Designing A Light Robot

[Munchskull]

I was wondering what tips and tricks your team uses to design a robot that is light and effective? What lightening patterns does your team use? Where do you use 1/8in wall vs 1/16in wall? ect.

[MichaelBick]

Building a light robot is all about materials and geometry.

We use 2" x 1" x 1/16" wall 6061 aluminum tube everywhere, except for the drive side rails. The tube is plenty strong for FRC purposes. The only issue we have ever had with 1/16" wall tube is crushing the tube by over tightening screws. Using 7075 aluminum instead of steel and #10 screws instead of 1/4-20 helps a lot too.

As far as geometry goes, try to triangulate and use flanges to build rigid but light structures. We also try to use as little lightening as possible, preferring to use thinner materials instead.

[RonnieS]

Originally Posted by MichaelBick

Building a light robot is all about materials and geometry.

We use 2" x 1" x 1/16" wall 6061 aluminum tube everywhere, except for the drive side rails. The tube is plenty strong for FRC purposes. The only issue we have ever had with 1/16" wall tube is crushing the tube by over tightening screws. Using 7075 aluminum instead of steel and #10 screws instead of 1/4-20 helps a lot too.

As far as geometry goes, try to triangulate and use flanges to build rigid but light structures. We also try to use as little lightening as possible, preferring to use thinner materials instead.

Minimize your bolt use and get some aluminum rivets. You would be surprised how much lighter your robot gets if you go through and design the entire bot first with material applied correctly. When you just pick up parts and start building you don't have a grasp for real weight until you pull out the scale and realize your 20 pounds over.

-Ronnie

[Munchskull]

My team already uses aluminum rivets. How much differences does using 10-32 bolts make?

[MichaelBick]

Originally Posted by Munchskull

My team already uses aluminum rivets. How much differences does using 10-32 bolts make?

Rivets (especially aluminum rivets) will be far lighter than bolts. 10-32s are about 30%-40% lighter than 1/4-20 bolts, which can probably save a couple pounds depending on how many bolts you use.

[Munchskull]

Also my team often uses 1/8" sheet metal for structural attachment, is that overkill?

[MichaelBick]

Originally Posted by Munchskull

Also my team often uses 1/8" sheet metal for structural attachment, is that overkill?

For gussets, probably. We usually do 1/16" unlightened gussets or 1/8" lightened gussets. Honestly though there isn't a lot of weight to be saved there.

[MrForbes]

We usually let the chassis be heavy, so we are forced to make the rest of the robot light. And we like using a variety of materials. Thin aluminum tube, polycarbonate sheet, thin aluminum gussets, thin plywood, etc. If you do it right, you can have some weight budget left over, and maybe put a couple wood 2x4s in the bottom of the robot, to impress the judges.

[GeeTwo]

Mostly, we stopped using 80-20, started using KISS. It's better to never build a 10 pound tertiary manipulator than to shave 10 pounds off your drive chassis or primary manipulator in the last few days before bagging.

As others have said, use materials (especially fasteners and adapters) with good strength-to-weight ratios.

Also, use parts that actually fit together with at most a single adapter. For a prototype, you can bolt two hubs together for a shaft adapter. On the real robot, use the right shaft from the start or spend the money for a COTS shaft coupler.

Develop a weight budget and weigh sub-assemblies regularly (every build session). Learn to recognize that you're going to be overweight early enough in the process to take corrective measures (parts replacement, redesign or reallocation) that preserve functionality.

[evanperryg]

Originally Posted by Munchskull

I was wondering what tips and tricks your team uses to design a robot that is light and effective? What lightening patterns does your team use? Where do you use 1/8in wall vs 1/16in wall? ect.

Since strength wasn't all that important this season, we used 1/16" tubing everywhere. Wherever we could, we used rivets, and wherever we couldn't use rivets, we used aluminum bolts. (except on the collector... learned that lesson the hard way) Aluminum bolts are way lighter, although they aren't nearly as strong.

[Munchskull]

Where do you purchase aluminum bolts?

[cgmv123]

Originally Posted by Munchskull

Where do you purchase aluminum bolts?

http://www.mcmaster.com/#aluminum-cap-screws/=yevh92

[IKE]

Minimizing thickness is my preferred method.
In a 2 foot long piece of 1x1 box, how many lightening holes does it take for 1/8 to match 1/16 with no holes...

[Cory]

Originally Posted by Munchskull

Where do you purchase aluminum bolts?

You don't want to use aluminum bolts in 99.9% of FRC applications...and anywhere you might, you'd be better off using nylon bolts (screwing electronics down is the one area that comes to mind).

Aluminum bolts are going to shear very easily, as well as potentially gall, since most threaded mating parts in FRC are aluminum also.

[evanperryg]

Originally Posted by Cory

You don't want to use aluminum bolts in 99.9% of FRC applications...and anywhere you might, you'd be better off using nylon bolts (screwing electronics down is the one area that comes to mind).

Aluminum bolts are going to shear very easily, as well as potentially gall, since most threaded mating parts in FRC are aluminum also.

This is an important thing to consider. We made the fatal decision of using aluminum bolts to attach our collectors at Wisonsin, and got knocked out in quarters after one of them sheared.However, we did use them in other areas on the robot where they weren't taking so much stress, and never had an issue with them.