Weight

FIRST General Forum
#21

Have we considered the possibility that the teams that run up against weight problems each year just arenā€™t taking 130 as a serious limitation until much too late in the process. They tend to do this because they are unconsciously thinking ā€œ130 pounds - thatā€™s a lot. We donā€™t have anything to worry about - if we run into problems, then we will just cut a bunch of holes at the end.ā€ As a result, they donā€™t plan their robot weight budget properly, and have to resort to hacking off entire subsystems or drilling 1482 lightening holes at the last minute.

I think we need to be going the other way. Rather than promote the belief that 130 pounds is a rather generous number, why not reduce the weight restriction to 120 pounds (or less)? I theorize that at 120 pounds, including the battery, nearly all teams will recognize that the weight restriction is a hard problem right up front and will begin to plan accordingly. As a result of the earlier (and arguably better) planning, I would predict that teams will have more weight-conscious designs and the number of last minute ā€œslash-and-hackā€ weight reduction efforts will be reduced.

So, rather than increasing the weight restriction, we need to decrease it by 10 pounds or so (or just increase the mass of the battery or other non-negotiable parts by 10 pounds while keeping the restriction where it is, which would have the same effect). And then have FIRST throw a copy of the Atkins diet book in with each kitā€¦

-dave

#22

i think i am going to take this discussion in another direction for a second. in this past year it seemed like it was a huge scandal about adding stuff to the robot during the competition and not getting re-weighted. while part of me would love to see the weight increased (make my hair stay in) part of me would like more of a challenge of decreasing the weight limit to 12o (giving a new challenge for the upcoming year) i think that as long as people still tend to bend the rules at the competition adding up to 5 lbs over weight and still competing i think that the weight limit should remain the same as it is still a great ch allege to some teams.

i personally think we should go back to alot of old rules like only using whats in the kit + 200 from small parts. that would be a challenge!

#23

Two points:

1.) We used every motor except for a seat motor at the UTC Regional and still made weight with a 59 inch tall robot. This said the weight goal is not out reach. With a tighter electronics package to reduce wire we could have been under weight, but then we would have added more functions because we could. Most teams seem to feel if the goal is 130 you want to be no less that 129.

2.) I feel the weight is already too high to be safely handled by two people. I belive the OSHA policy is a 35 lb max without lift assist devices. As a guideline the company I work for likes to keep lifts even lower. I would actually like to see a weight reduction to challenge the veteran/powerhouse teams. Having to trade off weight durabillity and functionallity more in a game like last years would make an even better contest.

My $0.02

#24

Our weight budgeting always seems to start something like this:

battery: 12 lbs
electronics / wiring: 10 lbs
chassis: 10 lbs
gearboxes/drivetrain: 100 lbs

remaining functionality: -2 lbs

I probably see it that way because Iā€™m always in charge of remaining functionality, and it never seems like enough. I think 130 pounds is a good, aggressive weight limit, but truthfully weā€™ll work to whatever the requirement is (higher or lower) and budget according to whatā€™s most important. We feel our drive train is the most important so we make it robust, but we have to make choices - is having two speeds worth not picking up a widget in this game?

Weights and cost work this way: start with a top down budget to all the components from the requirement (with margin) to see where you need to be, then do a bottoms up detail roll-up early on to make sure you can get there. We use goals and requirements - requirements add up to 130 and goals usually about 110. Update it frequently to make sure youā€™re on track.

#25

I totally agree with you about the weight being a little too much for 2 people to handle. Itā€™s good we have carts and donā€™t actually carry the robot everywhere.

I also think that 130 is just about right to include max.functionallity and still let two people carry it with moderate difficulty. I like the weight limit as of now because it is just enough to let us build what our wild imaginations tell us, yet safe. Reducing might limit us to a lot things, and increasing is a safety hazard.

#26

How many carbs in aluminum?? :eek: :smiley: :yikes:

#27

I agree with Lavery, I think that 130 is pretty generous (even though Iā€™ve seen us go over it, but usually by just a little). I think 120 would be a better idea then 135 or 140. In real life you canā€™t just hope theyā€™ll bump up the weight limit. For example, shooting a payload into orbit (and especially if going out of orbit) you have to be very cautious with how you use your resources, because it costs much much more to launch something that weighs more.

