Battery Smoke

[Mike Hendricks]

Originally Posted by Adam Shapiro

More recently I have seen teams that build extensions to the tether/programming ports for easy access, while setting the RC a bit further back for protection. I think this is an excellent idea, however make sure you keep the indicator LEDs visible at all times, and make sure it isn't too hard to get to the RC to make changes or to secure wires (which should be done frequently since they have a habit of coming loose). It's very easy to overlook your controller as a point of failure, but it hurts a lot if that's what ends up breaking on the field.

A slightly late reply, but I'm going to do it anyways.

We've put extensions on our tether and program ports in previous years, but the IFI people don't seem to get a kick out of it. In the 2 years we went to the Championship (2004 and 2005), the IFI people strongly advised against doing this, as it can cause interference with the radio.

Just to add to what Adam said, at our second regional this year (San Diego), one of the teams in our alliance had a poorly covered controller. A bad tangle with another robot, caused the opposing robot's arm (or appendage, or something) to grab all 8 (or so) PWM cables and bend every single pin that they were using on the PWM side of the controller. They carefully bent the pins back, and by some miracle, didn't break any. But, everyone should know that the controller is the single most expensive part possible on the robot, so treat it accordingly.

[beemusicgeek]

in pre season this year a few of us stupid people in the team decided to stick a threaded metal rod on the two terminals of the batery. The next day it led to a short that melted the battery, the wires, when it cooled, were then stuck inside of the casing.

[Adam Shapiro]

Originally Posted by beemusicgeek

in pre season this year a few of us stupid people in the team decided to stick a threaded metal rod on the two terminals of the batery. The next day it led to a short that melted the battery, the wires, when it cooled, were then stuck inside of the casing.

You have to be extremely careful when dealing with components like this. We tend to take these things for granted but these batteries are nothing to shake a stick at. They are capable of extremely serious current output and can be very dangerous to yourself and everyone else. A good rule of thumb is to treat the battery as if it could attack at any moment: don't make any sudden movements, and certainly don't encourage it (like prodding it with a threaded rod for instance )!

[RyanN]

Originally Posted by Al Skierkiewicz

While we are on the topic...
A good way to insure the connection of the terminals to the battery post is the use of star washers. By placing a star washer (internal or external star lockwasher) between the battery terminal and wire terminal, you will prevent the terminals from rotating around the provided bolt. An additional lockwasher under the nut will prevent the hardware from loosening as well. Any time the terminals rotate, you have the ability for the hardware to loosen and the resistance of the connection to climb. In addition, the lockwashers will pierce any surface contamination on the terminals giving you a lower resistance connection.

We use a bolt with nylon lock nuts to secure our terminals to the battery. I torque these bolts down as tight as I can (unlike what you do with automotive batteries). We have not had a single problem with the bolts coming loose or with the terminals rotating. I always use new terminals when I am preparing a battery, so I know I am getting a good low resistance connection to the battery. I am also very peculiar with how students carry batteries and I have seen engineers on our team who also carry the batteries incorrectly by the cables. This year I wrote a message on all of our batteries on the proper way to carry them.

On another subject. In Atlanta our robot developed a problem with our gear tooth sensors grounding to the frame causing us to look through the robot to pass inspection. It took me about 5 minutes to figure out, but what I want to know is why the screw holes on the gear tooth sensors are grounded? We have about a 1" nylon spacer to extend our gear tooth sensors out to the gear teeth, but the bolts that hold them to the robot go through the nylon spacers and then bolt directly into the frame, which caused it to be grounded. I don't believe it was like this at Lone Star or at the Bayou regionals.

[Al Skierkiewicz]

Originally Posted by RyanN

We use a bolt with nylon lock nuts to secure our terminals to the battery. This year I wrote a message on all of our batteries on the proper way to carry them.

It took me about 5 minutes to figure out, but what I want to know is why the screw holes on the gear tooth sensors are grounded?

Ryan,
Your method is one of the better ones I have seen. Unfortunaltely, the softer metals that make up the battery terminals and the copper wire terminals will deform with time under that kind of stress. So check them on a regular basis just to be sure.
The gear tooth sensors are infamous for causing the kind of circuit to frame short you describe. Many designers use this method of grounded mounting holes to help reduce noise and insure that part of the circuit is at the same potential as the frame. In our competition, FIRST has made a decision that the frame of robots remain neutral. I agree with this decision simply based on the electrical designs I have seen over the years. As this thread has pointed out, the battery is capable of significant (welding) currents. As such, I would not want a robot to be electrically destroyed by the failure of another team to insulate sensors or custom circuits. There are nylon shoulder washers used to insulate power transistors that can be effectively used to insulate the sensor packages from robot frame.

