Small diameter flywheel?

[stoney]

But I think my real problem here is one formula does not cover everything that's happening.

Actually the formula and laws of physics as they relate to mass, inertia, and angular momentum are directly applicable to everything related to the discussion ... you just refuse to accept the proven scientific principals on which it is based. kinda like you claiming 2+2 doesn't equal 4 in sneaks world.

...3 pounds rotated to 6000rpms should require the same amount of energy no matter what the diameter...

Now, back to your original premise in which you made the blanket statement that diameter played no role in the torque required to accelerate a flywheel of given mass to a specified angular momentum (rpm) ... a claim which was quicky disproven by presenting incontrovertible principles based on the relationship between mass, moment of inertia, and radius of gyration (flywheel diameter). The only variable associated with your initial claim was flywheel diameter .. which you claimed played no role in the torque required to accelerate the flywheel. Now having had that claim dispelled, you have attempted in interject any number of other unrelated variables such as zero gravity, friction, homogeneity, fins vs finless .. ad nauseam... none of which bear any relevance or offer any legitimacy to your original statement which was based specifically and singularly on diameter.

 

[JamesClarke]

Actually the formula and laws of physics as they relate to mass, inertia, and angular momentum are directly applicable to everything related to the discussion

Agree. In my physics class in college we figured the angular momentum, inertia, and kinetic energy of objects close to flywheels. Assuming all things are equal besides the mass and the radius the smaller lighter flywheel is going to accelerate and deaccelerate quicker than the bigger heavier flywheel that is going to have more kinetic energy stored. I would say that the formula almost I=1/2M (r1*r1+r2*r2) the r1 being in inner radius of flywheel and r2 being outside radius. Now both flywheels have the same r1 so its kind of irrelevant. So a smaller flywheel with less mass is going to have less inertia meaning it will have less resistance to accelerate and deaccelerate.

Now if someone has time to figure the kinetic energy of a rotational mass with the angular velocity would be interesting to see.

 

[sneaks12303]

The wheels I'm looking at are the arc 6607 weight is 2.85lb small diameter and the arc 6618 weight is 4.9 lb full size. And it will only be ran on short tight corner tracks no long tracks around here really. I get in and out of the throttle alot.

The 6607 is for a 390 and the 6618 is for a 200 ? What motor ya got ?

 

[sneaks12303]

Actually the formula and laws of physics as they relate to mass, inertia, and angular momentum are directly applicable to everything related to the discussion ... you just refuse to accept the proven scientific principals on which it is based. kinda like you claiming 2+2 doesn't equal 4 in sneaks world.



Now, back to your original premise in which you made the blanket statement that diameter played no role in the torque required to accelerate a flywheel of given mass to a specified angular momentum (rpm) ... a claim which was quicky disproven by presenting incontrovertible principles based on the relationship between mass, moment of inertia, and radius of gyration (flywheel diameter). The only variable associated with your initial claim was flywheel diameter .. which you claimed played no role in the torque required to accelerate the flywheel. Now having had that claim dispelled, you have attempted in interject any number of other unrelated variables such as zero gravity, friction, homogeneity, fins vs finless .. ad nauseam... none of which bear any relevance or offer any legitimacy to your original statement which was based specifically and singularly on diameter.

The same amount of energy relative to our 2 flywheel choise's..NOT the entire universe..or a 12" vs a 6"....BECAUSE the actual difference in diameters is too small . Please , Do not use my suggestions on anything but these clones...You guys are doing physics of the known observable universe...You would be better off thinking of these motors more like "Quantum Mechanics" Where E=MC2 falls apart....And Welcome to "Sneaks World"

 

[Bumpy]

Something to think about...The flywheel is the heaviest piece of rotating mass in the motor. A smaller flywheel spins slower cause it covers less distance in 360*. This is a good thing coming out of the corners and braking . This is a bad thing for top end and momentum tracks...I found the larger diameter wheels got a wee bit more rpms at top end. The difference between diameter/same weight is not nearly as much as an ultra lite vs an AKRA legal steely..Now heres the tricky part...3 pounds rotated to 6000rpms should require the same amount of energy no matter what the diameter...So whats going on ?

