Re: Problem with Jags stopping unexpectedly
 

I'm of the strong opinion that unless you're using CAN, the answer to virtually every "problem with Jaguars" thread should simply be: "Don't use Jags".

They're so much more trouble than their worth, and unless you're using CAN, they provide virtually zero benefit over Talons or Victors (and they take up more space and fail FAR more often).

Re: Problem with Jags stopping unexpectedly
 

I don't know if that's fair. I'm not saying that isn't correct, but I don't think it's necessarily "fair". The Jag wasn't specifically designed for FIRST applications, it was designed for broad use/appeal (but I'd assume its 90% use-case has been in FIRST Robotics).

We've had about even odds that a Victor or Jag would fail on us in a given situation (though to be fair the Victors were twice as old), but pretty much all of them were our fault (metal shavings in the device, reverse-driving the controller, etc.). We've only used Talons one season, and we had a bunch of Jags leftover from previous seasons so we used those this year. That's where we ran into the "not specifically designed for FIRST applications" wall.

But the Jag has some very useful features, the primary one we use is the built-in limit switch connectors. Ramping is another very nice feature I wish other speed controllers had. CAN is another one, I guess, but we've not gone a full season without having CAN issues appear in FRC so I've not allowed my team to use CAN yet. Keeping my fingers crossed for the roboRIO.

The design of the Jag seems more geared towards hobbyists or those who would write their own firmware for the device. It doesn't seem like it was really meant specifically for FIRST.

-Danny

Re: Problem with Jags stopping unexpectedly
 

Greetings,

I just wanted to give the group an update on our findings. During QCR, we replaced the jags with talons. This solved the problem with the controllers going into a fault state. We found that the fault state the jags were going into was a low voltage state. This worried me more than an over-current, honestly.

During our matches in QCR, we noticed we were draining batteries VERY quickly. At first, I thought it was normal since it is common knowledge that mecanum drives take a lot of juice when strafing. In some of the later matches, we were barely functional during the last 20 seconds of a match. We got a warning from the FTA that our measured voltage was dropping to 7 volts at the beginning of the match. This sent up red flags to the team.

At the end of QCR, we sat down and came up with some possible causes of our voltage issues:
1. inefficiency of our octocanum drive train.
2. An main power line (6 gauge wire) that was too long for the application and was spliced/soldered together. We built a new main trunk with main breaker that would be a straight swap once we got to worlds.

At Worlds, we cleaned up the slop in the drive train by realigning the modules and lubing everything. No noticeable effect. The main trunk was swapped out after our first match Thursday. The total length of the trunk was over three feet. Once it was replaced, the voltage issues disappeared and the robot drove very well for the rest of the event.


TL;DR: Keep your 6 gauge wire runs as short as possible. Create your own anderson connections if needed to keep from splicing the main line together.

Re: Problem with Jags stopping unexpectedly
 

I'm curious - was the wire or your wire splices getting hot? I'd expect it to if you were losing that much power to a resistance or partially open circuit.

Re: Problem with Jags stopping unexpectedly
 

Yes, wires were getting noticeably warmer.

Re: Problem with Jags stopping unexpectedly
 

It seems to me that you were having issues not related to the length of the wire, but likely the quality of the splicing.

When splicing wire, I generally tend to never allow soldering wire gauges larger than 16. The reason is that with large wire gauges you effectively have two large heat-sinks drawing the heat away from the connection, and it's incredibly easy to end up with a cold-solder joint. In those situations, the joint (and subsequent wire) will be prone to internal arcing, heat buildup, and poor connectivity.

I don't think the actual length of wire had anything to do with your problem. Generally speaking, #12 wire has 4 times the resistance of #6 wire. As a general rule of thumb, if your battery and your motors are in fixed positions but your PDB can be moved around it's always best to use more #6 wire to allow your PDB to be closer to your motors than to use more #12 wire to allow your PDB to be closer to your battery. "Big Al" has, on many occasions, talked about the per-foot resistance of #10 and #12 wire, and has proven that there are "noticeable" and "non-insignificant" voltage drops that can be avoided by using #10 wire for motors (instead of #12) and reducing the length of that #10 wire as much as possible.

