What else do we want?

[archiver]

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/5/2000 3:02 PM MST


In Reply to: Re: 60 amp fuse problems... posted by James Jones on 7/5/2000 11:19 AM MST:



Okay, here's the deal.

As it turns out, three 30 Amp circuit breakers in parrallel will trip before the one 60 Amp fuse. This fact was experimentally determined using a big power supply and an even bigger potentiometer ;-).

So, knowing this fact, you can build from legal kit materials a device that can be put in series with the 60 Amp fuse that has the purpose of protecting the 60 Amp fuse.

The effect of this device is to trade a death sentence for a 2 second reboot of the Robot Interface. Not a bad deal.

The reason that I need to write a 'white paper' on the topic is that it is a bit tricky to actually wire the 3 circuit breakers in parallel.

Actually, we made a few of the devices at the Nationals that plugged between the battery and the robot that we used as 'loaners' for teams having 60 Amp fuse problems. They worked like a charm.

Joe J.

P.S. It has not been my experience that fuses get 'old' after hard useage. I have seen a few 'semi-melted' fuses, but even they seemed to be functioning just fine, it was only inspection that made them know to us, not performance.

[archiver]

Posted by Jerry Eckert.

Engineer from Looking for a team in Raleigh, NC sponsored by .

Posted on 7/6/2000 11:11 PM MST


In Reply to: 3X30 posted by Joe Johnson on 7/5/2000 3:02 PM MST:



: Okay, here's the deal.

: As it turns out, three 30 Amp circuit breakers in parrallel will trip before the one 60 Amp fuse. This fact was experimentally determined using a big power supply and an even bigger potentiometer ;-).

: So, knowing this fact, you can build from legal kit materials a device that can be put in series with the 60 Amp fuse that has the purpose of protecting the 60 Amp fuse.


The device is constructed from legal kit materials, but is using them in this manner legal?

Rule C5 states that 'Electrical devices may only be wired as described in Section 2
and/or the Robot Rules.

The wiring diagram in section 2 does not show two or more 30 amp breakers wired
in parallel connected to a single device.

Rule C15 states 'ONE [emphasis mine] 30A circuit breaker (provided in the Kit)
must be installed in series with each speed controller on the +12 Vdc input.

Jerry

[archiver]

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/7/2000 7:21 PM MST


In Reply to: Re: 3X30 posted by Jerry Eckert on 7/6/2000 11:11 PM MST:



As the the rules you site, you make good points. Perhaps I have been involved too long in FIRST. The rules from year to year are blurring in my mind. I honestly remembered the rule to be something along the lines of 'only things on the electrical components list may be used to conduct electricity.' Reading the rules more closely, I concede that it seems to be a stretch of the rules.

All I can say is FIRST folks have known about it for years and have never said it was illegal. One of the teams that used the technique told me they were given the green light as well. Beyond this, FIRST folks were involved in looking for teams that might be interested in the 'loaners' we had available at the Nationals.

Anyway, I don't think the spirit of the rules were broken by allowing teams conduct LESS current than the 60 Amp fuse would provide (though for a shorter period of time).

Going forward, I hope that FIRST makes this option explicitly legal. It is a needless worry for a number of teams.

Joe J.

[archiver]

Posted by Ken Patton.   [PICTURE: SAME | NEW | HELP]


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.

Posted on 7/10/2000 11:43 AM MST


In Reply to: Con-Fused.... posted by Joe Johnson on 7/7/2000 7:21 PM MST:



I didn't realize that people were doing this. Rule C1 in update #2 is pretty explicit: '... circuit breakers, and fuse may not be tampered with, modified or adjusted in any way...' Figure 2.1 in the rulebook is pretty explicit too.

If there are any performance gains to be made - say, by allowing more motors at a given gear ratio - then I would question whether this is even within the spirit of the rules (its not within the letter in any case). It seems to me that the reason you would want to do this is to allow more stuff (features or performance) to go on in your robot at any given time.

Does this have an effect on how much current you can draw in a transient condition (say, the initial start of the match)?

Ken

[archiver]

Posted by Mike Dubreuil.

Student on team #175, Buzz, from Enrico Fermi High School and UTC/Hamilton Sundstrand.

