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Biped Leg 3dof v1


Biped Leg 3dof Right Side Cad Model


Biped Legs 3dof - weight: 540g each

Description


This page describes the legs that are used for the Biped Robot 6dof. Each leg has 3 torque-controlled degrees of freedom and a passive ankle joint. The Hip Actuator Modules were modified to reduce the length. There is a right side and left side version for both hip actuator modules - they are mirrored versions of each other. The length of the Upper Leg and the Lower Leg was increased from 160mm to 200mm.


Biped Hip Modules


Biped Hip FE and Hip AA Modules

  • the timing belt of the second stage of the biped hip modules was rotated by 145 degrees
  • this makes the modules shorter and more suitable for the biped robot
  • only the shell structure was modified - all the internal parts of the actuator modules are identical
  • a comparison between the Quadruped Hip FE module and the Biped Hip FE module is shown below


Comparison Quadruped Hip FE module (top) and Biped Hip FE module (bottom)

Hip FE Actuator Module


Biped Hip FE Actuator Module - weight: 155g


Biped Hip FE Actuator Modules - shell covers removed


Cad Model Hip FE Actuator Modules - right side version and left side version

Hip AA Actuator Module


Biped Hip AA Actuator Module - weight: 153g


Biped Hip AA Actuator Modules - shell covers removed


Cad Model Hip AA Actuator Modules - right side version and left side version

Upper Leg Module


Extended upper leg module for biped robot - weight: 170g


Extended upper leg module - shell cover removed


  • initially we were using the standard quadruped upper leg module with a segment length of 160mm for the biped robot
  • we are now using an extended upper leg structure with 200mm segment length
  • the lower leg length was also increased to 200mm
  • the longer legs help to decrease the natural frequency of the system
  • the mechanical interfaces of both versions are compatible and all the internal parts are identical


Comparison Upper Leg Versions
Top: Upper Leg Quadruped Robots / Bottom: Upper Leg Biped Robot

Lower Leg with Passive Ankle Joint


Foot with passive ankle joint

  • the length of the lower leg was increased to 200mm and a foot with passive ankle joint was added
  • the line contact of the new foot helps to stabilize yaw angle of the robot


Biped Lower Legs - printed on Fortus printer.
Bottom: with carbon fiber reinforcement on both sides.

  • during experiments with the biped robot we found that the lower legs from our Fortus FDM printer with sparse infill are too flexible in the lateral direction
  • we recommend to reinforce the lower legs with glass or carbon fibers on the top and bottom side
  • alternatively you can 3d print the lower legs on a Markforged printer with internal fiber glass reinforcement


Biped Lower Leg - printed on Onyx Pro Markforged printer with internal fiber reinforcement - weight: 60g

Core Components


Actuator Module Core Components - weight: 95g

The internal components of the actuator modules are described here:

Off-the-shelf Components


  • Steel pin - diameter 5mm / length 28mm
  • Silicone tube - O.D. 12mm / I.D. 8mm / RS 163-9362
  • 4 silicone tube pieces - 2 x 25mm length and 2 x 8mm length
  • M2,5 x 20mm socket head cap screw with washers and locknut
  • Rubber band

3D Printed Parts


3d printed parts for two biped legs


The recommended printing direction for all the parts below is the positive z direction of the stl files.

All the STL files for 3d printing the biped legs can be found here: STL Files Biped Leg 3dof.












  • Lower Leg Structure 200mm - STL file
  • reinforce with glass or carbon fiber on both sides when printing the lower legs on a FDM printer with sparse infill
  • alternatively the lower legs can be printed on a Markforged printer with internal fiber reinforcement
  • weight without fiber reinforcement: 28g
  • weight with fiber reinforcement: 32g


Bill of Materials - Biped Legs 3dof v1


Bill of materials for two legs - left side version and right side version.

Description Quantity Ordering Information Comments
Actuator Module Core Components 6 Actuator Module Core v1

Actuator Module Core v1.1
Hip AA Structure Right Side Base 1 STL file 3d printed part
FDM or SLS printer
Hip AA Structure Right Side Cover 1 STL file 3d printed part
FDM or SLS printer
Hip AA Structure Left Side Base 1 STL file 3d printed part
FDM or SLS printer
Hip AA Structure Left Side Cover 1 STL file 3d printed part
FDM or SLS printer
Hip FE Structure Right Side Base 1 STL file 3d printed part
FDM or SLS printer
Hip FE Structure Right Side Cover 1 STL file 3d printed part
FDM or SLS printer
Hip FE Structure Left Side Base 1 STL file 3d printed part
FDM or SLS printer
Hip FE Structure Left Side Cover 1 STL file 3d printed part
FDM or SLS printer
Upper Leg Structure Base 200mm Rev A 2 STL file 3d printed part
FDM or SLS printer
Upper Leg Structure Cover 200mm Rev A 2 STL file 3d printed part
FDM or SLS printer
Lower Leg Structure 200mm 2 STL file 3d printed part
Use FDM printer and reinforce with fibers or use Markforged printer.
Foot Structure 2 STL file 3d printed part
FDM or SLS printer
Helicoils M3 x 4,5 4 Ordering Information Hip FE Interface
Helicoils M2,5 x 3,75 48 Ordering Information Actuator Shells
Fasteners M2,5 x 6 34 Actuator Shells
Fasteners M2,5 x 10 14 Actuator Shells
Fasteners M3 x 22 4 Hip AA Interface
Washers M3 4 Hip AA Interface
Fasteners M3 x 16 4 Hip FE Interface
Fasteners M3 x 12 4 Knee Interface
Steel pin 5mm x 28mm 2 Passive Ankle Joint
Silicone tube 8 RS 163-9362 O.D. 12mm / I.D. 8mm
4 x 25mm length
4 x 8mm length
Fastener M2,5 x 20mm 2
Washer M2,5 4
Locknut M2,5 2
Rubber band 2

Actuator Module Wiring


Biped Wiring

Description Wire Length Comments
Hip AA Motor Phases 20cm RHAA and LHAA
Hip AA Encoder Wire 28cm RHAA and LHAA
Hip FE Motor Phases 27cm RHFE and LHFE
Hip FE Encoder Wire 33cm RHFE and LHFE
Knee Motor Phases 35cm RK and LK
Knee Encoder Wire 42cm RK and LK

View the Biped Leg Cad Model in your Web Browser



Biped Leg 3dof Right Side
Click on the picture to view the biped leg cad model in your browser

More Information

Open Dynamic Robot Initiative - Webpage
Open Dynamic Robot Initiative - YouTube Channel
Open Dynamic Robot Initiative - Forum
Open Dynamic Robot Initiative - Paper
Hardware Overview
Software Overview

Authors

Felix Grimminger

License

BSD 3-Clause License

Copyright

Copyright (c) 2019-2021, Max Planck Gesellschaft and New York University