Sneaks, the issue is related to the radius of the rotating mass. The formula is (allow some slack, haven't done Physics in a while) Inertia = mass x radius squared divided by 2 (I think)
Mass is the weight divided by ~32.
So for two flywheels of the same mass but one having a smaller radius the inertia will be less for the smaller radius.
Inertia is the tendency of a body to resist acceleration.
So on paper a smaller diameter flywheel of the same mass will accelerate more quickly in either direction. Acceleration to desired rpm will occur more quickly and deceleration to lower rpm will also.
That's my wack Physics lesson for today.
No questions?
Good.

 

[sneaks12303]

The 6607 is for a 390 and the 6618 is for a 200 ? What motor ya got ?

My bad , Is see which 6607 your looking at...Arc makes 2....For Short track dirt with an SA motor, I still like the 6618. For a more mild Akra motor, that 6607 would help because of the lighter weight..

 

[stoney]

.... So a smaller flywheel with less mass is going to have less inertia meaning it will have less resistance to accelerate and decelerate .....

James thanks for the reply ... just for clarification ....When you say "smaller flywheel" you are referring to "smaller diameter flywheel" ... correct?

the original premise was based on flywheels of the same mass, but different diameters. You would then be in agreement that the "smallest diameter flywheel" would have the least inertia, and would require the least torque for acceleration and deceleration .... and the "largest diameter flywheel" would have the most inertia and require the most torque for acceleration and deceleration .... agreed ??

 

[sneaks12303]

Sneaks, the issue is related to the radius of the rotating mass. The formula is (allow some slack, haven't done Physics in a while) Inertia = mass x radius squared divided by 2 (I think)
Mass is the weight divided by ~32.
So for two flywheels of the same mass but one having a smaller radius the inertia will be less for the smaller radius.
Inertia is the tendency of a body to resist acceleration.
So on paper a smaller diameter flywheel of the same mass will accelerate more quickly in either direction. Acceleration to desired rpm will occur more quickly and deceleration to lower rpm will also.
That's my wack Physics lesson for today.
No questions?
Good.

Yep , accelerate and decelerate easier, like I said better for coming out of the corners and better for breaking...But without the extra inertia of the larger wheel I was seeing better rpms with larger..But the torque diiference when you overlay the graphs was barely detectable..Its the lite weight vs heavy weight where I see bigger differences that could be felt..

 

[Bumpy]

Sneaks "Yep , accelerate and decelerate easier, like I said better for coming out of the corners and better for breaking...But without the extra inertia of the larger wheel I was seeing better rpms with larger...."

I'm out of ideas.
That's why you're the Sneaks and I'm just reading Bob's.

 

[stoney]

The same amount of energy relative to our 2 flywheel choise's..NOT the entire universe..or a 12" vs a 6"....BECAUSE the actual difference in diameters is too small ....

Same principals, laws, and formulas are still applicable regardless of the magnitude difference in diameters. Just as applicable for a .006" difference in flywheel diameters ... as they are for 6" difference in flywheel diameters. The larger diameter flywheel will have the higher inertia and require more torque to accelerate .... the smaller diameter flywheel will have the lesser inertia and require less torque for acceleration.

If you reread my earlier post I gave you the formula and demonstrated that torque required to accelerate a flywheel increases by the square of the radius ..... so it doesn't take a large magnitude difference in diameter to make a measurable change in the torque required.

....Welcome to "Sneaks World"

No thanks ... I'm good ... Someday when you're ready we will welcome you ours

 

[JamesClarke]

James thanks for the reply ... just for clarification ....When you say "smaller flywheel" you are referring to "smaller diameter flywheel" ... correct?

the original premise was based on flywheels of the same mass, but different diameters. You would then be in agreement that the "smallest diameter flywheel" would have the least inertia, and would require the least torque for acceleration and deceleration .... and the "largest diameter flywheel" would have the most inertia and require the most torque for acceleration and deceleration .... agreed ??

