From top to bottom: Traxxas, Phoenix and HXT 2mm gold connectors [_DSC1028](//res.cloudinary.com/moot/image/upload/t_d3-gallery-s2/v1403532679/:tosqa:OTA2:_dsc1028.jpg.jpg) The Traxxas connectors have two types: A and B. The big gold-plated lugs (different for both ends) are easy to solder onto. The connectors feel sturdy and lock securely. However, the physical connector is way to large to be a feasible option for Tosqa. Also, there is no board-mount option. The Phoenix connectors are the ones we are using now. The 2mm gold bullets have a solder cup in which the wires are soldered. There are both female and male pins. A female and male pin slide into the shroud after soldering. The connectors are hermaphroditic, meaning that it is possible to connect two power sources together and blow up stuff if you want to. Size-wise, they are narrow but long. There is no board-mount option available but with some hacking of the shroud it is possible to securely mount them on a circuit board. Big disadvantage: single-supplier.
I've opposed the screw terminals for these exact reasons, but the decision was made for prototyping convenience. The most obvious candidate for power entry is EIAJ; these are locking barrel connectors. Problem with these is that this is mostly a Japanese standard, and aside from the usual japanese suppliers we don't often get to see them. These connectors usually go up to a few amps, enough for a single stepper in almost all situations. Another note on EIAJ: the standard was devised to create parity for power input connectors: every size corresponded to a certain voltage (range) and maximum current. We will not adhere to this standard. This means that we MUST include a sticker or board marking that indicated barrel polarity, voltage and current rating. The other option that I think is not a bad idea is to use Molex Mini-Fit. Yes, this requires crimp tools but it is so incredibly ubiquitous and both crimp tools and premade wires are so easy and cheap to come by that I think we can risk it. Same deal (IMO) with JST XH; these are also used by practically all RC battery pa cks. The nice thing about Molex MIni-Fit is that a 2-pin connector immediately suits all our needs; it is officially rated to 6A, accepts 14-28AWG depending on the contacts used, it is the smallest solution (marginally bigger than the terminal blocks), it is positively locking and keyed. Official crimp tool: http://nl.farnell.com/jsp/search/productdetail.jsp?SKU=1703928
Molex Mini-Fit seems like a good choice too, although requiring a crimp tool is sort of annoying. What is your opinion on XT60 connectors? They are very popular in the RC hobby world. They are rated at 60 A which is overkill but they are available at lots of places (including Dealextreme and Conrad) and can be soldered straight onto a wire.
They aren't (officially) PCB mountable. I've seen people cut slots for one side and solder it down on the other side, but it is very bad design. It will eventually crack solder joints (or worse even, rip off the pads) in a machine environment.
Let's steer clear of the barrel-type connectors. Clearly marking the polarity, voltage and current rating is a good idea, but it shouldn't be the default way of preventing people from messing stuff up. Molex have specified 30 mating cycles for their Mini-Fit connectors. In my experience with computer power supplies the connectors actually fit a lot less secure after only a few cycles of plugging and unplugging. JST RCY or JST XH aren't ideal either. Getting a good crimp is not trivial. If you don't crimp with exactly the right force the wires tend to either slip out or break off after a while. I've seen people mount the XT60 sideways like this: [XT60 side mount](//res.cloudinary.com/moot/image/upload/t_d3-gallery-s1/v1403599210/:tosqa:9hmD:current_xt60_1.jpg.jpg) or straight up like this: [XT60 top mount](http://www.hobbyking.com/hobbyking/store/catalog/PCB004.jpg) The second one seems fairly secure, no?
I'm not sure if you're talking about the same mini-fit connectors that I'm talking about :P I have found these connectors to be quite secure, even after a couple of mating cycles. AMP Mate-N-Lok, the other, often called 'molex', connector in computers is what I experience as annoying and broken after a few cycles. The top-mount XT60 requires slot holes, which not every PCB manufacturer is willing to plate. I've had trouble with these with both Iteadstudio and Seeedstudio. Also, it's quite a bit bigger than mini-fit.
If the crimp tool itself is not a specialty item, I think it should be ok: we can supply basic pre-crimped cables and fab labs / serious amateurs can afford the investment. Let's choose based on the connectors, not the tools needed during the build phase: quality, preventing mistakes / plug-and-play convenience, and cost / availability.
Molex Mini-Fit = the 20-24 pin ATX connector that goes into a motherboard, right? Another popular choice in the RC world is the Tamiya connector. It looks a lot like Mini-Fit. However, on a lot of forum threads I read about people switching from Tamiya to XT60 and never looking back.
Yes, Mini-fit is the 20-24 pin ATX connector, as well as e.g. PCIe and ATX12V power supply connectors. Tamiya is mini-fit, but rotated by 90 degrees. The reason people in the RC world require heavier duty connectors is mostly current rating. Mini-fit only goes up to 6A per contact (8A/contact for gold-over-nickel plated) with 20mohm max resistance, which is unacceptable for the kinds of currents that 10/20/30C battery packs deliver. We only need to supply up to 3 or 3.5A even for the larger SSBs (when we get to those), so we're well within boundaries.
Molex also carries the Micro Fit 3.0 line. It has wire-to-wire and wire-to-board options, 5A current capacity and seems a bit smaller than the Mini Fit Jr. and Tamiya. JST RCY unfortunately has no wire-to-board options so that option is out imho
Micro-fit is a good 'fit' as far as capacity and board space goes, but my complaint with it is that tooling is inordinately expensive and the 'low cost' Molex tooling doesn't work with it. If you can point me to a proven good crimping tool that accepts micro-fit pins, I'm all for it.
The [Engineer PA-09](http://www.engineer.jp/en/products/pa09e.html) and [Hansen Hobbies crimp tool](http://www.hansenhobbies.com/products/connectors/tools/crimp_dx/) list Micro Fit as supported connector families. I have the Engineer tool, so will try out how it goes.
The Engineer seems to be the only one out of the two that has a proper beak width; the Hansen seems more like a general purpose one that will probably overcrimp micro-fit contacts. Let me know when you test it out with an actual micro-fit connector (can you test that soonish? I'd like to order one too if it works. Also, where do I buy it?).
Provided I ordered the right parts I should be able to let you know on Thursday. The crimp tool is not exactly cheap, but it's available at [Kiwi Electronics](http://www.kiwi-electronics.nl/engineer-pa-09-jst-crimping-tool) among others.
€50 is pretty cheap in connector-land (unfortunate reality). I'm mostly trying to shy away from any connector/contact that requires the loathed €400+ crimp tools. €50 can be assumed to be reasonable for an enthusiast hacker and/or commercial entity with at least a couple dozen units to sell. I know that lots of crimp tools exist that 'do' micro-fit and are waaay sub-€50, but they almost always make bad or inconsistent crimps. The requirement for the DC in-connector is not that 'a' reasonably priced crimp tool exists, but that a *good* and reasonably priced crimp tool exists. Anyway, looking forward to the results.
I received the connectors and had a go with the Engineer pliers. The contacts crimp nicely. The connectors also look sturdy, mating force feels pretty good and they are fairly small. I've bought the 1 row, 2 contact version, but we could choose the 2 row, 2 contact sideways connector to save some more board space. Elektronica Online, the popular (cheap) hobbyist electronics store also sell a [tool](http://www.eoo-bv.nl/index.php?_a=viewProd&productId=14390) that looks like the Hansen Hobbies one. They also stock the Micro Fit connectors.
This is the 'sideways' style: http://5lair.free.fr/Wiring/Power5V/Pinout.png http://5lair.free.fr/Wiring/Power5V/Power5V_wiring_600x600.png