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Servo mounting for N gauge Peco points/turnouts


Rabs

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I'm using Peco code 55 track for Burwood and have decided on Servo operation as this offers the realism of slow action at a much lower cost than stall type motors. My kit is as follows:

  • Merg CBUS (connected to PC)
  • CBUS servo module (can drive 8 servos)
  • 9g servo
  • Adapter plate
  • Peco code 55 point

I'm not using microswitches for frog switching, as this is being done by separate relays.

 

I've come across a number of people describing methods of mounting and aligning servos manuallys such as here:

http://www.nscale.ne...unting-Question

and here:

http://www.youtube.com/watch?v=8oerWG-G2so

 

The disadvantages of this type of assembly are:

  • It requires you to be both sides of the table at the same time
  • Each point needs to be adjusted individually to ensure alignment
  • Many people recommend the use of double sided foam tape. I suspect (although happy to be corrected if people know better) that this will lead to motors falling off as the years go by.

This significantly adds to the hassle of setting up servo point motors

 

To address this I have designed a little adapter plate for N gauge Peco points.

All Peco points have a set of holes for mounting Peco's solenoid type motors. This is standard across the whole range of n gauge points. As the same motor is sold of HO/OO and O gauges I suspect that these also have the same mounting holes, but I've not measured these. I designed the plate to fit onto these holes and hold the servo motor in the correct location for this. This allows the point and motor to be assembled and setup on the bench, before mounting to the layout. Also, by using fasteners rather than adhesive it makes replacing faulty servos much easier in future. Here is the assembly designed in Solidworks:

 

blogentry-7500-0-20268900-1326548004_thumb.jpgblogentry-7500-0-65238500-1326548005_thumb.jpg

 

The red and blue components are components of the points where the red is stationary and the blue is the sliding bar.

The grey component is the adapter plate, which I machined on my CNC mini-mill (my other hobby project):

 

blogentry-7500-0-10894900-1326548903.jpg

 

And here is the first prototype:

 

blogentry-7500-0-00606600-1326548501.jpg

 

The plate is 5mm thick acrylic with:

  • A pocket and mounting holes for a 9g servo motor.
  • 0.95mm holes aligned to the holes in the point. These then have small stubs of 1mm brass rod inserted which grip the hole and the 0.95mm slot in the points - ensuring consistent location of the motor relative to the points
  • A hole below one of the holes in the point's throwbar
  • The motor positioned so that mid-throw of the servo travel corresponds to mid-throw of the points.

The thickness was chosen so that an N gauge point with 2mm throw is actuated correctly by a 9g servo going through 15mm horizontal travel, where the separation between the servo crank and the point slider is 30mm. The blue shim has a 1mm hole in it, for the 0.9mm brass rod. This has been temporarily attached with double sided tape for testing. When I make more of these I intend to make these in 1.6mm thick FR4 PCB material and to modify the plate design to include a locating recess for this. I added a blob of solder to the brass rod above the crank to keep it from dropping out.

 

Some videos of it in action (sorry about the poor quality and the inadvertent zooming!):

 

http://www.youtube.com/watch?v=K1q82f0QQXA&feature=youtu.be

 

http://www.youtube.com/watch?v=8AfX07p9RQM&feature=youtu.be

 

 

In conclusion:

  • With the plate machined, assembly and setup of the throw of the servo (I'm using a MERG servo control board) took less than a minute.
  • Nice, slow action
  • I was pleasantly suprised how quiet the servos are when you run them slowly
  • With the diameter of the brass rod I'm using I think that I'll leave the Peco spring in the point. It only leads to a little 'hop' as the point traverses - and it means that I can turn the servo off when not in use and be confident that the point will stay thrown.

I'm happy to share the design of the adapter plate with anyone who is interested - it wouldn't be difficult to make manually. CNC'ing it does help to make sure that they are made consistently though.

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