WHY does FIRST insist on using oversized wires??? I mean, I can understand that FIRST doesn’t want any wires to fail, but if you are using thicker wire than the leads on, say, the compressor, than the extension will not burn up, but the leads will. That’s not avoidable. Also, why do you have to use 6 AWG wires after the 120 amp breaker? If you have enough power to melt a 6 AWG wire, then it will trip the breaker. PLEASE TELL ME WHY!!!
Ummm… the 6 AWG wire from the batteries looks to be just about right based on a random google search. Check here: Recommended Current
As for the rest… many teams will attest that the standard wires to the drills aren’t thick enough to handle current right now, and go to great lengths to replace them. I don’t really think having wires that are too thick is THAT big of a problem unless you’re really pick about easy routing or you’re just that close on weight.
Wire size and current carrying capability is based on temperature rise for a given size wire at a particular current. Al of our wiring is out in the open and not enclosed in conduit so that raises the amount of current it can handle. Also factored in are the lengths of a given wire as to how much series resistance will affect the voltage supplied to the load. Again our wiring is fairly short compared to real world applications. As to the blue wires for the drill motors, even if they were four time the series resistance of #10 they are only four inches long each and the insultaion is 200 degree C rated. #10 is .001 ohm per foot so even at 4 times the resistance, 8 inches of #16 wire is only .003 ohms. At 129 amps of stall current, that only drops a little more than 0.3 volts.
Whena a branch circuit breaker is chosen, it is sized to protect the wiring in that circuit from reaching a temperature at which the insulation will fail due to heat rise. Hence the #6 is protected by the 120 amp delayed action circuit breaker. The breaker will trip before current flowing through the #6 has a chance to heat up to the point of failure. Like wise for the 40, 30 and 20 amp circuit breakers. First mandates some apparantly larger wires for those circuits that teams have had trouble with in the past. You could wire your entire robot with #6, if you had enough weight under 130 lbs. but why.
About the blue wires, I was referring to all these anecdotes I hear about the drills unsoldering their connections from excessive heat. I dunno what causes it, but I’m inclined to believe that it actually occurred if people say it did.
FYI: IF you want some really good, flexible 4 AWG wire [hyperbolization] 100x more flexible than the Kit 6AWG [/hyperbolization]). PartsExpress carries some great stuff…this 4AWG is made up of **1672 strands ** of 36AWG wire! It’s really amazing stuff. They also sell ultra-flexible 8AWG wire made of **675 strands ** of 36ga. wire. It’s great stuff…what we’re using this year. Makes wiring a lot easier.
Believe it! The quality control on the wire solder job is not very good. If you run the motors (in practice) long enough to get the brush assy. hot, the wires do start to melt the solder. Since the connection is not a good mechanical one first, the connection series resistance rises as the solder melts making the problem worse. Sort of a domino effect.
Aidan, I am missing something. Table 5.2: Minimum Wire Size and Protection by Device Type in Section 5.6.2: Wire Size, lists the minimum wiring sizes for devices and controllers. Are you saying this is a guidline?
Newark has some superflexible wire that is zip cord #10, red paired with black, part # 24-1930 for the 100’ roll, about $35/roll.
Wow! I really didn’t expect so many posts!
First off, let me tell you the deal. I wrote that post in a fit of rage when I ran out of 10 guage wire when the leads I was soldering to was 12 guage. I had plenty of 12 guage, but no 10. I, in my madness, went off, as I stated, ‘on a tangent’, and started ranting. I knew the answer, and saw the wisdom, but that was after I found more 10 guage.
Thanks for all the info. I didn’t realize that the wiring specs didn’t apply to downstream. That’s interesting.
Again, thanks for helping me get through the madness!
I can assure you that proper engineering has gone into FIRST’s selections. People like Al, Adrien and I would be all over FIRST if they were being too conservative or too risky.
Please remember that no engineering decision is ever black and white. Without compromise, engineering would be boring. Just as you and your team will make hard decisions as you struggle to build a robot, FIRST has had to make hard decisions concerning maximizing safety while making the number of rules as small as possible.
I do no believe that RULE 5.6.2 is a guideline. When I was doing inspections last year it was enfourced as a rule. This was true at 3 regionals and championship while I was assisting with inspections. There was more than 1 challenge but 5.6.2 was always brought forth as the rule.
Sparks and everyone,
Not to let anyone get misled at this late date by some of the early season discussion, we need to make some things clear based on the actual competition practice and rules. In the sections quoted by Aidan above, there is a small reference to conforming to the “robot power distribution” drawing. In that drawing you will find a table that states that certain motors and speed controllers wired to those motors be wired with #10. Additionally, the inspectors sheet required inspectors to check that wiring of the correct guage was used in each leg or branch of the circuit. As an inspector at GLR, MWR and Nationals I can assure you that we were trained to watch for these wiring minimums.
As to the original question relating to the wire size supplied with devices, we must add that resistance in wire (and the heating that takes place in that resistance) is also a function of length. The compressor and drills both have fairly short leads where the resistance is at a minimum. Additional information on the drill’s #16 is that the manufacturer chose the high temp wire with the knowledge that the wire may burn open at stall currents. Design engineers at the manufacturer consider the #16 a fuse and as such, FIRST chose to rule that it be left attached. Other than the challenge it presents in wiring, teams should not have too much trouble in leaving it attached. I will add that many teams have found the solder job less than adequate and remove the brush assy by moving aside the little keeper, correctly solder the wire in place, and replace the brush assy after cooling.
The drill motor as far as I know has not been dropped. We won’t know for sure until the kit of parts comes out. I know there has been some discussion but the most recent is on the “rumor mill” board and should not be believed. If someone has some concrete info please let me know.
The drill motor has some flaws but that does not make it a bad motor. It is a pretty good merge of speed, power, size and weight. Coupled with the transmission and drive system designed by FIRST, you can have a driving base within a few hours and then concentrate on other parts of the robot. Although you will see lot’s of people complain about parts (sometimes that includes me) all of us are held to the same constraints. That’s what makes this so much fun. We all have to overcome the same things and still try and compete. We have used FP, Bosch and/or Chalupas in our drive systems over the last few years. We won nationals with two FP and two drills in our crab steering modules. I expect to see several of the AndyMark multimotor drives using these same motors when I inspect this coming season.
The selling of the extras may be to just clear out the storage for new inventory. I use “chalupa” because many of us used that name when the motors were first introduced. Kind of an inside joke I know, but after 9 years of late night sessions and all of the other craziness you do get a little punchy. Maybe just a midwest thingy. Besides I can spell “chalupa”.
We’ve be thinking about using some more flexable wiring solution this year, but one question I have is do you still use the Power Connector that comes in the kit for the batteries? Is there anyone who uses a more flexible or convienent connector for their batteries?