One thing I would like to throw into the mix though as a thought, over the past 3 years I have noticed every year that the scales vary so much from competition to competition. In 2002, for exampleā€¦ at the local regional we weighed 129 pounds, yet when we got to Epcot for nationalsā€¦ we were weighing in at 134. I think many others have run into this issue as well, and I personally wish that the scales were all calibrated equallyā€¦ but at the same timeā€¦ it makes you want to try to keep as far under the 130 pounds as possible, in case you happen to run into a scale that overweighs you by 5 pounds. The teams who donā€™t look into that possibility could run into this problem, even if you design right around 130ā€¦ so Iā€™d suggest working around 125 because of this issue. Trust me, itā€™ll save you tons of frustration.

#28

At nationals in 2002 I remember that there were two scales that varied almost four pounds I think, so this is a very good point.

#29

i remember a speech by Dave Lavery talking about the mars mission, and how he thought it was incredible how so many of the same aspects that go into FIRST also went into the building of the mars robots. size, weight, and material limits, objective tasks, required functions, etc. he said that the game really helps you with possibe real-life objectives. did he call up the people building the rocket and say ā€œHey guys, itā€™s Dave. Uh, listen, could you maybe improve the rocket a little bit so I can make my bot 5 pounds heavier?ā€ No, he accomplished the mission as it was, and did better than anybody ever imagined. doing the game every year within the 130lb weight limit is all part of the challenge, and i think it should stay the same.

#30

Iā€™ve noticed that too - itā€™s frustrating but, unfortunately, itā€™s another real-world thing weā€™ve got to deal with.

I agree with keeping the weight limit as it is. Having a weight limit of 130 lbs is something teams have been able to count on year after year for a long time. While it would add to the challenge of next yearā€™s game, I think lowering the weight limit would cause a lot of frustration among teams especially if itā€™s lowered by as much as 10 lbs.

Upping the weight limit wouldnā€™t help at all. Like Cory said earlier, if you upped it 5 lbs, people would find 10 lbs of stuff to put on their robot. If you upped it 15 lbs, theyā€™d find 20 more lbs to add on. If you want to play that game, why have a weight limit at all? Oh yeah, because itā€™s part of the challenge. Itā€™s a constraint teams have to deal with. If you donā€™t want to worry about weight restrictions, go join Battlebots.

#31

I think Dave hit it on the head (as usual). Even after 8 seasons in FIRST our team still doesnā€™t place enough emphasis on the weight limitation. We discuss it. We think about it in the backs of our minds. But in the end we haul out the Rotozip and go to town. While itā€™s only a few pounds itā€™s still a glitch in the process.

I agree with everyone else in that 130 pounds is a part of the challenge. It is just one of the many design constraints that needs to be considered when developing a solution. Adding more weight doesnā€™t make the challenge any easier, it just makes the robots heavier.

Thanks to ChrisH for the weight management tips. You can be sure weā€™ll put those to work for us this coming season! :slight_smile:

Seah

#32

This is the best reason yet to change (reduce) the weight restriction on FIRST robots for next year. Veteran teams have become complacent about this issue. Many of them start designing some of their subsystems in the fall, working under the assumption that the weight limit will be 130 pounds. They then have (yet another) leg up on the rookie teams and others that wait until the kick-off to really start planning out their machine.

Imagine the utter chaos that would ensue if every team really had to start from the same baseline of knowledge - or lack thereof! :slight_smile: Imagine NOT being able to count on certain things to stay the same from year to year. It would do more to ā€œlevel the playing fieldā€ between veteran and rookie teams than almost anything else FIRST could do.

It makes you wonder what sort of sick, twisted mind would do such a thing to all those innocent teams out thereā€¦

-dave

#33

Uhhhā€¦that would be your mind Dave!!

Dropping the weight really would turn the veteran teams on their ear. Weā€™ll have to keep that in mind when considering new ideas for this coming season!

Thanks Dave!

Sean

#34

I donā€™t wonder at all Dave :smiley: . But I think it might have been more of a shock if you hadnā€™t tipped your hand ā€¦ :yikes:

Although Iā€™m sure it would still shake things up - I suspect anyone reading this would likely expect that it couldnā€™t happen.

