full balancing of e shaft rotors and counterweights assembled

[stuart wizy]

Stuart
I know what you are thinking,but I think you still misunderstand what we are on about,
The forces are greater yes,but the distance of movement of the out of balance item or Oscillation is the same.
The faster you rotate it the more oscillations per minute or second is what you get that is all.Each oscillation has more force at higher rpm,but it is over  a progressively shorter period of time,so the faster you go the object moves the same distance back and forth,but with greater force as the item speeds up.
The object just does not get more out of balance,it still has the same amount of imbalance.there is no real need to run things much more than around 300 rpm for balancing,as once you have balanced the item it is balanced no matter what rpm it runs.That does not mean that Jorgen is wrong to do so at a higher speed,it is just not totally necessary,just do what is needed to get the job done.
At the end of the day as long as you get your parts balanced it does not really matter I suppose.
Regards
Carl

cheers carl, i understand what u mean about the oscilation but going of my own experience with rotating parts for many years I guess ive come to my own conclusion!!!
it seems that this subject has very different views and methods all over the world from me trying to find this info out,
all i need to know is the oil weight  and i can turn these bob weights up and have a play!!!

cheers again for all the info guys:WaveBye

[dubber91]

i dont agree with the faster the RPM the more accurate the reading. It depends upon the application. Accurate in this sense is operating the shaft and dynamically balancing it at the RPMs it will experience in an engine (i.e. 900-12000 RPM). If you balance something at, say 20K RPM you may miss severall of the fundamental frequency nodes, and you will experience it during normal operation. Given that fundamental frequencies are always the greatest in magnitude i would consider these the most important frequencies engineer out.

However, what i am talking about is vibration, and NOT balance.

Again just my engineering 5 pennies

[stuart wizy]

i dont agree with the faster the RPM the more accurate the reading. It depends upon the application. Accurate in this sense is operating the shaft and dynamically balancing it at the RPMs it will experience in an engine (i.e. 900-12000 RPM). If you balance something at, say 20K RPM you may miss severall of the fundamental frequency nodes, and you will experience it during normal operation. Given that fundamental frequencies are always the greatest in magnitude i would consider these the most important frequencies engineer out.

However, what i am talking about is vibration, and NOT balance.

Again just my engineering 5 pennies

ok mate, I guess u know at bit about frequency nodes etc etc but listen to a simple explanation on vibration that any turner or cylindrical grinder will tell u the same thing because we work with things that spin round all day everyday, if there is vibration we get chatter when cutting so need to eliminate this by turning the revs down.
eg:-
put a piece of bar in a chuck on a laithe that is running out slightly say 1mm run out  (out of balance slightly)
place a 10 pence stood on its side on the tailstock of the machine
spin the chuck at 200 revs 10 p will stay put
turn up the revs to say 2000rpm and the 10 p will fall over because of the vibration.
which reading is more acurate here high revs or low revs?
with chuck empty you can spin 2000 rpm with 10 p still stood upright.
I use this method a lot when im turning shafts that have slots, keyways, milled squares on etc that are out of balance  to eliminate chatter caused through VIBRATION.

we build rotor milling and grinding machines,we machine every single component for each machine in house, when we build the workheads up on the rotor grinding machines we check for vibration all the way up to top revs on each individual machine upon final inspection to rule out vibration which would cause chatter when grinding.
http://www.renold.com/Renold/web/site/Products/MachineTools/Holroyd-Edgetek/Ancillary.asp

[dubber91]

ok mate, Im only trying to help.

some observations on what you just said. 1mm run out means an amplitude of 2mm if you treat the rotational moment as a wave. The reason your 10p does not fall over at lower rpm is because your no where near the fundamental frequency of the assembly. Say for arguements sake that 2000RPM is your fundamental freqency. then, 4000RPM you may experience the secondary frequency. In between you have the physical INBALANCE of the assembly also producing mild (and more importantly more noticeable)oscilatory motion of the entire assembly.
Thats why it vibrates more at higher speeds.
dynamic BALANCE should not be affected by the speed of the rotation. Vibration is another matter alltogether.
thats why you can do it the \'oldschool\' way you talked about much earlier works.

