I have included some more data for those of you that want to use the item line 5 profiles (20x20, 20x40, 40x40, 40x60, etc.) Although I have seen it mentioned on this site that the “automatic fastener” will not work for use on the robot, that is absolutely not true. In fact, there is no other system that uses an automatic fastener for connections of profile because there is no other system strong enough for it to work. The item automatic fastener (not bracket)has the highest strength to weight ratio on the market today and this attached data shows that fact. The automatic fastener for the line 5 profile weighs 1/4 oz and has a pull out strength of 500N (112.4lbs) and requires NO machining. I highly recommend they be used in pairs on each end of the profile. So the total weight for fasteners is ONE OZ. This is a fact. If you would like more factual data, please see the www.itemamerica.com website or call me at 262-363-4800 or email loren@item-midwest.com. I’d love to help you out with your projects and as a degreed ME with over 17 years of structural design experience, you can be assured of getting sound engineering advice. Go teams go!
The ITEM "Automatic fastener does have a high strength to weight ratio and is a good fastener - If you can afford it.
I advise against these types of fasteners because as it was pointed out in a previous post, THEY ARE SUSCEPTABLE TO VIBRATION. Field experience has shown they have poor seismic characteristics. A good fastener to combat this problem which team will encounter this year, are the fasteners BOSCH makes with serrated grooves on the fasteners. They meld into the aluminum T-slot and become vibration resistant. They actually carry a catalog specification for seismic loading, shear and tensile strength. The BOSCH fastening system is the best I’ve seen and I’ve researched 13 major brands.
Please post, for the students, engineers, and educators benefit, the factual data you have regarding your claim of vibration problems of the automatic fastener including the seismic data. I for one, would love to see that information and I’m sure others would also.
Have a great day!
Loren
Team 930
BTW - for those who would like structual and load data, please email me - the file is too large to post here. loren@item-midwest.com
Here is some experience with t-slot type fasteners on FIRST robots:
We have had steel t-slots nuts rip through the side wall of t-slots.
Universal fasteners have backed out of their milled hole, even when the hole is machined properly and tightened accordingly.
We sometimes have to drill thru the entire extrusion and put a nylock nut on the back side of a joint that is under a very heavy load.
There are factors which FIRST robot designers have to consider which industrial equipment designers don’t (at least not as much).
This 130 lb. weight limit is difficult to deal with. During the week before shipping, we will all be looking for ways to lose 2-8 pounds of weight on these robots. Sometimes a through bolt and a nylock nut is lighter than a automatic fastener.
In my 10 years of experience designing industrial equipment with t-slot type extrusion, I have not seen an industrial application that even comes close to a FIRST robot when it comes to vibration and dynamic loading.
One of the tips that FIRST gives new teams competing in FIRST is this:
“You are not ready to ship your robot until you drive it full speed into a brick wall three times w/o any problems.”
You can bet on this: there will be some machines that will be travelling up to 15 feet/sec, banging into the goals, other robots, and the field border. Parts will be left on the field.
As for team 45, we won’t be using any automatic fasteners on our robot this year. I’m not saying that they wouldn’t work, 'cause we haven’t tried them on a FIRST robot. Please let us know if they do for FIRST robot applications. I know they work well for industrial equipment, but that is a different story.
For my esteemed colleauge with team 930, the problems with Automatic fasteners that Andy & I speak of, and the “factual data” you asked for can be obtained from the following source: