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Modification of the antenna rotor model SPID RAK
with an absolute encoder  HH-12

© df1sr – 2015/12

After a couple of years of heavy use the azimuth angle encoder of the impulse type became unreliable and was not accurate enough for my needs. I decided to exchange the original impulse endoder for a digital absolute encoder with a 12 Bit resolution. This increased reliability and resolution. Here I want to describe the modification, so this modification can be replicated more easily.

Here you can see the mechanical modifications
that that have been made to

1.-Rotor SPID RAK
2.-Original mast mount (painted grey)
3.-New mast mount welded to the original mount (painted grey)

The mast mount 2 is open at the bottom, allowing easy access the the main rotor axis.
The rotor is mounted on the tip of the mast using the  new mount 3 that was welded to the original mast mount 2.
To protect the  parts from corrosion they have been given several coats of grey paint.

Main rotor axis and bearing

The second picture  shows the view up the original mast mount 2. You can see the greasy ball  bearing and main shaft 4.  To the right of the mount 2 I welded the  second mount 3. Both have been given a grey coat of paint to prevent  corrossion.

Encoder assembly installation

Into the original mast mount 2 I installed the magnetic clutch linking the encoder HH-12 to the main rotor axis. The angle bracket is attached to the inside of the mount 2 with a screw that holds it in place.
The encoder is mounted on an angle L-bracket. Onto the encoder axis I attached a magnetic clutch made from an aluminium disk and small magnets.
To allow for mechanichal play a rubber hose was used as the link between the encoder and the magnetic clutch.
The clutch can slip in  case there should be too much force on the encoder axis. This will  prevent the encoder from being damaged.      

Construction of the magnetic clutch

The magnets hold on to the main rotor axis inside the  original mast mount 2. As the rotor turns, the aluminium disk is turned.  That movement is translated to the encoder via the flexible rubber  hose. The dimensions of this assembly have to be adjusted to the mast  and rotor in your particular setup. The most critical part is the exact  position of the magnets and the diameter of the aluminium disk for the  clutch. This setup has proven to be both reliable, robust and  reproduceable. It has been in operation for some years now.
Magnetic clutch

Here is a closer look at the upper face of the magnetic clutch d at the top of the encoder assembly 5.
The aluminium disk was  turned to a diameter of about 39mm and four 6mm magnets have been  epoxied to the surface. They allign with the circumference of the main  rotor axis protruding into the original mast mount 2.
The magnets hold on to  the main rotor axis without slipping during normal use. Should there be  any blockage or obstruction of the free movement, the clutch will slip,  preventing the whole assembly or the encoder from being damaged. The  yellow substance is cured epoxy and not grease from the main rotor axis  in the original mast mount 2.

Magnetic clutch assembly
This drawing shows the upper part of the  magnetic clutch assembly.
A M6 bolt is used as the main axis for the assembly.
A rubber hose is clamped to the bolt on the upper end and to the encoder axis on the lower end.
The encoder is mounted to the LBracket (not shown here).

Bernhard K.
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