Homemade Prop Balancer

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..    ) a magnetic-balancer design from a major aero-hobby Co. that debuted back in the 90's? 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.)



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



I would say that it's a pretty sensitive/accurate method.. not to mention "fun and easy to make".

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

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