Friday, 10 July 2020

4th axis umbilical?

Now that I have some form of life in the servo motor, I can start to think about how I'll connect it up in the final installation. This is what I have in mind. I think it's mostly fairly obvious:
  • Mount the Servopack within the cabinet where it is easy to connect to the Acorn and mains power.
  • Fit a sealed (female) connector on the cabinet so that I can remove the 4th axis when not in use.
  • Make the connections to the encoder (signal) and motor (power) through separate screened cables running through flexible conduit to the above connector.
Seems reasonable so far. Thinking further:
  • The connector needs to be rated for mains voltage, as the servo power circuit is at mains potential.
  • I need 4 ways for the encoder circuit and 3 ways for the motor - plus screens. Something like a 10 way connector might suffice, to allow a couple of spare pins (a loopback perhaps?).
  • A quick scan of CPC, Farnell and RS suggests a circular military type connector would give a reasonable tradeoff of cost, voltage rating and robustness. There's a wide variety of circular military connectors but CPC keep some Amphenol examples:
Amphenol 5015-type connectors datasheet here. Claims to be good for 3kVac, although I doubt that's a sensible working voltage. However, it's a lot better than the mere 50V / 120V many of the other circular connectors were able to boast eg Buccaneer series.

As ever, CPC are cheaper than their sister company Farnell. The Farnell connector is £19 while the identical CPC one is £12. It's often like this and makes CPC my first choice if I can find what I need in their narrower range.

The stuff turned up today. Looks up to the job. Here's what the fully assembled socket / plug / backshell looks like:

Here it is alongside a short length of the conduit and an example of the plastic glands they come with. I need to terminate the conduit to the connector somehow.

I can see a solution here. Turn down the nut so it fits in the cable clamp housing. Chop off the cable clamp parts and screw the plastic gland into the nut, now located within the metal body of the clamp. That should work reasonably well - and may even be vaguely waterproof if I fit a washer where the plastic gland meets the cable clamp body.

So - mount the (female) connector on the cabinet and wire it up to the Acorn. Wire the motor and encoder through the conduit to the free plug. Sounds simple enough. Let's do it.

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