Save time? Use aluminum extrusion kits!

Technical Technical Discussion
21

The Bosch extrusion is NOT a superior product. A local business that builds industrial robots out of extrusion has completely quit using the Bosch because it is notorious for vibrating loose. And on a FIRST robot that is too risky.

Furthermore, some of the numbers you quoted are funny. The pullout strenght of 300+ lbs for the 20x20 is simply impossible according to the tensile strengh claimed. The material will fail and release the fastener before you get to 300 lbs.

The specifications claimed for the item extrusion are from actual test data posted by the manufacter. You will NOT see actual test data for the Bosch. Since in europe–where item originates–manufacturers claims must be absoluetly guaranteed, you will see very conservative estimates of structural strength. In our experience the material can be up to 3 times stronger than claimed in the catalog.

Which is better for a FIRST robot? You have to weigh strength and reliability against your pocketbook… But remember the free market ensures that “you get what you paid for”.

22

I’ve seen this before, but it wasn’t on ITEM’s site. It was on the Industrial Profile Systems website under applications. IPS was recently bought by Parker-Hannifin, the new link to IPS is: www.parker.com/industrialprofile/ The Applications section of the site is being restructured, claiming to visit back 12/19/03 (which, of course, has passed). “TechnoKART Robot” is listed on the image list, but without a link. I know this is the correct one because IPS is one of 470’s sponsors and before the buy-out 45’s picture was on the site.

23

I guess that I have a different opinion on something like this. Assuming that the robot needs to compete in 30 matches over it’s life time, that’s 1 hour of run time. I’d believe that the need of FIRST robots are significantly lower than industrial equipment, which is running for 8, 12 or even 24 hours spans. If this aluminum extrusion was so bad that a robot chasis could vibrate loose in a 2 minute round, I don’t think that Bosch would be in business!

Tim, since you’re a practicing engineer, I assume you made a quick napkin calculation about the pullout strength before you claimed that my numbers (from the manufacturer) were ‘funny’. I’d like to compare some numbers with you.

http://web.ics.purdue.edu/~mjadams/bosch2020.gif

Let’s go ahead and take the above 20mm extrusion piece, and pretend to load in a 15 mm long fastener, and assume that the bottom lip of the extrusion that holds the T nut in is 1.5 mm tall. That looks pretty close to scale. Then we’ll assume a 1700 N load on the bottom pulling it out. We’ll assume the fastener (a T-nut) does NOT span to the edge of the V cutout, but rather is a 1 mm short on both ends and there’s some bending going on.

Assuming the T-nut is 15 mm long, and for the sake of arguement we’ll even assume the piece of extrusion is only 15 mm long too, so you just need to just bend the flaps down to pull it out, and not shear the edges like you actually do, and which would multiple the strength SIGNIFICANTLY. We’ll treat the bottom flaps as two cantilevered beams, just to be safe

The transverse shear stress is 3V/2A
V is the shear force.
A is the area.
V = (3*1700N)
A = (15mm * 1.5mm * 2 sides)
Transverse Shear Stress = 31.875 N/mm^2

Bending stress = M*y/I
M = (1.5mm*(1700N/2 sides))
y= (.75mm)
I = (15mm * 1.5mm^3/12)
That gives me a stress of 226.66 N/mm^2

Since there’s transverse shear AND bending stress, Mohr’s circle comes into play here, so we’ll find that the max stress from Mohr’s favorite shape is:
226.66/2 + sqrt( (226.66/2)^2 + (31.875)^2 ) = 231.05 N / mm^2

With the tensile strength of the aluminum used in this extrusion being equal to 250 N / mm^2… it appears there’s a factor of saftey of about 1.1. We won’t go into some sort energy-distorsion or modified mohr for failure, I think my point is adequate as-is.

Since there were so many conservative factors in this entire calculation, I think that the pull out strength listed by the manufacturer is very apropriate.

I would enjoy comparing calculations that you did that say these numbers are “funny.” However, I’d appreciate if you’d include the shear stress needed to rip it out of the aluminum, since that would really be required to make the case.

Bosch is a Global company that originated in Germany… not to be too nit-picky. :slight_smile:

I agree. The numbers make this easy. :slight_smile:

Good luck everyone!!

Matt

24

As pointed out by Matt, Bosch is a German company turned International. Also, any good company will ‘downgrade’ their data when giving estimates data. Test Data is not the same type of data as Estimate Data.

If a company posts ‘Test Data’ they must post actual values recorded while testing their product. However, test data won’t tell you everything about the material. ITEM’s data is probably a hanging weight test (basically, hang more weight from the material until the ‘flaps’ fail or the material bends too far). But, there is no such thing as a perfect duplicate, and one piece may test differently the next (although probably very close).

Companies like Bosch provide estimate data which is often more useful for engineers looking to build something new. Estimate data often involves a safety factor.

The following is an example of a saftey factor in a product:

Super Rope, USA tested a specific rope type before release to the open market.
They test 20 ropes and conclude the rope can hold an average of 425 lbs before snapping.
In their product list, the rope is said to be able to hold up to 400lbs.

Look@ItGo Construction Company purchases the rope and begins to lift a cart of tools weighing 423 lbs with the rope. The rope snaps and sends the tools downward, most breaking.

Because Super Rope did not say “Our rope will hold 425 lbs” (as their test shows), but provided a downgraded value of 400, Look@ItGo has no way to claim Super Rope of being at fault for the broken tools caused by the failing rope.

While most companies will give their own safety factors, it is also important for those who are using the products to gather their own safety factors. In the above incident, if Look@ItGo was smart, they would have purchased a rope rated at 450 or 500 lbs and could trust that it would not break at a 423 lb load.

