# Does duration of ball contact with flywheel affect force

Does the duration of the ball in contact with the flywheel affect how much force the ball will be released at? Right now we have a 3000 rpm V5 motor flywheel and its not outputting as much force as the other robots I’ve seen with the same configuration. Im thinking the reason why is because the ball only comes into contact with like 1/8 of the circumference of our 4" flywheel, whilst other robots with the same gear ratio and rpm have the ball contact the flywheel for at least 1/4 of its circumference.

Does it not go far enough? or it doesn’t have enough power to hit the flags? And also what is your launch angle?

I’m not the best at flywheels, but I think it’s more compression against the hood than time of contact with the wheel.

It depends on the quality of the contact. if it is in full contact and not slipping, it should pick up about all the speed it can pick up very quickly. It is a conservation of momentum, with the flywheels loosing as much energy as the ball gains. Every instant that the flywheels and the ball are in full contact and not slipping, they will be trying to reach the same velocity. The mass of the ball relative to the moment of inertia of the fly wheel will determine how much the two objects will need to change speed to have an equal energy transfer.

m(flywheel)*v(flywheel) = m(ball)*v(ball).

or, more accurately

I(flywheel)*w(flywheel) = m(ball)*v(ball) - The flywheel is loosing angular momentum, then ball is gaining linear momentum. Angular momentum is based on the moment of inertia and the angular velocity, not the standard mass and velocity.

To make a flywheel launch farther/faster, you can take the following actions.

Reduce drag on the ball. If it is on a stationary surface as it is fed into and through the fly wheel, make it as low traction as possible.

Increase flywheel moment of inertia. This does not have necessarily mean the weight, but that is an easy solution. Mass at the edges of the flywheel will impart more energy on the ball than mass at the center. The ideal flywheel is a heavy metal ring with just enough framing to handle the applied forces.

Increase flywheel speed. The energy transfer will be equal, and the flywheel and ball will try to reach equal speed.

Increase the energy transfer rate between the ball and the flywheel. More traction at the contact surface will allow the energy transfer to occur across a shorter time period, more likely to complete the transfer before the ball leaves the launcher.

@Robo_Eng_13 so say if our flywheel didnt have enough traction, the ball would have to contact the flywheel longer for the ball and flywheel to reach equal velocity?

Yeah. You will only be able to transfer energy as fast as friction will allow. If the surfaces are slipping past each other, you are effectively decreasing your transfer rate by the coefficient of kinetic friction.

@Robo_Eng_13 has explained the gist of if fairly well, but (no offense, just for clarity) has many errors in the physics involved. So long as you’re not doing any calculations, you can use most of what @Robo_Eng_13 said well.

The one spot I’m not so sure about as far as the gist is here:

Yes, you’ll accelerate the ball faster with everything else being equal. Is everything else equal? Many people have pointed out that the hood on a single flywheel can provide some compression to help the grip of the flywheel. Some people specifically put matting on the hood. I’m not sure making sure the hood is slippery is helpful.

Absolutely. It can help, if that is what your geometry needs. But in a general case, with just the flywheel and the ball, it is a negative.

Correct me if I am wrong, but making the hood slippery would be detrimental. The force on the ball is related to the speed of the flywheel and the time it contacts the flywheel. This is called impulse. F*T=impulse. So by making your flywheel hood slippery you decrease time it contacts the flywheel and there for less force which translates to less distance.

Ok, but you also have to understand that the less time that the ball is contacting the flywheel, the more forward motion you have. This is because its not like moving energy from a power source to the battery, alot of the energy imparted onto the ball goes into the hood. If a ball touches the flywheel for a shorter time, can be a bad thing, for example shortening your hood (which isnt always a bad thing), but if your shorter time has the ball travel the same distance, then the ball has to be moving faster, which in our case is better. So, if the hood is the same length, then the one that touches the ball the shortest amount of time would be best, due to the ball speeding up more. However one reason people like grippy hoods is that the energy imparted onto the ball translates to more rotary motion than a low friction hood would, which can help increase your range (thanks aerodynamics). Another thing you forgot to mention is that with a single flywheel and a high friction hood, alot of the energy imparted onto the ball results in a faster spinning ball, rather than forward motion. So while yes, a longer contact time with the flywheel results in more energy imparted onto the ball, that energy goes into spinning the ball rather than forwards motion, which is what we want.

So you see why I doubted it as a general solution, seeing as you yourself are saying it could go either way.

How do you know when the compression is too much/too little?

Sure. Everything can. There is not a simple answer to “How make flywheel more good?”. There will always be different factors that make answers that suit one design wrong for a different design.

From my experience, flywheels always relied on three main components. The first two are kind of obvious: the velocity of the flywheel and the angle of the ball when it leaves the robot. The third one is the force of the ball against the flywheel while they are in contact; this seems to be a much bigger component then the amount of time that the ball was in contact with the flywheel.

That’s just my opinion. Flywheels have so many different factors, like @Robo_Eng_13 said, so there’s no right answer here.