Weight Concerns
 

Weight is on everyones mind throughout the build season...but how many teams try to keep it in check

Do you wait till the end than cut it out?

Today we found out that we just simply many not have the weight to do what we wanted so the first thing that we turned to was the hole saws :yikes:

Now we are confident that we can do what we want as long as we drill everything out (with proportion and structure in mind)

Re: Weight Concerns
 

We dont take weight in mind in design, after the design is chosen we add everything up and see where we are. We had some major weight problems a few days ago, our projected weigt was around 130.
in general we try and keep it low during build, but sometimes have to drop some funtion to be under 120.

Re: Weight Concerns
 

We've usually had the habit of wait till the end, then cut weight.

This year we're taking it in stride and hopefully this leads to less (no) swiss cheese-ing the robot at regionals.

Re: Weight Concerns
 

I am guessing that you have used plenty of plywood in the making of your robots. I do not like the idea because you run the risk of a fire hazard. We just had our electronics testboard blow up on us. We had the door to the programming room halfway closed and we still heard it explosion-it sounded like someone let off fireworks in class. the good thing to havine plywood robots, as I see it now thanks to you Nitroxextreme, is that they have very adjustable. what kind of plywood are you using anyway.

Re: Weight Concerns
 

Once again where going to be a little to light. I told the team I have some 1/2" steel plate that I would donate to solve the weight problem.

Re: Weight Concerns
 

Take a sheet of 3/4-inch plywood. Flick your BIC lighter and hold it up to the surface of the ply. You will let go of the lighter long before the plywood catches on fire. Don't worry about it.

Re: Weight Concerns
 

I am talking about in the middle of a match. From the inside. This may set off the sprinkler system and ending the competition.

Re: Weight Concerns
 

For the last two years we've done a very good job of watching our weight during the build time and not had to cut anything once we got to the competition. Unfortunately, we seem to be designing very heavy this year. Last night we were already 15 pounds over, and that didn't take into consideration our pneumatics or our hopper. Today we went on a diet and did a little redesign while we were at it.

Re: Weight Concerns
 

i wasn't talking about a wood robot when i said hole saw...we used a metal hole saw to swiss-cheese our chassis

Re: Weight Concerns
 

I would like to know what kind of wood you are using, how thick, and how much. there are various kinds of plywood out there that you could get at home depot and lowes and, know said peices of information, help in the regulation of your robot's weight.

Re: Weight Concerns
 

I've posted before on this. Take a piece of 1/4" Birch or Oak plywood, some 6oz. s-2 fiberglass cloth and some laminating epoxy. Put one layer of fiberglass on each side. The strength is amazing. Cost - 4'x4'x1/4" 24$, 1 qt. epoxy 18$. 2 yard x 60" S-2 6oz. cloth 16$ per yard. Put some fiber in your robot's diet and you'll loose weight.

Re: Weight Concerns
 

My sons and I built a 17-foot expedition canoe last summer. It has a hull made of 4mm Okoume plywood with layers of 6-ounce glass on the inside and outside. It weighs about 60 pounds, which is at least 15 pounds less than an aluminum canoe of similar length and width. The biggest advantage of metal over plywood (even a glass/ply composite) is that metal has better puncture resistance. The ply/glass composite will be stiffer and stronger for the same weight -- or weigh less for the same stiffness and strength. Lexan is really strong, but for its stiffness it is heavy.

Last season, Wooden Thunder was hit so hard that our 1/4-inch birch plywood electronics shield actually cracked -- but it protected the controller. It took us 10 minutes to cut and fit a new one, which was installed in time for the next match. Light, strong, and easy to repair are all advantages of good plywood.

I swear that some year we are going to build a robot that is all hand-laid composites, and only uses metal for gears, conductors, pulleys, chains, and stuff like that. The towers I designed for Woodie last year would have been 3-inch diameter carbon fiber-fiberglass-epoxy composites on a foam core. They would have only weighed a couple of pounds for both of them, and would have been insanely strong. I was outvoted by conservative teenagers (curse them...). Really, the biggest shortcoming of epoxy-laminated composites in FIRST is that you have to really plan ahead on your connections and attachment pads. You can't just run a bolt through a carbon fiber column in any old place.

