Hacked Servo Turnout Operating Units

[Stuart FirthParticipant]

Although this is for my American HO layout I thought it might be interesting.

From RMWeb, in an article by 2mm and P4 modeller Bob Isgar, subsequently repeated in MRJ I think, I picked up the idea a few years ago of ‘hacking’ a servo. This is essentially stripping out the electronics and the end stops so that it becomes just a motor/gearbox unit. The clever bit really is that you use the servo itself to throw a miniature toggle switch (double throw) which feeds one of its terminals. The other terminal is powered by another double throw switch on the control panel. So, you throw the switch, the servo rotates, thereby turning itself off again. Throw the control panel switch the other way and the servo does the same thing in the opposite direction. Except when actually in motion the servo is unpowered so there is no interference, no stall current. I made up a unit a while back but have recently started making point machines using these modified servos. It is a simple affair using PVC angle as a ‘chassis’ and Evergreen styrene square sections for the moving parts. A single wire on mine goes up into the tiebar but for more sophisticated modellers with scale tiebars 2 wires could be used. Power is as little as you can get away with basically – you seem to need about 4-4.5V to give enough ‘oomph’ to throw the toggle switch and the TOU. Otherwise, quite undemanding!

The switch on the unit is double pole so the other side of it is used to switch the crossing polarity.

• This topic was modified 1 year, 2 months ago by Stuart Firth.

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[Paul WillisParticipant]

Hi Stuart,

There are two articles on hacked servos in recent issues of MRJ.

– Bob Isgar first wrote an article in MRJ 296

– Keith Slater followed up with his own further thoughts in MRJ 301

I hope that the references help you track down additional information.

Best wishes,

Paul

 

[Nigel BurbidgeParticipant]

Stuart

I think I am going to have to pick your brains on servo motors at Ally Pally. I really can’t get my mind around them!

Nigel

[Stuart FirthParticipant]

Well I’m the same if you use them as intended, I simply can’t cope with the electronics side of things, but these are nice and simple. Will bring one to play with at Ally Pally!

[Nigel BurbidgeParticipant]

I look forward to it

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