Sunday, July 22, 2018

Mojo (#11) - First Walk - A Compliant Quadruped Robot

Mojo is walking!  ... somewhat  :)

All of the pieces are in place, and now the walking trials, tuning, and real work begins.  In the video, you can see the current iteration of robot and code. I removed the heavy tether and replaced the power sources. With the lighter power tether, it is just about walking. Sure there are some slips and a lot of falls. But, in this video you can see it make a few strides and move itself under its own motion!

Mojo Current Config, with power supply
This is the current configuration of Mojo - The Compliant Quadruped.

  • Robot Chassis is 3D Printed: Servo and Control Frame, 4x Legs - with 4 linkages and a self made Serial Elastic Actuator, thread, springs and metal rods and screws from a salvaged printer.
  • 8x 9g SG90 type micro Servos
  • PCA9685 16-channel servo control board
  • Arduino Mega 2650 micro controller
  • Power: 9v transistor for Arduino board, 5v 2amp Power bank for servos
  • Other Salvage: power switch, 9v transistor connector, barrel jack, USB cable, pieces of rubber from bicycle tub, etc.  :)

Quadurped ready to walk!

Mojo back top view
Lessons from the walking trials:  

There was a lot of "weakness" from the Left Hind servo.  It felt hot to the touch - so pretty my burnt out that motor.  This was the second failed servo. These are cheap servos, so I am expecting to go through them. (need to place another order).

The back legs have slippage and do not seem to be getting a full swing. I did identify some bad parameter setting in my code, and that seemed to help.  I also increased the pull on the knees.  for the swing phase, I will increase the distance from 50 degrees to 80 degrees. I am hoping this provides more momentum forward and lefts the back up more. 

Need sticky feet to help with the sliding.  maybe even change up the size of the front/hind legs.  But, the next big changes coming will be in the chassis frame.  it will be much bigger, have rollbars, a second deck to raise the knee servos, and have space for a control panel for switches, an interupt, and status led.  It was printing while this version was walking (you could hear it in the back ground!)
Next version of the robot frame (CR-10 3D Printer)

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