Telescoping tube pivot mount

I’ve been kicking ideas around for how to reach the top level of pegs and I thought about a pivoting telescoping arm. I’ve seen the 2481 robot from 2018 which seems to do it really well, but I’m not sure how one would fasten the tube to the pivot point without having a hex axle go straight through it which would prevent the tube from telescoping. Is there something obvious that I’m missing in my analysis here?

One thing worth noting is that our team doesn’t have the capability to custom machine so we’d be working off of the COTS thriftybot telescoping tube.



Maybe the pivot point doesn’t need to be through the center of the telescoping tube. Maybe the pivot point can be above or below the telescoping tube assembly?


Like if the pivot point went through the outermost tube below the lowest point that the other tubes can retract?

Take a look at this CAD rendering from the RI3D Zoukeepers. I think this is a great visual on how to do it. The trick is offsetting the pivot.

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ohhh, so the pivot point is not through the tube but above it, and the outer tube is fastened below it to the mounting plate?

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More like the pivot point does not intersect the telescoping tube assembly at all.

(My pencil cad isn’t very strong today)

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Yep. That’s 1 solution. There are others. For example, if you really wanted to pivot on the center of the tube, you could always have 1 shaft on each side and space in the middle. Getting that to be structurally sound will take some thinking though.

So you have to fasten the outer tube to that plate? How can you do that without hitting the inner tube?

How does a human being grab the tube without poking holes in it?

Maybe you can clamp it nice and tight?


A clamping mount seems like one possibility. There is also space in the annular area between the larger and smaller tubes for judicious placement of pins or similar to help a clamping mount be more secure. Use of epoxy or similar strong glue might also be an aid to clamping. Welding would seem very difficult with thin wall tubes and the need to avoid distortion that would interfere with sliding.

Oh sort of like a bearing block!!


Our team is thinking along these lines as well.

You can look at a variety of 177 historical robots for this. We created the telescoping pivot arm in 1996, and used variations on it in 1997, 1998, 1999, 2001, 2003, 2005, 2007 and 2011

This includes having the pivoted section extend, high and low pivots, and having the pivot raise vertically on an elevator.

Here’s a detail of the hub for an arm design I made some time ago. If you don’t have access to a medium-size CNC mill (work area of at least 6x6x4in or so), you will need to design a new hub, but the same principle of claming in should still apply. To locate the hub vertically, you can either create a key feature on the hub (as shown here) or just use a dowel pin pressed into the hub’s body.


From what I understanding from reading this thread, I think that team 27 (Team Rush) used a similar concept/mechanism in 2019. I’m not sure if CAD or a technical binder is available for this, but it might be something worth checking out.

I like this design a lot. Routing the energy chain in the tube is a great solution! I do have one question, what stops the tube from coming out of the CNCed bracket?


Each hub has a set of male keys that interface with the tube to prevent them from sliding out. The two hubs clamp to each other with the 4 long screws you see in the render above.

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would the clamping force from the bolts not be enough to prevent the sliding?

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Under normal circumstances, I think the clamping force would be plenty. However, we’re talking about robots here, and I think any robot in a competition will encounter shock loads comparable to hitting this arm with a hammer, which could definitely shift the arm around.


true. Without a CNC that would be difficult to manufacture