Building 8-Legged Trotbots, From Tiny to Towering

Robotics Technology
Building 8-Legged Trotbots, From Tiny to Towering
Figure A
Figure A. Photo by Beth Vagle.
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Three years ago, when I was 13, I was part of the team that developed a new type of walking robot we call “TrotBot” using Lego Technic parts, and then helped to scale it up to the size of an SUV (Figure A). We showed off our latest giant TrotBot at World Maker Faire 2016 in New York, along with our Lego prototypes that are always a hit with the kids.

Out of this amazing experience, I’ve developed a walking robot STEM challenge that I’d like to share with other kids and educators.

TrotBot is a mechanical walker, like Theo Jansen’s Strandbeest or Joe Klann’s Mechanical Spider, but we developed it primarily to appeal to kids, to inspire them to learn some engineering and to want to build their own walking robots. Therefore we had two design goals:

1. Lifelike motion — TrotBot mimics a galloping horse
2. High functionality — we wanted kids to be able to really play with their robots and get lost in their imaginations as they walked them on the bumpy terrain found in nature, not just on flat man-made surfaces.

Figure B
Figure B. Image by Ben Vagle
YouTube player

We reached our functionality goal by creating a mechanism that steps high, so its feet won’t get stuck on bumps or obstacles. To show what I mean, here’s my computer simulation (Figure B, above, and also shown animated in the above video) comparing TrotBot’s step (at right) to Strandbeest (left) and Klann’s spider (center), showing how the different feet move when walking forward (right to left in the diagram).

Photo by Hep Svadja
Photo by Hep Svadja
Figure C
Figure C. Photo by Ben Vagle
Figure D
Figure D. Photo by Ben Vagle

But really you’ve got to see TrotBot in action, scrambling over a woodpile (Figure C) or slickrock in the desert (Figure D); check out the videos below from my YouTube Channel.

YouTube player

We learned a ton from scaling up TrotBot, and I’ve taken those insights back down to Lego scale to create the most functional walkers I’ve seen, with an improved foot design that increases ground contact while maintaining the high-stepping gait.

Photo by Ben Vagle
YouTube player

I could have made a robotics kit out of laser-cut wood, but I think I can make the biggest STEM impact by publishing the plans in Lego, a medium that most kids are already familiar with. Also, Lego’s Mindstorms EV3 system has the basic automation components that walkers need, so kids and educators can use TrotBot as a platform to explore technology too. And once the designs are understood, it’s easy to transfer them from Lego to other mediums, such as Vex components.

Photo by Ben Vagle

Until now, the specifications of TrotBot’s mechanism haven’t been made public, but I always get asked at Maker Faires if we would sell TrotBot kits, or at least show people how to make it. I’ve finally delivered on my promise to those people, and posted detailed plans as well as the engineering insights behind them.

Figure E. Photo by Ben Vagle
Figure F. Photo by Ben Vagle

You’ll find complete build instructions for this Lego TrotBot at my new website DIY Walkers. It takes about one day of diligent work to make one. First you’ll build each leg’s mechanical linkage or “kinematic chain” (Figures E and F), then you’ll mount the 8 legs in a frame with the motors and gear train to drive them (Figure G).

Figure G
Figure G. Photo by Ben Vagle

In addition to Technic beams, pins, and gears, this build uses Lego’s Power Functions IR RX 8884 remote receiver, 8885 IR remote, 2 Lego Motors (I recommend the smaller 8883 M-Motors, but you can also use the half-speed, 4x torque XL 8882 motors), and an 8881 Battery Pack. I recommend lithium-ion AA batteries as they are lighter, last longer, and will improve walking performance. For the long axles connecting the legs to the frame, you can use Lego’s plastic axles, but I prefer to use 3/16″ OD brass tubes, to better bear the robot’s weight (aluminum rods are fine too). I’ll document another version soon incorporating the EV3 Intelligent Brick.

Photo by Ben Vagle

My hope is that DIY Walkers inspires more kids and educators to play with engineering via designing and building walkers (and not just TrotBot; I’ll be posting detailed plans on many walking mechanisms). Mechanical walkers can be a great incentive for students to master new skills, including design, kinematics, structural engineering, programming for control and optimization, project planning, and, trust me, problem solving!

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Ben Vagle

BEN VAGLE is a high school junior in Colorado. His childhood was spent observing animals in nature and building with Lego, and these passions are alive and well in his role as a young maker.

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