Mini extruded aluminum

[Ravi U]

We're just looking for teams who have experience with mini extruded aluminum. It's something we're considering. Anything that would be helpful or something we should be aware of about the aluminum would be greatly appreciated. Thanx!

[Porterhouse04]

It depends if you plan on using it for a frame or for some sort of an arm. We were thinking of using extruded alum for our frame because of its ease to bolt stuff to. the bolt heads slide right in for great modularity. This can also be a problem if you wish to remove something from the middle of the piece because you might have to take everything else off inorder to slide it out. I wasnt real clear on what you were asking but i hope this helps, good luck!

[kevin.li.rit]

Originally Posted by Ravi U

We're just looking for teams who have experience with mini extruded aluminum. It's something we're considering. Anything that would be helpful or something we should be aware of about the aluminum would be greatly appreciated. Thanx!

Do you mean 20x20 Profile or something else?

[KenWittlief]

there is a thread in here somewhere about a kit you can get from a company called "Item"

they have special prices for FIRST teams.

try searching on extruded or aluminum and it should show up.

[Jay H 237]

We've used extruded aluminum profile for some of our past robot frames with excellent results. Extruded aluminum profile is very durable and ridgid due to all of it's surface area and will avoid deformation compared to just regular extruded aluminum. As said above it is very modular due to the fact it has slots running it's entire length to attach fastners to. It comes in different dimensions and wall thicknesses. It also works well for prototyping since you can keep readjusting it and anything attached to it. To attach it together you can use gussetts or drill and tap the ends. For added durability you can use removable Loctite on the fastners(gussetts). If you don't have Loctite some teflon tape on the fastner threads will also give you the same result. It is possible to TIG weld it together but be 100% sure you won't have to add more hardware into the slots afterward. From a weight to strength ratio it's one of the best materials you can use although the cost is higher which can be a downside. As with any material the strength will be compromised if you "swiss cheese" it. Our robots used 80/20 but you can use MK, Bosch, Robounits, ect.

[KenWittlief]

one bad thing about it - when you have a kit like that, its very temping to start building 'something' before you have completely thought through what you want your bot to do, and how the bot will be designed to do those things.

Resist the urge to design with a screwdriver and hacksaw :^)

[Kevin Sevcik]

Our team has used extruded aluminum as well. About the removing nuts problem... we milled bigger slots into the slots so we could drop the nuts in without detaching everything and it worked relatively well.

While it is, indeed, very rigid and durable, it's not the best strength/weight option out there. A simple hollow square aluminum extrusion with the same weight per linear inch is going to be stronger than an extruded profile like this, because it will have all its mass at the outer extremities of the profile instead of wasted in the middle.

My current opinion is that it's great for prototyping or for a team without access to aluminum welding, but plain square tubing should be used if at all possible.

[Matt Adams]

Originally Posted by Kevin Sevcik

While it is, indeed, very rigid and durable, it's not the best strength/weight option out there. A simple hollow square aluminum extrusion with the same weight per linear inch is going to be stronger than an extruded profile like this, because it will have all its mass at the outer extremities of the profile instead of wasted in the middle.

This is true. However, you need to ask yourself, what is strong enough? I did this year... and I found a result that I like.

The moment of inertia of 80/20 1010, which is 1" x 1", is .04413 in^4
The moment of interia of 1" x 1" x 1/8 thick box is 0.0570 in^4

The weight of 80/20 1010 is 0.495 lbs / ft
The weight of 1" x 1" x 1/8 aluminum box is 0.511 lbs / ft

I would say that these two are comparable. However, after I've done some calculations, I actually think that 1" box and extrusion is overkill. 461 is going to use 20mm aluminum this year on our frame from Bosch.

20mm Bosch Extrusion
0.269 lbs / ft
Moment of inertia = 0.016 in^4

Quick number crunching calculation...

Let's say the 3' side of your frame has a robot ride up and apply all 130 lbs on one side right in the middle (worst case)

Stress at the ends and at the load point for a fixed end beam with a load F at the center, length L and section modulus Z (I / y) is:

F*L / 8 * Z for ends, -(F*L / 8 * Z) at load point.

20mm Bosch

(130 lbs * 36 in)/ (8*(.016 in^4)/(10mm/25.4mm/in)) =14,395 PSI.

The tensile stress for 6061 aluminum is around 30,000 PSI... I would say that 20mm is safe enough. Factor of Safety around 2ish... before bending would occur in the aluminum. And if it bends... you replace it. It's quick.

Using 1" box with 1/8" walls:

(130 lbs * 36 in)/ (8*(.0570 in^4)/(.5 in)) = 5,131 PSI.

Factor of safety around 6ish... that's a bit much for me.

My two cents.

Good luck everyone!

Matt