Small Title

26. RC for Lady Sarah (1)


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In this page, and the next two pages, I'll describe how I added radio control to Lady Sarah's steam regulator. This allows the loco to be stopped, started, and speed proportionally adjusted over one channel. Later, I'll tackle control of the reversing gear over the second channel.

I decided that only the servo(s) will be installed on the loco, as there will be plenty of room in the new tender for all other components and batteries to be installed, away from all sources of heat and oil.

This picture shows the micro servo together with the servo mounting bracket and servo linkage arms I made from 0.064" aluminium.

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This was going to be another "prototyping excercise". I don't know of anyone else who has fitted RC to a Kitten class loco. I made the linkage arm with six alternative bolt positions so I could experiment with the geometry whilst the loco was in steam.

I used a Naro Supertech Microservo supplied by IP Engineering. This has a nylon actuator spindle to which the aluminium linkage arm needed to be firmly attached. I first drilled a 3mm hole in the base of the arm, then used a round needle file to extend the hole horizontally to match the width of the spindle on the servo. I then wired up, and switched on, all the RC gear to make sure the servo was in its centre "at rest" position. Very carefully, I filed flat sides top and bottom of the servo spindle to form an oval profile.

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The servo spindle was reshaped just a little at a time, frequently offering up the oval hole in the linkage arm, and stopping as soon as a tight fit had been acheived. There is a small hole in the middle of the Naro micro servo spindle that will accept a short 8BA cheesehead bolt (1/4" or 5/16") with a retaining washer. Careful not to over tighten.

Channel 2 of the Hitec Ranger transmitter has a switchable 70%/30% neutral position that I used for the regulator control. This allows more forward stick travel in the 70% zone for fine adjustment.

This picture shows my first prototype linkage assembly. A bit unwieldy, but it worked! I set up the linkage geometry so that the loco's regulator was very slightly open when the control stick was at neutral. This helps to slowly warm the cylinders as the boiler reaches working pressure, and keeps down the condensate that would otherwise collect in cold cylinders. When running with the stick at neutral, the loco gradually slows - useful for impressively smooth stops at the platform. If a fully closed regulator is needed whilst in steam, the control stick can be pulled back into the 30% zone.

The cable from the servo passes through a hole in the loco footplate ready to be attached to one of two connection points under the tender floor.

The photographs and text on this page are copyright (c) Paul Backhouse 2000 and may not be reproduced or distributed without the owner's permission.

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