It's been a while.... Servos, signals & points
Entry posted by GWMark
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In talking with St. Simon on Wednesday at the HWDMRS club night I realised it has been a while since I put anything on my workbench thread - checking back here I find it has been more than a year - how time flies!
So, the latest thing I have been playing with is RC servos. This came about because we are looking at building a new club layout and need about 100 slow acting point motors - now that's a lot of motors and a lot of money for the likes of Cobalts etc. So I looked into servo - I used to fly RC helicopters, so knew a bit about them.
First step, get hold of some servos. I found 4 servos on ebay, brand new, micro sized (9g) for a stunning £6.07 for 4 of them shipped to the UK - what a bargain. So 4 were purchased, and a MERG servo controller board that I already had sitting on the top of a cupboard (for about 4 years) was built.
In order to test the servos I decided to build a simple board with a point, and an old ratio signal I had laying around from an aborted project about 10 years ago. The servos worked great, using the MERG software on a PC to adjust the speed and travel of the servo meant there was no need for any complex mechanical linkages, just as well because I probably would not be able to get them to work.
I had removed the over-centre spring from the Peco point, to make it more link the hand-built points we are hoping for on our final layout, and added an omega loop in the brass wire I used to link the point to the servo.
The servo was adjusted to hold the point blades firmly against the stock rails and all worked fine. I had the means to control 4 points and it had cost me about £12 in total. This looked very promising.
The next issue was DCC control. We will probably be using DCC for the new layout, the MERG unit I had uses switches for the servo control - how to make it DCC. You can just add the DCC accessory decoder from MERG, but that means two boards and more expense, so I looked around and came across a site by a chap in Canada that some of you may know, Paco's Official Site. He had a simple PIC based servo DCC decoder, so I built it, and it worked first time. A very simple and cheap (there's that word again) solution. Problem is it had no opto isolation and the programming of CV's was not reliable on my Lenz Compact that I use to play with DCC things. O this is still a work in progress - I have a lot of "works in progress" 
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