This year my team is looking at using a lot more motor controllers so we are considering using two power distribution boards. I’m not sure if this is legal and if it is, how I would do it. Thanks for any input!
Obligatory disclaimer that last year’s rules are not this year’s.
How many motors are you planning to use, and which kinds? Usually the manual has a maximum number of allowed motors of each type. For example, last year, teams could use a maximum of 6 CIM motors.
With the disclaimer above firmly attached, I point you to the 2013 rule R38, emphasize the wording “the Power Distribution (PD) Board” (which, I might add, is repeated in multiple locations later in that section of the robot manual), and as a former inspector remind you that the rule says that you gotta match the figure in that rule–in short, sorry, only one PDB is allowed.
I then go to R47 to remind you that only one motor controller or relay circuit is allowed per breaker, in case you were thinking of running 2 controllers from one output.
In short… not legal. Maybe you should look into pneumatics or servos; those are less limited in number, and have more flexibility to add a control area–but they also have limitations like limited power or limited positioning.
If you are using so many motors you need a second distribution board, chances are you likely will be operating awfully close to the 120Amps it takes to snap the Main Breaker (if not above 120A!).
I cannot find a specific rule disallowing the use of a second PDB, but I have never seen it before. In 2012 we had 15* motors each on their own Victor/Spike/Jag. We were cutting it close on slots, but we still had 2-3 left at the end. We never had a current problem, but I would bet we were running above 100A at times.
My $0.02: If your robot takes that many motors, your robot probably needs to be redesigned. 15* motors was a bad idea, because of complexity and the shear weight of the things. Our robot this year had a total of just 5 motors. 4 were in the drive-train.
*Plus 1 Vex motor, but it only needs the power given off by the Sidecar via PWM.
I would expect it would be ruled as illegal. But that is just an opinion. That aside, two lugs on the studs of the PD board would be OK if there is enough clearance to the body. Otherwise splice the wires before PD board. I probably would use the same compression lugs, bolt them together & tape them.
You’d probably shoot through the battery, drawing that much power on your robot. I doubt that everything will run at the same time!
R39 makes that illegal.
The new PDB for 2015 is being tested by a few teams. I has less “slots” on the PDB than the current one. Time to start thinking about less, not more PDB outputs.
The 2015 control system also uses up less slots then the current system.
If this isn’t a competition robot (Which I doubt it wouldn’t be), just jam multiple wires in the same slots :D. You are probably not going to be using every motor at the same time, are you?
Just make sure you do it right. The “Cheap n Dirty” way of doing things is why many battery explosions and fires happen! ::safety:: ::safety:: ::safety::
That makes them a lot more likely to trip the 40/30/20A breakers
Yes. I agree. That is why you group the motors that you know will rarely work together. Blooper: However, when doing this, a fire extinguisher is recommended because a wire can slip and short out!
You’ve heard from others that using two would be illegal, given last year’s rules. Since the rules quoted above haven’t really changed much over the past few years, you can probably assume they won’t change much this year, either.
However, your post brings up another concept… The game hasn’t been released yet, the season hasn’t started. How do you know how many motor controllers you’ll need?
Given the fragile nature of the M6 studs, I probably would not put more than one lug on them anyway. But. R39 refers to circuits that should be downstream PD board. To fully follow R39, the 2nd PD board would have to get its power from the first PD board which would limit the available power to the 2nd board to 40 amps. (Max breaker size). Of course then you run foul of R47 which limits loads through one breaker of the first PD board.
I think of the more of a thought exercise than reality since more than one PD legal is probably not legal to begin with.
Eric has perhaps covered all the bases on this one. To satisfy the rules, one and only one PD. However, as things change from year to year, the best method will be to address this through the Q&A when it opens after kickoff.
As a rule of thumb, when a team starts to load up the robot with motors, current does increase. Several teams tripped main breakers during last season for this reason. While the 120 amp breaker can withstand 600% over current for short periods, it is not self resetting. Once it trips you are done for the match.
Why (and how) would you make a decision to use so many motors without even knowing what the challenge is?
You’ve put the cart before the horse.
This is incredibly dangerous. From melting wires to blowing breakers/fuses, this is really not safe and I could see it failing inspection.
Yes. I know that it is dangerous. That is the reason why you do not group two shooter motors together or drivetrain motors together! Just choose motors that will always run independently. Also, yes. I am pretty sure as soon as the inspection finds out about this the team would get blasted. That’s why you do not use this at competition. Also, this adds a little bit of competition. This adds a quota and another thing to watch out about!
More competition also means more competition, usually!