pic: Battery connector.....

[MrBasse]

I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely.

It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for.

This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

[Nuttyman54]

Originally Posted by MrBasse

I'm suprised that nobody has said anything about the fact that a robot that can do that repeatedly is designed wrong. If you stay within the limits of your supplied hardware you wouldn't have this issue. Nowhere in the rules does it say you have to draw the amperage that you are. Would it make for a slightly les competitive machine? Maybe. Would it reduce the risk of melting connectors and destroying components? Definitely.

It just seems to me the a lower amperage rated connector is something that would result in an engineering challenge. I'm pretty sure that is what most of us are here for.

This seems comparable to someone complaining that their drill press doesn't work very well as a mill...

It's a safety issue. In ANY electrical system, you have safety measures designed to prevent this from happening. In our system, that is supposed to be the 120amp main breaker. FIRST has determined that drawing excess of 120amps continuous causes an unsafe condition and requires the robot shut down. What Andrew has shown, and has been repeated on several other robots, is that under certain circumstances the main battery connector fails before the main breaker, thus circumventing the entire safety system as it is designed.

[apalrd]

Way way way back when the Anderson SB-50 connector was selected and apparently Anderson approved the higher current rating, the kit (this is back when you could only use parts from the kit or Small Parts) contained 2 Bosch drill motors and 2 Fisher-Price motors, and an assortment of small motors. The batteries were the same as they are now, but they used a 60a main fuse instead of the 120a main breaker we now use. Shortly after, the Victor was used, then the IFI control system. Now the rules allow 18 motors of similar power to those 4 drill and FP motors, robots have nearly tripled in speed, and the games are significantly more complex.

Now, we design to the 120 amp breaker, and put a lot of effort into keeping that breaker from tripping. Sometimes we design a bit too close, and it safely trips, and we take steps to prevent it from tripping again. We know what it will take, thanks to data sheets and trip curves. We already do a lot of design based on the main breaker and 40a branch breaker trip curves. We know when they will trip, we can run simulations of accel events, travel times, and distances to optimize our gear ratio to our strategy. We know how far we want to push the main breaker and we certainly know that when we exceed it, we have to scale back a bit but the failure is safe (even if it could cost us a match). In addition, in our pursuit of perfection, we design to push the robot as hard as possible during a competition. Maybe we push too hard. Then we go and drive the competition-designed robot for hours to practice, or at fast pace off-season events, and the issues show up.

We don't have a number or 'melt curve' for the 50 amp plastic connector (and I can not design my robot to 50a instead of 120a and stay competitive) so we can't design around it. Sure, we could empirically melt a whole bunch of connectors with a several hundred amp current limited lab power supply and huge load (the only reasonably safe way to do it) to get data on connector melting vs time vs load, or we could spend $5 more and buy a properly sized connector so the engineered electrical limiting device (the breaker) trips first and safely instead of the undersized connector.

The whole point of the main breaker is to safely cut power when we exceed the electrical limits imposed by the FIRST electrical system. We shouldn't rely on a plastic connector to fail (possibly shorting and causing several hundred amps from the battery to start a fire) as an energy limit. The connector is far too small for our application (even if it was approved for the current draw way back when) and the company even makes a connector the right size for us.



It's not the robot, it's several robots over several years of practice and off-season events, designed at relatively common FRC speeds with quite efficient drivetrains. We run them (on the practice bot) for hours at a time, running roughly 50% duty cycle, but we can't upgrade the connector on the practice bot without upgrading all of the batteries (which we also need to take to competition, and plug into the comp bot).

[MrBasse]

And again, I'm not saying that you aren't doing anything that a lot of FRC teams are doing everyday. I think it is safe to say that everyone pushes the limits of the Anderson connector. However, I think what we can learn is that you have pushed it too far a few times. Either by design or by use. I'm not saying you should design for 50A, as that would take the amazing machines you make down quite a few levels. I agree that FIRST should upgrade the connector to a higher rated connector. However, I also know that they haven't. I also haven't seen hundreds of other teams reporting melted connectors. So perhaps it is something in the way you have designed/built/run your machines.

I appreciate the response and I see where you are coming from, but perhaps that should be where you go back and modify your approach a little rather than complain about the supplies you have been specified. Last year we ran our robot for hours and never melted a connector, the year before the same, the year before the same. Thousands of other teams have done the same (though maybe they are all being oddly quiet about this). It's not an attack at you, just a sign that something you are doing isn't quite jiving with the required components. The downside is that this problem creates a very unsafe condition.

