FSR Panel Repair/Damage Questions

[byi]

I am posting this here because it seems to be the only active thread concerning scoring systems other than the one about ordering info. Sorry if this is the wrong place. While I was testing my scoring system, I noticed that some of the fsrs were not functioning. After further inspection, I determined that the source of the problem is that the cables connecting the fsrs to the target board had creased slightly and broken the wire within. Any easy way to fix this? If not, can I peel off the broken fsrs easily or will I need a new target panel? Any suggestions would be greatly appreciated.

[tician]

I've not had any trouble peeling 0.2" circular FSR's intact off the bottom of a Bioloid foot plate, but I expect a 1.5" square would be a bit more difficult (still don't think it would be impossible). From the images above, it appears the pcb that mount to the back of the ABS plate still cause the polyester leads to bend a bit on a full size panel, so I expect you are not the only one to have broken/torn leads. On the 2010 scoring system thread I had a small explanation of how to replace the pins using a pair of needle nose pliers and a small flathead screwdriver, but it all depends on where the lead was torn and how many were damaged. If the shipping cost is not prohibitively large compared to replacement 1.5" FSR's, the easiest fix would probably be these connectors with a pair of needle nose pliers (insert the polyester lead fully into the crimp pins and close each pin before closing the plastic of the connector - the ~$2000 crimp tool manual has a few reference images of how it should and should not look). I ordered a few of them, but they were way to thick to fit through the slot in a Bioloid foot plate, so I never actually used any of them (they do appear to match the width of the polyester leads). The bare pins I bought and used are these (which require at least 0.140" of undamaged and unbent polyester lead for the crimp), but I think these might be a bit nicer (no datasheet to confirm the dimensions, but they appear the same sans the big square tube of metal to lock the pin into a plastic housing).

[byi]

It's not the leads that are the problem. The wire itself is damaged. i guess i could cut the wire and use the crimp-on leads to reattach it, but that would be rather difficult. I guess I'll take my chances pulling it off and replacing it. Thanks for the detailed info.

[tician]

Sorry for creating a nomenclature problem. There are solder tabs/pins crimped onto the polyester lead(s). What you seem to be referring to as leads, I call crimp pins. What you call wire, I called polyester lead(s) (ala 'lead' wires of a through hole resistor). Speaking from experience, it really if not that difficult to replace the pins when the lead tears (had to fix at least two on the Foot Pressure Sensor kits from HUV Robotics). The shortened lead length would probably require a simple jumper wire extension to connect it to the PCB, in which case the socket version of the crimp assembly would be the better choice (just push one end of a piece of wire into the socket and solder the other end of the piece of wire onto the pcb).

The FSR is made of a sandwich of polyester film filled with two traces made from a conductive substance. In the large square active sensing area, there is a spacer separating the conductive traces from a resistive element on the opposite piece of polyester. When pressure is applied, the resistive element contacts the conductive traces and allows current to pass between them. The more pressure, the larger the area of contact between the resistive element and the traces, and thus the lower the resistance measured at the pins on the end of the polyester lead.

[Tyberius]

You can peel them off and replace them, shouldn't need a whole new target panel.

[byi]

Thanks for all the info guys. Considering that repair looks to be slightly complicated, that I am not great with small parts, and that buying new FSRs is not too expensive if I remember correctly, I'll opt for trying to peel them off. Maybe I'll also add some supports to prevent that kind of break from happening again. Thanks again tician for such extensive explanation.

[Upgrayd]

I have found that putting a shot of hot glue under each bend prevents the conductors from breaking.

[byi]

Thanks. Will do.

[byi]

Anyone else having issues with the FSR's wires breaking really easily? I dropped a panel from a 4 foot shelf, causing it to fall exactly flat against the ground. One of the wires snapped clean in half from the impact. To break a wire from a decently short drop seems unusual. I don't know if I am doing something wrong or overestimated their durability, but I seem to be having a lot of trouble with the FSRs. Upgrayd, not sure exactly what you mean. Mind explaining a little more?

[Th232]

Upgrayd, not sure exactly what you mean. Mind explaining a little more?

I'm not Upgrayd, but hot glue around the bend would add mechanical strength to the wire at that point. Takes the force off the wires, prevents them from bending and so on.