Which CF Springs for pinkarm bot?

So I have 100$ - 300$ to make a bot for my team for our offseason(the budget doesn’t include the drivetrain).

So I decided it would be funny and more appealing to reuse a bunch of old parts to make a somewhat effective pinkarm bot using a TTB telescope kit we had left over from 2022.

I talked with a few people about CF springs, but I’m still wondering, for the teams that did do CF spring telescoping rods, what strength springs did you guys use? Our team is currently still entitled to six free springs from VulcanSpring.

Right now we are working with the 2 x 6lbs springs that were in the TTB kit. As for the telescoping arm, it’s a single stage 2x2 and 1.5x1.5 telescope, with a very light ≈ 5 - 8 lbs intake.

As to why I’m not doing a belt driven telescope, I don’t believe our team would approve buying new hardware for that when we have cheaper options, even if belt would be more reliable.


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We went to McMaster and found the next size up that had the same length (I don’t recall what it was, but you can look there.

We used the TTB arm in both 2022 and 2023 – in 2023, we replaced the endblock with a 3d-printed endblock with 8 small ball bearings (McMaster 6383K11) and it slid A LOT better than 2022. Also helps if you tie the string at the close end, so you’re pulling the internal arm instead of the far one so you’re effectively pushing it.

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We used 9293K12 from McMaster Carr and they worked exceptionally well. We did need to print new parts for the arms as the springs were slightly wider and we needed to compensate for that. We also used a replacement end block printed out of Onyx with bearings to allow a smoother extension and retraction. I can link our OnShape CAD if it helps with the files in it that we used.

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In 2022 we used 4 bearing in the side of more force(forward/back) and slider plates for the other 2 sides.

(Orange 3D printed part was for a dry fit test)

I also believe there is a thread about this early on and build season so try giving that a search.

CAD link would be great! We are also working on a 3dp telescoping block and gonna be trying out the delrin block from ttb as well.