and fire this and this of them at this and this rate, how do you decide what wheel do you use?

...how exactly do I go about building such a function? specifically how does the velocity of the wheel change the velocity of the ball?

You solve the problem as described in Post #38. Is the real here here that you don't know how to solve that problem?