[Jeff Pahl]

Originally Posted by Al Skierkiewicz

I think it is appropriate to discuss this now so teams know for next year. There were three battery incidents in Atlanta that I know of. Team A & Team B both designed battery trays such that the battery mounts on it's side. In both cases, a battery was inserted into the robot with the terminals down against the the frame. The result was that the frame (aided by the battery weight) pierced through the insulation (yes both terminals on both batteries were insulated) and the frame provide a nice low resistance short to the battery. Team A's battery swelled in all directions and distorted the case while providing significant heat. (It was a practice battery) Team B's battery provided so much heat that the positive battery terminal (which is soldered inside the case) detached from the internal terminals and pulled out of the battery. Both teams had designed the tray so that a battery when mounted with the terminals up had no problems. Just a simple mistake in the heat of battle.
Team C was having some trouble with one of the battery connectors and decided to bend the terminals inside the Anderson connector to make things easier. (don't do this at home) In the process, one (or both) of the terminals was released and backed out of the block producing a high resistance connection. Eventually it appeared that terminal pulled back far enough that it contaced the opposite terminal and shorted the battery.
Pictures will be added when they become available.

Here (finally) are the pictures of Team B's battery and Team C's connector to go with Al's description above:

The right Anderson connector was disected to determine the cause of the connectors being welded together. The terminals had backed far enough out of one of the connectors after being bent to only form a high resistance connection. The team became involved in a pushing match, which resulted in a lot of smoke and the connector becoming welded together.

[Qbranch]

FYI: Don't pull a me. NEVER use a bare aluminum bar and two threaded rods to hold a battery down... *holds up my scarred up hand* kinda burns....

How was I supposed to know the a brand new driver was going to rear end another robot?

What? Not safe? Yeah thats why I wear mechanix gloves around robots now...

-q

[lukevanoort]

Originally Posted by Qbranch

FYI: Don't pull a me. NEVER use an aluminum bar and two threaded rods to hold a battery down... *holds up my scarred up hand* kinda burns....

I wouldn't go so far as to say never do it, just be careful about it. (ie make sure everything is insulated properly) In the last three years we've used perforated steel angle and 1/4-20 threaded rod twice ('05, '07), and an aluminum plate with 1/4-20 threaded rod once ('06) and have yet to have a problem. Wingnuts on the threaded rod makes it nice and easy to change batteries too, while still keeping the battery secure. (Although I imagine something like a cotter pin or a latch would be faster)

[Rapt0r9]

I worked at a gas station for about two years. During that time I have replaced many car batteries. The one thing that I remember my boss telling me is to always connect the positive line first. He said is was because the line would spark is the ground was connected first and sometimes fumes accumulate around the battery which will ignite. I have never tested this theory but it hasn't failed me yet.

As far as robot batteries, we always mount our battery upright and have the lugs away from any potential shorts. Our electrical team was quite new this year and I had repeatedly found some of the freshmen shorting batteries together. They said that they were trying to "weld the metal together". Even worse was finding breaker pannels with battery wires connected WITHOUT CRIMPS. The copper wire was just mashed on the terminal and a nut was tightened down on top of it. That is why they never got to wire much of the electrical on the robot.

Actually, our team has a funny story involving batteries. My freshman year, one of the guys on electrical took a wrench and shorted the two anderson connectors with it. Needless to say he dropped the wrench immediately and has been somewhat named sparky.

[Gabe]

How to avoid battery accidents:

1. Insulate all battery terminals.
2. Insulate your tools. A good idea I just had is to use insulating shrink tubing on the shanks of all of your screwdrivers, or any other tool with a long conductive shank. I think of this because I remembered and incident where the terminal clips where being tightened with a long screwdriver (for more torque) and crossed the positive and negative terinals.

[Al Skierkiewicz]

Originally Posted by Rapt0r9

I worked at a gas station for about two years. During that time I have replaced many car batteries. The one thing that I remember my boss telling me is to always connect the positive line first. He said is was because the line would spark is the ground was connected first and sometimes fumes accumulate around the battery which will ignite. I have never tested this theory but it hasn't failed me yet.

This is common practice but why would you want to connect both at the same time? There is no big reason to connect the positive lead first. If there is going to be any sparks, either lead will produce them. It might occur if a high current load were still energized, i.e. the lights. During that small period of time when you are placing the connector on the battery terminal, some sparking might occur. During charging, lead acid batteries do produce hydrogen. In most modern batteries in good condition, the hydrogen is contained in the battery, our sealed batteries especially. If you are placing a new, off the shelf battery in the car, it is unlikely there will be enough gas to cause an explosion. In any battery with a crack in the case or defective vents or the fill tubes open, there might be some hydrogen present. As you know from chemistry class and the Hindenburg, hydrogen is a volatile gas.

[Alan Anderson]

Originally Posted by Rapt0r9

I worked at a gas station for about two years. During that time I have replaced many car batteries. The one thing that I remember my boss telling me is to always connect the positive line first. He said is was because the line would spark is the ground was connected first and sometimes fumes accumulate around the battery which will ignite. I have never tested this theory but it hasn't failed me yet.

As Al points out, if there's going to be a spark, whichever lead is connected last will do it. It sounds like your boss was telling you part of the proper procedure for connecting jumper cables. (The important point when jump-starting a car is that the final connection should be made to a spot on the frame of the vehicle rather than to the battery terminal itself, and it should also be the first connection removed after the car is started. That way the expected spark won't be near any gases produced by the battery.)