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Post  rdw777 Sun Apr 18, 2021 6:01 pm

Homemade Prop Balancer 02253410
Homemade Prop Balancer 3868da10

When I ran my Tee Dee .020 a few days ago I noticed it vibrated the test mount at certain rpm’s .... I used to have a commercial balancer similar to the one I made so just needed to find the right materials to copy it.... It uses a 1/16 music wire shaft sharpened to point on both ends with a Dremel cut off wheel.... Also the correct size aluminum tubing to fit the bore and fuel tube to hold it in place...

The points of the M/W go into little dimples made with an awl.... That’s the bearing point.... The aluminum can be tweaked for best fit to reduce friction....

Turns out the prop I was using was the worst of three I have.... But at least I can find out now...

Should be easy to replicate if you need a prop balancer....

Robert
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Post  944_Jim Sun Apr 18, 2021 7:24 pm

Kudos...I'm impressed!
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Post  dckrsn Sun Apr 18, 2021 9:10 pm

Hey there Robert. Didn't see you enter the room. WELCOME!
Big Homer Simpson "Doh" on this end. If I had known of your
balancer, I could have saved $$$ spent on balancers.
Regardless, thanks, and belated welcome to the forum.
  Bob
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Post  Cribbs74 Sun Apr 18, 2021 10:00 pm

Nice. I have a commercial prop balancer, but it’s really meant for large props. It doesn’t work really well with 3-6” props. Looks like you may have the answer.

Ron
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Post  OVERLORD Mon Apr 19, 2021 1:09 am

Great set up. Another possibility is to rest your music wire on 2 horizontal razor blades. That way, there is no need for making points that have to be well centered.
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Post  roddie Tue Apr 20, 2021 7:45 pm

Hi Robert/rdw777. I like your prop-balancer. Did you "spin" the MW in a drill-chuck while forming the points with the Dremel-wheel?" I've made tapered-plungers (crude meterering-needles) in this way. Yours looks good!

Many years ago I copied (expanded-on..  Wink  ) a magnetic-balancer design from a major aero-hobby Co. that debuted back in the 90's? Huh... The principle uses magnetic-levitation to reduce friction in the balance-shaft. A pair of magnets are placed in a field where the metal (Ferrous) balance-shaft fits in-between. One shaft-point comes in contact with one magnet and the other end of the shaft levitates in an adjustable air-gap.

I bought a "Kavan" prop-balancer consisting of a 3mm (.118") diameter X 7cm long metal shaft with points ground on both ends and two tapered cones which are too big for most 1/2A prop hub-holes. Its 3mm shaft is .007" undersize.. for the .125" diameter hub-hole which the Cox .049/.051 engines use.. but it's a nice balancer for propellers having larger hub-holes.

I decided to build a simple wood frame for it..  with two upright "sticks" for lack of a better description.. and sourced a pair of tiny Samarium Cobalt/Rare-Earth magnets which I glued on the ends of a pair of 5/16" X 1-1/4" length hex-bolts which I tapped threads in the uprights for. When assembled with the base and top plywood panels, this design will accommodate a maximum balance shaft length of 3.5" a minimum length of 2" and a maximum propeller diameter of 16".

Some photos with the Kavan balance-shaft.. (I have some .125'" diameter MW and want to make another balance-shaft expressly for 1/8" diameter hub-holes.)

Homemade Prop Balancer Prop_b12

... note the mag-lev/air-gap..

Homemade Prop Balancer Prop_b13

I would say that it's a pretty sensitive/accurate method.. not to mention "fun and easy to make".
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Post  rdw777 Wed Apr 21, 2021 6:47 am

Thank you all for the warm reception, I like this group Very Happy

Roddie, Your balancer is awesome! That’s minimal friction as you can get! I like the calibration method with screws.... My version can be a bit fiddly with getting the aluminum tabs tweaked just right..... Taking an idea from yours, Maybe a calibration screw on one side would help.....

I just spun the MW in my fingers but checked center (and flatness ) by rolling on a piece of glass using a strong light.... Fortunately the 1/16 id tube fits the bore of the .020 prop well.... A short length of tube that fits the primary tube od fits the counter bore on the drive plate side.... The cones on yours make a lot of sense though..... When adjusted properly a gentle tap will send the prop on a dozen or so revs.... A little mark on the base lets me watch tracking....Still need to fab tubes for .049 props...

bty.... I’ve really enjoyed your scratch builds in Modeling.... Inspiring me for a 1/2 A CL one of these days.... Enjoying rehabbing engines for now,

Thank you again,

Robert
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Post  Levent Suberk Wed Apr 21, 2021 3:52 pm

Be sure to use small magnets and place the point of balancer on exactly the center of magnet. With large diameter magnets it will be inaccurate because of magnetic flux.
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