Weight

[JAH]

Originally Posted by Cory

If the weight limit is raised 5 pounds, people will find 10 pounds more crap to put on their robot.

No matter what the weight limit is, a large number of teams will *ALWAYS* have trouble making it

Cory is exactly right. If teams got 5 more pounds, then they'd just make things more robust and add more to it and in turn be 5 pounds over that limit. I'm sure there would be some teams who would act blind to the new limit and be over a bit and be ok, but there are many who would not and would want to use every single pound available. The weight problems would stay about the same, in my opinion. I believe it should stay at 130.

[Mike Martus]

There are several important concerns that have been brought up here.

1. The 130 weight is a design constraint, part of the challenge.
2. Safety - 130 divided by two persons 65 each that is still a lot of weight if you fall or have a distance to go. A Major safety concern.
3. Next year I believe that the battery will not be included in the weight and there may be a gain if say FIRST decides that 120 lbs is the weight without the battery. A net gain of about 4 pounds or more.

No matter what the limit is set at, I believe that there will always be the "pushing of the limit" to build the best durable machine.

Teams that are consistently designing and end up with weight problems need to look at their design process and make corrections in "Weight Management".

[Swampdude]

For some strange reason we've never built a robot more than 135 pounds (prior to seriously considering weight reduction). Usually the kit material puts you in a standard range for extra robot material to wind up around 130-135 pounds, it's some kind of natural law. Anyhow, I have faithfully thrown my back out every year carrying these things on and off playing fields. But I still would like to see it go to 135. It has been our magic number.
This year we were really on the ball with weight reduction in the design (120 lbs) but, at the comps we had to beef her up to take the punishment everyone was dishing out, and wound up 131 minus shavings to 129.999.
The thing is, years past without trying too hard we got around 135, then this year we went overboard and got 120. It's not a big difference. Experience has taught me how to do a lot with 5 lbs - true. But inexperience and 5 extra pounds would make making robots (which is extremely stressful) much easier.
It would be good to see a weight study showing what the kit material puts you at for a typical bot configuration. Then see what kind of weight/mass ratio is left over. I bet it's not much.

[ChrisH]

Originally Posted by Mike Martus

There are several important concerns that have been brought up here.

1. The 130 weight is a design constraint, part of the challenge.
2. Safety - 130 divided by two persons 65 each that is still a lot of weight if you fall or have a distance to go. A Major safety concern.
3. Next year I believe that the battery will not be included in the weight and there may be a gain if say FIRST decides that 120 lbs is the weight without the battery. A net gain of about 4 pounds or more.

No matter what the limit is set at, I believe that there will always be the "pushing of the limit" to build the best durable machine.

Teams that are consistently designing and end up with weight problems need to look at their design process and make corrections in "Weight Management".

Some tips for Weight Management

1) "budget" no more than 90% of the weight limit. ie if the limit is 130 lbs then the total estimated weight of all systems should be no more than 117 lbs.

2) Identify and quantify non-negotiable weight first. So know how much your controller, breakers, lights etc. weigh. Subtract this weight from the budget.

3) what is left is available for adding non-essential systems. Note: depending on the game, a drive system may be negotiable.

4) Assign budgets for all subsystems based on criticality. A really critical system should have a bigger budget than a nice-to have.

5) Do a weight estimate for any proposed subsystem BEFORE you build it. Hint we've found that Inventor is pretty good at weight estimates if you put in the correct material data.

6) Use your estimates to trade off between systems.

7) Resist the temptation to say "I think I can get a couple of pounds out" and then use the lower number. Every item in your estimate should have documentation to back it up. If you think you can take weight out, fine. Prove it first, then change the number.

8) Track the weight of each subsystem continually. If possible weigh each part before it goes onto the robot.

9) Use a spreadsheet for your weight tracking. Constantly compare actual vs estimated weight. Beat on the designers of subsystems that are over weight to get the weight out. The spreadsheet can also be used to identify "heavy hitters". Items that are extraordinarily heavy (and thus prime targets for speed holes) or items that use a lot of weight for minimal functionality.