[apalrd]

I'm not complaining about the part as specified, I'm complaining that we are stuck using a part that was specified 15 years ago with 1/5th the power in the kit and 1/2 the main fusing capacity.

I don't think it's an issue of FIRST actually wanting us to use the connector for engineering reasons, I think it's a case where FIRST is using the same connector they have been using because they have been using it forever and have no motivation to change. I am trying to give FIRST a good motivation to change to an appropriate connector.

Since we went up to #4 main battery cables, we haven't melted any connectors. Using #4 was our engineering change to both melted battery connectors and main breaker trips, and it generally worked.

[EricH]

Originally Posted by MrBasse

Last year we ran our robot for hours and never melted a connector, the year before the same, the year before the same. Thousands of other teams have done the same (though maybe they are all being oddly quiet about this). It's not an attack at you, just a sign that something you are doing isn't quite jiving with the required components. The downside is that this problem creates a very unsafe condition.

If I may ask: How many motors are you guys running at a time? 4 CIMs? 6? A couple of window motors? A compressor? And how long at a time? 2.5 minutes? An hour? 6 hours?

See, here's the thing. Sure, hundreds of teams may have run their robot for hours over the season last year. But there are teams who will literally stop driving around only to change or charge the battery in any given multi-hour session. These teams may have 6 CIMS, a pair of MiniCIMs and a pack of other motors of the 550 and 775 varieties, plus the compressor, active at the same time, for much if not all of that time. That's one large amount of current potentially being pulled. Now, I haven't heard of any failures locally, but that doesn't mean that it's not happening--or not at the edge of happening. (The other possible explanation is that the connectors are wearing out due to fatigue/heating of the area around them, then not seating properly and adding a spark to the mix--then they melt, then they burn.)

And I'm pretty sure the Bees tend to run on the high end of both total run time, and time in a session, as well as lots of motors, and they tend to run enclosed bots, which will get some heat build up inside. If you're running on the low end of all of those with an open bot, you probably won't see anything similar.

[sanddrag]

I'm curious about the condition of the contact itself, prior to melting. Was it significantly worn or scratched from touching wires directly to it to test motors, or clipping alligator clips to it?

[MrBasse]

Originally Posted by EricH

If I may ask: How many motors are you guys running at a time? 4 CIMs? 6? A couple of window motors? A compressor? And how long at a time? 2.5 minutes? An hour? 6 hours?

See, here's the thing. Sure, hundreds of teams may have run their robot for hours over the season last year. But there are teams who will literally stop driving around only to change or charge the battery in any given multi-hour session. These teams may have 6 CIMS, a pair of MiniCIMs and a pack of other motors of the 550 and 775 varieties, plus the compressor, active at the same time, for much if not all of that time. That's one large amount of current potentially being pulled. Now, I haven't heard of any failures locally, but that doesn't mean that it's not happening--or not at the edge of happening. (The other possible explanation is that the connectors are wearing out due to fatigue/heating of the area around them, then not seating properly and adding a spark to the mix--then they melt, then they burn.)

And I'm pretty sure the Bees tend to run on the high end of both total run time, and time in a session, as well as lots of motors, and they tend to run enclosed bots, which will get some heat build up inside. If you're running on the low end of all of those with an open bot, you probably won't see anything similar.

With a four CIM drive and a compressor and a 775 powered shooter we would run for two to three hours of practice regularly. Just as a fun question... Would you run your KOP compressor for an hour straight and expect it to maintain peak function?

[EricH]

Originally Posted by MrBasse

Would you run your KOP compressor for an hour straight and expect it to maintain peak function?

Not necessarily--it'd probably do a couple of thermal shutdowns, for one thing; for another, it isn't rated for that. If my robot were going through air that fast, though, I'd have it shut down for an hour so I could hunt down the leak in the system.

That said, if I were using a lot of air, I'd reasonably expect a pretty good amount of runtime on the compressor in that hour.

[Nirvash]

Originally Posted by MrBasse

Would you run your KOP compressor for an hour straight and expect it to maintain peak function?

If by KOP you mean the VIAir, with proper cooling? Maybe. The older Thomas? With cooling, yes.

[cglrcng]

I did see that exact type of thing happen on our robot last year except not quite that far as they shut it off at the breaker. When the drive team came back from an early AM qualifying round, the student w/ the battery in his hands complained that I gave them a dead battery..."No way, no how" I said...as I checked it w/ a multi-meter myself I said just before handing it to him before the round.

I immed. began to inspect the battery Anderson clip Battery half (since it actually burned my hand during the semi-disgusted hand off) - and I saw melting of the clip & cables, and it was still very hot to the touch, so I took it apart and looked at the ends inside the clip...They were a bright orange copper color instead of alum. color.

