Does every spike need it’s own 20A Fuse (upstream) or can multiple SPIKES be wired to one 20A fuse if the current draw on M+ and M- is low e.g (powering solenoids on pneumatic vales)?
According to the RULES, every SPIKE needs its own 20A breaker (in addition to the fuse right on it).
I can’t find this specifically in the rules, but it seems implied by <R55>. Maybe you can show me the rule you are thinking of, because I can’t find it. You are right about the 20A breaker, although, on the compressor at least, you don’t need the fuse along with the breaker.
<R55> All active circuit breaker / power distribution panel branch circuits shall be protected from
overload with an appropriate value auto resetting Snap Action circuit breaker from the Kit Of
Parts…
Relay modules must be protected with a 20A circuit breaker.
Followed by…
<R56> Each power regulating device (Victor speed controller or Spike relay) shall control one and
only one electrical load (motor, actuator or compressor). Multiple low-load devices (e.g.
pneumatic valves) may be connected to relay modules (but only one motor may be
connected to each relay module).
The electrical principle is simple, based on total Spike failure. Each Spike is fed with a #18 wire and each #18 wire must be protected with a 20 amp circuit breaker.
I’m not sure I am in agreement. I interpret this differently. Perhaps this is a question for the First Q&A.
<R55>
…
• Relay modules must be protected with a 20A circuit breaker.
…
Relay Modules is plural (more than 1) with a single breaker.
Go ahead and ask FIRST Q & A if you’d like. But, my money is on Al’s interpretation.
Ask the Q&A, and if you are allowed to wire them together, print the answer and bring it to the competition. Without a direct answer from the GDC, you are likely to get grief from the robot inspectors no matter how the rule is intended. I know last year our chaining of all of the negatives from spikes controlling solenoids didn’t fly with the inspectors.
As the Chief Inspector for FIRST, I STRONGLY encourage that someone address this via Q&A. I could give you my interpretation and whether I would allow multiple Spikes on the same breaker but my preference is to make this “official” by using the Q&A.
Also, I didn’t sense any interpretations in Al’s response. I don’t think that he explicitly stated whether he would allow or disallow multiple Spikes per breaker. He did, however, state something very important - trying to actuate a pair of 20A Spikes simultaneously on a single 20A breaker (as an example) is asking for “failure” (ie an open breaker) and should be avoided based on solid engineering principles. IF multiple Spikes per breaker are allowed, 18AWG wire must certainly be used everywhere (per rule <R47> with a single exemption for pneumatic valves).
Russ
Asked.
To add to the confusion, I am also named Al. So Rosiebotboss is correct either way…
Did your question include daisy chaining the grounds to spikes? I would also like to see that clarified.
So as to allay confusion, I am Al, AKA Big Al, Al S, Mr. S or Mr. Skierkiewicz depending on the age of the person who is addressing me, what First program you are in and the length of time we have competed with each other. Certain others have used other unauthorized names when addressing me, Dana included. We won’t go there, thank you very much.
As to the Spike vs. Breaker controversy, we have been warned in the past about “lawyering the rules”. As a broadcaster, single points of failure are to be avoided at all costs. As an example, if the same breaker were used on on two Spikes, one to ingest the ball and one to eject the ball and the breaker tripped preventing you from doing either why would you design your robot to only use one breaker?
To respond to Daniel above. I would have ruled the same. The current that flows in the red wire is the exact same current that flows in the black wire. As you described the wiring you could have had a single #18 wire passing the current of several 20 amp breakers and Spikes. For instance, 4 Spikes fed from four 20 amp circuit breakers each feeding say 10 amps would then cause 40 amps to flow in the #18 wire you daisy chained for the negative return leads. Potentially, 80 amps could flow in the #18 without any circuit breaker trip.
Update 8:
Each relay module must be protected with one and only one 20A circuit
breaker.
Still doesn’t answer the question…
If multiple spikes are connected to a single breaker,
each spike is still connected one, and only one, circuit breaker.
Now, if they would have said:
“Each 20A circuit can protect one, and only one Spike.”, that would be a different story.
