Routing of Telescopic Arms

For the last few years, my team made large frame-like elevators, like this:
https://grabcad.com/library/frc-elevator-mechanism-1

We’re noticing that the best teams are instead using telescopic arms, which require much less space. How does the routing work for those (for the strings, or whatever mechanism they use to extend the arms)? I know how continuous and cascading elevators work, but I don’t know how they condense it so much. Does anyone have a diagram of how that works?

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I was a little confused as to what you were asking. I think I narrowed it down to “How do teams make telescoping arms/climbers?” It’s actually pretty simple (if you are going with cots).

Our team used the Thrifty telescoping tube kit. It consists of 2 side plates with bearings and constant force springs. Then you use nested 2"x2" aluminum tubing, 1.5"x1.5" aluminum tubing, and in our case 1"x1" aluminum tubing. Then the constant force springs are connected to the bottom of the next inner stage (shown below).

The point of the constant force spring is to pull up on each stage and extending the arms. If let go while compressed the arms spring up pretty quick.
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Then you just tie a rope or cable to the top hook and run it down the center of each tube to a winch or shaft. Then you let the rope out and the arms extend and vice versa.

That’s how our team did it. There are several different ways out there to accomplish the same thing.

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Is the question more about how to actively power in both directions? I think 3847 had a telescoping mechanism in 2018 with motors & chain. Search for their CAD library maybe

Most teams with telescoping arms don’t actively power in both directions. They use springs to raise it and a winch to pull it down. Whiles it’s possible to power in both directions, its not nearly as easy, especially when you consider all the COTS solutions available.

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I had the same thought but maybe OP meant the large pick and place telescoping arms like:

But they aren’t very popular so I’m not sure.

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Agreed. If the established spring-out / winch-in telescoping mechanisms work for your need, they’re probably the way to go. If not (e.g. if you need a manipulator on the extending end that is too heavy for the spring to lift), then the solution will be custom & more complicated.

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They definitely did - 3946 and 3039b allied with them at Red Stick Rumble. They spent most of the time between matches trying to whack that thing straight enough to keep it from binding. The Pink Team (233) is well known for arms which extend, rotate, and have a manipulator on them; check their site for designs as well.

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Hello. If you are asking as to how COTS telescoping arms work (as seen in 2020-2022 for climbing), I am able to give you an explanation. If you are looking for how a telescoping arm works that is powered in both directions I’d recommend checking the rest of the replies.

For COTS telsecoping mechanisms, such as AndyMark’s Climber in a Box, TTB Telescoping Tube, or WCP GreyT telescope, there are multiple stages made up of box tubing. (1x1, 1.5x1.5, 2x2, etc). Each piece of box tubing has plates that mount to the top of it that hold constant force springs, and each tubing is inside each other (1x1 inside 1.5x1.5, and the 1.5x1.5 inside 2x2).

The constant force springs from for example the 2x2 plates mount to the bottom of the 1.5x1.5 tubing, trying to lift it up and extend it. In order to retract the telescoping tubes, there is a motor and winch near the bottom that wraps and unwraps string to make it shorter and longer. The string is usually attached to some bolt near the top of the smallest stage to fully extend and retract the tubes. Usually the string and motor winch are inside the tubes.

As for rigging, as I said before the strings and motor winch are usually inside the tube, but that makes it a lot harder to replace the string if needed. Some teams such as 2910 have opted to have the motor winch on the outside to make it easier to replace the string. Hope this helps!

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The chain runs through the telescopic arm and kind of works like a cascade, there’s CF (constant force) springs that extend the arm whuch are in the middle of the arm while the chain is usually run through the side. This can usually be driven by 1 decently powerful motor on a Gearbox at the end of the arm to retract it. For wires cable carrier or energy chain is used and flush with the arm, functions the same as cable carrier on a CNC and just keeps everything nice and organized. The springs are usually mounted on tube clamps at the top of the largest tube, a 10-15lbs of force spring should work fine. The tubes have blocks inside them for bearings which help the stages slide. You can do 2-1.5-1" or like 3-2-1" but there are many more options for tube sizes. In the middle of the arm is a large sprocket for the pivot and then on the superstructure there’s just a gearbox with a large reduction so it has plenty of torque and just outputs to a smaller sprocket. Usually the end of the arm isn’t too heavy for most games so you shouldn’t really have to worry about anything if you have a 1" tube at the end of your stage. Lmk if you have any questions, 3847 has some pics of our robot from logo motion on their website somewhere iirc. Also it takes a bit of fancy machining and some good wire management to pull it off but it’s definently worth it depending on the game. The key to packaging it well is putting as much into the tube as you can, the chain inside isn’t necessary so you can just use CF springs and rope if you want. West Coast Products, AndyMark, and TheThriftyBot all sell pretty good COTS telescoping arms which are great for climbers and easily modifiable for a pink arm GreyT Telescope – WestCoast Products. Why extend vertically when you can go diagonal? P.S. I can put an explanation of the powered extension version on our website probably later this week for ppl interested.


(upload://aSUDeNe6QYlow1mfvmWtIDUj33s.jpeg)

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Sorry but I think our old site is down right now, working on a new one :stuck_out_tongue: I’ll try to upload some design stuff on our 2011 bot later this week and see if I can dig up a pink arm cad

We found out if you let it shoot up freely you’ll end up bending the 8-32 bolts that mount the constant force spring assembly on the 2x2 or 1.5x1.5 tube. That is with the thriftybot kit.

Oh, we didn’t know that. I guess we got lucky! But it’s not like we did it a lot…or like put a glove on it and start to punch things with it…we totally didn’t do that…

:lying_face:

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Just doing it a couple times can bend them but not a lot. Honestly you don’t even notice that they are bent until you go to take them out. We had a few failures of the original 3d printed block that goes in the bottom of the 1x1 and 1.5x1.5 tubing.

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Have you tried the WCP metal versions?

The failure in the 3D printed block was fixed when they sent us the milled delrin version of that part, there was a weakness in the shoulder on the 3D printed parts.

Do note that the use cases of a framed elevator and telescoping arms are very different. An elevator is usually much stiffer and can carry higher loads in both directions, while telescoping tubes are less stiff and usually can only support high load when retracting.

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Depending on what you mean by telescoping arm, this is not always the case. The actively-powered telescoping arms used for lifting manipulators are usually quite capable when it comes to loads, and I suspect that the longer aspect ratio means they handle moment loads better than typical elevators before they start binding

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