Yes smaller flywheel being the smaller diameter i guess by the time i read everything i forgot only comparing diameters not smaller diameter with less mass.

As with your second part i agree with that as well its going to take less torque for acceleration and deceleration.

I must of took the same physics class lol

 

[alvin l nunley]

Not being able to do it myself, the math, I'll just have to hope that someone can do it for us.
What about the rate of acceleration?
Seems to me that has got to be in the formula, and once that clutch is up to stall speed, the rate of acceleration is really slow.
I'm thinking you maybe could feel the difference between the two flywheels under heavy braking, like on a Sprint track, but not on an oval track, especially a track where you don't let off. And then you have to consider that you are accelerating, and decelerating, the combined weight of the kart and driver and flywheel. And I have this idea that the flywheel is the lesser of the three, by a bunch, and the difference between the two flywheels, as small as it is, compared to everything else, must be literally undetectable.
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.

 

[sneaks12303]

Another issue that arises with a smaller diameter wheel is magnetic speed across the coil .

 

[sneaks12303]

Just to get everyone back on track the comparison is a 6607 vs 6618 for short track tight turns . And sorry boys , they are not homogenous...they don't even weight the same..So who likes which , and why ?

 

[stoney]

Another issue that arises with a smaller diameter wheel is magnetic speed across the coil .

For two flywheels with different radius of gyration (diameter) at a given rpm, the larger diameter flywheel will have the higher angular velocity .... i.e. the higher magnet speed past the coil.

 

[sneaks12303]

For two flywheels with different radius of gyration (diameter) at a given rpm, the larger diameter flywheel will have the higher angular velocity .... i.e. the higher magnet speed past the coil.

I agree , so the larger wheel should have a hotter spark . And that coil is designed to be best saturated at a given mag speed. By reducing that speed (smaller wheel) we change things. Now, how does this effect ignition timing ?

 

[stoney]

Just to get everyone back on track the comparison is a 6607 vs 6618 for short track tight turns . And sorry boys , they are not homogenous...they don't even weight the same..

Homogeneity is not related to total weight... homogeneity referrers to the distribution of the mass ... not the amount of mass. Neither the 6607 nor 6618 would be considered homogeneous due to the large mass of the steel adjustable timing hub which is centrally located.

 

[stoney]

I agree , so the larger wheel should have a hotter spark . And that coil is designed to be best saturated at a given mag speed. By reducing that speed (smaller wheel) we change things. Now, how does this effect ignition timing ?

The strength or magnitude of the current induced in the coil is governed by Faraday’s Law, which means that the magnitude of an induced current is proportional to the rate of change of magnetic flux..

This means that the stronger the magnet, and the greater the speed of the magnet as it travels past the coil, the larger the current produced from the coil.

As long as the magnet is traveling at sufficient speed to fully charge the coil, and not so fast that it oversaturates the coil resulting in current leakage, there should little effect on timing or spark intensity.

Since a larger diameter flywheel would have the greater angular momentum resulting in a faster magnet speed past the coil, a larger flywheel may help to ensure a fully charged coil and increased spark intensity at lower rpm's ... don't know just theorizing ??

 

[swamprat]

Wonder how that little flywheel in my weedwacker keeps up with little flywheel it has....how about the old Mcculloch? I'm sure your old Mccullochs reved higher than a clone. Just makes me wonder.

 

[65ShelbyClone]

One thing not mentioned often enough is that a reduction in flywheel inertia will show power gains on an acceleration dyno, but not a steady-state brake dyno.

Now heres the tricky part...3 pounds rotated to 6000rpms should require the same amount of energy no matter what the diameter...So whats going on ?

It doesn't work that way and here's why:

Imagine a car driving around a 1.0mi circle track at one lap per minute. Imagine another identical car driving around a 2.0mi circle track at one lap per minute. Their "revolutions per minute" are equal, but the car on the small track is only doing 60mph while the car on the bigger track has to go 120mph.

Would everyone agree that the car doing 120mph has more momentum than the one doing 60? Therein lies the reason that diameter affects a flywheel's inertia even when mass and RPM remain unchanged.