We have used the ITEM brand aluminum extrusion for the past two years and have had awesome results. ITEM’s is stronger than other brands of the same size (Bosch, and others)–we had a 200 lb student stand and bounce on our box frame (frame stood on long end) and it only flexed a bit. It didn’t break or permanently deform. See the attached pictures!
This year, the ITEM company is selling kits of extrusion and fasteners at drastically reduced prices for FIRST teams. Go to: www.itemamerica.com and click on the FIRST link at the bottom of the home page.
All you need to use this structural material is a standard wood chop saw (miter saw preferred) with a carbide blade and a few allen wrenches. It cuts and machines easily for modification and is a breeze to assemble. Be sure to use cutting fluid on the blade.
The best part is that you can change the dimensions of your drive train or chassis in MINUTES, not DAYS when machining stock aluminum or welding.
We have already ordered kits for 2 of our rookie teams because it really does save time!
is to make sure you have triangles in your frame - like bridges do
we had a square frame last year made with something similar, and we had a 10" x 18" 1/8" alum plate in the middle that supported pnuematics
we moved the plate at our second regional, and our bot was weaving and flexing and swaying like it was drunk
then we realized - the rectangle plate had been acting like two connected triangles that were supplying the ‘three corner’ rigidity
we put it back! :c)
theres lots of ways you can do this - plexiglass side panels act as triangle - or even just small plates in the corners will be enough to stiffen up your chassis.
I disagree. We’ve tried the extruded frame for the last two years and have had some problems. First, the locking T-nuts are very expensive, and the bolts for them are non-standard and must be ordered rather than just going to ACE and picking them up. You can get the cheaper, non-locking kind, but you have to slide those in from the end and that is often impossible, or at least very inconvienient. Also, the bolts are notorious for coming loose (yes, we even used loctite). Plus, without said triangle plates, it is very difficult to hold a square, even with the inside-corner pieces that you can buy to accomplish this task.
159 has (tentatively, I can’t speak for every one) decided to weld a frame this year, and just stick with a design we think will work, rather than become obsessed with morphability.
Aluminum Extrusion rules! We’ve been using it since the 2000 build season and its just awesome…lightweight and durable…the best of both worlds.
Actually in fact our 2001 bot was used on one of their advertisement posters for FIRST teams in 2002…im sure that picture is somewhere here on the website, but i dont have time to search for it, otherwise I would. Im sure Kyle or Clark Gilbert has a copy of it somewhere that they can post
What you don’t see is that we do put on panels around the sides (polycarbonate) and on on the bottom for a skid-plate. The drivetrain is mounted on a thick 1/4" aluminum plate that easily screws to the extrusion using the T nuts. This adds the stiffness you mentioned, although the ITEM extrusion joints don’t flex much at all–it’s good quality stuff.
All you need to make the plates is a saw to cut the aluminum plate and a drill to make the mounting holes for the motors, gearboxes and speed controllers. Drill more “speed holes” to reduce the weight.
The controls are mounted on a similar panel that goes in and out with four screws. It has been a very easy design to build, maintain and work around in.
Sorry you had trouble. We did not have a similar experience… of course ITEM was one of our sponsors so we could just get as many T-nuts as we needed.
Also, the brand of extrusion is important… some stuff is cheaper, but that’s because they use a weaker alloy and lower grade fasteners.
The kits that ITEM is selling for FIRST come with the hardware (nuts, bolts, tnuts, etc.) used to assemble them. The nuts are reusable. All you need is a good drill (drill press recommended) and the proper size of metric allen wrenches. Ball-heal allen wrenches are best. Splurge on a good set of tools as you usually get what you paid for and cruddy tools will damage the screw heads.
Without reinforcement plates, our simple 30x36" robot box frame easily held the weight of our largest (250 lb) team member when they stood in the middle of the bars!
We got the Pro kit… Since most of the cost (90%+) is in the extrusion, you could divide the cost by the total number of feet in the kit. The pro kit comes with 60 METERS of extrusion, that comes to about $10 per meter… pretty cheap in the long run!