The Q&A clears up any confusion around what the rule is:
Thank you for catching the potential ambiguity in Rule <R55>. The intent is that each power regulating device (speed controller, relay module, etc.) must be protected by one circuit breaker, and each circuit breaker must protect only one power regulating device. Please refer to Rule <R55>, as amended in Team Update #8.
(bold emphasis is mine)
What I don’t get, exactly is WHY?
I mean, it makes sense that you don’t want to have three motors, each capable of drawing 15A running through three spikes, back to a single 20A breaker… but what about three spikes that each only drive a solenoid valve? It would be more than safe to hook every spike controlling a solenoid valve up to the same 20A breaker with absolutely no danger of popping the breaker, or overheating the wire.
What is also odd is that the rules specifically state that you may hook up more than one solenoid valve (or other low-current application) to a single spike. So it is okay to have three solenoid valves powered by one 20A breaker, so long as they all run through the same Spike Relay, but NOT okay to have three solenoid valves powered by one 20A breaker when they run through three different Spike Relays.
I will concede that this rule might make tech inspection easier… one breaker, one spike… that’s pretty easy to check, but I’m just a bit perturbed that a rule interpretation 2/3 of the way through build season requires us to re-wire part of our control board for no particularly apparent (to me) safety or engineering reason.
Jason
PS - In the big picture… Overall, I’m actually pretty happy with the rules, can live with this interpretation, and really don’t expect a “why” answer all the time from GDC, which has done an exemplary job of keeping up with the many (often repetitive) Q&A questions. I’m also pleased to be having this little rant here and now, and not on a Thursday after a tech inspector has interpreted rule 55 differently than we have. But I would have been much happier to see the allowance for multiple low-load devices extend all the way back to the breaker. It just makes sense to me.
Jason,
In my mind this is not a change, merely restating what has been the rule for some time. When looking at the power protection scheme, each Spike is fed with #18 wire which must be protected by a 20 amp breaker. It is the wire that is being protected. If you look at a failure mode in one of the Spikes, a dead short, then no more than 20 amps may flow in the #18 during this event. Should a short occur at the output of the Spike then the onboard fuse will blow. Following along that line, even four or five valves connected to the output of a Spike will still blow the fuse if one of them fails or the wiring becomes shorted. So let’s go further, one or more of the solenoids either become damaged or just naturally shorts a few turns due to a manufacuring defect. The current starts to rise in the branch protected by only one breaker. Not ideal but maybe not enough to trip the breaker.
Now let’s take it one more step, a team decides that if it is OK to hook up multiple Spikes to the same breaker if they are connected to solenoids then it must be OK to hook up a motor as well. (Believe me, this kind of deductive reasoning crosses the inspection table all the time.) Before you know it, you have a team running all the Spikes from one or two breakers and a van door motor as well. Of course, during practice there is no problem but the team starts having breakers tripping during a crucial match and suddenly a little curl of smoke appears.
I am more happy that this rule is in place to protect rookies and those teams that do not have electrical mentors. As you say the GDC has done a wonderful job and in this case, the rule keeps teams playing when they might otherwise have a failed robot. Robots that stay running are a benefit to all teams. There are no rules that I know of that are written to make inspections easier.
Perhaps rather than saying “to make tech inspections easier”, I should have said, “to make tech inspections possible”. The GDC has referred to the time constraints placed on inspectors at least once in the Q&A in reference to bumpers and that it is not practical to evaluate non-standard bumper designs at the competition, so I believe it is fair to say that some rules are written with the intent of making tech inspection fair, repeatable, practial and possible. Which, although it can sound quite a bit different from “easier”, is what I had in mind. I did not mean to imply that a rule that makes tech inspection “easier” would be a bad thing, in fact I meant to imply that this would be a fair and reasonable justification for a rule. The fairness and predictability of FRC’s tech inspection process is one of the highlights of the program.
We have modified our control board to meet the rule, for even though I believe I have cause to argue that it is good engineering practice to attach several low-current loads to a single breaker in order to minimize size and weight requirements on the electronics board, it is clearly poor engineering practice to build something that does not comply with the rule book!
Jason