How does your team crimp terminals?

[BitTwiddler]

I'm the electronics mentor for our team and I'm getting ready to hold a class in electrical fundamentals in the coming weeks.
I've been reflecting upon a chronic problem that seems to rear its ugly head every build/competition season - failed crimp-on terminals.
I try to watch carefully when a student completes a crimp and I make sure to do a tug test afterward. Yet later during testing, practice or worse during competition, a crimped terminal will fail. Especially at the motor controller. Its frustrating to say the least.
I'd like to hear what your team does to ensure that crimp-on terminals don't fail. I'm sure many of you have experienced similar problems. While I have experience in crimping terminals I'm no expert. I'd prefer to solder all my electrical connections but that's not always practical.

Thanks,
Dave Tanguay
Electronic & Programming Mentor
1726 N.E.R.D.S.

[Whippet]

We always solder our crimps to reinforce them. We've still had some come out, but not nearly as much as if we didn't solder.

[BBray_T1296]

Most of our smaller crimps we squeeze tightly and pull test. For our larger and most likely to be destroyed ones (Cim motors, high vibration zones, potential to get snagged on the co-opertition bridge) we soldier them. We also do regular (maybe bihourly) inspections on everything. We give all our wires a gentle tug and repair any loose connections

[Ed Law]

We do not solder wires to terminals and we never have problems with them. One thing I do is choose the right size terminal for the wire and invest in the proper crimping tool. Another thing I found out is if I twist the wires first before crimping, it is much more secure because it is much harder for the wire to "slide" out.

[androb4]

We use a 10-ton press.

Jk, a regular crimp would suffice. Perhaps soldering the connector in addition would be a great practice.

[Mr V]

#1 thing to do to avoid failed crimps is to not use insulated terminals.

#2 is to use a ratcheting crimper, with a die intended for the wire gauge and uninsulated terminals, they give extra leverage and don't release until the crimp has been completed.

#3 is a little dab of solder on those crimped un-insulated terminals before you cover them with heat shrink.

[Nirvash]

We/I use a good quality crimper, it isn't ratcheting but as long as you make sure to crimp all the way it shouldn't be an issue.
Make sure to match your connector to your wire size, too large wire in a crimp or too small will cause a bad connection.
I've never had an issue with insulated terminals, in FRC or at work with equipment that runs for thousands of hours with heavy vibration.
And of course, make sure to pull test your crimps.

[DonRotolo]

Originally Posted by Ed Law

We do not solder wires to terminals and we never have problems with them. One thing I do is choose the right size terminal for the wire and invest in the proper crimping tool. Another thing I found out is if I twist the wires first before crimping, it is much more secure because it is much harder for the wire to "slide" out.

Originally Posted by Mr V

#1 thing to do to avoid failed crimps is to not use insulated terminals.

#2 is to use a ratcheting crimper, with a die intended for the wire gauge and uninsulated terminals, they give extra leverage and don't release until the crimp has been completed.

#3 is a little dab of solder on those crimped un-insulated terminals before you cover them with heat shrink.

We do not solder our connections, use insulated terminals, and don't have a problem with failed crimps.

#2 above is definitely the one biggest thing we have done to ensure crimp quality. We spent under $40 for a high-quality, name brand crimper with the proper die.
We also made sure it was adjusted for the right crimping pressure. The 'right' pressure is when the wire strands actually deform and form a solid mass, with (virtually) no air between strands. We have sectioned our crimps, polished the surface, and examined them under a microscope. Probably overkill, but it was a learning experience for the kids.

And as Ed mentioned, twist the wire strands together - not just so they enter the terminal neatly, but also so you don't get stray strands that can short to other wires.

When stripping, be sure you don't nick any of the strands.

When pull-testing, pull as hard as you can. Pull to destructon during training, so students get a feel for the upper limit...then pull near that for 'production' crimps.

And, of course, use high-quality connectors (name brand, like 3M) of the correct size for the wire, and check them regularly during competition.

[Mr. Mike]

To get good crimps it takes good quality tools. Harbor Freight Tools has a ratchet and hydraulic crimping tools that seem to be of a good quality and price.
The best crimp will still fail if the wire is not supported.

[evanperryg]

We just don't use crimps. The only time we use them is on the terminals for motor controllers, and each of those is made on-the-spot (no premade cables) and examined for quality before putting it on the robot. Crimp terminals are, as you said, very unreliable. It takes the right tools and considerable experience to get consistently good crimps. But, they also introduce a lot of resistance into the circuit, which can result in reduced efficiency and reduced robot performance. I would highly suggest planning out your electrical system in such a way as to completely remove crimp terminals from your design.

[Ether]

Originally Posted by evanperryg

they [crimps] also introduce a lot of resistance into the circuit

Do you mean compared to soldering? Are you claiming this is true even for a crimp properly made with an appropriate tool and crimp size?

[joeweber]

Watch the direction you are crimping the terminal, there is a seam where the wire goes in. If you use the crimpers that has two half circles (which we will not use) you will just crush the connector when the seam is in the wrong place. We use the sta-kon tool that has a half circle on one side and a divot on the other side and make sure that the divot is opposite of the seam. You must crimp hard or it will not take, most students do not have the strength needed for proper squeeze pressure so make sure the person doing it has strong hands.
You can view this on one of our tips page
http://www.team1322.org/electrical.htm

[theawesome1730]

We use ratcheting crimpers to ensure a good crimp and then solder too just to be safe. Be sure to use the right terminals for the right gauge of wire. I prefer non-insulated and then put heatshrink on after the soldering is complete

[DonRotolo]

Originally Posted by evanperryg

But, they also introduce a lot of resistance into the circuit

Like Ether, I also question this statement. I think you are wrong.

[Ed Law]

Originally Posted by Ether

Do you mean compared to soldering? Are you claiming this is true even for a crimp properly made with an appropriate tool and crimp size?

I have actually heard the opposite. A good mechanical crimp is better than soldering in terms of less resistance. But I don't know if it is true.