Centramatics automatic hub balancer add-on?

[DanG]

I've been looking into a set of these for my truck and trailer and wondered how they would fly on a heavy-duty trailer hub windmill - of course a static balance is needed but think using one of these would make it fly any safer or more efficiently? They claim it becomes active at 20mph which translates into 190-210 rpm; using an active balancing hub might reduce noise at the very least...

Any insights or comments?

http://www.centramatic.com/New_Catalog/300series.php

"By using centrifugal force the free moving weights (durametal and synthetic fluid) sealed in the balancer automatically distributes to exactly where needed, placing the assembly in equilibrium or perfect balance. When a sprung assembly is out of balance, deflection is caused via the springs or tire sidewalls. These free moving weights sense this deflection and move opposite the heavy points to balance the entire assembly, wheels, tires, drums, hubs, even mud, snow or ice stuck to the wheels."

[disaray1]

 Porsche uses (and other manufacturers might too) this same sorta moveable mass technology in their flywheels to help balance the engine...and it works wonderfully. Absolutely silk smooth from idle to redline. It does fail though...of course with high horsepower thats gonna happen. Should work on wind gens....

 david

[happysmith]

I have the same idea and would like to try the ones made for truck wheels that are 22" or so in diameter.

They contain more mass and, due to their large diameter, are made to operate at slower speeds than the ones made for cars.

Did you know that the first automatic Maytag washers (the ones that were flat on top and had mercury switches in the lid) had a fluid filled vibration damper mounted around the top outside edge of the tub?

I had a mechanical engineering professor, who retired when he was 80 or so, who said that they used to place steel balls into covered grooves machined into the sides of large slow speed horizontal steam engines to provide dynamic balance.

There is an excellent book by called Mechanical Vibrations by Den Hartog that does an excellent, albeit complicated, job of explaining the principles behind the concept of active automatic dynamic balancing devices.

Glad I am not the only one thinking along those lines !

[happysmith]

Should have added that the grooves I mentioned that were cut into the sides of the slow speed horizontal steam engines were cut into the sides of the flywheels not into the sides of the engine itself.

Sorry for the oversight !

[outback]

this outfit is located on texas.i trhink this would be worth trying.sure would make them big props easier to balance

[tecker]

Would probably work better on small diameter high speed .

[DanG]

Since I'm not flying a mill here in the city it is a moot point for me but I am still curious...

I wonder where a little out-of-balance versus faster-spin-better-balance could be harmful... perhaps allow the turbine to run-away more perfectly if the load circuitry opened, the old 'Ma, the turbine went 'splody and cut the tractor in half' when it hit 50% higher RPM when accidently left open-circuit due to a more perfect balance...

Since many dual rotor outputs are robust enough we end up furling them early to limit outputs as well as protect the turbine, adding active balancing when the mill is screaming into a furl surely would reduce wear and tear and noise from both mill and tower if it actually quenches most of the harmonic vibrations.

Anyhow - although it may not have the mass to compensate for huge swept area mills it might cover many of the glitches that arise from normal weathering of wood in smaller ones. I also wonder what Centramatics would say about off-label usage.

[whatsnext]

There would not be a case imaginable where more vibration is better than less. Unless, of course, you are building a vibrator. Do you really think that using vibration to control speed would be a workable plan? Using a dynamic balancer really only makes sense if the mill builder finds it impossible to balance the rotating mass without one as all dynamic balancers absorb power by the very nature of how they operate.

John..........

[Ungrounded Lightning Rod]

They will retard startup much as cogging does.

When the mill is stopped, all the weights will migrate, through the viscous fluid, to the bottom.  This will create an off-center weight that must be raised to the top by startup torque before the mill will spin.

(Once it's spinning it will vibrate for a while - and also speed up/slow down with each turn, creating the forces that make the weights gradually migrate apart through the fluid to balance the system.)

I'd just balance the thing properly and have done with it, rather than hanging this gadget on it an possibly buying trouble.

On the other hand, if your site has significant below-cutin-windspeed periods, and adding the balancer doesn't keep the mill from starting once the wind is almost up to something that would drive it to cutin speed, you might add one specifically to try to keep the mill stopped when the wind is too low to produce power, attempting to extend bearing life.

[Ungrounded Lightning Rod]

Just realized that it might not work right on a mill.

It depends on springs supporting the spinning wheel, which causes a phase shift between the angle to the off-center mass imbalance causing the vibration and the actual displacement of the wheel.  In a suspension this occurs because of the springs between the wheel mount and the car, and because of the springyness of the inflated tire.  In the engine it's because of the springiness of the engine mounts.

A mill has no springs.  It wobbles as it attempts to rotate around the center of mass.  So it may not have the phase-shift required to make the weights move properly (unless the gyroscopic effects produce it).

Has anyone actually tried one of these things on an unbalanced mill?

[DanG]

Since power gained would be minute I guess the idea would be to better snub the ringing  I've heard in towers as oscillations build and thus also extend component life. I agree the sidewall flex & suspension slack provide the impetus for counter-weight migration so adding it might slightly exagerate or multiply any out-of-balance tendencies, and I also don't know how rapidly the memory of proper weight distribution is erased on standstill.

And as for a little out-of-balance being built in it's inevitable with wood and hand tools, one can balance them well but the product balance, especially over time, won't equal a aeronautical propeller or a maritime propulsor. If the active balancing would work on a static shaft it might better account for variations of blade flex when running in furl too, providing some extra leeway when installing a homebuilt turbine in extreme wind area... Thats why I posted, to see if there would be any benefit. I've never seen or heard of anyone trying one..

[vawtsup]

Removing the viscous fluid would probably be a better idea for

a wind turbine. Wouldn't be much of a differance at startup and

the ball barings would equilize a lot sooner.