1726 Electric Problem

[ay2b]

I don't know if any of this will help, but:

1717 had what I think is a similar problem - they would be driving and then all four of their drive motors would blink out simultaneously. I believe they eventually fixed the problem, but I don't remember the solution. They were also noticing a difference between on tether with the OI running off AC power, on tether with the OI running of the robot's battery power, and on radio with the OI running off the competition port power.

980 was also having electrical problems - we'd be driving along and then the RC would just reboot (sometimes several times in a second) or randomly turn off relays. (This reeked enough havoc to our auton mode, that the ref gave us a warning and we decided not to run autonomous until we'd fixed the problem.) We discovered that the red wire to the Anderson connector on the robot was very warm, so we think we were getting an intermittent connection there. We also discovered that the ground wire to the backup battery was loose within the plastic housing (although the "bad backup battery" light never came on). We replaced the Anderson connector on the robot, fixed the loose backup battery ground wire, re-downloaded the master code to the RC, added some printf() statements to the user code, and the problem seemed to go away.

[Al Skierkiewicz]

Jim,
I hate to say it but... This is a great photo of the damage done by loose wires and high current. Note the melted copper on one or two of the strands. This is why I recommend folding over the #6 before insertion (see my earlier post). It then fills the hole in the block and makes the screw a more effective clamp.
Jim, may I use this photo in my electrical presentation for the Championship?

[MrForbes]

Yes, you're certainly welcome to use the picture! We'll discuss putting in a longer wire with the end folded over, I just forgot to reread this thread last night...oops!

I would take a bigger close up picture of the wire, but it's pretty well mangled after being in my pocket all day and showing it off to people here

Also, the screw was discolored from the heat, we swapped it with an undamaged one.

[DonRotolo]

Think about the heat required to melt copper - those 'pearls' on the end of some strands were formed by heat.

That heat came not form contact resistance, but from arcing. An arc is electricity forming a plasma, reaching temperatures of several thousand degrees (often around 10k) in a split second. This is how many home fires start, because the plasma is not a dead short (which would trip a breaker) but a 'high resistance short' usually permitting around 15-18 Amps at 12 VDC. For homes, you can now buy an "arc-fault' circuit breaker, which detects the characteristic high-frequencies of an arc and cuts the power.

Glad the robot didn't catch fire.

Don

[RyanN]

I must agree with Al on this... it's a great photo of what can happen with a bad connection. Although I've never had an issue with it, I will tell our electrical team to fold over the wire upon pushing it into the maxi-fuse block. I've done this before with other connections, but I've always considered it trashy to do this, so I've never done this with our 6AWG wire. I've done it before with the small muffin fan wires to the little red ring connectors when they were just too big, then they kept on pulling out, so I soldered the wires one, and haven't had too much trouble since then. I'm not at all surprised that the copper melted with so much of a load at such a weak point. I'm sorry this happened to you, but take it as a learning experience that I'm sure you'll never forget, and will make sure that next year this will not happen.

For preventative maintenance, at the beginning of any regional/championship, and before the finals, I reinspect my electrical and make sure everything is all tight, nothing is chaffed, and that nothing in my control will go wrong.

Some preventative measures I have taken with our robot:
All PWM cables are held in with a small dab of hot glue. Hot glue works well for this, and easily comes off if I want it to. All the PWM wires that go to the controller are also hot glued in place.

Solder fan wires, and solder in the 40AMP ring connectors to the wire. (Unfortunately I didn't do this this year, but I still may, but it will have to be with lead free solder. I have never soldered with lead free solder before, so hopefully it won't be a bad experience)

Label EVERYTHING!!! It makes fixing something so much easier. Every victor, spike, circuit breaker, pwm cable, etc... is labeled.




Al, this is a question for you... I placed a label on top of our circuit breakers since the BUSS fuse block is hard to label. I did put a label on the long ways that says that all circuit breakers are 20AMP's... will an inspector ask me to verify that all breakers are 20AMP's? Should I put some temporary circuit breakers in for inspection? Is this fine? I don't remember anything in the rules about being able to read all the circuit breakers. <R50> states that "Circuit breakers must be accessible for inspection at each FIRST Robotics Competition
event." The breakers are accessible by opening our hood, and an inspector can easily see that these are the snap action breakers by the shape and the colors of the legs of the breakers. Will they take my word that they are all 20AMP, not that they all are required to be 20AMP, just the RC, and 3 spikes. Since you're an inspector, I wanted your input on this.

