Dynamic balancing of Props/shafts/rotating assemblies

[bigandy]

Good evening all.

I have been having a bit of a ponder about the balancing of small ducted fan rotors, props and shafts. I am finding it difficult to get a decent state of balance on the smaller stuff, and I was wondering about the possibility of designing or building a dynamic balancing type machine to try and improve the balance of the small stuff a little.

I have seen a few designs, where the rotating assembly sits in a couple of cradles, and is spun up to speed. There is then a box of electronics that read out the magnitude of the imbalance, and the angle of rotation (from a datum mark) where the imbalance is located.

Does anyone know of any DIY circuit references, or machines that are available out there that can do something like this box of tricks? I'm not too fussed about having a readout and angle, but the more advanced the better :)

I'm off to have a search through the RCgroups archives now for any links, although asearch for "dynamic balancer" has turned out rather a lot of results.... Hopefully that is a good thing, but in the meantime, if anyone has any useful info, feel free to post it!

Thanks in advance
Andy

[ZAGNUT]

this project might be helpful: http://www.turbinemuseum.de/Gasturbines/Balancing_Tool/balancing_tool.html


dave

[bigandy]

That's a brilliant link, cheers for that Dave!

Andy

[AndyKunz]

I spin boat props with air, and use an automotive strobe with a pulse generator feeding the sense. A pot adjusts the frequency (555) to get a steady reading.

If you mark the blades with a pen, you can easily read the numbers to see the heavy blade(s).

Andy

[bigandy]

Is that using the mechanics and sensors (piezo) as per the link in the post above Andy?

I've actually been reading up on a few different balancer designs (On the GTBA forums), and some of the theory when it comes to dynamic balancing, and the design of the mechanics becomes quite critical when you start to balance down to low inbalances.

I'm still deciding which way to go regarding the mechanics, but the link provided above seems as good a solution as any :)

Cheers
Andy

[AndyKunz]

No. The mechanics are a balanced magnetic balancer. You need to replace the the curved stock rod and centering plastic blobs - they are useless! Use compressed air to spin the prop up and the strobe to see which blade is heavy. If the strobe and prop are slightly out of synch, you can watch the free end of the rod draw a circle. It's actually very easy to see which blade is heavy.

I did a write-up on doing it this way for boat props several years ago. You can find it on several websites. Google for "andy kunz balancing props" (w/o the quotes) and the top few non-paid links are what you want.

Andy

[MDGrissom]

I've got a factory dynamically balanced Neutrino outrunner with a recently machined aluminum centrifugal impeller (also supposedly balanced by nature of the precision machining) but after the impeller was heat mounted (for tight fit) to the motor hub an imbalance now exists. When running the motor/impeller assembly I can ease a pencil lead up against the side of the impeller which leaves 1 half inch lead lines on only one side of the 1.5" diameter impeller hub. Note that the impeller does not wobble.

Question: Can I dynamically re-balance this assembly to some extent by lightly touching an appropriate spinning Dremel cutting bit to the spinning impeller hub where I touched the lead pencil to remove aluminum from the heavy side? Or, is it a lot more complicated than that?

[Bob Blackburn]

http://www.rcgroups.com/forums/showthread.php?t=1081834

Don has one of these and seems to like it!