Re: Weight Concerns
 

If your robot exceeds the weight limit, I'd say that making swiss cheese of the chassis will only add to the trouble. I'd recommend making the frames simpler for each of the devices on the robot. For example, we built a loader that weighed about 18 pounds because of the metal frame we'd constructed around it to make it stable. Then we realized that we didn't need the half of the frame on the inside of the robot, because that part was already well-supported. We replaced the inside half of the frame with two tiny bits of metal connecting the front and back halves of the loader. Now the loader weighs 9.5 pounds (and dropping). We estimated that, because of the particular brand of metal we're using (80/20), we could only have saved a couple of pounds with the swiss-cheese strategy. So, I think it's more important to design the robot right than to drill it at the end.

Re: Weight Concerns
 

That's it. If time permits this summer I'm going to do a " Easy composites for First Robotics" white paper.

Re: Weight Concerns
 

To expand on what Henry's saying about how we (418) deal with weight concerns, we don't think about weight during brainstorming - we certainly do when it comes to how specific components will be manufactured. After 2004 (before my time but I know the story well) when we were 20 lbs. overweight when the robot was finished, we make a point of weighing every component as we go, and estimating the weights of stuff yet to be built.

If your team has had weight trouble in the past, or if your design looks like it might have trouble when it's all done, it's a good idea to keep track of this during the build and not just deal with it all at the end, for a number of reasons - if you're weighing individual components, then not only do you later have references for how much each part weighs in the event that you need to remove functionality to make weight, but if you're coming up heavy at this stage then you know you've got problems. What we're doing that seems to be working quite well is keeping track of each subsystem on a weight board, and lightening every part as much as we can without losing structural stability before the robot is together - the other thing that we've spent a lot of time on is deciding what goes first if we're still too heavy; this is a big decision, and if people are really involved in their own parts of the robot, it can be a somewhat emotional one as well; give yourself time to discuss what you're willing to sacrifice if it should become neccesary to do so, but lighten as you go as well. Hopefully you won't have to sacrifice functionality, but if you talk about it early then when and if the time does come, you don't have to make the decision in the last few days before ship, which are already stressful enough.

Re: Weight Concerns
 

Some tips for managing weight:

Before you start anything, weight the parts that will absolutely be on your robot -

the controller, spikes, radio, etc.
Include some extra weight for wiring. Include the back-up battery.
Then add transmissions, drive motors and some drive gears and some chain.
Then add wheels or treads.
Add the pneumatic pump and mandatory controls (regulator, switch, etc.
At this ponit, you have the required basics covered.

Subtract all this from 120 pounds and this is the weight you really have to work with.

Assign maximum allowable weights to each remaining subsystem based on past history.

For example:

Frame 8 pounds -
Ball lifting mechanism with motors 12 pounds
Shooter mechanism with 2 motors 15 pounds
etc.
Make sure the estimates are realistic for your capabilities and materials.

It is important to know that you really don't have 120 pounds to work with.
A big percentage of that weight is already allocated to the mandatory robot materials.

Re: Weight Concerns
 

yea, im a little worried about the weight of our robot.

Hmmm..im gonna haveta bring that up in tomorrows meeting...
haha...this is why i love chief delphi! :D :D

Re: Weight Concerns
 

lol, our chassy was over 100 lbs when we put it together, thats without the stuff to use balls.....so..yea..as u can guess...were gonna have to drill some holes....or something..but were not making swiss cheese, our chassey is sweet, if u can check it out, plz try, u will be impressed

Re: Weight Concerns
 

Several years ago, Cyber Blue made a spreadsheet available that contained common robot parts and their weight and also allowed for the user to vary quantity and such. It's been very helpful, but is now a few years out of date. Do y'all still have anything similar?

