Hobbyelektronik  Applications FUNK E- Module PROJEKTE

 Modification of the antenna rotor model SPID RAK

with an absolute encoder  HH-12

© Georg, 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 the rotor:

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.

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 a.) The angle bracket made from a piece of sheet metal. b.) The encoder mounted on the top part of the L-bracket. c.) The rubber hose linking the encoder to the magnetic clutch. d.) The magnetic clutch made from a aluminium disk with four magnets

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 @ E-Mail Modifications

1.-Rotor SPID RAK

2.-Original mast mount (painted grey)

3.-New mast mount welded to the original mount (painted grey)

Main rotor axis and bearing

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).