I abruptly said...You do not have a battery problem folks..."You have a frame grounding problem," and pulled out the multi-meter from atop the battery cart and we began looking for the problem immediately. Sure enough, a frame grounding problem was immediately noted by a simple OHM check. That frame was grounded.

The hunt began....Sure enough, it took a while, but we found that (2 of the students had removed and reinstalled the CRIO the night before just before pit closing), and there was a nice short bright & shiny chromed Phillips Head screw near the bottom on the outside of the CRIO that was touching the lower chassis frame rail, that wasn't doing so the day before, (the CRIO's all come w/ that very unnecessary grounding screw), but, the CRIO is not supposed to be grounded to the frame in that manner at all. Same issue also cropped up w/ a grounded camera a few years back at champs that took a while to find.

Once that grounding issue to frame was cleared up...I have never seen that Anderson connector problem again. A simple ohm (00.00 meter read), check from battery to frame should tell you that you may just have the same exact problem I personally think.

I do know if they had not shut that robot power main breaker off very quickly, it could have been as bad as your pic or much, much worse. It did melt the outside insulation of the cables together right above the Anderson connector for about 2 inches (that was correctable as they pulled right apart and were still insulated properly, but those cable ends were junk), and melted slightly the connector itself...It was quite hot! That was very apparent.

Post back if you find it was a frame grounding issue please.

[Nirvash]

Originally Posted by cglrcng

I did see that exact type of thing happen on our robot last year except not quite that far as they shut it off at the breaker. When the drive team came back from an early AM qualifying round, the student w/ the battery in his hands complained that I gave them a dead battery..."No way, no how" I said...as I checked it w/ a multi-meter myself I said just before handing it to him before the round.

I immed. began to inspect the battery Anderson clip Battery half (since it actually burned my hand during the semi-disgusted hand off) - and I saw melting of the clip & cables, and it was still very hot to the touch, so I took it apart and looked at the ends inside the clip...They were a bright orange copper color instead of alum. color.

I abruptly said...You do not have a battery problem folks..."You have a frame grounding problem," and pulled out the multi-meter from atop the battery cart and we began looking for the problem immediately. Sure enough, a frame grounding problem was immediately noted by a simple OHM check. That frame was grounded.

The hunt began....Sure enough, it took a while, but we found that (2 of the students had removed and reinstalled the CRIO the night before just before pit closing), and there was a nice short bright & shiny chromed Phillips Head screw near the bottom on the outside of the CRIO that was touching the lower chassis frame rail, that wasn't doing so the day before, (the CRIO's all come w/ that very unnecessary grounding screw), but, the CRIO is not supposed to be grounded to the frame in that manner at all. Same issue also cropped up w/ a grounded camera a few years back at champs that took a while to find.

Once that grounding issue to frame was cleared up...I have never seen that Anderson connector problem again. A simple ohm (00.00 meter read), check from battery to frame should tell you that you may just have the same exact problem I personally think.

I do know if they had not shut that robot power main breaker off very quickly, it could have been as bad as your pic or much, much worse. It did melt the outside insulation of the cables together right above the Anderson connector for about 2 inches (that was correctable as they pulled right apart and were still insulated properly, but those cable ends were junk), and melted slightly the connector itself...It was quite hot! That was very apparent.

Post back if you find it was a frame grounding issue please.

I don't see how a Crio grounding issue could contribute that much to the failure of the main battery connector, the wires connecting it to the PDB would take serious damage if they passed that much current.
Also if a grounded frame was passing current, you have the even bigger issue of a positive line shorting to the frame as well.

[BBray_T1296]

Originally Posted by Nirvash

Also if a grounded frame was passing current, you have the even bigger issue of a positive line shorting to the frame as well.

The same amount of current leaves (red) the battery as enters (black). Either could have melted, the red just gave first

[Nirvash]

Originally Posted by BBray_T1296

The same amount of current leaves (red) the battery as enters (black). Either could have melted, the red just gave first

What I mean is, if your frame is 'grounded', it has the same potential of the negative terminal on the battery. No current should flow across it unless something with a positive potential is also shorted to the frame.

[Michael Hill]

Originally Posted by Nirvash

What I mean is, if your frame is 'grounded', it has the same potential of the negative terminal on the battery. No current should flow across it unless something with a positive potential is also shorted to the frame.

Agreed. Just because your chassis is grounded doesn't mean you're going to have battery melting problems. Heck, the chassis of most cars and airplanes are grounded and those batteries don't melt....well not usually (I'm looking at you lithium-ion...)