How Would You Fix This Ribbon Cable Connection?

Factual Questions
21

I reckon you’re right there - from the video it does look like free-hanging wires would get caught up in various gubbins, whereas a flat cable is at least inherently constrained in certain axes of movement. How about this: keep the FFC cable in its original position and run a couple of bypass wires over the top of the FFC, taping them together at periodic intervals. That way you’ll get a nice reliable wire connection, with the FFC still in place to give the wires some positional restraint. If you can, use some extra-flexible wire (this usually has lots of very fine strands and a flexible silicone sleeve, whereas ordinary hook-up wire of that gauge will have something like 7 or 16 coarser strands and a stiffer PVC sleeve). Matching the overall copper cross-sectional area to the existing red and black wires would be prudent.

The reason the FFC failed is because a design flaw violated a key specification: the FFC will have a minimum bend radius specified, and the way those two PCB slots are arranged means that a kink in the cable will be present from day one, which will get stressed with movement, which will work-harden the copper traces, which will lead to their eventual fracture.

It’s an unusual FFC (possibly custom) as the width is about twice what it needs to be to carry the conductors. Probably this was done for mechanical reasons as a wider cable would give it more lateral stiffness and help prevent it moving from side-to-side so much. The dark blue bit on the end is a stiffener that aids the manual insertion of the cable into the connector, and also thickens it up a bit so the connector contacts exert more force on the fingers. FFC cables and connectors can be very reliable in good designs, and guaranteed points of failure in bad designs.

22

No luck with a new connector end, it’s just too tiny and fragile. I was able to do it, but it wouldn’t hold, which makes me think the socket could be part of the culprit too because I was able to press the cable on the leads on the outside and it would work, but it wouldn’t make contact inside the socket. It would tighten down ok with the clip, but meh.

So I opened up the side of the box, and using the innards of an old Ethernet cable just tied all the bare wires together after clipping off the little circuit boards. Interestingly the one hidden inside the box is slightly different than the one on the rake housing. It’s a little longer and they also potted the wires where they’re soldered on, but otherwise it’s the same basic thing.

Anyway, after roughly twisting the wires together the motor runs fine. At first I couldn’t get it to work but then I realized I had the side panel with one of the proximity sensors face down on the table (sigh). I think these wires will work ok, there’s guideways in the plastic housing that should keep it out of trouble. I just need to get a soldering iron and some heat shrink. Then I have about 72 screws to put back in.