Re: Weight Concerns
 

Our team saves (well at least tries to save) every ounce out of our robot while we can...a mentor and i were having fun weighing everything that goes on the robot...so far with the shooter and the drive system we're at about 30 lbs. however, we have always been overweight in years past so we've already swiss-cheesed our shooter...i love how i just used swiss-cheesed in a sentence....I've never used cheese as a verb anymore...hehe :p

Re: Weight Concerns
 

Hole-saws are over-rated... there is nothing like a home-made hacksaw to do the trick.

Re: Weight Concerns
 

We always do a quick weight check before building (which always shows we have plenty of weight to work with) and by the end usually end up scraping the upper limits...no one's really figured out how that happens, but i have a hunch it has to do with the little fixes we make for problems that pop up along the way....

Re: Weight Concerns
 

normaly during the design of the robot we like to keep our weight in check or at a close average, we have done this for several years and have been pretty close every year with in 5 lbs of the total weight. another thing that alot of people forget about when building is the center of gravity and where yalls weight is efects how easy it is to tip over.

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So far, this year we haven't weighed our bot, but we have lightened parts to keep weight in mind.

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we're a new team, and so far I don't think anyone has realized that there is a significant weight limit. We're probably going to turn our bot into swiss cheese at the end.

Re: Weight Concerns
 

We are hoping to take ours to the local vet to have it weighed tomorrow.
We have the basic chasis without hopper, shooter, etc on it.

They we can weigh the big additions. Last year we were just over and we made a few plugs and then we were 4 ounces under.

Carolyn

Re: Weight Concerns
 

As of now, we are 90% complete and around 30-35 pounds UNDER weight.

We'll typically get the chasis built and working (wired), then weigh the robot, then we'll build the main component(s), weigh the robot, then go from there. If we're under...awesome, if we're over....we'll go machine holes in some non essential bars of our chasis.

Re: Weight Concerns
 

How much are the bumpers weighing? Are they coming out at the 15 pound limit (3 oz per inch) or are they weighing more or less?

We are just starting ours.

Carolyn

Re: Weight Concerns
 

There is a seperate 15lbs alloted to the bumpers + all fastners for the bumpers as per <R35>. http://www2.usfirst.org/2006comp/Man...obot_Rev_D.pdf , Page 11. We've yet to even really discuss/decide if we are going to build them or not. Odds are we will...we still have 15 days left. :)

Re: Weight Concerns
 

Make it work at a reasonable weight, then start thinking about what to cut. Mark what is not used, calculate weight in square in, then cut. Do this last after you spend forever measuring and calculating.

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This year our bot has more holes then it does metal. But it makes the bot look really hot.

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We're almost finished with our bot, but it weighs in 20 lbs over :( We at a lost, good thing we have 2 weeks to go on a diet.

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Hack saws = ok
Holes saws = good
CNC = very good
Water Jet or EDM = Friken sweet!

Re: Weight Concerns
 

Our team had hte same problem last year and the year before... We did th same things. Drilled holes. Worked pretty good.

Re: Weight Concerns
 

We haven't added a few things yet, and when we weighed ours the other day it was at 115...Because of the things we have yet to add, we went ahead and swiss-cheesed the bot, so now we SHOULD be underweight...I hope...

We had a really odd experience with the inspection scales last year at Chesapeake. Our shop scale showed ~119, but that thing can be a bit testy, so we weren't sure. When we got to Chesapeake, their scale showed 119.6. We measured out an extra .35 pounds of our arm material and added that; now the scale showed 118.4. :eek: We were lost...but decided not to mess with a good thing.

Re: Weight Concerns
 

You are at the end. Better find some metal removing tools.

I'm the weight guy for my team and have been for 4 years now. I weigh pretty much the entire kit every year. I then make an overhead weight with various control and ID components. Then I add to it as we add components. Our estimated weight is about 100 lbs right now, but we're missing some key items' real weights. We are already removing metal--some of our pieces have slots in them and I'm designing one system to be extremely conservative weight-wise.

