Prop Balancer for giant scale RC airplanes

[sscherin]

Thought I'd post this here since the small amount of MDF hardly qualifies it as a "Wood project"

I had a little problem.. How do you balance a 24" 4 blade prop?

I could have done the simple thing. Bought a regular size prop balancer and riged it up to hang off the edge of the table but no that wouldn't do..

So with about $10 in parts, some scrap MDF and a little time at the lathe I came up with this.. Nothing more than a really big dubro type balancer.






The wheels are CD-Rs I opened up the centers on to fit #608 roller skate bearings.. The Cd's are cut for a snug fit on the bearing then held on with a little CA. One is a Wii game the kids had scratched beyond repair.. It was my test piece before I "borrowed" a few CD-Rs from the teen basement dweller..

The grease in the bearings gives them a bit of rolling resistance. I popped off the dust shields and washed the grease out with starting fluid (outside)
Then I put on a little tri-flow oil to keep them turning smoothly.

The prop rod is a piece of 5/32 music wire.. Not a great choice as it's not perfectly straight out of the bin.. It will be replaced with drill rod..

I turned a pair of aluminum 60° cones to center the prop and they are retained by wheel collars..

overall it works much better than expected..

I plan to make a more durable version with wheels and body from sheet HDPE (AKA plastic cutting boards)

[jackellis]

Three comments.

First, an ingenious solution.

Second, just how big are giant scale RC airplanes. The diameter of that prop looks to be 20 or 25 inches. The prop on my (full size, four seat) airplane is around 78 inches.

Third, where do you fly them so I can avoid that airspace. It's bad enough sharing the sky with unmanned Global Hawks and Predators

[sscherin]

Giant scale is considered to be 1/4 scale or 80" wing and larger..

That prop goes on my 1/5 scale p-51.. 85" wing span..

[gsmittle]

Giant scale is considered to be 1/4 scale or 80" wing and larger..

That prop goes on my 1/5 scale p-51.. 85" wing span..

Wow! That's almost big enough to sit in! How long did it take to build that rig?

g.

[sscherin]

The balancer was only 4 or 5 hours (I'm slow) to build.

The P-51 is a kit I've just started work on.. If I'm lucky I'll have it finished by next summer..

The kit was made in the 80's and designed to use a 35cc gas engine on a belt reduction

I'm converting to to run with a 3,500w gear reduction electric motor.

The first step was to make the prop mount..
The original setup had an integral pulley/spinner back plate the 4 blades and spinner bolt onto.

Step 1 was to turn a new back plate for the blades and spinner to mount on that will fit the 10mm motor shaft..

This was a square when I started


Spinner fitted


assemble the prop




Mounted on the motor..



The kit

[gsmittle]

That is impressive! We'll expect video of her maiden flight! Looks like a fun and demanding project.

g.

[lrogers]

VERY nice! As soon as I saw that prop hanging in the balancer, I knew it was a P-51 being built! Have you settled of the colors/markings yet?
If things work out for me I may have to scale up your balancer to fit a 66" prop! Looking HARD at a Hawk or Challenger ultra light!

[sscherin]

VERY nice! As soon as I saw that prop hanging in the balancer, I knew it was a P-51 being built! Have you settled of the colors/markings yet?
If things work out for me I may have to scale up your balancer to fit a 66" prop! Looking HARD at a Hawk or Challenger ultra light!

if you do try a F696 flanged bearing..
I haven't got my hands on one yet but it should be a perfect fit in a CD-rom without mods..
15mm od to match the 15mm center on a cd plus a flange for easy alignment..

I'd laminate 2 or 3 cd's pr bearing to hold the larger prop..

[LCHIEN]

How about a few of these instead of having to drill CDs?
Seems like keeping the bigger hole concentric when opening them up to the bearing O.D. would be critical.

from Rockler, under $2.00 ea

http://www.rockler.com/product.cfm?page=30216&rrt=1

[sscherin]

That would be perfect.. I was thinking of using roller blade wheels at one point but I didn't find a deal that good.

[sscherin]

I made a bench mount and gave the setup a test run..
It's on a 8S (29v) 5,000mah pack with castle 110 HV ESC

I had to keep a foot on the workmate or it would pull it over..

http://www.youtube.com/watch?v=vFfIObkc25w