In conclusion, Bosch’s data may say that it is less rigid than ITEM’s, but in fact it could be better.

Remember, as Mark Twain said:
There are lies, there are ‘darned’ lies, and then there are statistics.

25

The BoschResxroth website lists actual test data from an independent testing firm. (thats what their website says)

Does anyone know about the interoperability of these systems? Can any system (80/20, Bosch, Item) with the same slot width use the same bolts, T-bolts, etc. I know i can sift through their documents and compare dimensions but I’d like to hear from someone who has tried.

26

Question for those who use the ITEM extruded. Which connectors do you use to connect 2 pieces perpendicular to each other. We ordered the professional kit and none of those connectors seem to work very well for connecting the corners of the frame together. Just thought I would ask. Maybe you all have a picture of the connections? Thanks.

27

Hi Anne,

The two fasteners that came with the Pro Kit are 1. Standard Fastener and 2. the Automatic Fastener. The Standard Fastener is what is primarily used to make the corner connections you ask about. The fastener is comprised of two pieces, the bolt and the pressure plate. Prepare the extrusion to make the connection by tapping the core bore (the hole in the center) to M5 x .8 (standard M5 threads) about 8-10mm deep. Then drill a clearance hole thru the other piece of extrusion - we used a 4mm drill but a 3/16" will work also - the hole is only there do you have access to the bolt head of the fastener. The clearance hole you drill will be 10mm from the end when making corner connections. Drill the hole completely thru. Now assemble the fastener by putting the bolt thru the pressure plate, making sure the flat side of the plate is facing the bolt head. Now thread the fastener assembly into the tapped hole, just finger tight and then slip the pressure plate down the slot of the other extrusion piece. As you slide down the slot, look thru the clearance hole you drilled - you will see the bolt head come into view. Once you have aligned the edges of the two extrusions so they are square and flush, you can put your allen wrench thru the clearance hole and tighten the connection. Make sure you tighten it well - this will ensure the connection does not come loose. I can email you the PDF pages from the catalog showing how they work. I can’t link them here, they are too large.

Hope this helps - good luck this year!!

Loren
engineering lead
Team 930
Mukwonago Masters of Machinery
M-Cubed

28

WE have Used Bosch in the past two years. 2002 we used 30x30 and it was very heavy but extreamly strong. 2003 out entire robot was pretty much built with 20x20 and 20x40 and we also had a linear sliding elevator on bosch.

pics are included below
pros: Flexiable chassis, strong structure, fast assembly if designed and cut right, flexible designing and quick changes.
Cons: Heavy(welded chassis can be much more stronger and lighter then bosch), high maintainance(we had to have 5 ppl with tork drivers to tighten all the nuts after every couple matches) and expensive. wow each t-nut was almost a buck each. tnuts break or bend quickly on over tightening, allignment is difficult at times.

2003
includes delrin sliders

http://www.mvrt.org/gallery/data/media/21/pic%20108.jpg

as you can see we made many many many custom plates to hold the extrusions.

WE are planning to use Bosch again this year!

29

We use an extruded product from AMC Quick Connect in Rochester Hills, Mi. their smallest section is 25.4 mm square. They use 6063-T6, which is a heat treated aircraft aluminum. They have a wide assortment of fittings and have given us excellent service. We are very satisfied with the ease of use and performance of this material and are sticking with this brand.

Our Martian robot had over 100 matches on it last year and held up extremely well. We did have to retorque fasteners from time to time. I would recommend that anyone with a bolted together frame to check and retorque the joints. A torque wrench might also be handy.

30

i saw that last year i wanted to use it this year. i spent 2 months looking for it and didnt find squat sence i didnt know the name. by now we’ve settle for a lot less pretty material. and too bad i wont be here next year.

31

im wondering if Item or anyother company sells extrusions. also are the 20/20 profiles for Bosch rexroth and ITEM the same? can i use bosch with item fasterners and back. Bosch rexroth fasteners are really expensive, t-nuts $.75 a piece and blocks $1.50. Im wondering how much is item and will it work with Bosch and if i can buy without the package. Other companies would work too. Does anyone have any experiance with the inch series?
info would be great!
Thanks!

32

You could try 80/20. They make 1"x1" 1"x2" 2"x2" and many other sizes. We used the 1"x1" last year and are using it again this year, and have found it to be strong enough for our needs. It is actually lighter than comparably sized aluminum tube, until you add the fasteners. This year we welded the frame and saved nearly 20 lbs from not using fasteners. T-nuts and fasteners do add up, both in weight and cost, however.

Cory

33

Yea well our school is not allowing us to use our welder so we cannot use the weld material. So need to get bosch and i want to find out where i can get the fasteners for cheaper. thanks
AmX

34

not to mention t-nuts can be almost as big of a pain as set screws

35

Well, seeing as this is a thread about aluminum extrusion, theyre kind of inevitable. They dont come loose all that often if you use them properly. We never really had trouble over two competitions, although they do need to be tightened periodically.

Cory

36

any time we can we try to eliminate t-nuts by just drilling and tapping to eliminate the t-nuts

37

We eliminated T-nuts by using 1/4-20 square nuts and 1/4-20 x 1/2" button head cap screws. These work extremely well and are quite inexpensive compared to the metric t-nuts.

If you tighten them with a long-handled allen wrench or a 3/8" drive allen head socket then they will not come loose in competition. The hardened cap screws are very tough. None have broken in 2 years of competition.

The square nuts do not turn in the extruded channel, and can even be forced into the channel from the side if the end is blocked, just like T-nuts. We got them from MSC.