Passive Low Rung Climber (Mechanism in 1 Day)

passive climb
Below is a video and CAD for a fully passive low rung climber that requires only a working drive-train to execute. I have accompanied it with a write-up with some tips and a backstory on what led me to make what I’ve jokingly dubbed my first “Mechanism in 1 Day” or mi1D. I’m publishing in the spirit of ri3D and the everybot in the hopes that some teams can get use out of it and apply this concept somehow on their own robot.

CAD: Onshape

Some tips:

  1. This is something I quickly made, it is not perfect. I created the CAD in about 10 minutes, the cutting took another 10 and the building and refining took about 1.5 hours. I added a bunch of holes so as to fit onto many bots, but I encourage you to copy it, modify it, and make it your own. The angle I chose was just what I thought would work, the distances are pretty random. All I did was make sure it was max height, that the rung would fit nicely in the hole, and that it would lift the “robot” off of the ground a few inches. You can make it better.
  2. Something I noticed during testing is that there would be times where only 1 plate would hook on and I’d have to give it an extra nudge, as long as your wheels are on the ground you should be fine, but I do think there would be an advantage to providing some sort of structure going across the two plates, especially something in line with the slope of the ramp.
  3. Grippy material would help stabilize this and any other climber. The rubber boom mic material that was in the KOP has a good grip on the rung. We ran it on our 2020 bot and wouldn’t slide at all when we were on the rung, we plan to use it on our 2022 hooks.
  4. In terms of manufacturing plates like this, if you have access to a CNC machine, you can take my cad model and make it. If you have a bandsaw or a host of other hand tools, you could print out the plate on a piece of paper, from the PDF, in my Onshape document paste it onto a piece of polycarb, aluminum, or thick wood and cut it out. This is actually how we made our original hooks for our 2020 robot when we had a backlog of machining to get done.

Back story: When the 2022 FRC game was revealed, I noted the dimensions of the rungs and immediately thought to myself that passive climbers would work very well for the low bar. I figured this is a design we would see a lot this year and that we would surely see a lot of in ri3D. In my estimation, at a minimum every robot should have something on it to get itself off of the ground. Otherwise it is hard to be competitive and hard to get ranking points. Passive climbers would do very well like they did in 2013.

For those unfamiliar, in the 2013 game there was a similar rung in terms of diameter, that was below max robot height. Many robots opted to sacrifice being able to traverse under that rung in order to build simple passive climbers that required no additional mechanisms.

Not seeing any passive climbers in the ri3D bots, I decided to sneak off to a laser cutter the other day, mock up the design you see in the CAD and videos above and cut it out.

Two days ago 118 released their awesome everybot: with what myself and one of our mentors like to call, the finger guns passive climber. The climber also has a passive low rung climber on it which is really clever.

I still felt that there was benefit to sharing this as a very straight forward, doable, low rung climber option for teams that requires no moving parts and very little weight. So after school today, with the help of a few students (Shout out Janna and Andy), we strapped these plates up to a dolly and made a demo of the concept. We hope that teams can get some use out of these and can utilize these designs.


I prefer to call them “yeet hooks.”


Nice swerve drive tho!


I expect to see a lot of these at competition, but not as much as we saw in 2013, for two reasons:

  1. In 2013, you had to climb to the lowest bar first, so going higher required a much more complex mechanism (or collection of mechanisms).
  2. Climber-in-a-box solutions available from everyone.

A lot of teams that may have slapped something like this on their robot will instead opt to purchase a climber-in-a-box mechanism to get to the mid rung instead.


If you had a single hook in the center of the robot rather than 2 hooks on the outer frame perimeter, you would avoid the issue with only one of the 2 hooks engaging with the rung. It would also allow a wide range of approach angles. Hanging from a single hook should still be plenty stable.

+1 on the nice swerve drive

We found that no curve was necessary in our design from a week ago. It reduced the swing to some degree, too.
Video: Robot driving on to low rung


Yeah :grinning:. I’m amazed they were able to test and make prototypes with their swerve drive base so fast. We are planning on using swerve next year and we will definitely reach out to them for help

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