Keeping the main breaker from tripping

[Cory]

Originally Posted by Nuttyman54

I personally would not want to rely on freezing my breaker as a primary method to keep my robot alive during a match, but under previous FIRST rules, I don't believe it was illegal.

To clarify, I don't think anyone cools their breaker to keep alive...they (or at least we) just do so in order to not start with an elevated temperature due to short match turnaround. An elevated temperature means your breaker will trip under lower current draw than a room temperature breaker.

[billbo911]

I doubt FIRST would rule it's use illegal because it modifies performance of the item being sprayed.
That said, I definately believe they might ban it's use for health reasons.

Dust Off is difluoroethane, a refrigerant.

Here is the "Safety" text from Wikipedia on difluoroethane.

The practice of deliberately inhaling or “huffing” canned air can be extremely dangerous or fatal. The intentional inhalation of 1,1-difluoroethane contributed to the death of actress Skye McCole Bartusiak, and caused a fatal cardiac arrhythmia in a 42 year-old man.[4] Several reports of fatal car crashes have been linked to drivers huffing 1,1-difluoroethane.[5][6][7] Due to inhalant abuse, a bitterant is added to consumer canned air products.

In a Du Pont study, rats were exposed to up to 25,000 ppm (67,485 mg m−3) for six hours daily, five days a week for two years. This has become the no-observed-adverse-effect level for this substance. Prolonged exposure to 1,1-difluoroethane has been linked in humans to the development of coronary heart-disease and angina.[8]

Though not extremely flammable in gaseous form, 1,1-difluoroethane can burn under some conditions. As such, there is also a warning label present on some gas dusters. When inverted to spray liquid, the boiling fluorocarbon aerosol is easily ignitable, producing a very large blast of flame and extremely toxic gases such as hydrogen fluoride and carbonyl fluoride as combustion products.

[Deke]

Originally Posted by asid61

To all teams running six or more cims on their bot and say that they have zero breaker issues, what speeds were you running?
Because there are only miniscule gains from running six cims on anything under 15 fps according to my drivetrain calculator. Maybe a few extra inches out of ten feet if you go from four to six cims.
Why do you run such low speeds on six cims?

It keeps the 40 amp breakers from tripping. By switching from 4 to 6 cims with a single speed the current gets divided through 6 40 amp breakers instead of 4 40 amp breakers. Thus you can push with a higher gear ratio and have decent enough speed to move around the field.

[jman4747]

Shouldint we be trying not to draw more current than the system is supposed to handle rather than stop a safety mechanism from activating? Like turning of a smoke alarm rather than putting out the fire?

[Caleb Sykes]

Originally Posted by billbo911

I doubt FIRST would rule it's use illegal because it modifies performance of the item being sprayed.
That said, I definately believe they might ban it's use for health reasons.

Dust Off is difluoroethane, a refrigerant.

Here is the "Safety" text from Wikipedia on difluoroethane.

On this note, when I went in to buy some compressed air recently to use on our robot between matches, I needed to show my ID upon purchase. When I asked the clerk why out of curiosity, she replied that "people must be huffing it or something like that."

[cgmv123]

Originally Posted by inkling16

On this note, when I went in to buy some compressed air recently to use on our robot between matches, I needed to show my ID upon purchase. When I asked the clerk why out of curiosity, she replied that "people must be huffing it or something like that."

I had to show ID to purchase a can of air (to be relabeled as "magic smoke" as a gift for a mentor) as well at a store that will not be named but whose logo is a bullseye. I wasn't yet 18 at the time so they wouldn't let me buy it after seeing my ID. I explained to my dad that canned air "used to be the way teenagers would get high" and then made him go to T**g** and buy it for me.

[asid61]

Originally Posted by Infinity2718

It keeps the 40 amp breakers from tripping. By switching from 4 to 6 cims with a single speed the current gets divided through 6 40 amp breakers instead of 4 40 amp breakers. Thus you can push with a higher gear ratio and have decent enough speed to move around the field.

But if you gear for like 12 fps anyway, why not just shift down? The 40 amp breakers autoreset, right?

[Boe]

Originally Posted by jman4747

Shouldint we be trying not to draw more current than the system is supposed to handle rather than stop a safety mechanism from activating? Like turning of a smoke alarm rather than putting out the fire?