Posted on 7/10/2000 3:03 PM MST


In Reply to: Re: Con-Fused.... posted by Ken Patton on 7/10/2000 11:43 AM MST:



Well you have to look at the reasoning behind a rule like this: safety and so you don't fry anything. The only real gain we experienced was that if our 60 amp fuse blew we wouldn't be dead in the water. The circut would not allow any more than 60 amps. So, we did not receive a performance gain. In fact, if my memory serves me correctly we did not use the circut as 'the 60 amp fuse'. The 60 amper was still wired in but the circut would protect it.


: I didn't realize that people were doing this. Rule C1 in update #2 is pretty explicit: '... circuit breakers, and fuse may not be tampered with, modified or adjusted in any way...' Figure 2.1 in the rulebook is pretty explicit too.

: If there are any performance gains to be made - say, by allowing more motors at a given gear ratio - then I would question whether this is even within the spirit of the rules (its not within the letter in any case). It seems to me that the reason you would want to do this is to allow more stuff (features or performance) to go on in your robot at any given time.

: Does this have an effect on how much current you can draw in a transient condition (say, the initial start of the match)?

: Ken

[archiver]

Posted by Ken Patton.   [PICTURE: SAME | NEW | HELP]


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.

Posted on 7/11/2000 3:41 PM MST


In Reply to: Re: Con-Fused.... posted by Mike Dubreuil on 7/10/2000 3:03 PM MST:




Does it really make the system safer? Specifically how?

It doesn't change the likelihood that you will fry something, other than the 60A fuse itself (and thats what its there for).

As you say, you experienced a gain because you would not be dead in the water due to a 60 amp fuse blowing. Why would your 60 amp fuse tend to blow? My guess is because you were on the ragged edge in terms of motors being driven at one time, or gear ratios chosen for robot speed, or both. What would you say to teams that didn't use Joe's mod, but instead backed off on gear ratio a little and settled for less speed than you guys did? Do you think it was an equal playing field?

The fact that people are doing this doesn't bother me as much as it surpises me. Its technically cheating isn't it?

Ken


: Well you have to look at the reasoning behind a rule like this: safety and so you don't fry anything. The only real gain we experienced was that if our 60 amp fuse blew we wouldn't be dead in the water. The circut would not allow any more than 60 amps. So, we did not receive a performance gain. In fact, if my memory serves me correctly we did not use the circut as 'the 60 amp fuse'. The 60 amper was still wired in but the circut would protect it.

[archiver]

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/11/2000 10:11 PM MST


In Reply to: Re: Con-Fused.... posted by Ken Patton on 7/11/2000 3:41 PM MST:



Ken,

Actually, I was sick when I saw the references that were sited that called into question the legality of the device I have proposed. My first reaction was to pull up the rules that would allow me to show how I had come to the conclusion that it was okay. Looking it up, I was really surprised to see that the rules were not as I had thought. If you doubt that I really believed this was okay, look at my first posting. It is clear from my wording that I THOUGHT the rule involved building things that carried electricity from legal kit materials. As to how I came to the conclusion that it was legal in the first place, I am afraid that it is lost at this late date. Another argument agianst my belief that the device was illegal is the fact that we openly shared the device with a number of teams and then posted a reference to it on this website.

Even so...

You call it cheating. I disagree for a number of reasons:

Many inspectors saw the device, inquired about it and said nothing negative and, more likely, compemented us on its cleverness.

A nunber of tech folks at FIRST knew about it and did not tell us it was illegal, on the contrary, they agreed to help us find teams that might be having 60 Amp fuse problems and could use one of our loaners.

A number of other FIRST teams tell us that they made a point of asking FIRST specifically if it was allowed and being told it was okay.

So...

I argue against the cheating label. Yet, at the same time, I promise to re-double my efforts to follow the advice I often give to rookie teams, specifically, to carefully read and fully understand the entire rule book.

As to the future, I hope that FIRST either make the device officially legal or find some other way to keep from having teams blowing the 60 amp fuse.

Joe J.

P.S. By the way, in the case of the Chief Dephi Team the advantage gained from this device has been more mythical than real. To my knowledge, this device has never been tripped by a Chief Delphi Robot, not even in practice, yet alone in a match. We installed the device in on CD4 in a fit of paranoia after a single blown fuse in a single match (that was as likely as not due to a programming bug coded by yours truly ;-) Paranoia dies hard. We never removed the device eventhough it has never been tripped either on CD4 or CD5.

