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.
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.
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.
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.
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.