Prop Balancer and Balancing

Levent, you could be right. I thought it may have been commercially made, but the cork compartment cap although innovative may be simpler than a manufacturer would do.

Magnetic Prop Balancers

I bought one of those magnetic prop balancers not long ago, but haven't tried it out yet. Like in all things, I gather that the skill in balancing is depended upon one's ability to ensure accuracy in alignment, to make it work properly. Also, the amount of tension on the shaft between magnets would be important too, as too much friction could affect readings.

But, my balancing polished steel prop axial dowel rods on razor blades has been a very reasonable measuring instrument, as simple as it is. I suppose if one wanted to also dynamically balance the blade, would require a level of instrumentation beyond the home shade tree mechanic model enthusiast in complexity and cost.


I have one of those Harbor Freight motorcycle tire balancers, have used it to balance motorcycle tires and trailer tires statically, but then my tires are not wide stance like some of the new bikes, which dynamic balancing is even more important (and, if one likes to travel at speeds above 100 MPH (160 kmh).

Surfer_kris wrote:

Levent Suberk wrote:
Not every time will self align. If the tip of shaft that touch to magnet is mistakenly off centered -such as placed to right of magnetic disc center or placed to left of magnetic disc center- then one tip of propeller goes to down. I tried it. Prop shaft must be exactly on center of disc magnet.

That is not possible as long as the axis is made from a soft ferromagnet, then the magnetic field cannot exert any rotating moments on the prop axis.

Sounds like you might have used a permanently magnetised prop axis, then there might be some rotating moment from the magnetic field onto the axis itself.

I used soft steel shaft.

You need to use soft iron, not steel.

Surfer_kris wrote:You need to use soft iron, not steel.

They are different but not too much.

GallopingGhostler wrote:Levent, that is similar to the one I have, maybe the same manufacturer, but is on a different wood base. I may have just bought the balancer itself and mounted it on a scrap piece of wood (51 years ago, hard to remember details now). But, has same number of steel dowels.

It was very simple, but good for balancing half-A props. Regarding comments on the magnet bearing balancers, should not be a problem with the half-A props because they are lightweight. Even with heavier props, still shouldn't be much of a problem, because of their heavier weight, balancing is proportional to weight, so there is greater margin for measuring error, that would not be good with the half-A's. They (unless the racing version engines using racing props) don't have the higher RPM's the half-A's do.

One can tell whether a prop is well balanced or not. The small Bee's complain. Being picky on balance has immeasurable benefits.

 Still obtainable https://www.ebay.com/itm/314211362781

getback wrote:[Still obtainable https://www.ebay.com/itm/314211362781

You dah man, Eric. So, it was available that way. Back 51 years ago, I wanted a balancer but did not want to pay full cost for the block of wood with storage compartment, so I bought the bracket with 3 screws separately. Then went to the base wood shop at Little Creek Amphibious Base, Virginia Beach, VA. Took a suitable piece of scrap from the toss bin. Sanded a little then mount the prop. Didn't even bother to finish the wood, because new props are clean. (Wiped down old before rebalancing, say after trimming from a ground strike.)

But for $40 asking, more than I'd want to spend on a balancer. Back in the day, it was a relatively inexpensive item.

Why in these days is fancier more beautiful?

Levent Suberk wrote:
They are different but not too much.

From your own description it does matter.

A soft ferromagnet cannot be moved around to different places on the disk magnet, as in your sketch, it will simply always be sucked back into the highest magnetic field at the centre of the disk. The magnetic field cannot exert any rotational moment on a soft ferromagnet either.

So from you own description, you have used an axis with a permanent magnetisation and this is causing your problems.
Did you make it yourself or is it a commercial balancer?

Funny, I used a shaft with pointy ends that was held between two fingers for over 40 years on motors that were going 30,000 rpm with no issues. Just the last few years I got one of the magnetic ones at a swap meet. It is much freer than the finger one. The one side barely rests on the magnet and the other end is just in the air. You can spin a bigger prop and it goes for maybe a minute. Good enough for the girl(s) I go out with. Wow, $40 for the feebay balancer.

With magnetic balancers, the shaft points must be true. The shaft will never be on the magnet center due to gravity. Residual magnetism in the shaft can be a problem.

My old Topflite magnetic balancer has poorly made cones (molded plastic) for the prop and if I recall and one of the points on the shaft isn't on center. Final check was always to rotate the shaft/cones in the prop and check again.

When I was flying electric pylon racers and APC E and Graupner CAM props first came out, we discovered they were perfect most of the time. Install it, run it to 30+krpm and feel for trouble to decide if it needed balancing.

Any form of balancing is tricky when the item to be balanced has little mass. At some point your are at the noise or sensitivity limit. We aren't going to get perfect balance. Eliminating gross problems in tracking, runout, and balance is a bigger concern than perfection, evidenced by less sensitive balancers being adequate.

For single cylinder engines the argument can be made that balancing is somewhat pointless if you align the prop for minimum vibration.

Here's a balancer that I made by using a "Kavan" shaft and cones set, held in suspension by a pair of tiny neodymium magnets that I got from Radio Shack (I really miss Radio Shack   )

I affixed the magnets to two hex-head bolts to allow for air-gap adjustment as well as for any bowing in the wood uprights. The cable is just there so I don't lose the shaft and cones when not in use.

gkamysz wrote:With magnetic balancers, the shaft points must be true. The shaft will never be on the magnet center due to gravity. Residual magnetism in the shaft can be a problem.