[archiver]

Posted by Ken Patton.   [PICTURE: SAME | NEW | HELP]


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.

Posted on 7/12/2000 2:53 PM MST


In Reply to: Cheating... posted by Joe Johnson on 7/11/2000 10:11 PM MST:



Joe-

I was not suggesting that you guys, or anyone else, intended to break the rules and gain an advantage by doing this. I totally believe that whoever was doing this was just trying to keep their machine from being stranded due to a blown 60A fuse. However, I think it's fair game for me to suggest that it might be possible to use this to create an advantage in terms of number of features that can run at one time, or the ratio that could be run for a given set of motors.

I want to raise my concerns because I think we competitors are all dependent on each other actively choosing to follow the rules. So hopefully I'm doing my part to exert some peer pressure.

Here's what is really bothering me: I think FIRST needs be more careful. I know they are dependent on the experienced teams for some new developments, because its usually the experienced teams that help solve the new problems (as you guys did here). And thats important - it makes for a better game if the robots run well. But these new developments - IF they depend on changes or clarifications in the rules - should be rolled out by FIRST to all teams in an update. That way (in my opinion) we won't have any concerns about anyone having an advantage.

So, sorry to stir things up - I don't think you guys cheat, you beat (nearly) everyone fair and square ).

Ken

[archiver]

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/13/2000 8:17 AM MST


In Reply to: Re: Cheating... posted by Ken Patton on 7/12/2000 2:53 PM MST:



I agree with you concerning rules clarifications/interpretations/updates/etc.

FIRST should make sure that all teams have access to the same information.

Perhaps they should have a web based forum to ask about rules & answer questions ;-)

Joe J.

[archiver]

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 7/13/2000 3:04 PM MST


In Reply to: seconded! posted by Joe Johnson on 7/13/2000 8:17 AM MST:



Joe, Jerry, Ken, et al,

I'm just a gearhead, but I've been confused since this '3x30

[archiver]

Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.

Posted on 7/13/2000 5:26 PM MST


In Reply to: Dumb Question posted by Dodd Stacy on 7/13/2000 3:04 PM MST:



Dodd,

The thing about fuses is that the amp rating does not tell all. Time is a very important factor.

A fuse that is rated for a particular amperage will be able to carry that amount of current forever at the rated temp (e.g. 20 deg C). They can carry twice that current for a shorter period of time, 3 times the current for an even short time, etc. As I recall, the 60 amp fuse can carry 120 amps for something on the order of 100 seconds.

Circuit breakers have a similar method of rating EXCEPT they typically have a much lower margin of safety (if you want to call it that -- it could be thought of as a higher margin of safety if you thing about 'safe' as being 'sure not to start a fire' rather that as 'sure not to trip' but I digress...) For example a 30 amp breaker while never tripping at room temp at 30 amps may trip in 30 seconds at 40 amps and 10 seconds at 60 amps.

Using the example numbers above, 3 thirty amp curcuit breakesr carrying 120 amps would trip in 30 seconds (each breaker carrying 40 amps). A fuse would require 100 seconds to trip. SO... 3 thirty amp circuit breakers would protect 1 sixty amp fuse. Yes, 2 thirty amp breakers would protect the fuse as well but it would be TOO well in a sense limiting current to much less than would normally go through the fuse without trouble -- note that 120 amps would trip them in just 10 seconds . Also note that 4 thirty amp breakers would do no good what ever as they could carry 30 amps each (120 amps) forever without tripping while the fuse would blow in 100 seconds. The numbers are approx. but the idea is the same.

As to mfg. variation, this is not a problem. Yes, one of the breakers blows first but as soon as it does, the other two blow almost instantly after because they are carrying 50% more current all of a sudden!

I hope this clears things up a bit.

Joe J.

[archiver]

Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 7/13/2000 8:40 PM MST


In Reply to: Timing is everything... posted by Joe Johnson on 7/13/2000 5:26 PM MST:



Thanks, Joe. Very clear. I hadn't realized that these devices (fuses) were so sluggish in their time response. I would not have thought they had sufficient thermal mass to absorb the I^2R loss above their rated current for so long before melting/vaporizing at the high resistance pinch point.

