Are standoffs and nylon rope good as structural materials?

With enough of them in the right positions, is it possible to make an efficient structure?

Standoffs are generally good. We used them this year to secure our gearbox into the drivetrain. Nylon rope, I have no idea. I’ve never used the stuff outside of the winch on a catapult.

What kind of a weird structure were you planning on building?

I was thinking of using string as reinforcement for structure, or where a lightweight but not overly strong structure is necessary. Standoffs (trussed) might be the main structural component in the robot, if they’re more efficient than c-channel or bar.

I love standoffs. They’re easy to build with, place, and they are extremely rigid. The only problem is that when stockpiled, they become extremely heavy.

I’ve wanted to use string as a method of bracing. Never actually looked into it though. I would think it’s a good idea however.

I think chain might work better than string because it doesn’t stretch.

If you haven’t seen, team 24 has often taken several standoffs stuck together (12+" long) and used that to brace their tower, attaching it at the ends with shaft collars which can be at any orientation. I’m guessing it works well for them. We’ve regularly used 8 2" standoffs to attach our drive to the primary crossbeam in our robot, and it’s very sturdy.

I’ve considered making a robot entirely made out of lexan, standoffs, and sheet metal for college. Not sure it’s lighter than regular aluminium metal, but it’s probably cheaper (the screws are the heavy part - they’re steel).

I’ve never placed them end on end, however I have used single 3 inch standoffs as braces. Works really well, sideways, but it doesn’t fix torsion problems as well as i’d like.

I thought you can only use a 3" cube of lexan now. . .?

There’s the standard HS materials, custom sensors, and:
Plastic cut from a 6x6x1" block
Steel OR aluminum cut from a single sheet no larger than 12x12" and no thicker than .07"
Two 3D printed parts, each less than 3x3x3"

So I’m thinking lexan bearings, sheet aluminum corner brackets, standoffs for the frame, and as few screws as possible. At that point, motors and batteries are half of the robots weight.

Cool idea. String can withstand a huge load (versus chain) and is very light.
One limitation is that it can only brace in tension, not in compression, but you may be able to design around this.
As was mentioned, the string stretching and becoming slack could cause you issues. Perhaps, if you could somehow use a screw and a standoff to rig up an adjustable tensioner (as below), you might be in business. From info I could find, nylon guitar strings stretch when they are new, but then stabilise (stay in tune). Perhaps the braided nylon would behave the same?

Good luck, hope it works :slight_smile:
Paul

http://www.polythene-sheeting-and-tarpaulins.com/acatalog/tensionclosed.jpg

Standoffs work great but can wiggle a bit in the square holes as there is only one attachment point. Used all over the place and can be much lighter than other elements. Over used and the weight of the screws can be more than you think.

String as a structural element I have not seen of too much in Vex. But if it works for the golden gate bridge it can definitely work in tension.

However i have not seen the golden gate bridge be driven around like you would move your robot. The string may get some slack and not exactly work like you might hope.

But it’s worth experimenting with!

One thing worth noting is that standoffs have a tendency to get loose when connected to metal. A few solutions are Loctite, or putting a teflon washer between a the metal and the standoff.

Yes. Last year (Sack Attack) I was able to create a robot that used nylon rope to extend and retract a linear slider. it used 1 motor, two high strength 36 tooth gears and a pulley system. This was significantly stronger and faster than a rack and pinion gear system, and allowed our robot to extend its arm to 5’ 2" and de-score the oppponet’s high goal easily without having to leave our side of the arena.

This year we experimented with using nylon cord with a winch to enable us to hang, but we have decided on a different method for hanging.

The nylon chord we can use is extremely strong and as mentioned previously is great in tension and awful in compression.

And do remember lots of early aircraft used cables for supporting most of the structure of the wings. It had to be light and extremely strong. The only downside was aerodynamic drag, which I assume at the speeds our robots move, shouldn’t be a problem.

The other problem most of you will face, the art of tying knots might be something you have to research a bit too.:slight_smile:

Good luck with the build…

If you need more than a square knot your are doing something seriously wrong.

Vex string is rated at 100 pounds so as long as you only require tension, string can easily take any weight you want to throw at it.

Alrighty then…

actually a square knot or reef knot is best for joining two ropes, assuming you are joining one end to structure than a bowline of some type (shown on that same site) or clovehitch would be better.

But if you want to attach to structure add tension and replace the metal turnbuckle shown earlier then use a trucker or teamsters knot.

Yes i once won a boy scout knot tying competition while wearing my gloves…:stuck_out_tongue:

The square knot is so easy and I just finished teaching some new scouts how to tie it so it was on the top of my head.

Also a monkey could tie it and it has an obvious look that makes it easy to recognize.

Really my point was that you don’t need be particularly good at tieing knots or even spend time researching it.

Extra Note) if anyone needs a pulley for rope nylon spacers work extremely well as the point of contact for the pulley. I recommend a long screw supported on both sides with spacers in between.