About a year ago, a member of my family sent me a video featuring [Theo Jansen's] StrandBeest, knowing that I was interested in all kinds of wacky and hackish inventions. My initial reaction was something to the effect of “wow that’s a neat device, but that guy is a little crazy.” For better or worse, the idea that this was an incredible invention turned over in my head for some time. Eventually, I decided that I needed to build one myself. Apparently I’m a little crazy as well.
Theo’s original beest runs on a complicated linkage system powered by wind. He was nice enough to publish the linkage lengths or “eleven holy numbers,” as he calls him at the bottom of this page. He doesn’t, however, really explain how the connections on his PVC power transmission system work, so I was left to try to figure it out from his videos. As you’ll see from build details and video to follow, this isn’t trivial. Keep reading past the jump to learn the adversity that I encountered, and how it was overcome in the end.
The Build Begins
For reasons that I’m not entirely sure of, I started building the leg linkages out of wood instead of PVC pipe. Perhaps it was this four-legged miniature Jansen-style walker that inspired it. Some of the linkages were scaled directly from this design. That’s also likely how I decided that it might be possible to walk my StrandBeest version around with four legs. That or possibly this awesome simulation. Given how much effort it took to make each leg, the fewer the better from the perspective of getting it finished.
To begin with, I was never sure I’d finish more than one leg, but after trying out the process on the first linkage set, as seen on [HAD], soon I was testing two legs. Finally it was on to four legs linked together with a central PVC shaft — also seen on [HAD] and in the video below.
I thought that was pretty cool, so the build seemed to be done for the time being. I literally hung it up in my garage to see if I could think of anything better to do with it.
Inspiration to Finish the Project
Months later, I was contacted by [Jay], who recruits for the Columbia, SC Maker Faire, about doing something for the show. My dormant ‘Beest, now dubbed the [MountainBeest], seemed like a great candidate. [Jay] volunteered that they had a winch available (why not?) to hoist the [MountainBeest] up and down spider. This was great, as I had serious doubts about its ability to walk on its own.
Although I could have probably hooked up a series of cables to actuate the legs remotely, this didn’t seem quite good enough. Electronic remote control seemed like a better idea, and fortunately I had a windshield wiper motor and controls left over from a failed “giant hexapod” project that [HAD] featured in 2012.
Some Issues with the Build
The mechanical build was simple enough, but power transmission with PVC pipe is getting into somewhat uncharted waters for me. My first idea was to use sprocket gears off of a bike that I converted to single speed, and windshield wiper motors to power the legs. This idea had some potential, but I was supporting the driving gear quite poorly. Additionally, the wiper motors tended to go faster and start more violently than the [MountainBeest] liked. As seen here, even after upgrading to a larger single speed chain, things didn’t stay together.
My “custom” single speed bike, however, looks awesome with its new chain. It’s good to have a backup plan.
The [MountainBeest] backup plan was to use one slower motor on each set of two legs. This would get rid of any pesky chain issues, and theoretically allow the ‘beest to turn when walking. It took some work, including modifying the frame and coming up with an interesting motor mounting solution seen in the picture below. It did work, however, and that counts a success in HaD land.
One continuing issue I’ve had with the extremely low geared motors I was using, is that at certain points in the mechanism’s travel, it tends to put a huge amount of torque on the shaft. In order to fight this, I came up with a PVC coupler that absorbs some shock and allows it to flex as seen on [HAD] here. These are known in their more traditional settings as a “beam” or “helical” coupling. My PVC version is seen in the video below.
After solving (or at least mitigating) most of the mechanical issues with my “walker,” the electronics were fairly simple. I used a four-channel radio transmitter with a PWM relay switch from Servocity. This was able to handle the DC motors nicely, despite possibly being overkill. After wondering what I could do with the other two channels, I remembered that I had a Pan/Tilt mechanism already built.
After attaching the camera mount to the polycarbonate shell, it was simply a matter of plugging the servos in. In a few easy steps I had a ready-made GoPro mount to add sight to my creation!
Below is a video of it completed in the garage, and there’s more information on the final build here. Unfortunately, the torque required to actually make the legs walk was too much for the little motors I was using. It’ll make a great display though, and actually walking will be a good goal if I ever decide to make revision 1!
So sometimes one just needs a little push to actually finish a project! Hopefully my [MountainBeest] can make a good showing at the Columbia, South Carolina Maker Faire this year. I’m certainly looking forward to it. If you happen to be in the area on June 14th this year, or want to make the trip, be sure to stop by and say hello!
Full disclosure: I’ve received promotional consideration on some parts used in this project not in connection with this article.
Jeremy Cook is a manufacturing engineer with 10 years experience as his full-time profession, and has a BSME from Clemson University. Outside of work he’s an avid maker and experimenter, working on everything from hobby CNC machinery, to light graffiti, and even the occasional DIY musical instrument. When he’s not busy creating (or destroying) something, he writes for his blogs JcoPro.net and DIYTripods.com.