My students had suggested to use compression lug connector with heatshrink to connect power cable at the battery poles. I saw on previous years robots that many teams were using instead a mechanical lugs ground and then isolated them with electrical tape. Are both solutions viable for the competition ?
I think it may depend on the inspector, but in previous years they’ve wanted us to cover the entire connection (with tape or whatever material). The shrink tubing only covers the wire connection point, not the lugs on the Power Distribution Board.
The only rule on those connections is R03 A, which defines what can be attached the the battery without counting towards the robot weight:
the 12V battery and its associated half of the Anderson cable quick connect/disconnect pair (including no more than 12 in. of cable per leg, the associated cable lugs, connecting bolts, and insulation) and
We can break your question into two parts:
First, what type of connector to use. Both types, if rated for the correct gauge wire and current specs, will certainly work. As an experiment, you can have your students hook them both up and look at the resistance between the wire and the terminal - any resistance there will cause a decrease (even though it’s slight) in robot performance, as that resistance is consuming some of the battery power.
Second, what type of insulation to use. Both electrical tape and heat shrink work great here, and are both sufficient for any insulation you need at terminals or between wire splices on the robot. Heat shrink tends to look a little nicer, which matters to some teams. Electrical tape is easier to remove, which is both a plus and a minus… if you think you’ll need to get at whatever it’s protecting, then it’s great. If you don’t, then having it peel off on you (for example, the end can peel up if it’s repeatedly rubbed against something) is pretty bad (as it can lead to a short), and something you might need to watch for.
Bryce, that depends on the size of your heat shrink. My team uses appropriately sized heat shrink that covers the wire and the entire terminal and associated hardware.
But you are correct - you need to have the entire connection covered. It’s a safety thing… with our robots and tools primarily being made out of conductive materials, we do not want to short the batteries and deal with the ~500A current that will result.
hey do you guys think that for the battery connector is it enough just to crimp it? we also soldered it but thats not very stable, and we’d definitely be able to pull it out if it wasnt for the electrical tape. how do we make a stable battery connection?
Well… I’ve found that if you’re going to use a crimp joint on the battery lugs, you want a vise to do the crimping if possible. The longer the handle on the vise, the better! (For the best quality of crimp, that is.)
There is also a bag of copper connections in the KOP; those can be used with the batteries. Make sure the wire is between the plates, then screw down as hard as possible.
That depends on what you mean by “Crimp”. To connect to the terminals on the battery, take your wire and do the crimping (with a crimper) to connect a ring terminal to your wire. Now, take the ring terminal and put it up against the hole on the terminal on the battery (there is a hole in it if memory serves me) and bolt it, then cover with heatshrink or electrical tape (though heatshrink is preferable)
You should only a crimped lug if you have a proper crimper for the size wire you are crimping, and they are expensive. Otherwise use the mechanical (screw) lugs. I suggest using a vice to hold the mechanical lug and a large screwdriver. Either way if you can move the wire in the lug it is not properly terminated and will cause a problem at the worst time.
Electrical tape or shrink tube is only used for insulation.
Don’t forget to put the heat shrink on the cable BEFORE you connect to the battery… Otherwise you have to disconnect the bolt then redo and shrink it :yikes:
You must use the right crimper for the crimp lug or you are risking failure.
To solder it, you need a lot more heat than it sounds like you are using. Also use rosin flux (Radio Shack sells it in atube). Soldering is a reasonable alternative to crimping, but try to avoid getting a lot of solder into the cable near the lug, because that makes the wire stiff and subject to breaking like solid wire.
The first bit, use the right crimper, NOT a vise which flattens the lug.
The second bit, there is a torque specification from the manufacturer that gives optimal performance. Cranking down as much as you can will exceed that spec. However, it would be prudent to re-torque the screw often.
That being said, do what you want. But we are trying to steer you away from known ways of creating problems for yourself.
It’s a lot faster and easier to remove the pin from the Anderson connector.
If you are set on crimping them, but do not have the money for a proper crimper, I would suggest that you contact an area electrical company to see if you could borrow theirs or have them crimp them for you.
Our team has done this in the past with much success!
I’m not a fan of using a vise either. I’ve done it, but I’ve never really liked doing it.
For reference, Home Depot has sold a crimper in the past for about $35 that works very nicely. It looks like a bolt cutter. It’s not necessarily the one that meets the spec for Anderson SB50-compatible reeled or individual connectors, but it is sized for the #6 AWG crimp lugs that FIRST has provided (it has a #3 die, as well as a couple others).
By the way, FIRST provides the wrong size of crimp lugs for the battery—theirs are for a Ø0.250 in stud, when they should probably be for a Ø0.190 in or Ø5.00 mm stud to match the battery terminals. (Ø0.250 in is correct for the Bussmann 120 A circuit breaker, and Ø6.00 mm = Ø0.236 in ≈ Ø0.250 in is correct for the power distribution block.)
Also a good idea.
JW, is there any particular method that you’ve developed to use this? I usually lever a screwdriver in and then use a second screwdriver to pop it off the spring (if you can call it a spring), and I find it an incredibly tedious and annoying process.
A medium flat screwdriver and a pair of small pliers. It’s really easy.
Just make sure that you don’t short the battery terminals by accident (e.g. with the pliers). That would end badly. (It may be a good practice to stick a battery plug in the opposite Anderson SB50 terminal, or disconnect it at the screw lug.)
Thanks everyone for all the suggestions. My team has decided to use a compression lug (bluedie374) COVERED WITH heatshrink tubing. The full pole connection will have to be isolated. Then we’ll validate the electrical resistance (should not exceed milliohms), and then we’ll do a pull strength test. The tool used for compression is taken from HomeDepot.
I’ve used this crimper with good results. The dies are not perfect and their sizes are weird and it flattens the hex a little and puts “wings” on the sides of the crimp, but it goes make a good solid connection.
Crimp, solder with a blowtorch, repeat.
A proper crimp does not need solder; indeed, the ‘right’ crimp is made worse with solder.
That being said, a ‘pretyty close’ crimp can be improved with solder.
We have used the crimping die on these pliers with great success. Two students squeeze it shut, it does take some effort.
I use a very small screwdriver or awl from the “contact” side of the connector to push/pull the spring out of the way, then pull the wire and pin out the other side. It’s easy. I even used a paper clip once.