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Re: [TowerTalk] Various small prop pitch motor info requests.

Subject: Re: [TowerTalk] Various small prop pitch motor info requests.
Date: Wed, 17 Aug 2011 10:53:10 -0400 (EDT)
List-post: <">>
Gene, be sure you save those old brake parts. You may some day have an  
antenna large enough to need them!
It is possible to windmill a brakeless PPM with an antenna of sufficient  
Gerald K5GW
In a message dated 8/17/2011 9:39:22 A.M. Central Standard Time, writes:

Hi Alton  -

I just finished overhauling my standby ppm and replacing the one that  was 
the tower.I certainly don't claim to be an expert, but got lots of  good 
from Kurt's site.  Since I'm not a  purest I took some  shortcuts which 
have to "wait and see" about.
RE removing the  brake - I just took off the gear,removed the windings and 
cleaned out the  area. You need to short the two brake terminals. Don't 
solder wires to the  two terminal  screws because you'll have to remove the 
nuts to get  the end plate off.  You probably know about putting small 
capacitors  on the brush cups on the other end of the motor. You also want 
check  the brushes. They lift right out of the cups. I can't remember how 
long  they should be. Perhaps Kurt's site mentions it. I have heard of guys 
buying slightly oversized brushes and filing them down to fit. You also  
should check the comutator and have a motor rebuild shop turn it down if  
needed. I also had them put the armature on their growler.  I also  used 
lithium grease on the gears. With the OO reference, the low speed  
went together with no problem I found the high speed one a bit  of a 
just juggling it around. There is a little space between the  outer case 
the outer edge of the low speed bell that, with the aid of  a flashlight, 
helps to see what's going on. Another thing I did was to add  a fourth 
lead so the gearbox so it would, with proper selection of  leads, be 
compatible with either a left hand or a right hand motor in case  I need to 
change it  out in the future. You also need to be a bit  careful when 
reassembling the gearbox to have the right amount of the  spline coupling, 
for coupling the motor output spline to the gearbox input  spline, sticking 
out of the gearbox. Too much and the motor won't sit down  where it 
Too little and it leaves a weak spot. I did not replace  any of the 
The large bearing that is under the bevel gear was in  good shape. Since I 
think that's mostly there for horizontal forces (in  our case) and 
important for the old aircraft installation, I  wouldn't think it would be 
too critical in our situation.  I think  Kurt has some good suggestions re 
mating the ppm to the mast. I just  welded a small plate to the top of the 
bevel gear and a slotted cup onto  the plate. Then a couple of 5/8" bolts 
through the cup and mast to  hold/clamp things together. This has held  for 
about 15 years, but  has developed a fare amount of slop. I'm turning a 
fairly large LP (7-60  MHZ, 46 foot boom with 15 elements) so I think 
advise on this would  be well taken. You might also  want to talk with Blue 
Heron regarding  direction control/indication. That would require a small 
sending unit in  the motor,sort of where the brake was. Being of the "old 
school" I use  selsyns and a gear meshing to the ppm bevel gear.
Good luck with the  project. I'm sure it will be well worth the effort.


Gene /  W2LU

----- Original Message ----- 
From: "Alton McConnell"  <>
To:  <>
Sent: Wednesday, August 17, 2011 7:37  AM
Subject: [TowerTalk] Various small prop pitch motor info  requests.

reMorning Everyone:

I am finishing up the  rebuild of a small prop pitch motor.  We all know 
MRC 0017  bearing that is located in the adapter plate is no longer 
available.   My MRC 0017 races look ok but the bearing assembly is sloppy 
the ball  bearings are black and need to be replaced.   The largest ball 
I measured had a diameter of 0.1860 inches or 4.72mm.  Does anyone  know 
the spec ball diameter was?  Otherwise, I will have to  guess at the size 
when I order replacements. I would rather not order  loose ball bearings 
times to get this right!   I have also  heard of people machining solid 
bronze bearings to replace this bearing in  its entirety.

Also, I understand that there is an improved lip seal to  replace the seal 
under the adapter plate bearing,  Does anyone have a  part number? (I 
replaced  the seal in the gear box housing and  reversed its direction 

Any further advice on sealing up the gear  box before I put the gear train 
back in the housing?  I have the  gears assembled with the “00” out and 
everything assembled  correctly.  The 1971 QST article was very helpful 
I used Arctic  Cat low temperature lithium grease and greased everything in 
sight!   The unit works.

Any advice on a can to put over the top of the prop  pitch motor?

I have the splined gear and need to make a mast  attachment.  Any photos of 
recommendations would be  appreciated.

I have found K7NVs site.  Very useful info.

I  now need to rebuild the electric motor.  How does one remove the brake  
from the prop pitch electric motor?  The end with the break appears  to be 
threaded.  Is a special tool reguired and hose does one get  around this.

Many thanks!

Alton,  NU8L

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