Re: Weight Concerns
 

i dont think its possible to have a robot that is underweight without swiss cheesing it :rolleyes:

Re: Weight Concerns
 

We try to take it out as we go, but we don't have too much trouble. Our weight trouble comes at the end, most often, and we aren't there yet. We'll just swiss cheese it if need be. There is always some place to cut from.

Re: Weight Concerns
 

Our rookie year was two years ago, so this is only our third year. But over at 1410, we have never been overweight. The key is to keep it simple. The more simple a design, the less it should wiegh. Also, remember that you don't have to use a robot made entirely of metal. Actually, this year we will be bringing weights to comp. so that we can be at 119.576 lbs.

Re: Weight Concerns
 

^ lover and worshipper of the three- eyed demon who calls himself Hiei

our bumpers are complete and way underweight. we utilized those pool noodle thingies. we mounted them on 3/4" ply and covered them with a synthetic fiber covering. (i actually think it's a table cloth... >.<)

Re: Weight Concerns
 

We weighed our robot today and it's .4 pound overweight. We don't even have all the stuff on yet! D:

Re: Weight Concerns
 

Speaking of weight... Chris Fultz and I have a weight loss bet. The person who loses the least has the lead the "chicken dance" at the Boilermaker Regional. So far, I'm down 18 lbs. This may change, as my loving wife came home with some discount Ho-Ho's yesterday. What is she thinkin'? Maybe I should try a hole saw or two.

Oh... you guys are talking about robots. Ours is overweight too. It could also lose 18.

Andy B.

Re: Weight Concerns
 

Been there, done that, decided to do it different this year.

Gave each sub team (drive platform, shooter, ball picker-upper, electronics, etc...) a weight limit, and they need to do whatever necessary to stay under their weight. Sub teams can give up weight to another. This plan also helps keep a handle on center of gravity - not as critical as last year, but that ramp is steep.

Oh, we'll likely be a bit over this year, but we'll find that 2 or 4 pounds somewhere. Maybe fill the hollow stuff with helium...

Don

Re: Weight Concerns
 

no concern for our team what so ever XD

Re: Weight Concerns
 

Well, Team 1675 probably has one of the coolest robots ever........but saying that we already weigh 60 pounds with just the chassis, drive motors, and wheels. Our shooter is a tad on the heavy side and our ball picker up is somewhat light thank god. I'll see if we can release some super top secret plans........and put a picture up, or jus check out

http://www.chiefdelphi.com/forums/sh...highlight=1675

maybe you'll get the picture.......if you can see it. ;)

Re: Weight Concerns
 

If you don't manage weight from the beginning, weight will manage you at the end. After brainstorming, we set weight budgets for each major subassembly and then continue to refine the estimates as the build process continues.

Re: Weight Concerns
 

Team 213 usually runs into weight when the robot is nearly finished, and we put it on the scale and it is about 135 lbs. We are no better this year, we have not really considered weight as the demon that it is. I don't know if we will be overweight this year, but I am guessing so, seeing as we have plenty of CIM motors and aluminum sheet. Who knows though. Probably another swiss cheese robot. Check out our picture on the image gallery to see our machine. Team 213's machine. Also click on the link below to get to our team site (which is new) to get more detailed info on our team and our season so far (lots of pics).

Re: Weight Concerns
 

With 10 days left we decided we were about 18 lbs over.

I felt bad but when Andy Baker said they were in the same boat I felt better.

Time to get a dose of reality and trim the frame or redesign with less 8020 aluminim tubing.

I think the plan was good but the execution was prototyped but not perfected.

Re: Weight Concerns
 

you wanna hear a scary number...119.5 is the unoffical weight of our bot...+/- 3 lbs.

Re: Weight Concerns
 

we are not even done with the robot and still are a few pounds over weight :ahh:

Re: Weight Concerns
 

we're constantly checking now by going to wach group asking "how much do your stuff weigh?", cause our chassis and harvester makes a pretty good 91.5 lbs :ahh: so yeah that put us all in really high gear to drill holes and our hopper team and launcher team is trying to keep the weight factor in mind, now when we add it all up, I think we're right 120 lbs.