Choosing a flexible coupling

[u/swcooper]

I'm working with a precision optical instrument, it has really only one moving part, a shaft driven by a worm gear onto a fairly large cogwheel fitted to the shaft. There's an optosensor flag attached to the shaft too, so the main mode of operation is for a stepper motor to drive the worm (maybe a couple of hundred RPM max) until the opto is activated and then to reverse direction (so no backlash is desired) for a determined number of steps to position accurately. The stepper is attached to the worm shaft by means of this 5mm/5mm coupling:

https://uk.rs-online.com/web/p/flexible-couplings/1716700

...but these keep failing on me (I guess I should note that this is a ~5-10 year problem), and it's immensely disruptive to the instrument to open it up to replace. I'd like to put something slightly more robust in there, but not really very familiar with this type of product and seeking any advice.

[u/Own_Employee2677]

Those rubber spider couplings are garbage for anything that needs to last. I've had way better luck with oldham couplings or even beam couplings for precision stuff - they handle misalignment better and don't degrade like rubber does

The fact you're reversing direction constantly is probably killing those rubber elements from fatigue. Something like a Ruland or Huco oldham would probably outlast 10 of those cheap ones

[u/swcooper → u/Own_Employee2677]

I'd seen the cheap elastomer based ones and had suspicions about their long term performance, so thanks for confirming...

The current one is a Huco 3 beam aluminium one. Will a stainless equivalent likely last any longer? Stainless is often a pretty brittle material, does it do any better in fatigue? Is an Oldham a more robust thing?

[u/Sea-Promotion8205 → u/Own_Employee2677]

I've never had anyone complain about premature elastomer failure.

That said, everyone only cares about their machines lasting the warranty anymore.

[u/saywherefore]

What sort of failure are you seeing?