Steve

[dubber91]

ok mate, Im only trying to help.

some observations on what you just said. 1mm run out means an amplitude of 2mm if you treat the rotational moment as a wave. The reason your 10p does not fall over at lower rpm is because your no where near the fundamental frequency of the assembly. Say for arguements sake that 2000RPM is your fundamental freqency. then, 4000RPM you may experience the secondary frequency. In between you have the physical INBALANCE of the assembly also producing mild (and more importantly more noticeable)oscilatory motion of the entire assembly.
Thats why it vibrates more at higher speeds.
dynamic BALANCE should not be affected by the speed of the rotation. Vibration is another matter alltogether.
thats why you can do it the \'oldschool\' way you talked about much earlier works.

Steve

[stuart wizy]

ok mate, Im only trying to help

some observations on what you just said. 1mm run out means an amplitude of 2mm if you treat the rotational moment as a wave. The reason your 10p does not fall over at lower rpm is because your no where near the fundamental frequency of the assembly. Say for arguements sake that 2000RPM is your fundamental freqency. then, 4000RPM you may experience the secondary frequency. In between you have the physical INBALANCE of the assembly also producing mild (and more importantly more noticeable)oscilatory motion of the entire assembly.
Thats why it vibrates more at higher speeds.
dynamic BALANCE should not be affected by the speed of the rotation. Vibration is another matter alltogether.
thats why you can do it the \'oldschool\' way you talked about much earlier works.

Steve

cheers steve
the aim of what i am trying to do is allow the full rotating assembly to rotate much quicker than stock for longer periods of time whilst lowering the vibration without using the centre bearing which costs a fortune!
With my lightened rotors and a really good balance using the bob weight method above, i reckon it should rev higher with less vibration hopefully reducing the chatter that would be caused with apex seals chattering on the rotor housings at really high revs.
I could do it the oldschool way and then maybe take it to manchester for the dynamic balance to improve it from my balance.
what im thinking of doing is sticking the whole thing on one of our good laithe beds gripped in a collet at one end, revolving centre at the other end and 2 roller steadys on the 2 main journals bearings so that the origanal suporting method is achieved, then spin up at different revs and get our inspector to take some readings on vibration up to top revs.
get before and after readings to see how much difference it as actually made.
Interesting little project that wont cost me anything but the dynamic balance.
I just need to know the oil weight, are the rotors full of oil or say half full cause of centrifugal force when spinning, thats what i really need to know?
Again cheers for any info by everyone
cheers
stu

[shaunwil]

So the big question is at what frequency does resonance occur in the assembly.

Shaun

[dubber91]

or what frequencIES

you will never engineer them out. Vibration is much harder to deal with than balance: balance is simple static and dynamic equations whilst vibration and \'noise\' are more difficult. It is all down to wavelength, and the damping on the system. the damping in this case is the oil pressure on the journals, which is largely non-adjustatable. IIRC the lower the rotating masses, the higher the fundamental frequency, thus noise and vibration on a lightened assembly should be taken above the range on the stock motor, and should not cause you troubles.
At the end of the day dynamic balancing is a simple case of balancing the equations shown above. distances a and b are generally fixed, thus it is a case of adjusting the radius of rotation of the balancing masses, and the size of the masses themselves. The problem occurs because the shaft itself is not a simple element, rotors dont have fixed centres of mass, and the assembly is not supported by point supports. Thats why dynamic balancing is done practically rather than mathematically.
As with anything mechanical, you can only go so far with balancing: there are too many variables. The shaft may expand, the rotors change size, the oil changes viscosity and the bearing/shaft interface changes. Like using a timing light to time the engine, you can balance it just so, but it will not remain dynamically balance in all occurences. Your job is to ensure it is for the majority of driving scenarios and you dont end up with a motor that shakes itself to bits!

Good luck with it all: Im sure it will be worth it.

Steve

[stuart wizy]

or what frequencIES

you will never engineer them out. Vibration is much harder to deal with than balance: balance is simple static and dynamic equations whilst vibration and \'noise\' are more difficult. It is all down to wavelength, and the damping on the system. the damping in this case is the oil pressure on the journals, which is largely non-adjustatable. IIRC the lower the rotating masses, the higher the fundamental frequency, thus noise and vibration on a lightened assembly should be taken above the range on the stock motor, and should not cause you troubles.
At the end of the day dynamic balancing is a simple case of balancing the equations shown above. distances a and b are generally fixed, thus it is a case of adjusting the radius of rotation of the balancing masses, and the size of the masses themselves. The problem occurs because the shaft itself is not a simple element, rotors dont have fixed centres of mass, and the assembly is not supported by point supports. Thats why dynamic balancing is done practically rather than mathematically.
As with anything mechanical, you can only go so far with balancing: there are too many variables. The shaft may expand, the rotors change size, the oil changes viscosity and the bearing/shaft interface changes. Like using a timing light to time the engine, you can balance it just so, but it will not remain dynamically balance in all occurences. Your job is to ensure it is for the majority of driving scenarios and you dont end up with a motor that shakes itself to bits!

