Mr. Skierkiewicz, I do not recall the 120 A breaker ever tripping last year, I guess we were cutting it really really close.
Seeing that much of our main power distribution equipment is rated for ~50+ Amps, would there be a noticeable advantage of upgrading some of that equipment to ratings of ~120+ Amps say in a pushing duel between two robots?
There is very little you can change other than wire. If you think of this in real world terms, (and I am just guessing here) with the amount of heat generated by your robot last year, you would have been dropping a significant amount of voltage in the wiring that was getting hot. Assuming you cut little or no wire from the #6 connected to Anderson connectors and you added some additional #6 then you had a lot of series resistance. I use an easily understood term for this loss called the “wire foot”. Each piece of wire has resistance that translates to a voltage drop just by current passing through it. A “wire foot” is 100 amps (approx stall current on drive motors) flowing through a #10 wire which drops about 1/10 of a volt per foot of wire. Since 1 foot of #6 is about 1/2 WF, and you were passing more than 200 amps through your #6, a quick calculation would be 2 (twice the standard current) x 0.5 WF x 6 ft of wire=0.6 volts in just the #6. Add in the other wiring and the internal resistance of the battery (11WF) and you should have been resetting the RC on a regular basis as the voltage would have easily been drooping to below the 8 volt cutout for the RC. (200 amps x 11WF=2.2 volts just in the internal resistance of the battery) By substituting #4, you would have dropped the loss in the primary wiring (battery, connector, main breaker and breaker panel) by half or 0.3 volts. You can easily pick up that much by cutting the #6 wire length in half. Remember, you have to account for all the wire, black and red in your calculations.
Jay,
I agree completely with what Al has posted. You had some very serious problems in your 2006 robot for the wire to become “pudgy” after a 2 minute match. Melting insulation could cause a short circuit of your battery…
My team pushed the envelope on motor utilization in 2006. We won two regionals and Galileo division at the Nats. We burnt out 4 sets of FP motors and quite a few drive train components doing it. We used 4 small CIMs, 2 FPs, 2 large CIMs and an air compressor. Almost all were running full power and/or full speed during the majority of time in our matches… We sucked so much current from the 12V battery that the “low battery” indicator on the OI would light up (even during practice matches).
Only once did our 6 AWG wires get warm. Investigation revealed that a frame had “racked” to the point that turning that assembly by hand was impossible. We fixed the mechanical issue and the wire temps returned to normal.
By increasing the wire gauge, you are treating the symptom rather than the root cause and other components will start to fail (connectors, batteries, et cetera). Failure of these types of components can be “very interesting” (translate: scary).
You might also consider that some protective devices, like the 120A CB, may have failed closed (contacts welded shut) on your robot to allow such high wire temps to occur without tripping.
As a mentor, I would have a hard time allowing my students to operate a robot with the conditions you describe. I would very likely take the unpopular position and force my team to withdraw from the competition if the root cause could not be determined and corrected.
Let me put it another way. If the main power wires coming into my house were hot and “pudgy”, I could not and would not sleep in that house.
I strongly suggest that you follow Al’s advise. Get a good clamp-on DC amp meter and compare motor measurements to design specifications.
Even though it is not against the rules, in no way would I endorse going to 4 AWG wire…
Regards,
Mike
Ok,
So I checked the Rockwell site for the terminal blocks supplied in the kit this year. The are listed for accepting wires from #14-#6 and are rated for 75 amps each. The spec sheet says you can double up on some guage wires (not #6) but must derate the current handling. For our purposes with the 120 amp circuit breaker, 50 amp Anderson connector and 40 amp branch circuit breakers, this seems like an good product for our use (other then weight and size). I was unable to find a spec on current handling for the jumper though. If anyone can find it I would appreciate a post on the subject.
I think that’s the main reason they’ve added this requirement. In essence, the main goal of good wiring is being able to edit it efficiently. Anyone going from FIRST to small scale electronics will want to be very familiar with efficient power bus use. And being able to find all connections to main power helps a lot while you’re staring at a big jumble of wires (depending on how good your wiring is >_>).
Does anyone know where to buy spare blocks (This Years).
I know this thread is a little old, but I really want to confirm whether ghhs is right. Is it okay to use power distribution block from 2006 instead of the DIN rail? R27 seems to indicate that you can’t. But then there’s R28 having me wish I knew what COTS meant. Honestly, after four years of FIRST, I still have no idea how to understand the rules.
According the robot rules you must use the DIN Rail mounter terminal blocks as shown in both the robot rules section and Tips and Guidelines.
<R57> The 12V battery, the main 120-amp circuit breaker, the power distribution block, and circuit
breaker distribution panels must be connected as shown in the 2007 Power Distribution
Diagram. In particular:
The battery must be connected to the ROBOT power system through the use of the
Anderson Power Products (APP) connector.
The APP connector must be attached to the battery with either the copper lugs provided in the FCI Burndy Bag or appropriate crimp-on lug connectors.
The battery terminals and the connecting lugs must be insulated with shrink tubing and/orelectrical tape.
The main 120-amp circuit breaker must be directly connected to the hot (+) leg of the
ROBOT-side APP connector. Only one 120 amp main circuit breaker is allowed. This
breaker must not be bypassed.
The power distribution block must be directly connected to the APP connector and main
120-amp circuit breaker. No other loads may be connected to the main 120-amp circuit breaker.
All circuit breaker distribution panels must be connected directly to the power distribution block. No intermediate connections are permitted.
The rules are also supplemented by the Tips and Guidelines and the robot wiring diagram all available on the first website here…http://www.usfirst.org/community/frc/content.aspx?id=452