Do we need to use the gnd stud and MAXI fuse block

Just wondering if the Ground stud is something we have to use. We have a centrel location where the grounds meet before going to the battery but its not the supplied ground stud. Also we are using the chippuwas the window motors and the compresor do any of these have to be attached to the MAXI fuse block its heavy and we would rather not use it

you are required to use the large fuse block and the 40 amp fuses for the chalupa and drill motors

If you dont use the ground stud you will have to branch the ground from one fuse block to the second one - you would be better off using it, but Im not sure if thats required.

BTW -you really dont want to run the chalupias or the drill motors on 30 amp breakers - that limits the amount of power they can draw, and when push comes to shove in a match, they will open on you at a much lower power level

power = current times voltage

30 amps * 12 volts = 360 watts
40 amps * 12 volts = 480 watts

since you are using two motors, that means the power available to your drive train will be either 720 Watts with the 30 amp breakers, or 960 watts with the 40 amp breakers

33% more power - its worth the extra space and weight to have the maxi panel on your bot.

It sounds like you have your own custom way to distribute the ground. That is OK as long as it isn’t electrically connected to your frame, and it is rated for the current that goes through it. For example, if it is on the same circuit as the 120 amp breaker, it must handle at least 120 amps.

The Chippuahaus are the only ones of those that CAN go on the MAXI fuse block. In the rules, it never states (that I can find, perhaps Ken could point me to it) that you CAN’T use anything else. Last year, we got the OK from FIRST ahead of time to use the 30 amp breakers. However, we still had trouble from the inspector as well as the head inspector. We had to talk to the FIRST staff person at Cleveland to confirm.

Ken is right that you CAN get more power out of the motors if you use the 40 amp breakers. However, I was tought to when I designed a system using a DC motor, to always design it so the it uses half the maximum power (1/4 the stall torque). For the Drill motors, this is at barely above 30 amps, and for the CIMs it is barely under 30 amps. Thus, with my designs, I feel somewhat safe using the 30 amps. If we had no weight limit, of course I’d use the higher breaker, but sometimes there are more important things.

The electrical system must adhere to the electrical robot blueprint. You can leave out the Maxi Fuse block and #6 to #10 transition block if you do not use the Drills and/or Chips but you must use the ground post.

Al, I can’t find that in the rules, nor can I find where the ground stud is required. Can you please point me to that either in the rules or in the Q/A?

I have been treating the electrical blueprint as a suggestion. One reason for that is that the blueprint shows the current sensors in line with the drill motors, but we aren’t required to use the current sensors for the drill motors (or at all).

Joe,
I was confused as well until you check the entire document as a whole. There are places where exceptions are carved out. (like current sensors are optional) and other places that refer to the drawing as if the entire rule section was illustrated in the blueprint. i.e. 5.6.1 Power Distribution Circuits
Exception: The Ground (GND or Common -) wires from low current items such as relays controlling solenoid pneumatic valves, custom circuits, sensors, LEDs, and fans may be connected as a group to one common wire that leads back to a Common (-) terminal tab on an ATC panel, or directly to the ground stud.
I expect a more precise list in a future team update. I am betting that the inspectors will be checking against a list that includes the stud, the maxi block and the #6 to #10 transition block.
On a personal note…I assisted with robot inspections at the Midwest Regional and was questioned about a number of robots at nationals and I can tell you that FIRST (and many other engineers) were very concerned about the way the robot electricals were handled by some teams. The wiring bordered on hazardous and departed widely from the electrical rules last year. I do not expect that same problem this year. I expect inspectors will be well versed in electrical layout and will not allow robots that fail inspection to compete. If anyone has a question about wiring or electrical, please post it here soon or PM me and I will try to answer. The electrical is not as easy as it seems and I don’t want to see a robot die because of a failed electrical system that could be easily fixed. Please ask for help!

However, I was tought to when I designed a system using a DC motor, to always design it so the it uses half the maximum power (1/4 the stall torque). For the Drill motors, this is at barely above 30 amps, and for the CIMs it is barely under 30 amps. Thus, with my designs, I feel somewhat safe using the 30 amps.

I dont understand this statement at all - when your motors are not moving and you throttle up, the motors start at the stall torque and will draw the stall current, no matter how your system is designed

and if the motors cant get up to the speed at which they draw less than the rated value of your breaker, for any reason, the breakers will trip - I suppose you could have your bot geared down low enough that the wheels will spin without stalling, keeping the motors at a high RPM rate, but I dont see how you can guarentee that will always be the case, that wheels will never ‘hook up’ on you, or that you wont be pushed backwards, or have something else trying to stop your wheels from turning.

I cant think of any reason to limit your drive motors to 30 amps when you are allowed to use 40.

Almost right, motors start at stall current with full voltage applied, If you are ramping Motor speed up, useing a Victor, voltage will be less than full. And Current will be less. This would not apply to motors which are switched on and off with a spike. Hope this helps.

the victors dont work by reducing the voltage, they work by switching the full voltage on and off - pulse width modulation - this does average out to look like less current is being drawn, but if you put a current prob and scope on the motor leads, you will see it is pulling quite a bit of current during those little pulses, no matter what ‘speed’ you are telling the victor to run at.

All,
Let’s not forget that the breakers don’t trip at their rated current unless it has been exceeded for some length of time. That is why 40 amp breakers don’t trip for the short duration stall of a drill motor at 129 amps.

To add to Al’s response. The circuit breakers are thermal devices. The current that passes through the breaker heats a filament that will mechanically open the circuit if the temperature exceeds its rating. The data sheet will show how long a set current can pass through the breaker before it trips.

Tim Tedrow

Good Point, Tim,
The circuit breakers will trip more easily for a given over current if they are already at elevated temperature. Trip a breaker once in a match and it is more likely to trip again in the same match.

The use of freeze-spray has been discussed several times before - it is generally agreed that pre-cooling before a match can give you better breaker performance. However, can freeze spray damage the breakers? If you freeze your hot breakers right after a match, will the rapid cooling affect their performance in the long run? How about for their duty-cycle - say three competitions?

It is my opinion that the freeze spray can do no more harm than the tripping of the breaker in the first place. At high currents and high temperatures, the contacts of the breaker have to be pitting when the circuit opens. There is a lot of current and a lot of inductance, potential power, etc., stored in the motors that would cause arcing when the breaker trips. Many teams have used freeze spray but it can only hold off the problem a few seconds. The breakers have no thermal mass so even if they are cold, they can’t hold it.
As far as damage from direct application, there is no significant connection between the bimetal device and the case and they are sealed pretty well so there is no intrusion of the freeze spray in liquid. If the breakers are constantly cycling (a buzzing sound will be heard) then the overtemp of the metal parts will surely have some permanent effects.

thanks everyone this is very late but im also testing a new signature pic and couldnt think of anywhere else to post it