SLU-70 Lugs

[Joe Ross]

Originally Posted by Al Skierkiewicz

I thought it important to resurrect this thread and remind everyone that although the rules were relaxed for this last weekend (difficulty in obtaining the parts) SLU 70 connectors will be required at nationals. Home Depot, Menards, Lowes, Ace Hardware and of course Terminal Supply are all sources of this connector. Please watch for changes from FIRST, until then, Be Prepared!

Other people have mentioned that parts you get from Homedepot have a different part number and different manufacterer, but nobody has said what it is.

At my Home Depot it was a Thomas&Betts BTC0208-B2 and cost $1.71 for a pack of 2.

[Al Skierkiewicz]

Originally Posted by Rombus

Since im going to be doing wireing next build year, what about soldered lugs?

Rick,
The electrical rules have changed each year for several years now. You will need to check next year's rules in order to be in compliance for your 2006 robot.

[de_]

Could someone post a picture of one of these against a ruler. Our Canadian Home Depot does not have anything remotely near that part number but they do have lugs that might well be them.

(Just in case anyone's interested) In my experience, copper screw lugs used with large soft twisted copper wiring are very susceptible to loosening over time and or wire strands breaking, especially in high vibration & constant flexing due to repeated install/remove cycles our robots operate in. Consequently the team has to REGULARLY inspect/re-tighten them (in turn requiring the repeated removal / replacement of the insulation). Safety, reliability and simplicity is everything for “average” teams, and in my experience, a properly sized round crimp lug SOLDERED to the wire then heat shrinked requires no maintenance, has the highest strain strength, has the lowest electrical resistance (and hence lowest heating, highest peak load), has a virtually infinite life, is easier to completely insulate or better still heat shrink (including the battery post) and is materially cheaper. The soldering knowledge is easily transferred from a mentor to the student with one demonstration or a few web pictures. Personally I think these should be allowed in future competitions.

DE

[Al Skierkiewicz]

Originally Posted by de_

Could someone post a picture of one of these against a ruler. Our Canadian Home Depot does not have anything remotely near that part number but they do have lugs that might well be them. DE

It appears that different parts suppliers are used from time to time. A close inspection of the lug will show at least "SL" and "70" on the face of the mounting tab (adjacent to the bend) when you inspect the connector through the bag. They will be labeled for use with #2 through #8 wire. The collar is at least 3/4 of an inch in diameter. It was my experience when inspecting, that teams regularly left too much insulation on the wire and the connectors failed due to one of two reasons. 1. The connector was gripping some or all insulation and when the PVC was compressed enough, it allowed the wire to loosen in the connector. 2. There was not enough wire exposed. The connectors have a dimple that must depress the wire bundle to hold it in place. Without enough wire in the connector, the compression will actually force the wire out, like the cartoon banana squeezing out of the peel.

[sanddrag]

We used the lugs with #6 welding cable and had no problems at all. So, I guess they are not really that bad afterall. Certainly a lot easier than to solder on terminals. Getting heat to stay in something that large is not easy.

[eugenebrooks]

Originally Posted by sanddrag

We used the lugs with #6 welding cable and had no problems at all. So, I guess they are not really that bad afterall. Certainly a lot easier than to solder on terminals. Getting heat to stay in something that large is not easy.

We had no problems at all with our SLU-70 lugs, here is how we handled them.

* We dissasembled them and carefully cleaned them to prepare for plating.
* We soaked all of the parts for a half hour in a tin plating bath.
* We carefully stripped 6 gauge rubber insulated welding cable to a length that supported full engagement in the lug.
* We tightened the lug on the wire until it could not be made tighter.
* We then lightly clamped the wire, not the lug, in a vice in order to not bleed too much heat away from the lug when soldering.
* We soldered the wire to the lug where it was clamped, and the screw where it went into the threads.
* After cooling, we cut/ground any excess screw away to make it easier to insulate with heat shrink, removing any hazard associated with the stickout of the screw.
* We applied 7/8 inch heat shrink in the proper color.
* The lugs have a 1/4 hole, and the hole in the batteries is for a #10 screw. We backed up a aviation quality (AN) #10 bolt and nut with hardened washers, to avoid any tendency for this connection on the batteries to loosen.
* We insultated battery connections, and the bolt on the fuse box, with electrical tape.