Also, I generally tend to prefer crimp connections (even for lengthening wires) over soldering the wires together. For the same reason it's done in home electrical systems, crimp connections tend to be less prone to mistakes and can be done relatively quickly. If you're concerned about the crimp connection, you can very often also solder the mating location of the crimp connector to ensure it won't go anywhere.

One last piece of wisdom, I generally tend to not trust screw terminals, especially for large-gauge wire (anything larger than 20AWG). Most of the screw terminals in this class I see used in FRC are the ones used to connect the batteries to the 6AWG battery wires - they have a ring terminal on one end to connect to the battery, and a screw connector on the other to create a press-fit onto the 6AWG wire. Wire tends to "spread out" and settle, and this means your connection will eventually become loose - this creates voids between your wire and the connector causing arcing, heat buildup, and poor connectivity. When teams tell me their batteries aren't keeping a charge or are taking a long time to charge, or their wires are heating up (and obviously the robot isn't using some 6-CIM beastly transmission), I usually check the batteries and have them tighten/maintain/replace the connector to the battery and that usually solves the problem.

Be well.
-Danny

Re: Problem with Jags stopping unexpectedly
 

Guys,
The terminals that Danny describes are really meant for low strand count stranded wire or solid conductors. Thomas & Betts STC0414 4STR CU LUG terminals have a wire clamp. I prefer these or equivalent for stranded wire. It is important that you strip the wire such that at least 1/8" of wire extends beyond the clamp when you terminate the wire. If not the wire will simply be pushed out of the connector when you tighten the hardware.

Re: Problem with Jags stopping unexpectedly
 

3081 has had good success with the KOP Burndy YAZV6CTC14FX lugs, using this procedure.

1. Carefully strip the #6 wire so that the bare wire is long enough to fully fill the barrel of the lug, and leaving about 2mm of bare wire showing between the lug and the insulation. You can tell that the barrel is completely full by looking through the inspection opening of the lug. Finally, inspect the insulation you removed to ensure that you did not cut any strands of wire off of the #6 wire. If so, try again.

2. Cut a piece of larger shrink tubing to cover the barrel end of the lug plus 1/2" of the wire. Slide that on the wire.

3. Slide the wire into the barrel of the lug. Ensure that there are no stray strands outside of the barrel.

4. Crimp the wire into the lug. We use Vice Grips to do this. It usually takes three passes of crimping before the wire is physically attached to the lug. You should crimp in the long direction of the barrel, in the middle of the barrel. If you can pull the lug off of the wire at this point, it is not crimped enough. Grab another lug and try again.

5. Using a high powered soldering iron or brazing torch, heat the lug in the middle of the barrel. We use a Weller WEL8200PK gun to do this.

6. Insert solder into the inspection opening of the lug, and load the inside of the lug with solder. You can easily put 12-18" of fine solder in the barrel.

7. Allow it to cool a bit.

8. Slide the shrink tubing into place and use a heat gun to shrink it.

Re: Problem with Jags stopping unexpectedly
 

Can you give us the wattage of the "high power" soldering iron? Given what I've come across, that could mean 100W or 1kW.

Re: Problem with Jags stopping unexpectedly
 

We use the same terminal but we crimp using a vise. Place the terminal in the vise such that it is at a 45 degree angle with the corner of the jaw and crimp only half of the terminal. Turn the terminal and repeat for the other half. You are left with an "X" mark on the terminal. Do a tug test to make sure you have a good mechanical connection. Then use a 50 watt or higher iron (with a large, flat tip) with solder on the tip to heat the terminal. Using .031 solder, at least 6" of solder should be used. Be careful, if you add too much solder, it will wick under the insulation giving you a very stiff wire coming out of the terminal. If you add solder to the tip of the iron it will help conduct heat to the terminal. Finish with 3/8"-1/2" heatshrink. You can also bend the terminal to a right angle it that helps you terminate on the battery, PD or main circuit breaker.