[Alan Anderson]

Originally Posted by RyanN

Al, this is a question for you... I placed a label on top of our circuit breakers since the BUSS fuse block is hard to label.

I'm not Al, and I don't play him on TV, but I'm going to chime in here and say that labeling the breakers doesn't seem very helpful to me. It's the position on the breaker panel that determines what device gets the power, and any given breaker is easily moved from one slot to another regardless of how it's labeled. If you pull two breakers, the labels don't help you put them back in the same place they came from, and you can thus lose track of which breaker slot is associated with what circuit.

I updated our electrical tracking spreadsheet this year to produce a worksheet full of wire and component labels that we printed on sticker paper and cut out. One part of the sheet is sized to fit in the recessed line between the rows of breakers, and it labels each of the twelve breaker slots. One slot's label is 0.6" wide and 0.25" high, enough for a short line of easily-read text or two lines of tiny but still readable letters.

[RyanN]

I see your point... I think I will make a spreadsheet with all the breakers and label them by using the spreadsheet. I was anticipating that we would not need to take more than one breaker out at a time, but it could happen, and I do see where an inspector may ask about the breakers. Hopefully the electrical tape used to keep the labels on didn't break down and become gooey.

[Al Skierkiewicz]

Ryan,
A good inspector needs to follow a certain size breaker to a certain size wire. 20 amps can be 18 AWG and so on for the larger breakers. So the answer is yes, they need to see the rating on the top. We mark everything with a 3M EIA (10 color smae as resistor color codes) marking tape. It comes in a convenient size dispenser with tape that is only 3/16 wide. It is a little pricey at $30 but worth every penny when looking for a problem.
The position on the breaker panel is marked with a color relating to a particular load. The breaker has the same color as does the wire(s) leading to the Victor or Spike and so also the wire leading from the Victor or Spike to the load. We also mark the Victor fan or the top of the Spike and the device it is controlling. Finally, we mark the RC output and the PWM cable with the same color. That way if the RED motor is not running we look to see if the RED fan on a Victor is not turning, then we look to see if the red breaker is in place at the RED position on the breaker panel. If The RED Victor fan is turning we then check to see if the RED PWM is inserted at both ends. All of this can be accomplished without referrring to documentation. Even the chassis is marked for our drive motors and steering motors. Likewise the pneumatic cylinders and the valves. We can even figure out problems on past robots without docs. Thanks to a former Motorola engineer who I shared electrical with many years ago, Steve Tine, we have been using his idea ever since.

BTW, we also produce a spreadsheet (in color) that lists all of this info for all devices including sensors, motors and valves so that software, hardware and electrical sub teams are all "on the same page".

[SteveJanesch]

Going a little off-topic, here....

At my insistence this year, 1533 copied Al's method of marking devices, wire ends, and PWM cable ends with color-coded tape. I cheaped-out and found a set of small rolls with five colors (plus we had black) at the local Home Depot, but that gave enough color combinations to give everything unique markings. This really saved us when we had to strip the robot down to the chassis and wheels on Thursday at Peachtree to rebuild the transmissions (which we'll have to do again at Champs, darn it). Everything went back together smoothly, quickly and properly.

Thanks, Al. Thank you, thank you, thank you.

One thing where we may have differed was combine colors for similar functions. We have two CIMs in AM Supershifters on each side. The right side motors are blue and white, the left side are red and yellow (single colors), and their Victors are each marked with a single color. The PWM cables and shaft encoders are then colored blue+white and red+yellow for the two sides, and the shifter servo cables are similar. When the shifter cables are connected together in a Y-cable, the single end becomes blue+white+yellow+red.

- Steve (thanks again, Al)

[Al Skierkiewicz]

Originally Posted by stj_1533

Thanks, Al. Thank you, thank you, thank you.

- Steve (thanks again, Al)

Anytime, glad it helped.