I do, however, think one change might be in order. I agree with most that the weight limit should NOT be increased, but since we are changing out batteries throughout the competitions, and we are subject to ā€œspotā€ weight checks (which I think are a good thing) I think the official weight should be specā€™d W/O battery. I would like to see the limit at 120 (or whatever makes sense) without battery.

#35

This would certainly remove all possibility of a team using a battery with the innards removed for weigh in, as some have been rumored to do in the past. Note: I have no personal knowledge of such an occurrence, but I have heard rumors about it for years. I am not picking on any particular team as I canā€™t remember any that those particular rumors have been directed at. I think it is an urban legend myself, but it could happen ā€¦

As an inspector, I have tried to always make sure that the robot could actually operate with the weight-in battery to minimize the chance this could occur. As a team member, weā€™ve always weighed both our batteries and marked them so we knew which one to use for weigh-in. Some years it has made a difference and others it hasnā€™t.

Yes the scales have varied from event to event in the past. In Houston I think the difference between the scales that were there was like four pounds. I know there was one scale in particular that we directed robots that were just barely overweight to. The inspectors had no clue as to which one (if any) was ā€œrightā€. This year seemed to be better and I noticed that they had calibration weights in the inspection area at the events I attended. So letā€™s not beat on a problem from past years that has been fixed.

Personally I think that robots should be weighed every time they enter the competition area. Just put a scale at the robot entrance to the arena. Before you can enter, one of the crew must verify that you meet weight. It would certainly stop complaints that ā€œso and so put an entire new arm on after they weighed inā€. While it would make things a little bit more difficult for the queuing crew, it might also prompt teams to be a little more prompt for their matches. If teams knew they were going to need to weigh-in and there might be a line then maybe they would leave their pit before the very last second.

I know in LA we inspectors tried to watch out for the ā€œmorphing robotsā€. If we recognized that a robot was sporting a new appendage, then we would send the team back to the scale. But it would probably have been pretty easy to slip several pounds of ballast past us, if it wasnā€™t too obvious.

#36

While it wasnā€™t taken to this extent, at the West Michigan regional this year, each robot that was chosen for the elimination rounds had to weigh in again. A sticker was placed on the battery they used for this weigh-in, and that battery was the one that had to be used for their first match in the elims. This helped with the issue of different battery weights in some ways (you could choose which battery to weigh with), but it also hurt you if you tried to use a lighter battery that you didnā€™t normally use for competition.

Our team has had the same experiences, as most if not every team has. In 2001, for one example, at Great Lakes we weighed 118.5, at West Michigan we weighed 117, and at EPCOT we weighed 123.5! Thatā€™s a huge difference to try to plan for. Iā€™m in agreement with all the people who think we should weigh in without the battery and drop the weight limit to another number.

Hereā€™s a suggestionā€¦what if, for a year or two, we changed the robot specs back to what they were in 1992? The robots were small but could still be presented with challenges that they could complete successfully. Iā€™m not familiar with the rules and the specs from the early years, but Iā€™m sure that parts exist that we could use. It would provide a very different challenge than what weā€™re used to now, with the 10-foot tall bars, different zones in which to score, and ramps. Just a thought.

#37

In my first year (associated with FIRST), the weight was 85 pounds, the current limit was 40 amps (total) and the base constraint was a 30" diameter circle. These constraints (and others) varied from year to year until recently.

We truly anticipated the kickoff because it defined not only the game but the design constraints as well.

This is real world. Being handed ā€œimpossibleā€ constraints forces the engineering/ā€salesā€/manufacturing team to consider trade offs.

A few years ago, I had posted on a few threads here where the issue was the size of the main battery current limit (Then a 60 amp fuseā€¦ If it blew, you were dead.). I had stated that the Bobcat had never blown a fuse and the teams that had done so had not paid attention to their power budget.

Anyways, the total power was raised (which caused a slew of new problems) and, in retrospect, Iā€™m still not sure that FIRST did themselves or us a favorā€¦

Tackling ā€œimpossibleā€ design challenges led to an amazing and unprecedented era of technological developments in the late 20th century. We put men on the moon, telescopes in orbit and robotic rovers on distant planets. The outcome of which can be symbolically represented by the enabling technologies inside the laptops most of you are using to read this message.

