Alan Marconett

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LOKI BIPED ROBOT

Loki now has feet with proper overlap (to allow the CG to stay over the foot supporting the 'bot), and a continuous recycle of 5 basic states (gait) allow it to walk. Similar sequences allow turns, and all sequences can be transversed in both directions.

I can currently use the ultrasonic sensor to stop forward walk, and reverse direction. I then realized that I need two sensors (or sensor rotation to detect which way to TURN to avoid an obstacle. So I added the IR sensors.

The battery pack, while it can be secured below the controller board adequately, is still a little to heavy for the S3004 servos, so I leave the battery back connected via a cable.

Image:LokiUpdate3b.jpg

LOKI NOTES

  • Cheap walking robot, low cost parts, can be made at home
  • Loki is inspired by the efforts of David Buckley http://davidbuckley.net/DB/Loki.htm
  • Original construction was wood (I later found out)
  • My Loki is constructed of PCB material to a similar size
  • Currently using four Futaba S3004 R/C servos, need bigger knee servos
  • Battery is a salvaged 6-cell Ni-MH 7.2v 1300 mAH pack
  • Controller board is a $15 (bare) “QwikFlash” 18F4620 PIC board available from http://www.picbook.com/
  • 50Mhz, 64K Flash, 3K RAM + EEPROM
  • Blue Tooth wireless for telemetry and monitor control
  • EEPROM gaits editable over wireless link.
  • PIC programming via ICD2
  • Control program written in Hitech ‘C’, used to develop gaits
  • Two modes, autonomous and control via a small monitor program
  • Parser used to decode commands received by monitor
  • EEPROM commands save, view and execute steps in sequences
  • Autonomous control currently consists of simple obstacle avoidance while doing a simple walk.
  • Sensors include two Sharp GP2D12 IR range finders and a SRF08 Ultrasonic Range finder
  • Body and feet PCB material CAD designed and cut on my CNC’d Sherline mill
  • Loki’s gait is exaggerated due to the need to clear the toes of the overlapping feet
  • R/C servos are driven by two timers and interrupts in the PIC
  • Servo commands set new angle for servo, and time to get to new position
  • Gaits are stored by strings of servo move commands, similar to those of the SSC32 (LM) servo controller.
  • To walk, a simple array of 6 strings is repeated in an endless loop.
  • More strings allow Loki to make turns.
  • An FSM (Finite State Machine) selects the strings to be used, and changes the string selection upon recognition of an object by a sensor.

Image:LokiUpdate5b.jpg

Loki Body in PCB stock

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Loki Feet in PCB stock

Image:LokiFeet.jpg



SHELOB HEXAPOD ROBOT

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