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 Tjerk Lammers
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rotator test page PPM gearbox sketches

PPM gearbox pictures, sketches and notes


This is where your new rotator started its journey:






Illustrations from a 1943 Curtis flyer



High speed reducer assembly.

This is an early model without jacks in the housing for power connections to the motor.

Rear housing assembly.

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.

Note: 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.


Gear assembly


Early 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



This 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.

The 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 gear shaft.


The motor


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 jumper wire.


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.



© Tjerk Lammers ZS1J / ZS6P