Question on Servo Control using AM-1 or AM1s

[JRad]

Can either of the Accessory Modules (AM-1 or AM-1S) be used to directly control a servo?

I would like to electrically control a few turnouts on my indoor large scale layout. I've used Aristo motorized switch machines in the past, but the few I have left in-stock seem to have died (bad gears). They might still be available, but they weren't a great design, so I'd like to try something else. Piko makes an electric machine for large scale, but it's pricey.

Several acquaintances in the Large Scale community are using servo motors to move their points using a Tam Valley controller and DCC and/or a manual push button.  I'm also aware of the SparkFun controller that simply needs a single pole switch (or switchable output) to activate.

I have heard that the AM can control servos, but it's not covered in the documentation for either module, only standard motor control.

I do have some spare Loco Modules that I could load an accessory program into for experimenting, but it would be nice to have at least a little knowledge of how it should work before I start hooking stuff up.  I don't want to let that Magic Smoke out of my LM

[G8B4Life]

No, you wouldn't be able to drive a servo directly but with the AM-1 you would control the servo driver, with the AM-1 being a big expensive push button controlled by the HC. This is the same way as your acquaintances in large scale are doing it, the DCC decoder is driving the servo driver (the TAM valley board) which drives the servo's. The AM-1S I'm not sure, it's not designed for turnouts so the programming in it may not have it show up as turnout's on the HC.

It would take some experimentation I guess. I have a (old) turnout servo kit but I don't have an AM-1. I could load an accessory project into a spare LM-2S but the accessory project firmware for the LM-2S is MIA on Rings server!

- Tim

[JRad]

Thanks Tim -

I have purchased a few of the cheap servo testers that can be modified to work as a servo driver with just a SPST switch and a resistor.  I have a spare LM already on the bench and will load the accessory program to experiment with a turnout and a servo mounted on a small piece of wood for testing.

If I understand the AM-1 turnout program correctly, I don't think it it could be applied to a servo driven turnout, at least not without a little bit of electronics in between.

[KiloWhiskey]

The AM-1 should be able to operate a low voltage relay that could trip the servo tester

Kevin

[JRad]

Thanks Kevin.

I went ahead and ordered an AM-1 and have successfully set up a modified servo tester on the bench, which drives an RC servo using a toggle switch to throw the points. I haven't confirmed it, but a friend who is also developing a servo driven system for his RR says that servo draws about 200ma when moving.  I need to measure the current being dawn by the IC on the tester through the switch, which is a ground sink, to see if it might be safe to directly connect it to the AM-1. If not, I have plenty of small relays that could be used.

My test setup...


At top, an RC Servo connected to the turnout with brass rod. Directly below the servo is an SPST switch which currently throw the points.   On the breadboard: Top Left is the Servo tester, below that are two 10K trim pots for adjusting both ends of the servo travel. The board at the right is a DC Buck Converter to bring my 12V accessory bus down to 5V for the servo system.

[JRad]

Passed functional tests using a lighting output of LM-3 to trigger.  Waiting on AM-1 for further experiments...