Another benefit of fluctuating constraints is that it levels the playing field. Designing a robot (or robot subassemblies) in pre-season becomes less profitable to veteran teams in terms of something which will be used this year. Pre-season activities become slanted more toward educating the workforce (mentor and student alike) to be able to respond to whatever twisted and devious challenges Messrs. Flowers, Lavery and Kamen (et al) might throw at us.

Also, fluctuating constraints in a very tight timetable forces a discipline on the team which is beneficial to everyone involved. We learn (or relearn) the importance of a structured timeline, (sub)system requirements and intelligent trade off analysis. Moreover, it forces the entire team to actually read the rules and approach the design as a team exercise!

Therefore, a proposal for varying constraints:

Weight: 80 to 140 lbs.
Base size: 20 to 30 inches by 30 to 48 inches.
Height: 20 to 60 inches.
Geometry: Approximately every other year, use cylinders, pyramids, trapezoids, etc.
Power: 80 to 120 amps at 12 VDC.
Cost: Between 3K and 5K (with no subsystem constraints).
Components: More variation (example: Skip using CIM motors for a year or vary the number of Drill motors from 2 to 4 for a year).

Bottom line: Some people will complain no matter what the design constraints areā€¦ I say: Let ā€˜em and bring it on!

#38

I want to second (or third or fourth) the thanks to ChrisH for his comments on how to manage weight budget. We have been bitten for the past two years by the weight constraint (despite paying attention to it and modeling all parts of our robot) and had to delete a module each year. We were planning to implement something like ChrisHā€™s system this year, because wondering where we were in terms of weight caused a lot of stress. We didnā€™t think of ā€œWeight Czarā€ as the title for the Configuration person though!

When people talk about the ā€œbad old daysā€ of 80 lbs in FiRST, they do not seem to remember that we have a lot of weight allocated to required components, many of which are heavier than their equivalents back then. The battery, control system and cables, backup battery, fuse panels, blinky lights, numbers on four sides of your vehicle, etc. are all a substantial portion of a robotā€™s weight (25 lbs). If you use pneumatics, I think you have 10-15 lbs taken in valves, compressor, tubing, regulators, etc. Also, the motors (drills and chips in particular) are more powerful but heavy.

This past yearā€™s requirement that all modules must fit into the 130 lb probably made teams with lots of design and fabrication resources have to either make design compromises in the modules or cut the number of modules on their robots.

I would say that the 130 lb constraint is ā€œcomfortable.ā€ It does limit teams that can ā€œdo everythingā€ and make them prioritize what is important. Teams that donā€™t pay attention to it will get bitten. However, teams that are just getting started are not likely to bump into it. It is consistent with the size constraints. I.e. a robot that is 30"x36" with all the required components will come in around 130 lb.

If FIRST knocked 5 lb off the weight requirement, it would present a challenge to most teams. I donā€™t think adding 5 lb would be a good idea though. Knocking 10 lb off the requirement would create a significant imbalance that would probably result in less exciting competitions.

Regarding procedural changes at competitions, such as weigh in before competing, FIRST should be very careful about this. The staffs putting on competitions are clued in about the previous yearsā€™ procedures. When you throw something new at them, they take some time to accommodate it. I suspect that you would have a lot of forfeits on matches in the beginning, either because of battery-to-battery variation, scale-to-scale variation, last minute repairs that result in a couple of ounces on a robot, etc. You would also have a continuous line at the weighing station throughout the competition.

What would you gain? The truly competitive teams are extremely unlikely to be gaining an unfair advantage by going over weight. They would probably reserve 1-2 lb and add an adjustable weight mechanism. At the weigh in station, they would add/subtract the few ounces necessary to get them into weight. The teams which are not so experienced would be the ones getting eliminated. And, does this really help FIRST achieve its mission?

#39

I think weā€™re heading towards less weight actuallyā€¦

#40

ā€œlevel the playing fieldā€ā€¦ could this be a hint about next yearā€™s game? :smiley:

i donā€™t think we should worry about changing the weight limit, bu8t instead worry about makign the scales in use more accurate. my team weighs our robot with some of the most accurate scales around. i remember one time where we knew our robot was 129.4 and when we put it on the scale it read 130.7! all we did was pick it up and put it down again and the scale read 129.8! my numbers may be slightly off, but the idea is what is important - the scale was varying. the fact that it can have almost an entire pound variance of weighing the same exact thing really shows how innacurate they are.