My team has like two spools of solid core wire. Is this legal for FRC?
Solid core wire tends to wear down/break under vibrations or bending, so I wouldn’t recommend it for FRC. Solid core is great for houses, but houses don’t usually move that much.
But it’s technically allowed still? I’ll stay away from it based on your advice but never know when u could need it in a pinch
Last I knew only stranded was legal
Per the 2018 rules, it would be legal.
Per the 2017 rules, it would have been legal.
Per the 2019 rules… Sorry, can’t answer that one until January 5, 2019.
It does need to be insulated and copper; but it’s not illegal. It does need to be the correct gauge, and as noted you could get some adverse effects, but I can’t find anything saying it was illegal to use.
If you use it on your robot, I think you would be in a bigger pinch when you need your robot most. However, if you make some sort of programmer board with a pdp and roborio and motor controllers, use it up for that sort of stuff.
You could also use it for other projects you might make that dont move as much, such as a motor testing kit, or electrical practice(however I would recommend you teach the dangers of whiskers from stranded wire, so this only works to an extent). but definitely not on a comp bot.
Also, i’m assuming its 14-10 awg, but the same applies even more strongly for the smaller sizes.
A lot of the small gauge signal wire that gets used is solid core. In the larger gauge sizes, IE 12 & 14, it in a lot stiffer than stranded so that can be a problem anywhere it is expected to flex. But in answer to your specific question Yes solid core wire is legal unless you can find a specific rule against it. (it will have to be in the 2019 manual :))
Rather or not is a good idea is an engineering question supply chain question. When you get in the real world you are going to be constantly trying to answer that question.
I agree with using it for prototype board situations, (or any thing where the PCB is rigidly mounted). You won’t go through 2 spools quickly, but a good use may be linking individual LED boards together or using solid connections in prototyping applications for delicate soldering in close proximity to other contacts (you don’t want stray multi-strand “whiskers”, which was already mentioned).
Just a point of curiosity for someone who knows more about EE stuff: is solid or multi-strand more prone to signal noise (induction noise due to proximity to a current source)? Or does it matter at all?
No. There should be no difference.
Unless your team is really tight on finances, I would take it to a scrap metal dealer and get rid of it. While it can be used in “applications that don’t move”, it will be difficult to ensure that some of it doesn’t make it onto your robots.
Some other applications could be to use it on systems that aren’t your actual robot and may see less physical action. See if there are any custom driver station implementations, pit devices, or team needs where the wire could be put to use. You could even use the wire as a learning tool for giving to students to improve their soldering technique.
On the last of these suggestions, be careful using it for soldering/crimping practice- it has different characteristics than stranded.
I highly recommend using stranded wire. It wicks up solder very easily and it suitable for crimping. Plus, it won’t break after a few bends the way solid core does.
For soldering, I would argue that solid is better for practice because you really do need to heat it up and get flux to it, where stranded might let you sneak by on capillary effect.
For bending, each two diameters of solid core copper wire has one good ninety degree bend in it. Returning it to straight is a high probability affair. Those who expect to get a second bend without damaging the wire have left the path of wisdom.
Totally true! Most FRC applications heavily favor stranded wire over solid core, but in industry you don’t always get so lucky so in my mind you have a perfect opportunity to give your students a leg up by introducing them to a different design constraint and teaching them how to tackle it.
In addition to its other shortcomings, depending on the gauge, solid core wire can be surprisingly heavy. I had a team at an event a few years ago take fifteen pounds of solid core wire off their robot to make weight. Rewiring your robot at the competition is maybe not recommended 
How do you figure that solid core wire is significantly heavier than stranded?
Also, I don’t think we even have 15lbs of wire across the entire robot…
According to this chart - first one I found - AWG#14 solid wire is the same or lighter than all stranded except 19/27. So, no, solid wire is generally not heavier than stranded for a given gauge. (FWYI, “19/27” means 19 wires of AWG27)
AWG Strand In. mm area Weight* Weight^ DC* DC^
14 Solid .064 1.630 4110.0 12.40 18.500 2.6 8.6
14 7/22 .073 1.854 4480.0 13.56 20.180 2.3 7.6
14 19/27 .073 1.854 3830.4 11.59 17.250 2.7 8.9
14 41/30 .073 1.854 4100.0 12.40 18.450 2.5 8.3
14 105/34 .073 1.854 4167.5 12.61 18.770 2.5 8.2
*Lbs/1k ft, *DC Ohms/1k ft ^kg/km, ^DCOhms/km
Source: http://www.thelen.us/1wire.php
You may be surprised if you add it all up. Would be a good experiment.
Everyone,
Solid wire is not illegal for FRC. However, the PDP terminations are designed for terminating stranded wire. The manufacture recommends that current handling be derrated by two wire sizes when using solid wire. So when you normally would use a #12 wire for a 40 amp breaker, #10 solid would be required. The contact area of solid wire is that much less when using these terminations. The same is true for stranded wire that has been tinned (soldered) into a solid bundle.
As stated before, solid wire is not intended for moving devices. It fractures with all of the movement and eventually breaks. Al’s corollary for Murphy’s Law applies here…If it anything can go wrong it will go wrong…On Einstein!
I also moved this to Electrical.
I don’t use solid core for soldering practice, but I do always use it for teaching soldering to first timers.
Twist about 2 inch stripped ends together and show how you have to get the copper up to the temperature to melt the solder to form a solid ‘hot’ joint. Apply heat at one point and the solder at another point until the hot copper can melt the solder and wick it along the joint, without touching the solder to the iron.
You can easily show a cold joint by trying to melt the solder on to the cold copper.
Seeing the solder wick down the joint gets the lesson across and produces an experience of satisfaction. You never have trouble getting volunteers for soldering projects.