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So, I'm planning out my second hobby robot(I'm 15). I am planning on using a 7.4V LiPo battery and my idea is to solder on a 3-pin header to connect to the electronics. Anyways, should I solder to crimp terminals and then attach it to the pack? Or should I solder directly to the battery leads Keep in mind I have a decent background in hobby electronics and am just starting with robotics. My soldering skills are also decent!
Thanks!!
I find it's always cleaner to use connectors rather than soldering directly to leads, no matter what component you're trying to attach to your robot. You have to think about things in terms of maintenance. If a battery goes kaput (technical term :D) and you soldered directly to the leads, you'll have to desolder and solder again. If you used a connector, you simply pop out the battery and replace it with a new one.
If you want to take your designs to the next level, you should start planning where your wires will be routed through the chassis, covering them with wire loom, spiral wraps, cable carrier, cable ducts or even just cable ties w/ cable tie holders (google wire management products and you'll find even more options). The ideal situation is when the wiring throughout your chassis is static and never replaced or moved (except when a wire is the point of failure). To replace any part or to work/modify it, all you should have to do is unplug connectors.
As a final note, ALWAYS color code your wires: Red = +12V, Black = Gnd, Orange = +5V, Yellow = +3.3V, Green = Sensor Signals, Blue = Communication lines...you get the picture. You can define them any way you'd like (although I'd recommend to stick w/ red = power, black = gnd) as long as you're consistent. On the other hand, NEVER assume someone else has color coded their wiring. This has bitten me in the rear because I had assumed red would be power and black would be ground, but I was mistaken. The extra time you take in the beginning to do things cleanly will save you hours if not days later on in the project.
I must agree with Andrew Capodieci in that you should use a connectors and 1 mm headers (or whatever the balance lead is). There is a good chance that at some point you will want to remove the battery to replace it/inspect it for damage or whatnot.
If I had to do one of the two, then I would crimp for low current applications, and solder for high current. Crimping is probably fine for small robots, but I wouldn't dream of it for anything that wouldn't fit in a 20 cm cube or especial anything aerial. However, using a connector would be the best option in both situations.
Really, the decision of whether to crimp or to solder comes from the thickness of the wire. Thin wire is too brittle to be crimped, and must be soldered. However, iff the wire is too thick then a soldering iron can't apply heat faster than the wire dissipates it (and the jacket will melt long before your solder does). At that point, your options are to use a torch (like in pipe soldering) or to crimp the connections.
For our batteries, we spot-welded nickel plates to the tops and bottoms of Li-ion 18650 cells to make battery packs, and then added crimp terminals to the connections between packs.
Crimp connections done properly are very reliable -- most residential wiring uses some form of a crimp connector.
