Can someone post this on FIRST q/a

[Venkatesh]

Could someone post a question related to my method on FIRST's Q&A? I won't have the ability to post that question for some time.

[Al Skierkiewicz]

Originally Posted by Aidan F. Browne

Al --

Please read the whole rule. The intent is that the connector provided in the kit is the connector that must be used. This is not an error.

"<R20> The 12v battery must be wired directly to a quick connect / disconnect connector (provided in the kit)"

Aidan,
I must disagree. The wording is not very clear but implying that the word "a" is meant to identify one half of a connector is a stretch. The phrase in parenthesis implies a suitable connector is included other wise it would read without parents. Although the wording of this rule has changed from last year, it's implication for veteran teams is that equivalent or better substitutes are allowable. I know that I read in the Q&A recently, a similar question was answered that FIRST recommended using the supplied connector and if a team used something different they risked incompatability with other teams should the need to share batteries arise. That question appears to have been removed from the Q&A as I was not able to find it this afternoon. Realistically, today's answer seems oddly worded in that the question seemed related to the connectors popping apart not replacing a kit part with something better.
I agree and it has been my stated opinion that the Anderson Power Products connectors work fine for most teams. There are teams that draw excessive amounts of current during match play that would result in heating, and fire using the 50 amp connector. A rule of thumb is any team that uses most or all of the motors including both drills combined with both Chips and/or both FP's will draw more current than the supplied connector can handle. You and I both know that the stall current on any one of these motors is over 100 amps.

[Biff]

Originally Posted by Al Skierkiewicz

Aidan,
I must disagree. The wording is not very clear but implying that the word "a" is meant to identify one half of a connector is a stretch. The phrase in parenthesis implies a suitable connector is included other wise it would read without parents. Although the wording of this rule has changed from last year, it's implication for veteran teams is that equivalent or better substitutes are allowable. I know that I read in the Q&A recently, a similar question was answered that FIRST recommended using the supplied connector and if a team used something different they risked incompatability with other teams should the need to share batteries arise. That question appears to have been removed from the Q&A as I was not able to find it this afternoon. Realistically, today's answer seems oddly worded in that the question seemed related to the connectors popping apart not replacing a kit part with something better.
I agree and it has been my stated opinion that the Anderson Power Products connectors work fine for most teams. There are teams that draw excessive amounts of current during match play that would result in heating, and fire using the 50 amp connector. A rule of thumb is any team that uses most or all of the motors including both drills combined with both Chips and/or both FP's will draw more current than the supplied connector can handle. You and I both know that the stall current on any one of these motors is over 100 amps.

This max draw is an issue, while testing on Carpet, with only the Cims installed in a full stall tank turn, (full left and right on the sticks). I mesuared 150 Amps on the negitive battery lead with a Fluke DC clamp on meter. I haven't tested with the drill motors on yet. I hope it can break traction or it will be a big rush for trick wheels.

[Aidan F. Browne]

Originally Posted by Aidan F. Browne

Al --

Please read the whole rule. The intent is that the connector provided in the kit is the connector that must be used. This is not an error.

"<R20> The 12v battery must be wired directly to a quick connect / disconnect connector (provided in the kit)"

As you can see, the rule clearly states that the connector is provided in the kit. The reason that the word "a" was used, is that there are two of the connectors provided (the entire connector is made up of two mirror-image halves).

Sorry to hear that all your previous equipment uses a different connector - but for 2004 the rule has changed.

All,

It is reasonable for you to ask for an explanation as to why you are being asked to use a 50A connector when you have experienced higher currents on your robots.

Here is the reasoning:

Anderson Power has been completely in the loop in selecting the connector for use in our application. They know what the specs are on the wires, breakers and maximum current draws. Anderson Power has determined that worst-case current draws do not exceed the true rating of the part.

Now - you ask - how can this be? Well - a commercial data sheet (in ~ 2 pages) tries to rate a part for use without knowing all of the conditions in which the part will be used. For this reason, data sheets are often very conservative. Once an actual application is studied - and all the environmental and usage characteristics are understood, parts are very commonly approved for use above their "rated" parameters. Time, frequency, temperature and other parameters all play into the "true" stress rating of a part. This is the case here.

To alleviate any of your concerns about a single SB50 connector carrying the entire current load for your robot, understand that in addition to Anderson's analysis of the situation, worst-case testing has been performed. Basically, tests have been run where a fully-charged Exide battery has been connected to the kit breaker through an SB50, and then the output leads downstream of the breaker were shorted in "crowbar" tests. The SB50 performed acceptably, was not overstressed and did not exceed its "true" ratings.

Now -- before you cry foul -- yes - there have been some part failures -- the worst known was the famed "WPI connector" from last February -- the picture of which has been widely distributed. That part was returned to Anderson and an extensive root-cause investigation was performed. It was proven that the reason that happened to that connector was that the two haves of the connector were only halfway connected and that there was only a point contact between the contacts. So - the failure was not because the part was overstressed, but that the part was not used as designed.

So - bottom line -- the Anderson connector is adequate for use on FIRST robots. There are over 25,000 successful uses of the connector in real FIRST matches. The 2004 rule is that you must use this connector. It is safe. The only concern is to make sure that you leave enough slack in your 6 AWG wire to ensure that you can properly mate the connector. It is also good practice to zip-tie the connector together each match to ensure it does not partially separate during impacts in competition (although this is not required).

Hope this helps alleviate the confusion and frustration.



Aidan

[Raul]

Aiden,

I appreciate your explanation and it makes sense. It probably will work fine in most of our applications. But why take a chance that someone may not properly engage them.

Also, we have conducted some testing (we at Motorola often do independent testing on products that we use) and have found that the voltage drop across this particular connector is significantly worse than the one we have been using in the past. We have a graph comparing connector voltage drops that was done a while back. We will try to dig it up and post it here.

We are not trying to gain any advantage by using a different connector; in fact the ones we have been using weigh no less. We are just trying to implement proper engineering practices. What is the big deal with not letting teams use an equivalent or better connector this year? Did someone complain about the use of different connectors? If not, why change a rule from a previous year that was not broken in anyway? I thought we wanted to simplify the rules.

Raul

[Joe Ross]

I'll be interested to see the response to this question

Section: 5.2.6 Status: Unanswered Date Posted: 2/12/2004
Q: Why are we being forced to use the Quick connector supplied in the kit that is only rated for 50A and wired to the 120A circuit? Why can't we do what we have done in all previous years and use the properly sized connector of our choice?