No teams that I know of used canned air to allow them to draw more current. They use it to cool down the main breaker during quick match turnarounds (such as during the finals) so that they can still draw as much current as they would be able to if the breaker was at room temperature. Running quick match turnarounds without cooling the main breaker off can result in tripping the breaker while not pulling more current then the breaker should be able to handle.

[Monochron]

Originally Posted by Cory

To clarify, I don't think anyone cools their breaker to keep alive...they (or at least we) just do so in order to not start with an elevated temperature due to short match turnaround. An elevated temperature means your breaker will trip under lower current draw than a room temperature breaker.

I agree that this is likely the usual case for cooling breakers and I am generally doubtful that FIRST would call that illegal for the listed reasons.

Maybe a better question would be is the breaker thermally triggered because that is simply one of the many ways the creator decided to implement it, or is the "left over" heat from previous operation indicative of actual risk?

The question would be, what is the case where the breaker trips meant to prevent?

• Is it to protect the breaker itself from damage?
• Is it to protect the motors from excessive currents over time?
• Is it to protect the motors from excessive heat.

I can't find any documentation stating which is true, but I would guess that it is a combination of all of the above.

If so then in the last case (protecting motors and components from excessive heat), then cooling the breaker DOES circumvent the system and add risk. Risk of overheating a motor, controller, etc. because the breaker "thought" that the system was much cooler than it was.

Any thoughts?

[jeremylee]

Originally Posted by asid61

Because there are only miniscule gains from running six cims on anything under 15 fps according to my drivetrain calculator.

I also see small gains in acceleration and top speed in my model for conservatively geared robots. Some reasons I'd still consider 6 cims over 4 on a single speed bot geared at 12 ft/sec:

1. 6 cim is more efficient than 4 cim during high loads like pushing and turning (less motor heating, less speed drop under load, robot seems a little stronger)
2. Distribute load between motors to reduce heating for back to back matches
3. Redundancy, we lost a talon last year, robot was still very much driveable other than not driving straight

[dellagd]

Originally Posted by asid61

But if you gear for like 12 fps anyway, why not just shift down? The 40 amp breakers autoreset, right?

Yes, they auto-reset. The datasheet is on AndyMark's site here.

Essentially the goal is to have a high speed which is great for getting across long distances fast and a low speed which is good for fine maneuvering/pushing.

If you are having your high speed at 12fps (I think that's what you're saying?) there really isn't much incentive to use shifters anyway.

When robots use shifters, its usually because they want to have a really fast gearing that would stall the motors if you tried to push at that gearing. Therefore, its best to be able to downshift so you can hold your own if you get into a confrontation. 12fps isn't much for a high gear, that's usually what people do in single speed setups.

[Cory]

Originally Posted by Monochron

The question would be, what is the case where the breaker trips meant to prevent?

• Is it to protect the breaker itself from damage?
• Is it to protect the motors from excessive currents over time?
• Is it to protect the motors from excessive heat.

I can't find any documentation stating which is true, but I would guess that it is a combination of all of the above.

It is to protect from uncontrolled discharge of the battery. The breaker protects whatever the branch circuit is, so essentially the main breaker is protecting the wiring from battery-main breaker-PDB.

[Monochron]

Originally Posted by Cory

It is to protect from uncontrolled discharge of the battery. The breaker protects whatever the branch circuit is.

So I'm guessing the reason it trips based on heat and not some sort of chip detecting high current is for lower price or some other manufacturing reason? In which case the residual heat is nothing more than a side effect. Well jeez, I'm surprised FIRST doesn't recommend cooling it down if what you say is true

[Ryan Dognaux]

I can see it now - FIRST bans using canned air to cool parts. Teams then begin keeping multiple spare main breakers in a cooler on ice and swap them between elimination matches.

[Cory]

Originally Posted by Monochron

So I'm guessing the reason it trips based on heat and not some sort of chip detecting high current is for lower price or some other manufacturing reason? In which case the residual heat is nothing more than a side effect. Well jeez, I'm surprised FIRST doesn't recommend cooling it down if what you say is true

Generally breakers have 2 methods of protection. If you have a slow increase of current until you get to a continuous amount that will trip the breaker, the trip occurs via a piece of metal bending as it heats up until it no longer makes contact with the circuit.

If you were to have a short you'd see a huge sudden surge of current, which would cause a solenoid to pull the contacts apart.

I assume the one we use features both methods, but I've never looked inside one before.