Weight Saving Techniques

[IKE]

Originally Posted by Andrew Schreiber

No... it's still required. Playing out here is rough. (This is partially joking, it's a lot rougher than I remember MI being though)

It was a rough game this year.

[BrendanB]

Originally Posted by IKE

It was a rough game this year.

True but its a rough year every year up here even with bumpers.

[bkahl]

Originally Posted by Kevin Leonard

A lot of people on this thread have mentioned using thin-walled aluminum as a great weight savings technique.
A lot of people on this thread have not competed at a New England event.

Originally Posted by BrendanB

True but its a rough year every year up here even with bumpers.

Originally Posted by Andrew Schreiber

No... it's still required. Playing out here is rough.

I'm going to start by attesting to the New England defense, our robot took a BEATING this year.

195 always goes overkill on material thickness, but its almost always for good reason. Our intake this year was made of welded 3/16" aluminum. Overkill? Maybe... but did it hold up? Yes.


Here's some general tips (Yeah, they're probably repeats, but they can't be over stated.):
-Over account for electronics weight...wiring does have weight, and its more than you'd think. (IIRC we left 20-30 lbs for electronics this year.)
-Go a size above what you think will work for Aluminum thickness. Its better to be safe than sorry.
-Always do CAD estimates, but know that the estimate is lighter than what it will actually be. CAD is just mean like that.

As for weigh-ins... I suppose we got lucky last year in Hartford.

[MechEng83]

Originally Posted by bkahl

-Always do CAD estimates, but know that the estimate is lighter than what it will actually be. CAD is just mean like that.

CAD isn't mean. It's a computer program. GIGO. Your calculation is only as good as the information you put in.

Just for general information, material nominal dimensions are sometimes given at what is known as "minimum material conditions" (unless specifically noted otherwise with a tolerance). This means that the 0.125" sheet you buy might actually be 0.127". The 1"x1"x0.0625" square tubing usually has pretty good dimensionality on the 1"x1", but the 0.0625" is very much a minimum requirement. Strength calculations for structural tubing are based on the nominal size, so the piece has to be at least that strong. Suppliers will target thicker materials to make sure that with manufacturing tolerances, they meet/exceed the minimum. They, of course, have an incentive to minimize the excess material to save on cost, but there is always the extra bit. Extrusions also don't have sharp intersections on internal corners. The fillet of material will add to the weight.

CAD models can account for this if you model all features and include the maximum material conditions.

[abhem]

Im sure the obvious technique is to always use aluminum as opposed to steel whenever possible. Swiss cheesing is also a great choice. To save on weight, our team uses gusset plates to secure vertical and horizontal posts rather than using crossbars. Although crossbars are very handy to secure posts, gussets work equally well, if not better when made correctly. They also save a ton of weight and lots of physical space on the robot.
Using gussets to secure "swiss-cheesed" bars/c-channel/etc. is a powerful combo to save weight