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" <email@example.com>
Sent: Wednesday, August 17, 2011 7:37 AM
Subject: [TowerTalk] Various small prop pitch motor info requests.
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.
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