June 23, 2013

REX 2013 Project: Rotating Climbing Wall

Every year during the freshman orientation, residents of my dorm (East Campus) build a variety of large wooden structures in the courtyard between the parallels.  Or rather, they design the structures, and then enlist the labor of excited freshmen to actually do most of the construction.

This summer, as not-a-frosh, a couple hall mates and I are joining in on the design side of things.  Our plan is to build a giant rotating cylindrical climbing wall.  Basically like this.  The cylinder you climb on will be 12' in diameter,  8' long, with the axle about which it rotates suspended 8.5' off the ground.

I started out by working on the design of the rotor.  I began by making these hexagons out of 4 x 4's.  Then I checked the mass properties in Solidworks, saw that it already weighed over 800 lbs, and started over with 2 x 4's.  

Here's the completed rotor design.  The hexagon is extended to a dodecagon around the outer edge.  The  board that make up the edges will be cut so that the actually make a circle, rather than a polygon.  The outside of the rotor made of sheets of 1/2" plywood.  The curve radius is large enough that I don't think it will be too difficult to bend the wood.

How 'bout that moment of inertia?

Here are some renders with a base added in:

The axle is a big steel tube, and it passes through a giant bearing on each side of the base.  The bearings, combined with the huge moment-arm on which a climber's weight acts means that climbers should have no trouble turning the rotor.  In fact, it may be too easy.  To limit the rotation speed, the rotor will have a brake attached to it.  So that the spokes and axle don't have to transmit any torque, the brake will act on the outside of the rotor.  A car wheel on another axle will press against the outside of the rotor on one side.  This wheel will have an adjustable brake attached to it.  I do not yet have a car wheel, but I do have a brake disk and caliper.  I think this 1' diameter truck disk will be sufficient.  The caliper, which came from the shop of a now-defunct electric car team, should also be adequate.

For lack of something better to do with the 3D printer I won, I printed a miniature model of the structure:

We've contacted some climbing gyms and climbing hold manufacturers to see if we can get the climbing holds sponsored for free.

Construction will begin toward the middle August.


  1. Hi,

    Love the blog, two quick questions?

    - Why are you going with the break on a separate friction driven wheel instead of the axle?

    (probably rubbish idea: chopping a junk yard un-driven rear axle in two to give two brake/bearing modules)

    - Are you sure about that bend in the 1/2" ply?
    for a 12' dia. I get it as a 4" deflection in the middle of a 4' pice to get the correct curve. This seams a bit ambitious, but I guess with lots of muscle, a leaver and some big-ass screws you could probably bend near anything round the drum.

    (another unsolicited suggestion: two layers of 1/4" and laminate it with contact adhesive.)

    What ever happens sure it will be awesome. Looking forward to seeing how it turns out

    1. Since this post I had the opportunity to try bending some 1/2" ply, and decided to use something thinner. 11/32 ply should be about 1/3 the stiffness.

  2. Just saw the bit about breaking on the outside stopping the spokes having to take any torque...Whoops. Sorry missed that sentence first time round.

  3. Hello Ben, I own one of the top climbing hold companies in North America called Kilter and I would really like to talk with you about this project. ianpowellprime@gmail.com