My old Topflite magnetic balancer has poorly made cones (molded plastic) for the prop and if I recall and one of the points on the shaft isn't on center. Final check was always to rotate the shaft/cones in the prop and check again.

When I was flying electric pylon racers and APC E and Graupner CAM props first came out, we discovered they were perfect most of the time. Install it, run it to 30+krpm and feel for trouble to decide if it needed balancing.

Any form of balancing is tricky when the item to be balanced has little mass. At some point your are at the noise or sensitivity limit. We aren't going to get perfect balance. Eliminating gross problems in tracking, runout, and balance is a bigger concern than perfection, evidenced by less sensitive balancers being adequate.

For single cylinder engines the argument can be made that balancing is somewhat pointless if you align the prop for minimum vibration.

Yes, the single cylinder motor itself is only balanced at certain rpms. The Top Flight is the balancer I snagged too. On the old Fox .35 stunts, we purposely took the heavy blade and placed it on the counterweight side of the motor to lessen the vibration on the Fox racers when we had that event here. Those motors were not really balanced.

Surfer_kris wrote:

Levent Suberk wrote:
They are different but not too much.

From your own description it does matter.

A soft ferromagnet cannot be moved around to different places on the disk magnet, as in your sketch, it will simply always be sucked back into the highest magnetic field at the centre of the disk. The magnetic field cannot exert any rotational moment on a soft ferromagnet either.

So from you own description, you have used an axis with a permanent magnetisation and this is causing your problems.
Did you make it yourself or is it a commercial balancer?

I made the shaft from a screw.

Here some info about magnets:

https://www.kjmagnetics.com/blog.asp?p=magnets-are-weird

Levent means that when you release the shaft and it's not on center, the magnet drawing it to center and friction between the shaft point and magnet can induce torque on the shaft. I think this observation is an imperfect shaft as mentioned before. Made from a screw? I assume it was ground by a professional grindshop and inspected for accuracy after? That was my point about the Topflight, it was made to a price with some tolerance deemed acceptable.

Shaft may not be perfect, but I did my best with it. I ought to take photos of it at the time. I took and keep the magnets from balancer and throw balancer to trash can. I searched propeller shaft minutes ago but couldn't found. If I find it then I am going to make another trying and take photos of this phenomenon.

Best is razor blade balancer.

gkamysz wrote:With magnetic balancers, the shaft points must be true. The shaft will never be on the magnet center due to gravity. Residual magnetism in the shaft can be a problem.

My old Topflite magnetic balancer has poorly made cones (molded plastic) for the prop and if I recall and one of the points on the shaft isn't on center. Final check was always to rotate the shaft/cones in the prop and check again.

Greg,
I had the same problem with my Topflite magnetic balancer and did the same thing as you.
I got tied with it and gave it to a friend, which my friend, still to this day really doesn't balance his props.

Levent Suberk wrote:
Here some info about magnets:

You will have to include the magnetised prop axis and then study the total resulting field. The balancer uses a cylindrical bar magnet and the axis will get magnetised into a cylindrical bar magnet (albeit with a much smaller radius). The lowest energy is then when the axis of these two line up:

Some more craziness playing with small props… Spinning them with the Dremel tool at the same speed the engine turns them rather than firing the .020 up every time….Taking mental note on the feel while spinning…. It’s subtle but differences can be felt…. Done outside and facing away!!!! No fly away’s yet !!!…. I don’t think I would try it on anything larger….. Can only get away with small props!!!….Interesting to note the prop noise without the engine ….They really sing!



Packing lead filings in the hub has brought some of the props near without doing anything else…., Others still need some tip weight…. For tip weight I’ve been scuffing them a little, Cleaning with alcohol, And applying CA with an applicator tool that I control the amount with..,.. But I don’t know if I like that out on the end of the prop…(Yes, I’m watching for it coming loose Andrew ).,,, Is there a better way?… Is shortening the heavy blade a little OK?….

My Dremel doesn't run very true nor it it well balanced. I'm not sure I would trust it for this use. Maybe the newer ones are better.

sosam117 wrote:
Greg,
I had the same problem with my Topflite magnetic balancer and did the same thing as you.

Yes the plastic cones need to be balanced on their own, in order for it to be accurate for the lightest props. I simply balanced them individually on the prop axis, sanding away on the outermost plastic region until balanced.

For the smallest props I use a piece of music wire and some heat shrink tubing in order to centre the prop, as shown earlier, works great.

rdw777 wrote:Some more craziness playing with small props… Spinning them with the Dremel tool at the same speed the engine turns them rather than firing the .020 up every time….Taking mental note on the feel while spinning…. It’s subtle but differences can be felt…. Done outside and facing away!!!! No fly away’s yet !!!…. I don’t think I would try it on anything larger….. Can only get away with small props!!!….Interesting to note the prop noise without the engine ….They really sing!



Packing lead filings in the hub has brought some of the props near without doing anything else…., Others still need some tip weight…. For tip weight I’ve been scuffing them a little, Cleaning with alcohol, And applying CA with an applicator tool that I control the amount with..,.. But I don’t know if I like that out on the end of the prop…(Yes, I’m watching for it coming loose Andrew ).,,, Is there a better way?… Is shortening the heavy blade a little OK?….

Great fun There were advertisements of Dremel mototool in RCM magazine with a mounted propeller

I made the experiment with a cardboard piece and a needle. I am going to make a new shaft from same screw and try again with a propeller.

I just tried with my Topflite. I was unable to reproduce anything like that. However, the shaft returns to center best I can tell visually. The large jaws influence the field and may be a factor.