Quote:
Originally Posted by eagle33199
The biggest way to lose weight... Ask the inspector to take his foot off the scale 
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Quote:
Originally Posted by Al Skierkiewicz
Cmon! Jeff and I only did that to you once! OK maybe twice but that was all I swear!
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Al, it may have happened once or twice when you weren't around
On a serious note:
Weight management is a subject that is very near and dear to my heart after spending 15 years building spaceflight hardware. When the contracts include penalties that run on the order of $60/gram for being above the spec limit, you learn to pay a lot of attention to weight.
The first thing I tell rookie teams in any of my presentations is to buy a decent scale. It's an investment, just like any other tool. One I like is
this one from Grainger. It's just over $200, has a 400 lb capacity, and has a remote display so you don't have to try and get your head under the robot. The extra capacity means you can set a plywood platform on it so the robot will fit, or that you can weigh your crate before you ship to Championship after your well designed under-weight robot wins your regional

If you really can't afford to buy a scale, try the one the wrestling team uses. Or find a local company (sponsor) that will let you use their shipping scale a few times. Buy a small scale and weigh all the parts of your robot. There really is no excuse for showing up at the competition being 10's of pounds overweight.
The rest of the secrets have been mentioned several times in this thread already:
1) Make a weight budget.
2) Enforce the weight budget.
3) See #2. If a subsystem is not going to make their part of the budget, make them negotiate with the other subsystems to see if anyone has any excess. I usually withhold 10 lbs as "Engineering Reserve". The team members would rather negotiate between themselves than try to get any of that from me. If we have any left, they get to add decorations, etc. Or I get to add weight to put the CG where it needs to be.
4) Use the CAD tools not only to pay attention to the weight of parts you design, but to decide how much work to do to to purchased parts. We use the CAD models from AndyMark, etc to evaluate different lightening schemes vs. the amount of work. Keep in mind the added benefit of reducing the rotational inertia of moving drivetrain components such as gears and wheels, just don't get carried away to the point that structural integrity is compromised.
4) Design from the beginning with weight as a design parameter. Think about how you can make each part lighter while making it strong enough at the same time. It is much easier to put holes in a part before it is assembled than after the robot is together. Avoid the "we'll just put it all together and see how much it weighs" trap at all costs. It never seems to come back apart to do the necessary work later. Making shavings before you put the electronics in is much preferred to getting metal bits inside them. The holes also look a lot nicer if they are carefully laid out, nicely finished (deburred), and if the part is painted, the holes are too. And if you design them into the part and lay them out properly, you can avoid having an over-enthusiastic freshman drill holes too close to the edge of a critical structural part.
5) Take advantage of the bumpers. You get to rigidly attach a 5" wide strip of 3/4" plywood to the side of your robot. That can provide a lot of structural support if you take it into account during your design process, and it's free weight.
6) See #2.
7) Use creative materials. Composites. Plywood (yes, really. We built most of our 2011 robot from 12mm Baltic Birch plywood). Plastics. Avoid steel unless absolutely necessary, and only for small parts where needed.
8) Pay close attention to the number of fasteners. An ounce here, an ounce there, suddenly you are talking about pounds.
9) Same goes for wiring. Plan your layout to minimize the number of inches of high current (large gauge) wiring runs. This has the added benefit of keeping the resistance down. Just make sure you don't cut everything so short you don't have any slack to work with or that things are so tight they pull out of the connectors.
10) See #2
As I have mentioned on CD before, the three things I say most often during build season are (in no particular order):
1) Is your homework done?
2) That's in the rules.
3) How much does that weigh?
If you pay attention to weight during weeks 1-5, then it is a non issue during week 6. Nothing pains me more as a Robot Inspector than to have to help a team cripple or remove their well thought out game mechanism, rendering them unable to do more on the field than drive, just because there is no way to lighten up their robot enough at the competition any other way.
My final comment on the subject: Thinking you will just drill a few holes in things when you get to the regional if you are overweight is a recipe for disaster, or at least a very non-inspirational event. If you ever think about taking this approach, please sit down and calculate how many 1/4" diameter holes you need to drill in a piece of 1/4" aluminum plate to reduce the weight by 1 lb. I promise you will be surprised.