Ratchet Strap Climber in a Box

One of the main reasons Vector has been able to do so well this year was because of our robot’s straightforward design. Simplicity in the design meant that issues were, for the most part, easily diagnosable and fixable, allowing for shorter repair times and more practice time. However, one issue has plagued our team since worlds, leaving us stumped.

For whatever reason, our Andymark Climber in a Box’s Dyneema would catch on itself while spooling. The Dyneema would somehow double spool and pinch itself while winching, preventing us from climbing any higher than the midbar. At worst, it was happening almost every single climb, but we could never recreate it in the pits. The issue started around champs, and we haven’t been able to find a proper solution since then.

For our recent off-season competition, Robot Remix, we decided to try switching away from Dyneema. The most obvious replacement was a 1" ratchet strap, as it would eliminate any inconsistent spooling while being strong enough to climb. We designed a custom spool that slips onto the thunderhex shaft, and can be 3d-printed. It uses two cross bars to catch and pull the ratchet strap’s loop. For reference, think of the 2020 everybot climber spool mechanism.


Benefits:
-climber’s heights relative to each other remains more consistent than with Dyneema
-impossible to have winching issues since the winch is the same width as the strap
-more consistent winching speed as diameter remains the same throughout the entire spool
-customizable spool

Downsides:
-custom spool needed
-ratchet straps have to be cut to the right length, and loops have to be stitched using heavy-duty thread

The ratchet strap system immediately worked with no issues, and our drivers managed to get a few decently fast climbs without any spooling issues. At Robot Remix, we managed to climb every single time with zero issues.

My only regret is that we didn’t do this sooner.

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We’ve done 1" wide straps for a few different spool mechanisms over the years. It can work really well, but does have one downside - the effective diameter of your spool changes as you run the mechanism. The more the strap wraps around it, the thicker it gets. And with that change you impact the speed and the force of your mechanism. Not an insurmountable obstacle, but one you need to consider when pairing it with a motor/gearbox! It would be very easy to design it such that it stalls halfway down as the effective diameter increases to a point where you don’t have enough force to continue lifting.

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Hi, thanks for the input. We thought about this, but realized that with each climber being powered by a falcon on a 12:1 vp, we wouldn’t have any torque issues. While we did notice the climbing speed changing as we winched in, because it was consistent, it ended up not being an issue.

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3946 used a flat ratchet-style strap as our custom ROPE for the SteamWorks climber. While we had a fairlead to bring the strap towards the middle of the shaft, once the wraps got going, it wrapped up into a neat cylinder rather than the not-so-level-wind you get from round cord. I suspect this is something of a crown pulley effect, where slipping a bit to one side tends to pull things back to center. The bottom line is that you may not need flanges on that pulley other than to support the cross bars.

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I have always preferred flat webbing to dyneema cord personally. Nice mod.

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