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.