Monday, October 7, 2019

Mojo3 - A Compliant Quadruped Robot Dog (#1) - Back to Work!

Time to get back to work!  I have moved my home and office and started a new business.  time now to stop playing 'Factorio' in my spare time, and time to start building new robots!!  Afterall, the Totally Not Evil Robot Army isn't going to conquer the galaxy by themselves (yet)!

Over the summer there have been a few developments worth mentioning (look them up!).  Such as Boston Dynamics starting to offer their Spot robot for commercial purchase.  Not as favorable, some robot shops in Bristol, England have gone out of business. But, on the upside, the good people at ETH Zurich Autonomous Systems Lab are still producing awesome robot projects.  The community is continuing with things like this past weekend's Toulouse Robot Race. Plus many new videos on YouTube:  Oracid1 has a good quadruped playlist, and even James Bruton found the benefits of compliance in quadrupeds! ;)

To get back into the design phase, I am planning on starting mark 3 of Mojo, the compliant quadruped robot dog. Hereby to be called Mojo3 (so original!)  In the next design, Mojo3 will improve off the systemic issues of Mojo2.  Primarily, I will remove the servo from the direct load bearing connection between the leg and the body. With basic common engineering sense, I will use a bearing for this connection, and utilize a cam system to move the leg. 

Next I will incorporate the knee flexor servo into the primary leg servo, attempting to remove a servo (x4) from the design. This should again use a cam system to translate the leg motion into the up-down motion of the knee flex.  I will reduce the weight of the robot, Mojo2 was 263g (seems light) without the battery. This is due to the heavy servos. I will attempt to use the 9g servos again, lets see. compact and agile will be the plans, along with off the shelf components.

Here is the first drawing of Mojo3!  Can you see the various components??

Mojo 3 - Compliant Leg sketch-draft
Next we have to spin up the CAD design!


  1. You're actually using CAD? Impressive! Will be nice to Mojo3 in action. Gonna have to try out Factorio though... You know, for the times I don't have it to ink.

    1. NOoooooo! introducing someone to Factorio is like giving crack to kids! ;)
      That game has consumed hours of my 'free' time. Those Italian open-source developers, really have an interesting concept, especially for automation geeks!

      yes, I am using OpenSCAD for the CAD - also a free open-source software. It uses a programmatic approach to CAD. I found to be easy to design in, even though it doesn't use a click and draw GUI style.

      The CAD is an integral part of the process, since I use the CAD design to generate the files necessary for the 3D print. I find that it has extra benefit as a real visualization verification step prior to investing the time in the 3D print. and it looks cool! ;)