Every so often one needs an absolute position detector, rather than a block detector. The best I’ve used employ their own light source, but older designs use Cadmium Sulphide (CdS) photocells and depend on ambient light in the room. Both have driven me crazy with their limitations. This article describes a new design, using ambient light “seen” by the detector in two places – typically between the rails and just to the side of the track.

Hi I purchased a Builders In Scale 1001 SM-1 SwitchMaster Switch Machine.  It is a stall motor type  and I need to mount it on a Free-Mo Module that has to be operated from both sides of the module.  Since this is a Junction module it needs to be as flawless as possible or easily repaired on the spot.  So the best I can figure is to wire in pair of 3 way electrical switches on the facial one on each side, but is that the best way?

Dan in MD

Peter has done a super job of describing how he has used servos to throw switches on his layout - see:

http://model-railroad-hobbyist.com/node/25958

I would like to suggest an alternative method of using controlling the servos.

I have come up with a simple modification to an eBay servo tester that turns it into a unit that is well suited to operating switches and comes at a very attractive price (I paid $1.24 for the controller including shipping to the US)

I have a Athearn SD 40-2 that has a serous electrical problem. When I remove the shell the chassis runs great but as soon as I put the shell on my power supply reads a short. I do not have any metal inside the shell and I have removed the power strip and have soldered jumper wires to the trucks. Can anyone please tell me what to check next?