[Top] [All Lists]

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

To: "Alton McConnell" <>
Subject: Re: [TowerTalk] Various small prop pitch motor info requests.
From: "Gene Fuller" <>
Date: Wed, 17 Aug 2011 10:40:18 -0400
List-post: <">>
Hi Alton -

I just finished overhauling my standby ppm and replacing the one that was on 
the tower.I certainly don't claim to be an expert, but got lots of good info 
from Kurt's site.  Since I'm not a  purest I took some shortcuts which I'll 
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 to 
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 planetary 
went together with no problem I found the high speed one a bit of a problem 
just juggling it around. There is a little space between the outer case and 
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 motor 
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 belongs. 
Too little and it leaves a weak spot. I did not replace any of the bearings. 
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 certainly 
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 Kurt's 
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 the 
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 and 
the ball bearings are black and need to be replaced.   The largest ball that 
I measured had a diameter of 0.1860 inches or 4.72mm.  Does anyone know what 
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 five 
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 also.)

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 here. 
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

TowerTalk mailing list 


TowerTalk mailing list

<Prev in Thread] Current Thread [Next in Thread>