We use the square crimp and have found that it is actually the best for contact (at least for us). One of the problems with having the bare wire (even when it is tinned) is the fact that the wire can break very easily and can come out of the PDP and other places like the PCM or VRM extremely easily. In my opinion, ferrules are a great thing to invest in.
You never want to tin wires for use on clamp terminals. Tinning essentially turns the wire into a solid wire and depending on how good the person who is doing the tinning, the tinning action can then push solder up under the insulation. This causes wire fractures inside the insulation that will never be seen by anyone looking for an issue. Solid wire is not recommended for moving parts and devices like a robot.
If you do a good service loop, that’s a lot less likely to happen because the connector isn’t supporting the weight of the cable, just of the couple of inches of service loop. If you banjo-string it, you’re going to have problems.
Service loop: give yourself enough slack that you could disconnect and reconnect the wire without cutting any zip ties/removing fasteners. Zip tie, lace, or otherwise secure the insulated wire firmly (but not so firmly you risk damage to the insulation or wire inside) to the panel or chassis on a part that doesn’t move relative to the connector, just beyond the slack loop. In some implementations, this will cause a piece of wire that looks like a U or S going into the connector, other ways of doing it leave a full circular loop. You also want to keep in mind the bend radius of the wire when you’re doing this to make sure you don’t bend it so tightly the wire breaks inside the insulation.
Banjo string: wire that is under tension at the connector and/or end to end (i.e. so tight you could play it like a banjo)
There are several styles of crimp tools. Ratcheting tool troubles are normally operator error. Of the two styles, one uses a two-piece solid patterned jaw to crimp and leave a textured impression, the second uses several parallel plates that slide together. When using the first, an oversized ferrule will still make an acceptable connection. When using the second, the tool will damage an oversized ferrule. (Thus the operator error most common with ferrules.) Be sure to use the right ferrule for the wire. This applies not only to diameter but also length.
We prefer to ferrule everything we can. The ridges on the ferrule, left by the tool, increase the retention strength on the Wago and Weidmeuller connectors.
