Friday, May 8, 2020

Mojo3 - A Robotic Dog (#10) - New Video Out

 New Video Out

There is a new Video on YouTube showing Mojo3's first (stumbling) steps.  Check it out to see what it is like to try to tune this little robot in both physically and with software.

Only 9g Servos

The biggest challenge with this little robot is trying to only use inexpensive 9g servos.  These are great hobby servos, easy to use and code, and inexpensive if you burn one out. They do have their challenges in the amount of force that they have. I found this to be restrictive in my first attepts with the original Mojo robot dog design.

I believe with good design and engineering, it should be possible to build a little quadruped robot with them. You can see in the video that my in my first tests, the rear servos were struggling to meet the position commands issued by the controller.  The front and back "hips" and "knees" were given the exact same position commands literally using the same computer array of positions.

Then I changed the rear "hip" leg gear positions. I rotated the rear/hind "hip" leg out by about 30-40 degrees. This was easy to do in my new leg design. I simply pulled the hip off of the mount, rotated it back and put it back on.  There are marks for calibration visible in the pictures. The result was a much smoother "hip flex" motion.

New Hind Leg Configuration

The next step in developing the walking gait is to explore how each leg should move to proppell the robot forward. I am starting with just basic movements of the hind/rear legs.  I have replaced the front feet with "training wheels" (like a kids first bicycle). Now the hind legs can attempt to walk without any resistance to the front legs.

More work to come! 

Mojo3 Robot Dog
Mojo3 with 'training wheels' for front feet.

PS:  Quadrupeds on Wheels is going to be a thing!!  Check out this video of Hybrid Locomotion by ETH - ANYmal.

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