10) Assign a single person whose whole job is to make sure you meet weight. We call ours the "weight czar" a term that comes straight out of the aircraft biz. In fact, at the "bird factory" I work in, every program has a whole department dedicated to tracking the current estimated and actual weight of the aircraft. We wouldn't do that if we didn't think it was important, there too many other things we need to throw bodies at to waste them on something unimportant.

11) Remember that nothing ever gets done within the budget. That's why you only allowed 90% at the beginning, to account for unknowns and overruns. If that doesn't work this year, then next year cut the budget to 85%

[Stu Bloom]

Originally Posted by ChrisH

Some tips for Weight Management

...at the "bird factory" I work in, every program has a whole department dedicated to tracking the current estimated and actual weight of the aircraft. We wouldn't do that if we didn't think it was important, there too many other things we need to throw bodies at to waste them on something unimportant ...

Chris is ABSOLUTELY correct. Regardless of what the numerical limit is, it would benefit us all to use these weight management ideas.

Here at Rolls Royce we also have several people dedicated to tracking the weight of our engines. Any change that is proposed for any flight engine is heavily scrutinized for weight impact. We pay a hefty financial penalty if our engines exceed contractual weight limits.

[dlavery]

Originally Posted by punkrawker303

Who want[s] a little more weight for there[sic] robot instead of 130lbs? I mean at the last couple days you [could] have more weight then you need or should have. I think they should add 5 more pound[s] to the weight limit. [W]ith this 5 pounds you could open the possibles [possibilities] with 5 more pounds. What could you add to your robot that is 5 pounds that could really help you? [S]o who likes the idea[?]

Have we considered the possibility that the teams that run up against weight problems each year just aren't taking 130 as a serious limitation until much too late in the process. They tend to do this because they are unconsciously thinking "130 pounds - that's a lot. We don't have anything to worry about - if we run into problems, then we will just cut a bunch of holes at the end." As a result, they don'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 "slash-and-hack" 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 kit...

-dave

[Greg Needel]

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!

[Peter Matteson]

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

[Gary Dillard]

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 I'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 we'll work to whatever the requirement is (higher or lower) and budget according to what'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 you're on track.

[Bharat Nain]

Originally Posted by Dzdconfusd

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

I totally agree with you about the weight being a little too much for 2 people to handle. It's good we have carts and don'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.

[Stu Bloom]

Originally Posted by dlavery

... And then have FIRST throw a copy of the Atkins diet book in with each kit...

How many carbs in aluminum??

[miketwalker]

I agree with Lavery, I think that 130 is pretty generous (even though I'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 can't just hope they'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 example... at the local regional we weighed 129 pounds, yet when we got to Epcot for nationals... 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 equally... but at the same time... 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 don't look into that possibility could run into this problem, even if you design right around 130... so I'd suggest working around 125 because of this issue. Trust me, it'll save you tons of frustration.

[Cory]

Originally Posted by miketwalker

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 example... at the local regional we weighed 129 pounds, yet when we got to Epcot for nationals... 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 equally... but at the same time... 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 don't look into that possibility could run into this problem, even if you design right around 130... so I'd suggest working around 125 because of this issue. Trust me, it'll save you tons of frustration.

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.

[Mike Ciance]

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 "Hey guys, it's Dave. Uh, listen, could you maybe improve the rocket a little bit so I can make my bot 5 pounds heavier?" 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.

[Katie Reynolds]

Originally Posted by miketwalker

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.

I've noticed that too - it's frustrating but, unfortunately, it's another real-world thing we'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 year's game, I think lowering the weight limit would cause a lot of frustration among teams especially if it's lowered by as much as 10 lbs.

Upping the weight limit wouldn'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, they'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 it's part of the challenge. It's a constraint teams have to deal with. If you don't want to worry about weight restrictions, go join Battlebots.