Re: How does your team crimp terminals?
 

There is no substitute for a ratcheting crimper. MCM sells a nice one that is color coded to the terminal. Terminals are colored for the wire size range they are meant for. The intent with crimping is to form a "cold weld" as Don hinted above, a proper crimp forms a solid mass of metal with no air gaps between strands. However, we still don't trust that and use uninsulated terminals and solder every one after a solid crimp and tug test. We reserve insulated crimps for the practice robot and prototypes simple to save time in assembly. When the wire size is too small for the terminal you have (fan wires for instance) simply strip long and fold the wire once or twice to fill the terminal before crimping. If you use the Thomas and Betts style crimper (http://www.specialized.net/Specializ...2X190_PLI.jpg), the tool has an opening with a "tooth" on one side. The terminal should positioned so that the tooth is opposite the side with the seam on the terminal. When crimped the seam should not open. If it does, remake the connection.

Re: How does your team crimp terminals?
 

A proper crimp connection cold-welds the wire to the connector. There will be an excellent mechanical and electrical connection.

Whippet, if your team is soldering wires to connectors and still having them come out, it is time to seriously evaluate your soldering procedures and training. Though soldering is completely unnecessary if a crimp is performed properly.

Here is an article that goes into great depth on the finer points of crimping, crimping tools, pull tests, etc. It is definitely worth a quick read through. Note that the article is 4 pages long!

http://www.pbase.com/mainecruising/w...ination&page=1

Some of the article is specific to boats, but much of it translates directly to robot applications. Like others have said, a ratcheting crimping tool is absolutely key to reliable crimp connections.

Edit: in some of the forum discussions linked in the above article 'pull testing' is discussed. Most notably that pulling a wire by hand results in a tug test of around 20lbs of pull force, a fraction of the force required by actual pull-test specs.

Re: How does your team crimp terminals?
 

Many people seem to use uninsulated crimps. Where do you get these? We get insulated crimps, remove the insulation, crimp, solder, and heatshrink. They hold quite well.

-Mihir Iyer

Re: How does your team crimp terminals?
 

I am always seriously surprised to hear people recommend ratcheting crimpers. In my experience, ratcheting crimpers that are under $200 seem to not work properly. Two of our mentors are master electricians with 50+ years experience combined in the field, both prefer manual crimpers (found in the electrical section of home depot, etc.) These work much better and allow the kids to crimp the heck out of any connector. Its virtually impossible to over-crimp an insulated connector with a hand tool...

Soldering has the tendency to increase more than crimps do (done properly, it will be minimal however) ever notice we don't solder battery lugs on?

Re: How does your team crimp terminals?
 

McMaster has them. Although I have used this method in the past, with great success, it is a lot of work for little or no benefit over a good crimp connection.

Can you cite a specific example or experience where a ratcheting crimping tool that was properly adjusted failed to work when used properly?

It's nice that two people prefer manual crimping tools, but that is a far cry from any substantiated evidence. Manual crimping tools DO NOT provide ANY consistency across multiple users. Some students can squeeze hard enough for manual crimping tools to work, but ratcheting crimping tools ensure consistent crimps and alert weaker students (no, not everyone is created equal) that they need to find someone to finish the crimp for them.

They do have to be adjusted properly to work properly. Though getting upset that they don't work when they haven't been adjusted is like getting angry when parts come out wrong on a mill that hasn't been indicated. I have a $12 ratcheting crimping tool that I bought at Harbor Freight that have served me well.

Re: How does your team crimp terminals?
 

It should be stated here that ratcheting crimpers are designed for the terminals to be inserted in one direction only. Generally for right handed operators. The dual crimp shown above, is intended to crimp the terminal in the two places of different diameter on the insulated terminals. Those of us that are left-handed must cope with the crimper. Since they are ratcheting, all operators will crimp exactly the same way. With manual crimpers that is simply not possible. Experienced electricians using the tool everyday know the difference. Students who only use the tool for a few weeks in the spring won't remember the "feel" from year to year.

Re: How does your team crimp terminals?
 

A good connection starts with the right tools for the job, some samples lugs connected for the kids to compare( lug fixture), and a testing procedure for the kids to follow.

• Wire strippers sized accordingly
• Wire cutters
• The correct crimper for the lug
• The right gauge wire selected for the job (Zip wire) ( standard servo wire with the right pins and hoods)
• Heat gun
• heat shrink tube
• holding vise
• Magnifier lens
• conductivity testing tools( multi tester or cable tester)
• The right solider gun for the wire being used
• flux

Try to standardize your lugs and cables. Try to use the same lugs for motor controllers. Motors that you may use over and over or need to replace quickly it would be good to use a XT-60 or Dean's type connectors which allows you to unplug the motor quickly.

Use good pliable wire for the motors at the correct gauge for the draw.

Lastly the idea of cable strain relief is important. Making a solid connection is wasted if the cable doesn't have the proper strain relief.

Re: How does your team crimp terminals?
 

I'm the mechanical mentor on the team that the original poster is the electrical mentor on....

