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Uncoupling NZR chopper couplers

Here’s the first of a number of posts on a problem that has vexed me for a long time.  Namely how to uncouple scale couplers in a hands off, invisible way.

The little video below shows that a) I’m no Peter Jackson, and b) I’m well on the way to having the problem sorted.


The answer is simple and based on neodymium magnets.  The idea is to arrange a magnet in the hook, and let magnetic repulsion do the heavy lifting.  I’ve done enough experimentation to assure myself that it is workable, robust, reliable and pretty easy to achieve.  Basic points are:

  • The orientation and position of the magnet in the hook need to be consistent.  I’m currently working on this with the intention of producing cast hooks with an an appropriate recess.  But a file also works pretty well.
  • It’s a pretty slow sexy movement too – no distracting buzz or snap, just a gentle hook lift.
  • For coupling (and to an extent uncoupling) the coupler needs to be self-centering.
  • The uncoupling magnet can be placed below rail level.  I have used servos to present magnets to lift the hook and drop a hook if it is lifted. I’m also working on 3D printed servo horns to make the uncoupling station conveniently reproducible.
  • There is no major alteration or commitment to implementing the system on rolling stock.  Replacing the hook is all that is required on the vehicle, and unfitted vehicles can be run with fitted units with no problem.  A mechanism to present the uncoupling magnet needs to be fitted at each point where uncoupling is to occur.  The hassle this presents will vary from layout to layout i expect.
  • In a yard situation a ‘magic wand’ with a magnet at each end allows vehicles to be uncoupled without touching them.  Just waving the wand between the vehicles does the job. This is a real bonus of the system.
  • Once the hook is lifted vehicles can be pushed around – provided the coupler centering and free-running allow this.

This is S scale and the sizes of the parts make it very practical.  I’m not sure how it would scale.  For 9mm you might need a magnet rather too large to make the idea attractive.  For NZ120, finding a magnet to fit the hook might be a challenge.

This is not my primary focus right now, but expect some updates over the coming months.

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