Good luck with it all: Im sure it will be worth it.

Steve

so in theory a less mass rotating of centre object ie rotors, should reduce vibration at higher speeds if it is balanced.
I would love to rev over 10,000rpm knowing she is lightened and balanced as well as u can possibly get.
Ive read some good write ups on apex seal chatter occuring on stock 13bs  running over 9k, stating that the motor can loose compression because of the intermitant bounce of the seals on and of the rotor housings through the vibration leading to higher combustion temps, warped seals and even full det.
Idealy the centre bearing would cure a lot of the vibration at extreme revs.
The guys in puerto rico seem to know a bit about high reving rotorys,
listen to this of the line:-http://www.rotorespr.net/forum/viewtopic.php?t=1469

[stuart wizy]

http://www.rotorespr.net/forum/viewtopic.php?t=1469

[dubber91]

so in theory a less mass rotating of centre object ie rotors, should reduce vibration at higher speeds if it is balanced.
I would love to rev over 10,000rpm knowing she is lightened and balanced as well as u can possibly get.
Ive read some good write ups on apex seal chatter occuring on stock 13bs  running over 9k, stating that the motor can loose compression because of the intermitant bounce of the seals on and of the rotor housings through the vibration leading to higher combustion temps, warped seals and even full det.
Idealy the centre bearing would cure a lot of the vibration at extreme revs.
The guys in puerto rico seem to know a bit about high reving rotorys,
listen to this of the line:-http://www.rotorespr.net/forum/viewtopic.php?t=1469

not less vibration.....but the resonant frequency should increase. But it is impossible to say by how much. The issue is then that each component in the engine has a resonat frequency. Anything that acts as a mass and spring. That means that side, apex corner and oil control rings all have separate resonant frequencies! Obviously mazda didnt have much problem with resonance and noise, or did well to engineer it out in there original design.....

[stuart wizy]

not less vibration.....but the resonant frequency should increase. But it is impossible to say by how much. The issue is then that each component in the engine has a resonat frequency. Anything that acts as a mass and spring. That means that side, apex corner and oil control rings all have separate resonant frequencies! Obviously mazda didnt have much problem with resonance and noise, or did well to engineer it out in there original design.....

just found this through pineapple racing, my theory is right:Giggle

Technology For Low Vibration, Distinctive Rotary Sound

Dynamically Balanced Rotors: To further refine the superior balance of the twin-rotor configuration, Mazda shifted from the previous static balance setting and instead adopted dynamic balance calculated from the mass of oil entering the rotors. This improvement, together with the effect of the long span engine mount system (mentioned previously) realises extremely low vibration.
this is info Ive found on the renesis engine improved on 13b so it seems all rx8s are dynamicly balanced with oil weight worked out.

[stuart wizy]

also this for the renesis:-

Lightweight Rotor, Three Injectors Per Rotor, And Long-Span Engine Mount: The previous 13B-REW engine generated its maximum power output at 6500 rpm, whereas the Renesis power peak comes in at 8200 rpm. This step-up to a higher revving engine was achieved by virtue of an 11 per cent reduction in rotor weight. Additionally, the flywheel weight has been reduced by some 20 per cent compared with the previous engine. Combined, these weight-saving measures reduce inertia to assure the quick response befitting a genuine sports car engine.

[dubber91]

all adds up doesnt it?

As it happens the original 13bs are all \'dynamically balanced\' but not to the extent of the later REW motor. The dynamic balance of earlier engines is mathematical: the assemblies arent physically checked for balance. This obviously takes out massive amounts of time and therefoe cost to the OEMs. Each component would just be weighed to ensure relativly close tolerencing on a mathematically (and probably physically) balanced model.
New CNC and closer tolering of components mean dynamic balancing is possible.
Remember by reducing rotating mass (and affective inertia) you will lose engine braking performance. Not that its too much of an issue

[stuart wizy]

got it, just need to take difference between my lightened rotor and stock rotor from 5474gram , it doesnt say if this includes oilweight though:confused:
see below:-
http://www.mazdamotorsports.com/webapp/wcs/stores/servlet/Tech?storeId=10001&subject=balancing