Nope, we had no problems with the SLU-70 lugs at all!
Lots of build hours went into making them trouble free.

We would much rather have picked up a solid copper lug with the proper hole diameter for the fuse box (1/4"), or the battery (#10), crimped it on with the hex crimping tool designed for the lug, and them slid on a piece of heat shrink just a little bigger than the wire. This would have taken only a few seconds...

Hopefully, that is what we will be doing next year!

[gburlison]

Originally Posted by de_

(Just in case anyone's interested) In my experience, copper screw lugs used with large soft twisted copper wiring are very susceptible to loosening over time and or wire strands breaking, especially in high vibration & constant flexing due to repeated install/remove cycles our robots operate in. Consequently the team has to REGULARLY inspect/re-tighten them (in turn requiring the repeated removal / replacement of the insulation). Safety, reliability and simplicity is everything for “average” teams, and in my experience, a properly sized round crimp lug SOLDERED to the wire then heat shrinked requires no maintenance, has the highest strain strength, has the lowest electrical resistance (and hence lowest heating, highest peak load), has a virtually infinite life, is easier to completely insulate or better still heat shrink (including the battery post) and is materially cheaper. The soldering knowledge is easily transferred from a mentor to the student with one demonstration or a few web pictures. Personally I think these should be allowed in future competitions.

DE

I completely agree with everything that you have written. In the prevous 4 years of competition, we have crimped and/or soldered properly sized lugs and have had no problems. This is the only year that we have had wires pull out of a lug connected to our battery (SLU-70 lug that was only screwed down). If these lugs are required next year we will definately look into soldering them on. I still have not seen a satisfactory explaination as to why they were required this year.

[Al Skierkiewicz]

Originally Posted by gburlison

I still have not seen a satisfactory explaination as to why they were required this year.

The word from FIRST (unofficially) is that lacking a donor who would supply 1000+ crimpers for #6 wire and the associated terminals to be included in kits, it is and was necessary to find a cheap alternative. Given that rookies and veterans alike have a hard time with the #6 termination, this connector was chosen for it's ease of use, price and availability. What was most surprising is the sheer number of teams who did not read the rules and were required to change the connectors at competition. At the Championship alone, Spare Parts ran out of all their inventory by 1 or 2 o'clock on practice/inspection day. This after weeks of regionals and repeated reminders here and from FIRST that the SLU was required. If you know of a supplier/manufacturer would be willing to step forward with a crimper and terminals for next year's KOP please put them in touch with FIRST.

BTW, I have our students insert a star washer between the wire terminal and the battery terminal. This simple addition will bite through any surface corrosion to give a low resistance connection and it prevents the terminals from sliding past each other and loosening. Add the appropriate locking hardware and the connections will never come apart.

[Mike AA]

Originally Posted by Al Skierkiewicz

... If you know of a supplier/manufacturer would be willing to step forward with a crimper and terminals for next year's KOP please put them in touch with FIRST.

BTW, I have our students insert a star washer between the wire terminal and the battery terminal. This simple addition will bite through any surface corrosion to give a low resistance connection and it prevents the terminals from sliding past each other and loosening. Add the appropriate locking hardware and the connections will never come apart.

Al, do you think that many teams would have crimpers for the #6 crimps available to them from their sponsor? I would imagine many teams would and thus there wouldn't be quite as many that first would have to get sent out. Also as an alternative to crimping soldering would work and only requires solder and a soldering iron, not an expensive crimper. I have occasionally used the crimper at electrical supply houses, if teams asked the supplier around them they may be able to "lease" the crimper, I had to do this when making some splices with my 2500 watt inverter which I used 8 2/0 crimps and if we would have been allowed to use crimps I would have used it this year also.

