A couple of points when considering robot weight, just from my experience:
- Make sure you use a reasonably accurate scale. Make sure it/they are tared correctly! (I saved us 4.4lb in '99 by noticing that we were weighing the scales)
- don't forget the electronics, especially wire. Whenever you weigh a pile of parts, just put the whole spool of wire on. Consider a "dummy box" that is full of random stuff that weighs the same as the electronics.
- Remember which parts you can't modify, and make sure everyone knows what they are! Don't be scrambling through tech inspection because a freshman put holes in a few motors to save weight. Make a "can't modify me" sticker for these items if you have to.
- During build week 4 or 5, review everything on your robot, and know what is required versus simply nice to have. Have a checklist of things you would ditch to save weight. make sure they are easy to remove. This is also useful for prioritizing what things still need to be built. Build the must-haves first.
- Remember your triangles and circles. Many things can be made of much lighter weight material if they are structurally sound, like triangles.
- Certain parts can be considered disposable! In 2009, out front cross beam (bumperless area) was 1/16" Alum. L instead of 1/8" because it saved on weight. We had to straighten it at least three times per comp, and had a spare. It could be replaced in a few minutes, and the pit crew could straighten the bent one while the robot was off at a match.
- Have a weight adding plan. In 2007, we strapped over a dozen Lead diving belt weights (plasti-dipped due to the lead-ness of them) tie-wrapped onto the robot. Because they were small and easy to attach, we put them in strategic areas. Each one added a little over a pound. We used them to move the center of mass of the robot more to the center, and closer to the ground. Never came close to tipping.
- Have a parent with a sense of humor that will duct-tape a 12" crescent wrench to the bottom of the robot three days before ship. Makes you think about losing weight sooner, and you get a few free pounds back when he fesses up.
- Consider welding your frame instead bolting it, if you intend to use many brackets. There is surely a local millwright or welder that will be excited to help out, and they are handy for other things too! Hardware adds up. Consider tapping holes instead of using a nut. Makes a great learning experience, and you only have to buy a few extra taps
.
- There are many jobs that a tie-wrap can do just as well, or at least adequately when compared to other fasteners. Same thing with plastic/nylon bolts or nuts.
- Hollow shafts and tubing can save weight very quickly without sacrificing much in the way of strength.
- Know your safety factor on a design. A safety factor of 5 or more is simply adding weight. Also know which hole will take your safety factor from 3 to 1 and don't drill it (Another good item for stickers)
- You will be shocked to know how much weight you can get of of 1/16" polycarb with just a 1/2" hole punch and a couple of freshman-hours. (Actually only a few ounces)
Hope this helps!