{"id":10480,"date":"2015-07-05T11:55:01","date_gmt":"2015-07-05T01:55:01","guid":{"rendered":"http:\/\/legoeng.local\/?p=10480"},"modified":"2020-05-01T15:53:02","modified_gmt":"2020-05-01T05:53:02","slug":"trotbot-walking-machine","status":"publish","type":"post","link":"http:\/\/legoeng.local\/trotbot-walking-machine\/","title":{"rendered":"TrotBot Walking Machine"},"content":{"rendered":"

After teaching a challenge-based LEGO Engineering class for two years, I wanted to offer a really difficult challenge for a dozen of my most motivated\u00a0students (grades 6-8). I settled on linkage-based walkers, like Theo Jansen’s\u00a0Strandbeest<\/a>.<\/p>\n

Rather than copy prototypes or plans, I had the class study various linkage mechanisms, their trade-offs, and how they can be implemented into robots of their own design. While a more difficult path, this led to deeper\u00a0understanding, and ultimately to a second stage of the challenge the following year where we built a minivan-size robot using\u00a0a new\u00a0leg mechanism we developed.<\/p>\n

\"TrotBot\"<\/a>
TrotBot<\/figcaption><\/figure>\n

If you want to skip to the end of the story, we posted highlights of the TrotBot project here<\/a>. If you want to read how this challenge evolved from my more standard LEGO Engineering classes, read on.<\/p>\n

Stage One: Walking Machines in LEGO<\/h2>\n
\"Building<\/a>
Building Walkers<\/figcaption><\/figure>\n

Stage One spanned\u00a0eight two-hour classes, roughly broken down as follows:<\/p>\n

    \n
  1. Discussion of animal gaits and the minimum requirements for a stable walking robot<\/li>\n
  2. Exploration of various straight-line linkages by prototyping in LEGO Technic beams, allowing students to rapidly modify the configurations to test the effects on the curve drawn by the end of the linkage. This was assisted by taking a Bic pen out of its plastic sleeve to pass through the beam’s final hole, allowing students to draw many curves to compare configurations. The following image shows an example of using a Bic pen to draw the foot-sweep\u00a0of Klann’s leg mechanism, and examples of how changing bar lengths affects Klann’s foot-sweep can be seen at Klann’s site<\/a>. Students also used\u00a0Mekanizmalar’s<\/a>\u00a0simulations\u00a0as guides for prototyping linkages with Technic beams.\n
    \"Klann<\/a>
    Klann footsweep drawn with pen<\/figcaption><\/figure><\/li>\n
  3. After a decision was made on what linkage the student wished to use, we then had a few basic robot classes on gear trains, crank\/axle systems and the transfer of torque, frames (which had to support the geometry of the chosen leg mechanism, gear train and motor, and how to incorporate triangles for strength with little weight), etc.<\/li>\n
  4. Several classes of robot assembly. Building walkers can be really frustrating, perhaps too frustrating for many students. Like building a finicky Swiss watch, if the linkages are not spaced properly they will lock up.<\/li>\n
  5. Playtime by running the robots on obstacle courses, which was in reality the final testing of the students’ chosen mechanism and builds, and also allowed us to compare the performance of a few different mechanisms such as Klann’s Mechanical Spider and Jansen’s Strandbeest.<\/li>\n<\/ol>\n
    \"Klann\"<\/a>
    Klann’s spider nearly finished<\/figcaption><\/figure>\n

    Because we approached this challenge from basic principles, we ended up developing a few of our own walking linkages. One of them was designed to have a high foot sweep, and performed\u00a0better on the obstacle courses than the other walking machines. This linkage led to Stage Two of the project the following year.<\/p>\n