I think we mostly have problems, because we have several different students working on the wiring, and some of them know about how to strip the wire to the proper length, how to find the correct terminal for the application (wire size, ring size, etc), and how to properly crimp. But not all of the students know this stuff, and we mentors don't always catch it when mistakes are made.

All this talk of adjusting ratcheting crimp tools properly makes me think this discussion has gone way over our heads here in southeast Arizona :rolleyes:

btw I have a good crimp tool, and I don't have any trouble with using it to crimp insulated terminals on wires on cars and stuff at home...but building robots with students is a whole different challenge!

Re: How does your team crimp terminals?
 

A ratcheting crimping tool is a great solution to (part of) the problem you mention. It will help ensure that all of the crimp connections are done with the same force.

Getting students to match yellow crimp fittings with the yellow dot on the crimping tool is a whole different ball of wax though :D

Re: How does your team crimp terminals?
 

We do it like this.

As others have pointed out, a good crimp leaves no air around the strands. And it must be extremely difficult to pull out. Crimping pre-insulated terminals correctly is not an easily repeatable process -- that is why my employer does not permit that practice in our factories. Non-insulated terminals, like the ones pictured in my link above, work much better and give good results with the right tool. The one I pictured can be made to work well with practice, and is relatively inexpensive; however, if your budget allows then I highly recommend a ratcheting type crimper like the ones that previous posters have mentioned.

Re: How does your team crimp terminals?
 

The problem we have, is getting students to let someone know that we ran out of blue or red terminals with the specific ring size that they need for what they're working on at the time. They will use yellow terminals on #18 wire, etc. It's fun.

Re: How does your team crimp terminals?
 

When crimping, you want to end up with a connection that won't come apart, and a big mass of metal that has no air in it. Whether this is done with a really good crimper, or by soldering, it will be OK. A good crimp can't be pulled apart by hand.

The idea behind the no air spaces is the same reason why a cold solder joint isn't good. You want the solder to melt and to go into all the little cracks and form the mass of metal that will conduct electricity just like you want all the strands to be pushed together really well.

Re: How does your team crimp terminals?
 

Re-quoted for truth.

But, the OP was asking about doing some training for the electrical team, and this is the direction to go...especially in light of your comments about differring levels of expertise.

A pliers-like crimper (like what Richard Wallace linked to) can delver excellent crimps in experienced hands, which I think is what hobbes20xxxx is alluding to. But as James CH95 notes, our students are often not "experienced". Or as strong as a guy who twists 400 wire nuts a day. So, ratcheting crimpers offer greate consistency and repeatability.

Soldering is extra insurance, but if you allow solder to wick into the strands (under the insulation), you have what is essentially a solid wire...and we all know how those hate stress and straing, tending to break. So, unless it's soldered properly (neither too much nor too little) it is less reliable to also solder. Sometimes even I will over-solder a connection, but I can catch my error.

So, what are the other points improtant to cover with your students? (One related pair of points is "Bad crimps lose matches" and "only people who are trained are allowed to crimp".)

Re: How does your team crimp terminals?
 

I know I'm repeating things, but there is no excuse for a bad crimper. Wiring problems can cost matches(not cheap at all). In previous years our wiring was atrocious and we got a LOT better this year. I believe we got this crimper but a cheaper one should be fine.

One thing that I didn't see other people mention is wire strippers. I'm not sure which one of these we got, but either should be good depending on what features you want and how much you want to pay:

www.mcmaster.com/7221K61
www.mcmaster.com/7221K24

It really helps speed up electrical and helps get more consistency. Honestly for the price of electrical failures(assuming 16 matches if you make it to finals, that $300 a match) I'm not willing to skimp on electrical equipment.

We also have our crimps in an organized box and wire on labeled rolls. I make sure students know what size wire they are using for what(drive is usually a bit bigger than everything else, we use larger wire if we have extra weight that year). Our crimper has the size of wire/crimp slots labeled and the crimps fit snugly into their slots. This has prevented most of the issues we have had in previous years.

Re: How does your team crimp terminals?
 

Wow,
I see my request got a nice diversity of excellent responses.

Like I said, I've done crimping before, mostly with push-in connector pins and coaxial connectors where using a ratcheting crimper tool ($200 and up) is mandatory. I didn't realize how inexpensive good ratcheting crimpers for insulated/non-insulated terminal are. For now I think we can make do with the heavy duty manual crimpers we have. I'll put a ratcheting tool on the future wish list however.
I was unaware that I've been putting my terminals in the tool upside-down as some of you have pointed out. I always thought that having that "valley" at the seam was a good thing. Never to old to learn huh?
I now realize that I'm going to need to spend some time sharing what I've learned here and have a "learn to crimp correctly" session as part of the training for the students.
I have mixed feeling about the need to solder the newly crimped terminals. While I enjoy soldering things together I'm not convinced soldering is required in this application. If I worked for NASA I'd probably feel differently.

Thanks to everybody who contributed to my request for information.
Dave