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The Connector Addict?

I love the Pen Addict’s slogan: There are worse addictions…..right?

I’m not a connector addict, although I do like trying out new connectors.  Partly it’s because I haven’t found the ideal connector system (or systems; I often want some variety so that the same connector type isn’t used for a variety of incompatible uses, and thus you have to be careful where you plug a connector in).

But I still enjoy receiving the occasional Mouser order with some new connectors.  So along with an order for some MDR connectors for my Copley Accelnets, I included connectors I haven’t tried such as:

  • Kycon USB B high retention force connector.  The big feature: minimum removal force is increased from 10N (standard USB) to 15N.  I like them; USB plugs come out too easily, but this connector makes it a lot harder for a USB cable to become accidentally unplugged.
  • Amphenol USB A locking connector.  The big feature: the connector has a locking tab that grabs onto the little square holes on a USB A-type plug.  That’s even better than the Kycon: it takes over 95N to separate the plug from the jack without unlocking.
  • TE/AMP MTE connector.  Nice, affordable IDC connectors, except you need really expensive tooling to use them easily.
  • Molex Micro-Fit Jr 3.0mm BMI.  I wanted to check out the blind mate version of the Micro-Fit; I’m still not a Micro-Fit fan.
  • Phoenix PST 1.3/8-LV-5.0 header with shroud.  The shroud provides polarization.  The Phoenix PST headers and PT terminal block plugs are a very affordable removable terminal block system.
    • One gotcha: you have to use the shrouded headers with the PT 2.5 series (e.g. PT 2.5/8-PVH-5.0) not the 1.5 series (e.g. PT 1.5/8-PVH-5.0).
  • Phoenix ST-Combi connector and ST-Twin terminal block.  I’m looking at using these for DC power distribution.

May 23, 2011   No Comments

Prototyping Is Good

I like automation software because the end result is visible, not just “in the cloud” with no clear connection to anything physical.  Furthermore, I’ve found it’s very good to experiment and prototype first; I do not rely on virtual designs (living only in CAD software on a computer) to be 100% correct.  Even if we had and knew how to use expensive simulation software, it’s still not real.  Toyota, which does make extensive and valuable use of simulations, is moving back to make more physical prototypes and do more testing with those prototypes.

First, it’s hard to get all the details right.   After I assembled my CO-DB9-RJ45-2 adapter board, I plugged it into a AMC DX15 servo drive and then I finally realized: oh, no, the power plug is on the wrong side and will hit the next connector!  (BTW, the simple solution is to use a fixed terminal block instead of a header and plug).

Second, there’s no substitute for actually trying to use, first, the components, and second, the whole machine.  You can’t simulate the feel of quality components.  And there are lots of little things that can bite you later.  That’s why I now prefer to get samples of connectors I’m interested in before using them on a PCB.

I really like the concept of IDC (insulation displacement) terminal blocks: all you have to do is insert the wire and clamp down.  There’s no wire stripping, no ferrules to crimp, and no screws.  So I used a lot of Phoenix IDC terminal blocks in one of my first PCBs.  They worked great for many wires, but one set had problems: one component had wires with really thick insulation (for no good reason IMNSHO), so we really had to cram the wires in, which isn’t a good thing.

So while I still like IDC connectors, such as the eCon style connectors (3M MiniClamp, Tyco RITS) I only use them when I know what the wire gauge and insulation diameter will be.

I’ve also started using a lot of spring clamp connectors.  They can handle a much wider range of wire (and insulation) sizes than IDC, but can still be quicker to assemble than screw clamps.  However, they have their quirks, too:

  1. I have a bunch of used early Wago DIN rail spring clamp terminal blocks which are significantly harder to use than the newer models.
  2. Large spring clamps can take a lot of force.  I realized that when using some 4.0mm 32A Phoenix DIN Rail spring clamp terminal blocks.  I’m not sure I’d want to use anything larger.
  3. It can be hard to get the wires into a spring cage plug: it takes one hand to hold it, one hand to operate the screw driver, and one hand to insert the wire — but I only have two hands.  When the plug is in its header, it’s easy to operate.

November 27, 2009   No Comments

Connector Annoyances: Micro-Fit Genders

Connectors can be very annoying.  Right now, I’m annoyed by Molex’s Micro-Fit 3.0mm connector family.

Here’s the scenario: some motors we use come with the feedback cable wired with a Micro-Fit receptacle.  We custom build a cable with a sub-D connector at one end and a Micro-Fit plug at the other (which connects to the feedback cable).  I was investigating building a simple PCB to test the cable, and therefore needed a PCB mount receptacle.

That part doesn’t exist.  All the standard Micro-Fit PCB headers are plugs.  You can get Micro-Fit PCB receptacle headers if you use the Micro-Fit BMI (Blind Mate) series, but according to Molex, BMI parts only mate to other BMI parts.

That’s another reason I like sub-D connectors: they’re available from multiple sources, in all kinds of variants.  And you can choose solder cup, crimp, or (for some sizes) IDC ribbon cable; Micro-Fit is only crimp.

November 5, 2009   1 Comment

Why Are Standard Servo Motors So Different?

Recently, I had to select a servo motor.  We had already chosen to use a NEMA 23 mount with a 0.25″ shaft, and had other requirements such as maximum length, torque, speed, and voltage.

I was amazed at the different shaft diameters and lengths supposedly standard NEMA 23 motors have — I recall 0.25″, 8mm, and 0.375″ diameters, and can’t remember all the lengths.  It was even worse when I had to select a NEMA 17 motor a while ago– at least one manufacturer’s supposedly NEMA 17 mount wasn’t the same as everyone else.

Then of course there are all the non-standard mount motors – but I only use those as a last resort, since I’ve already had motors go out of production twice; at least with a standard mount, there’s a possibility of finding a suitable replacement.

Maybe there are other standards: maybe the various European and Japanese 40mm, 60mm, and larger motors really do follow a standard, but I don’t have time to analyze them all.

Connectors are even worse.  I can understand why manufacturers use different kinds of connectors, and I know there are no connector standards.  A motor intended for harsh environments needs a tough but expensive connector, while a light duty motor is much better off with a cheap connector (such as Molex or Tyco/AMP crimp connectors) or flying leads.  But, just like industrial Ethernet, it’s easy to think: do we really need all those choices?  Couldn’t we have just three or four?

I personally like sub-D connectors a lot, since you can get high power (Combo-D), can use crimp pins or solder cups, and choose from a wide range of backshells (including straight, right angle, and 45 degree in metal, metalized plastic, and plastic) and manufacturers.

Of course, pin-outs are even more varied.  For example, on the controller side, Galil (DMC-21×3/AMP205x0 combo), AMC (DX30, DX60, etc), and Copley (ADP series) all use HD15 connectors for feedback, but each one uses a different pin-out.

Oh, well, at least commutation and incremental encoder signals are pretty standard: three signals, either RS-422 differential or single ended (TTL or open collector) –  except if you use some Japanese motors (e.g. Panasonic).  And I’d better leave absolute encoders for another time…I’m not even sure how many “standards” there are for them.

October 8, 2009   3 Comments