Our team spent a lot of time searching the internet to find a hook to hook onto the horizontal bar that could hold over 100 lbs. We didn’t have much success.
Can anyone give ideas where to buy one or how to make one? We are a young team, so we don’t have much fabrication experience. It would be better if we could buy one then figure out how to attach it to our ascension mechanism (which we are still working on too). Right now the hooking spot is a horizontal piece of steal, so if the hook was connected to a flat piece where we could just screw it onto our steal plate, that would be perfect!
Bent aluminum rod worked for us in '10. We fell once but it was because of a bent eye hook, never had a problem with the actual hook.
We went with a modified shark hook in 2010; it was fashioned from some black steel IIRC. Worked like a beaut.
If you make something from scratch, use extremely few parts, let’s chances for failure.
May I suggest Lexan, or square tubing.:]
Thank you for these ideas, keep them coming if you can :]
I have a vise, torch, and big hammer in my shop, so I could probably make a hook from steel that would work. But I don’t know what you have available.
If you have a jig saw or band saw, you could cut a hook from sheet aluminum rather easily. You might need to order the aluminum though, if you live in a small town. 1/8" aluminum will probably work, if you design the hook so it has sufficient width.
Also, not having any idea what you are going to attach the hook to, it’s hard to be more specific about how you could make the hook.
and plywood works too! http://www.chiefdelphi.com/forums/showthread.php?t=111128
It’s not too hard. Bend some aluminium rod in a pipe bender, mill a hook out of some 1/4" plate, make some out of thinner plate and standoffs… whatever works for you. I bet you could do it with Kitbot frame material.
Repurposing some C-clamps might be a reasonable approach. Particularly ones similar to this http://www.sweetwater.com/store/detail/CClamp
Or use them as inspiration for building your own.
Here’s a fairly simple one to make.
If you decide to make your own (I personally wouldn’t because I was also an eyewitness to the incredible badassery of a shark hook - it’s very light and it’s just about the right size for the pipes once you grind the barb off), you can easily model a hook in any material in either Solidworks or Inventor and then run a simulation to see if it would yield under the 100+ pounds of force. I’d be happy to explain the process if you’re curious.
Again, thank you all very much. Additional ideas always welcome.
As we try something and it doesn’t work, this gives us additional ideas to continue working with.
We prototyped a hook out of 1/4" 6061 aluminum plate, it easily supported a robot equivalent of weight.
Modify a climbing carabiner, large size, by removing the gate or the locking mechanism of the gate (depending on whether you want to lock onto the bar or use the hook elsewhere). I’ve seen teams lift robots with them before. If they can hold a 200lb human, they should be able to hold a 150lb robot–just make sure you get one rated for that weight.
As an added bonus, they’re not going to be terribly expensive.
Carabiners are traditionally rated in kN (approximately 225 lbs). The ratings are specific along the different parts of the carabiner, if you are going this route talk to your local outdoor store and see what they have.
Most carabiners are rated to 23kN, which is close to 5000 lbf. I warn, if you compromise the alloy structure of the 'beaner you significantly reduce its integrity, thus its holding strength. So if a team is going to use (aluminum) climbing 'beaners you need to design a coupling device that does not drill, cut or otherwise damage the unit. Steel ones are another story.
For Breakaway, our team fabricated a hook out of carbon fiber. It wasn’t used in competition, as we followed our normal path of late mechanical construction and the winch mechanism was never integrated on the robot. It continues to be the object of strength testing to this day.
It was moderately simple to make (compared to the rest of the Breakaway robot that also used significant CF components). The mold was made by gluing+screwing a couple of 2x4 pieces together, and cutting out the hook shape on the bandsaw. After sanding and sealing with epoxy, we polished and waxed the surface, and then used PVA for a mold release. The hook layup was done with a wet process: 3 layers of 3K 2x2 twill CF, one layer of segmented 0.25" Nomex honeycomb, and 3 more layers of CF. Wrapped in a vacuum bag and left overnight. The whole thing took about 4 days in total to fabricate (3 for the mold making, and 1 for the layup).
Having described this, I believe the team will use a conventional, non-locking hook this year fabricated from aluminum. CF is a fun material to work with, but you have to be particularly careful of post-layup machining as the dust becomes hazardous.
I am an avid rock limber and when the gate is removed the holding force along the long axis drops considerably usually from around 25kN to around 7kN it should be stamped right on there though but 7kN is still far more than you would ever need (about 1500lbs-force)
Everyone, thank you for your hook suggestions! We used the one posted by Greg. The sweetwater clamp works perfectly! We used two of them on top of our ascent mechanism.
Thanks again to everyone!
What is the thread diameter and pitch on the lower threaded hole? Would be sweet if it threaded straight onto a Bimba.