-Mike

[Al Skierkiewicz]

Originally Posted by Mike AA

Al, do you think that many teams would have crimpers for the #6 crimps available to them from their sponsor? I would imagine many teams would and thus there wouldn't be quite as many that first would have to get sent out. Also as an alternative to crimping soldering would work and only requires solder and a soldering iron, not an expensive crimper. I have occasionally used the crimper at electrical supply houses, if teams asked the supplier around them they may be able to "lease" the crimper, I had to do this when making some splices with my 2500 watt inverter which I used 8 2/0 crimps and if we would have been allowed to use crimps I would have used it this year also.

-Mike

Mike,
I can't give you all the data that FIRST used to make this decision. Being sensitive to rookies and wanting to keep a level playing field for primary electrical must have certainly been part of the discussion. Whatever the reasons, it was in the rulebook and needed to be followed as closely as only using the supplied motors. I can tell you that in the years that I have inspected (and before that assisting teams with electrical problems), I have seen some of the scariest electrical wiring on robots that potentially would have caused fires. As a matter of fact, two robots that I know of in Atlanta had small fires due to wiring errors. It is imperative that teams know that the battery we use is capable of producing extreme heat under the conditions that some teams use them. A simple loose connection on a battery where the drive train is pulling more than 200 amps is capable of several thousand watts in a 1/4 sq. in. area. (I^2*R=200^2*1ohm=4000watts)
I would prefer to be able to use a connector of my own choosing but we need to keep rookies (like yourself) in play. If I can take a less than desirable part and make it work so can rookies and teams without an electrical mentor. I hope that if we must continue to use this type of connector, the SUA-70 is a more suitable part for #6 wire and certainly either type would be OK. Soldering makes this a reliable connector and heat shrink insulation makes it look nice.

G,
You make the same argument that hundreds of teams made either over the connectors, the use of adhesive tape, the drill motors last year, pneumatic rules or a variety of other systems you are more familiar with. FIRST sets the rules that we all must follow. I would consider it a real world constraint (like gravity) until we can come up with a solution that FIRST will adopt. Andy Baker found a nice little crimper for various size wires and the crimp connectors used by electricians and manufacturing everyday. The tool is about $400 though and asking a team who is already shelling $6K for competition to come up with another $400 doesn't seem to make a lot of sense. Many connectors can be crimped effectively with a small vise and finished up with solder but we still have the inexperienced teams to deal with. I received several requests for help from teams who lost there electrical mentors this season and were lost as to what to do. If anyone has a good suggestion you can send them to me and I will pass them on to FIRST.

[eugenebrooks]

Originally Posted by Al Skierkiewicz

FIRST sets the rules that we all must follow. I would consider it a real world constraint (like gravity) until we can come up with a solution that FIRST will adopt. Andy Baker found a nice little crimper for various size wires and the crimp connectors used by electricians and manufacturing everyday. The tool is about $400 though and asking a team who is already shelling $6K for competition to come up with another $400 doesn't seem to make a lot of sense.

Wrangler Power Products, www.wranglernw.com,
has high quality solid copper lugs and crimpers.
http://www.wranglernw.com/commerce/I...temNo=38%2D101
is an inexpensive hammer style crimper (part number 38-101) for #6 and larger wire for, $45.95.
Part number 38-101J, for $203.50
http://www.wranglernw.com/commerce/I...emNo=38%2D101J
is a high quality hex crimper.
I own both of these, as well as their larger hex crimper, and
all these tools work well.

Any team that can afford a set of wrenches
can afford a $46 dollar crimper.

Gravity is not just a good idea, it is the law!
FIRST's mandate of an inferior screw attached lug is just a bad idea...

[Mike AA]

Originally Posted by Al Skierkiewicz

...As a matter of fact, two robots that I know of in Atlanta had small fires due to wiring errors. It is imperative that teams know that the battery we use is capable of producing extreme heat under the conditions that some teams use them. A simple loose connection on a battery where the drive train is pulling more than 200 amps is capable of several thousand watts in a 1/4 sq. in. area. (I^2*R=200^2*1ohm=4000watts)....

Which is kinda odd, they want us to make good connections but they say use #6 on a 120 amp breaker, #6 will really only properly sustain ~60 amp. But THAT, is another story


-Mike
-Electrician

[eugenebrooks]

Originally Posted by Mike AA

they say use #6 on a 120 amp breaker, #6 will really only properly sustain ~60 amp.

-Mike
-Electrician

The rating of 6 gauge wire varies, depending upon the application.
For open chassis wiring 6 gauge wire is listed at 101 amps
http://www.powerstream.com/Wire_Size.htm
and this rating is referred to as conservative.
The robot construction guidelines document, Guidelines_c.pdf, listed
6 feet of 6 gauge wire as carrying 125 amps, based on a 2.5 % voltage
drop for 12 volts. The power dissapated in by the wire in this instance
is 37.5 watts, about a half watt per inch. It is going to get warm, and
you don't want to be giving away .3 volts like that, but it is safe for short
durations in the open air.

One of the things that was refreshing in the 2005 electrical rules
was the reasonable limits for allowed current in the wiring, making
for a lighter robot.

[Al Skierkiewicz]

Originally Posted by eugenebrooks

The rating of 6 gauge wire varies, depending upon the application.
For open chassis wiring 6 gauge wire is listed at 101 amps
http://www.powerstream.com/Wire_Size.htm
and this rating is referred to as conservative.
The robot construction guidelines document, Guidelines_c.pdf, listed
6 feet of 6 gauge wire as carrying 125 amps, based on a 2.5 % voltage
drop for 12 volts. The power dissapated in by the wire in this instance
is 37.5 watts, about a half watt per inch. It is going to get warm, and
you don't want to be giving away .3 volts like that, but it is safe for short
durations in the open air.

One of the things that was refreshing in the 2005 electrical rules
was the reasonable limits for allowed current in the wiring, making
for a lighter robot.

I agree with Gene on the wire rating. In many cases the wire gauge tables are set for max voltage drops in normal runs (volts/ft at some current) and allowing a safe temperature rise in the wire based on insulation. (ratings differ between open air and in conduit and there is a derating factor as you add more conductors in the same conduit.) Add to that the tables for the 120 amp breaker and over current of as much as 600% for a few seconds and the wire is safe for our use when currents go above 120 amps in a two minute match.

I do not agree on the wire rules allowing #12 and #14 as I think it allows teams to shoot themselves in the foot. In thinking the lighter wire is good for weight when all it does is limit the current supplied to critical motors. I still recommend #10 be used on most motors, not a rule, just a suggestion.

[gburlison]

[quote=Al Skierkiewicz]The word from FIRST (unofficially) is that lacking a donor who would supply 1000+ crimpers for #6 wire and the associated terminals to be included in kits, it is and was necessary to find a cheap alternative. Given that rookies and veterans alike have a hard time with the #6 termination, this connector was chosen for it's ease of use, price and availability. What was most surprising is the sheer number of teams who did not read the rules and were required to change the connectors at competition. At the Championship alone, Spare Parts ran out of all their inventory by 1 or 2 o'clock on practice/inspection day. This after weeks of regionals and repeated reminders here and from FIRST that the SLU was required. If you know of a supplier/manufacturer would be willing to step forward with a crimper and terminals for next year's KOP please put them in touch with FIRST.
QUOTE]


This explains why they were supplied in the KOP. But it does not explain why they were required. We only used the lugs supplied in the KOP the first year we competed (2001) and have purchased better hardware every year since. Having to go backwards and use inferior hardware just does not make sense to me.