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Old 07-18-2018, 07:39 AM   #16
whsammler
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Loving this thread.

Fingers & toes crossed it all works in the end.



Glen
Collector of Wehrmacht Optics, Ordnance & Field Equipment.
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Old 07-18-2018, 08:13 AM   #17
Dufleuve
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Hello FS,

Again, a very interesting technical restoration.

Thanks a lot for sharing with us.
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Old 07-25-2018, 06:06 AM   #18
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Key to the performance of the PKS12 autopilot are the SR5 and SR6 control relays. These are sensitive electromechanical devices, and I only had one "perfect" relay, the others had problems. One of the relays had a broken winding, which is usually a terminal failure, but I wanted to see if I could repair it given the rarity of the relays. I took some photos during the repair event (which took me about three days), they give a bit of an idea of the construction of the Patin relays.

This is core of the relay:



What you see is the rotor, the top plate holds the connections to the five coils in the rotor, the two "antlers" is where wipers of the output potentiometer are connected to. Inside the rotor sits a permanently magnetic core. Normally the core is connected to the housing allowing the rotor to turn around it. As photographed, the core rotates inside the rotor windings. It orients inself to the earth's magnetic field (it works like a compass), for this reason the core and rotor mechanism was housed in a magnetically shielded housing.



This is the magnetic core removed from the rotor windings. Each end has a pin, which sits it a jewel bearing inside the rotor. The two pins on each end of the magnetic core can be screwed in or out to adjust the bearing play.



This shows the jewel bearing inside the rotor. One of my relays was "loose"; it could move laterally quite a lot and I suspected a broken bearing pin. I found that the jewel had actually slipped out of its housing, I could repair that particular relay by putting the jewel back in its place and re-adjusting the bearing pins.

On the relay with the broken winding (shown in the first picture, I re-attached the winding ends to the soldering posts after which the winding measured through so I thought it had a chance.

To be able to do this repair, I had to remove all the wires connecting the rotor to the connector on top of the relay so they had to be replaced. Sounds simple enough, but these wires are about the width of a hair. First they had to be threaded through a rubber disk:



The disk screws into the bottom of the plug, each of the wires had to be soldered to the correct binding post on the inside of the plug. With the plug fitted back into the relay, each of the wire had to be threaded through a tiny Pertinax disk and soldered to the binding posts on the rotor:



Not easy to do if you have sausage fingers:



This shows how the wires run from the plug on top to the rotor on the bottom. The wires have to be so thin to reduce the friction caused by the wiring to be as small as possible.

With the wiring back in place the output potentiometer and wiper arms can be fitted and the relay built back into it's housing. My satisfaction was short lived however as the repaired winding failed shortly after and to date I have not been able to measure any continuity in the winding. Rewinding the rotor is not feasible as the wiring has been covered in shellac which is extremely difficult to remove without doing more damage.

In any case, I was able to repair one of the relays (the one with the dodgy bearing), so I just have enough to operate the PKS12-b-1...

regards,

Funksammler
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Old 07-25-2018, 10:01 AM   #19
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In the mean time I have been working on the interconnecting cables and the "power stage" of the autopilot. All the various elements of the autopilot are connected via cables to a central interconnection board. I have fastened the connection board together with the main switches to a small wooden board:

The wiring quickly adds up. Wiring up equipment is always a nerve wracking exercise as a single mistake can have disastrous consequences. It involves a lot of measuring, drawing, checking and carefully tasing individual units before linking everything together.



I had to move the autopilot upstairs I as did not have a power supply strong enough to start the Ward-Leonard Umformer in my workroom. The Ward-Leonard amplifies the steering signal coming from the steering box and feeds it to the rudder servo. While running the power usage is not too bad, but it needs a high startup current! Here is the setup of the autopilot as it is today:



In the foreground you see the Steering box and the cable interconnection board. Behind it is the rudder servo, the LI-Gerät, the 500Hz generator and the Ward-Leonard converter. Lying between the steering box and the interconnection board is the "Koppelschalter" which activates the autopilot.

I made a few movie clips to show the autopilot in action. The first one shows the various elements of the autopilot:

https://youtu.be/S8Mi3URpTI8

The next clips demonstrates that the rudder servo is uncoupled. After flicking the coupling switch, the rudder servo locks and starts to work:

https://youtu.be/1rpgwduX_Lo

The final clip shows the autopilot in action. As I move the steering box, the various signals are translated into a movement of the rudder servo:

https://youtu.be/S7ic1OWOOPU

So the autopilot is alive in principle but a lot of work needs to be done. A few more elements are needed to complete the system: I need to find a functioning PFK/f3 FührertochterKompaß, a WK12 Wiederstandkasten (interestingly the PKS12 b-1 used the resistor box from the Siemens K12 and K22 autopilots) and a Left/Right switch.

After that the autopilot needs to be built onto a rotating platform like my other autopilots and the fun of tuning the system can begin!

regards,

Funksammler
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