It's also interesting in the context of a 120 second match. If a 60 amp fuse will carry 120 amps for 100 seconds, perhaps it will carry 100-110 amps for 120 seconds? That would say we can run at a steady average system power of about 1 kw throughout a match, if the battery can maintain a 10 volt or so potential under a 100 amp draw. That's a lot of power.

Seems to me like it would be hard to blow the fuse unless you are stalling one or more motors for a significant period of time. But since each motor is protected by its own 30 amp breaker, and since the stall current on the 'big' motors is so high (I dimly recall), I would think the standard FIRST wiring schematic would provide adequate protection. At least if the drivers refrained from stalling multiple motors simultaneously for 10 seconds or more.

I only know that we've used all the more powerful motors (2 drills, 2 F-P's, and 2 van doors) and never popped a breaker or blown a fuse. Maybe we're not trying hard enough (but the GraceHopper wasn't exactly undergeared as it was).

Dodd

[archiver]

Posted by Michael Betts.

Engineer on team #177, Bobcat Robotics, from South Windsor High School and International Fuel Cells.

Posted on 7/14/2000 10:49 AM MST


In Reply to: Enlightenment, It's Electrifying posted by Dodd Stacy on 7/13/2000 8:40 PM MST:



First, let me say that I am more than a little concerned at the revelation that this 3X30 was allowed by FIRST and implemented by several teams without any mention of it in the Q&A section of the updates. I will bring this up at the Team Forum in August.

Secondly, I agree completely with Dodd:

'I only know that we've used all the more powerful motors (2 drills, 2 F-P's, and 2 van doors) and never popped a breaker or blown a fuse. Maybe we're not trying hard enough...'

The Bobcat has not blown a 60A fuse in the last few years (except once, when an attempt was made to connect the battery backwards). In fact, we used every motor (11) in the kit two years ago (to get onto the puck, et cetera) and never blew a fuse.

Many teams have demonstrated that competitive robots and 60 amp fuses are not mutually exclusive.

The Bobcat design team has always opted to err on the side of reliability within the restraints of the contest rules. In the last four years, we have never failed to make the cut for the finals in any contest we entered (in or off season).

It all comes down to trade offs.

One of the great challenges in engineering is the trade-off. Design requires a balance of functionality, reliability, efficiency, speed and power. Execution requires a balance of design, quality of manufacturing and strategy.

If you want high reliability, you will sacrifice some speed and/or power. It's that simple.

It is normal for someone to become frustrated if they are blowing fuses and, in a contest this size, someone always will (regardless of the size of the protection devices). After the frustration passes, it's time to review the design (Dr. J's superb white paper on motors was required reading this year), take some measurements and take corrective action (find the source of friction, reduce gear ratios, et cetera).

In the end, reality does not care about your design calculations and a real-world engineer has to learn to deal with it.

'We're gonna vent our frustrations,
And if we don't we're gonna blow a 50 [60] amp fuse
You can't always get what you want...'

With apologies to Messrs. Jagger and Richards.

- Mike

[archiver]

Posted by Ken Patton.   [PICTURE: SAME | NEW | HELP]


Engineer on team #65, The Huskie Brigade, from Pontiac Northern High School and GM Powertrain.

Posted on 7/17/2000 10:34 AM MST


In Reply to: Timing is everything... posted by Joe Johnson on 7/13/2000 5:26 PM MST:



From the manual, here are the specs for the circuit breaker (theres a plot on the data sheet also):

they will hold 100% of rating forever
they will be sure to trip when held at 135% of rating
they will trip in 2.5-6.5 seconds when held at 200% of rating

So for these short periods of time (which are long enough to 'launch' your robot from rest) you can overload the circuit breakers.

Ken

[archiver]

Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 7/16/2000 3:14 PM MST


In Reply to: seconded! posted by Joe Johnson on 7/13/2000 8:17 AM MST:



: I agree with you concerning rules clarifications/interpretations/updates/etc.

But the issue here seems to be only one of a creative use of components that, based on my readings, is not explicitly forbidden. I mentioned this somewhat in the other post that I just finished on this, but the only rules that I find on the use of the breakers is that they must be used in certain instances, and that they may not be modified. Without knowing the technical info behind the 3x30 device, it appears to fall into the rules that I have found...

Nate