I’ll try to get a sheet from ITEM that specifies the cost per part and post it here.
We’ve been using the same stuff since we started. It durable and easy to build with. But stay away from those Zinc T-nuts They crack, stick the the brass. We had about a dozen cracked t-nuts by the end of Annapolis.
On another note we built our cart out of aluminium profile as well. And it rocks.
I was hoping I could find it here on the forums!! I have a copy of it, but it’s on my computer at home, and that computer is no where near being hooked up…
It would make for a good example, but that thing is sooo old now I don’t even know if the deals/kits are still the same.
Maybe Baker will come out hiding from the robot design frenzy week and talk
I’m wondering what all comes in the kit…well I can read the little advertisement, but all the teams I’ve been on have never use extruded aluminum…does anyone have a picture of a kit, or of some of the elements within the kit?
So here’s my question; what’s the difference between this and 80/20? It looks like the same extrusion profile from these pictures, except 80/20 has a lighter version with four holes running down the length of the extrusion as well as a solid version.
these have grooves that allow you to put fastners anywhere along the length - you hook them in and they will slide anywhere - also the end pieces are easy to use
its like a hi-tech erector set - except you are not limited by holes in the metal for placing attachements.
Hopefully I can answer your question regarding the differences in extrusion systems. My engineering company used many other brands in the past, but because we require performance and value, we settled on the “item” brand (not to be confused with the IPS brand - which is not and has never been the same as “item”) extrusions in our shop. As Tim mentioned, there are wide differences in dimensional tolerances and alloy which in turn reflect on the strength of the extrusion. Equally important is the method of attachment - other systems have copied the item fasteners but they do not work unless you have a high strength extrusion to use them in. item has been in business for over 26 years and is the world sales leader in structural aluminum systems. So why is this important to you? It means you get a highly engineered and respected building system with very high level of engineering support. item is committed to staying at the top which is why they have decided to support FIRST teams with an outstanding value in the form of “kits” that contain the neccessary extrusions and fasteners to put together a modular and strong robot. Team 930 has used these kits exclusively for the past two years - and as anyone that has seen our robots will attest too - they are strong, rigid, and light and we have never had a fastener break or come loose. If you or anyone else reading this post has any questions about applying the system to your project, please contact me at loren@aes-wi.com.
As a side note, I would like to clarify what size extrusion is in the kits. The extrusion size(s) - depending on which kit you use - has 20x20 and 40x20 size extrusions. This is the outside dimension size in millimeters. The weight (size 20x20) is 0.48kg/m (approx. .33lb / ft) and the 4th moment of inertia is 0.72cm4 - for those that want to do the calc’s - which I highly recommend you do when comparing systems. The pullout strength for a fastener connected in the t-slots is 500N (112lbs.). More engineering information can be obtained at www.item-international.com or contact me at loren@aes-wi.com.
If you’re really looking for quality, then you want to go with Bosch 20 mm.
Bosch Rexroth:
3m of 20x20 for $20.00 (no discount)
I = .67 cm^4, (.016 in^4)
W = .4 kg / m, (.269 lbs / ft)
Pullout = 1700 N, (382 lbs.)
Tensile Stress = 250 N / mm^2
**Item: **
3m of 20x20mm for $25.50 (discount)
I = 0.72 cm^4
Weight = 0.48kg/m (.33lb / ft)
Pullout = 500N (112lbs.)
Tensile Stress of Aluminum = 245 N / mm^2
I’ll leave the choice up to you.
It’s considerably lighter, just slightly less rigid, about 20% cheaper, and has better fasteners.
I believe Raider Robotix’s 2002 robot, Silver Scorpion, used extruded aluminum. That robot was the one that required the least maintenence of all. It practically never broke, or required much more maintenence than a change of battery in between matches.
I have a copy of it, but it’s on my computer at home, and that computer is no where near being hooked up…
