Book-inspired Suspension Bridge in Virginia

We were delighted to finally receive photos of a suspension bridge that was inspired by our book, Building a Small Cable Suspension Bridge With the Cable Locking System.

According to the builder, Mo Goldman, the bridge is just under 40′ feet in length and 4′ wide (basically half the length of our bridge) and is located in Virginia just outside of Charlottesville.

The posts are aluminum, 13′ in length, 6″ round with 1/4″ thick side walls, easy for two guys to carry. The post holes are 3′ deep and about 2′ around; the posts are placed on a concrete footer prior to pouring around them. Everything was hand-dug and poured because they were limited to access with a Polaris on one side.

It was fun to see that Mo set up a temporary cable to move materials across. That’s how we moved our gravel for the opposite side, one bucket at a time. But Mo took it further and carried the posts, other materials, plus wheelbarrow and even himself across their “zip line.”

Mo also followed the idea of setting up the catenary curve between two trees/structures located away from the creek to plan and build the cables and stringers on dry ground.

Mo didn’t use our cable-locking system, but instead used a system often used for this type bridge – an appropriate length “eye” bolt placed in a drilled hole in the beam. The suspenders were then connected with a chain connecting link, which uses a threaded portion mating to a free spinning nut to open or close it.

He wrote to us about the bounce in his bridge which was more than he expected, though not a big deal. I noticed that he paid attention to harmonic resonance in the arrangement of the stringers so they were assumed off the “nodes,” so wondered if the decking material he used could be partly responsible (a suspension bridge is going to bounce, that’s a given). He used a material called Trex, which is a deck material made from recycled plastic and wood fiber. Trex tends to flex more than standard lumber does. We concluded that he needed to stiffen the deck, so now he is working on some ideas.

Mo even put up a sign on his bridge similar to ours and inspired us to remake our sign so that it names the creek, too. We hope others who build a bridge based on what we did will also send us photos and notes about their building experience.

Meanwhile our book is available in paperback and as an ebook via Amazon.com.

 

Zip Line Challenge

My spousal unit, who actually writes this blog, is an author and illustrator of books for kids. She ran across this website for aspiring engineers, and thought it would be interesting to some of my readers. DiscoverE (formerly the National Engineers Week Foundation) helps to unite, mobilize, and support engineering and technology volunteer communities. They hope to increase the collaborative footprint in K-12 education and celebrate with the public as it discovers the value of engineering education and careers.

I was especially intrigued by their Zip Line Challenge for kids. It’s actually a model that challenges kids to transport a ping-pong ball down a zip line from start to finish in 4 seconds or less. The activity discusses many of the considerations when designing and building a zip line. I’ve uploaded the PDF so you can download it from here, or you can get it from the website listed above. There are a lot of other creative engineering related activities there, all free to download and use in your classroom, home, summer camp, whatever.

Check it out: zip-line-challenge_091316

One of these years I hope to finish my zip line. All is ready, but now the brush has grown up so much I have to hire a tree climber to clear the 420 foot long pathway.

View from the zip line tower to the landing 420 feet down the hill.

Thanks for stopping by! Be sure to check out our bridge book if you’re thinking about a DIY suspension bridge. Here is the link: Building a Small Cable Suspension Bridge with the Cable Locking System.

And if you’re curious about Robin Koontz’s books, look her up on Amazon as well: Books by Robin Koontz

Images, diagrams, and text copyright 2013-2017 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.

Zip Line!

When I created this blog I promised something would be posted about zip lines aka ziplines. So, here is the first post about all that.

I visited Costa Rica a few years ago and rode on my first wild zip line. That is, it wasn’t a carnival ride or a rope in someone’s yard. It was down a mountain, in the rainforest, and attached to trees, and pretty freeking amazing. When I got home, my spousal unit said, “You’re going to build one of these, aren’t you?” And I said “Of course!”

I set up a a 420 foot zipline on our property. So far I’ve built the tower and ladder, which is a great treehouse getaway:

and I built the lower platform:

and have installed and tested a temporary (smaller diameter) cable. Here is a fun movie of a sandbag wearing my spousal unit’s blouse slamming into the platform:
Zip Line Test with Fake Spousal Unit Getting Seriously Hurt.

While I was pleased at the 32 MPH speed, this test proved that I need to raise the final cable a bit on the tower tree and on the base post as well when I finalize everything.

There are more photos of the building process on my website: Zipline Photos.

The full size cable is up on the hill ready to install but at this point the path down the mountain needs to be cleared (again) before we continue with the construction. For now, I’m working to finish building our house, so this project is on hold for the moment, but will be completed at some point.

What’s funny about this particular project is that when my spousal unit’s elderly relative heard about it, she wrote us out of her will, telling another relative in private (which of course didn’t remain private) that “Building a zip line is pure Tom Foolery! These people have time to burn!” Well, building a zip line is what I do on the weekends rather than watch football. Just don’t call me Tom.

Thanks for stopping by! Be sure to check out my book about building a bridge. It includes some cool ideas that apply to other projects, like how to put a really tall post into a deep hole when you aren’t that tall. Amazon has the book on sale for about $12.00 right now. Here is the link:

Building a Small Cable Suspension Bridge with the Cable Locking System

Images, diagrams, and text copyright 2013 by Marvin Denmark unless otherwise noted. Please do not copy and post my content anywhere without my permission. Thank you.