PPM gearbox pictures, sketches and notes
is where your new rotator started its journey:
from a 1943 Curtis flyer
This is an early model without jacks in the housing for
power connections to the motor.
This is an early model without jacks in the housing
for power connections to the motor.
Front housing assembly.
The Gear Train
The small, medium and large prop pitch units all use
the same dual epicyclical (planetary) gear train configuration. Each of the two
planetary systems, one high speed and one low speed, produce several gear
reductions. This is a rather clever design producing a 9576:1 gear reduction in
a very robust but small package for the torque it can produce when compared to
the most common amateur antenna rotators.
Cross section of the gear train without the top bell gear with splined tube.
The reference to the 6203 bearings, #24,
in the low speed planetary carrier does not mean that standard 6203 bearings
will fit. The standard bearings are too thick and do not have a retaining ring
groove. However the ID and OD of the special bearings that are in the carrier
are the same.
model gear train. The later ones have the same basic configuration. The early
ones had a high speed planetary carrier that was one piece, machined out of
aluminium. The later ones have a two piece carrier made out of forged steel.
The drive shaft on the earlier ones had a slot at the motor connection end for
the spade drive on the motor (like a flat blade screwdriver) .The later
versions used a splined connection. The axles for the
two high speed planetary gears on the early models were removable shafts, on
the later ones the axles were integral with the gears. The tube spacer, #20,
measures 45,3 x 14,3 x 10,3 mm
photo taken from K6NV’s website shows the early model high speed planetary
gears with the removable axles (shown just below the two gears). The basic dimensions
and bearings, and fits for bearings were the same for early and later models,
so the parts in most cases are interchangeable.
drive shafts for the different versions are not interchangeable because of the
motor to drive shaft connection. The earlier one had a slot and the later one,
as shown here, is splined at its end.
The illustration below, from an article in the August
1971 QST edition, is of utmost importance as there is no way that you will be
able to assemble the unit unless you follow this critical instruction.
Low speed planetary assembly with the three
gears properly aligned before sliding it onto the high speed planetary bell
The motor is a 24 V DC unit and contains
two sets of field windings to enable it to turn in both directions. There are
LH and RH motors but more on that later.
At the cover end of the motor is/was the
friction brake that was de-activated by the electro-magnetic coil as soon as
power was applied to the motor. Remove and discarded its components. The coil
has to be disconnected from the two terminals which are then bridged with a
The pulse counter and magnetic spinner,
available from K7NV, will be mounted here as shown.
You could roll your own from a piece of 30
x 12 mm mm aluminium. The purpose of the screw and
nut shown are to balance the spinner, which is of utmost importance to prevent
vibration as the motor spins at high speed. Balance the spinner on a pivot at
the centre hole punch mark before drilling the final 7/16” mounting hole to
determine the screw/nut position. The magnet measures 10 x 2 mm and can be
staked or epoxied into place.
The pulse counter, part no P-20A, is
available from George Risk Industries Inc.