How to build a compliant humanoid robot - Mounting motor output spool
Published on Nov 19, 2013
The motor output spool is secured to the motor shaft by a grub screw and an additional support bearing is then added to withstand the radial loads placed on the motor shaft by the tension in the tendon.
The support bearing is mounted into a carrier which also provides a cage around the motor output spool to prevent the tendon falling out of position.
These components are all held in place by hand applied polymorph. Note the dyneema is wetted to prevent accidental burning with the hot air gun.
How to build a compliant humanoid robot - Pulley reinforcement
Published on Nov 19, 2013
An example of applying polymorph by hand to strengthen the structure between the motor output and the pulley. A small retaining piece is also added over the top of the pulley to join the two half of the pulley mount and to prevent the tendon from falling off the pulley.
Note the use of wet tissue paper to prevent accidental burning of the dyneema tendons with the hot air gun.
How to build a compliant humanoid robot - Arm motors
Published on Nov 20, 2013
Mounting of the arm motors to the 3D printed guide with a hot fitted polymorph gasket (0.4g).
Note the rotation of the motors to allow connection to the EPOS driver boards without twists in the cable.
How to hand build a humanoid robot - PTFE eyelets
Published on Jun 11, 2014
PTFE eyelets are used all over the robot and are essential for the tendons to glide smoothly. They are surprisingly tricky to keep in place due to their low friction nature so it helps to flare both ends of the tube to make a hollow dumbell shape.
PTFE tube that is a loose fit on the dyneema is cut into short lengths (8-10mm) and then flared at both ends with a tool made of a hinge, two bits of wood and two or more speaker stand spikes.
The key to this process is to get everything hot enough in advance for the PTFE tube to stretch easily.
One use of the PTFE eyelets is in the fingers for pulleys:
1. pre wrap the formed eyelet with a small ring of polymorph so it's a bulging cylinder
2. dig a hole in the finger section with a soldering gun
3. quick flick of a hot air gun on the eyelet polymorph to just heat the surface
4. insert in the hole
How to hand build a humanoid robot - finger ligaments
Published on Jun 11, 2014
The simplest way to actuate a finger is with a single tendon connected all the way to the tip. This leaves the three joints of the finger underconstrained so such a finger is likely to move in painful looking ways and has very little grasping capability. One easy remedy to this is to add extra ligaments from the back of one finger section to the underside of the next.
How to build a compliant humanoid robot - Self stabilising balance
Published on Sep 8, 2014
The balancing algorithm shown is so far only able to control the motors in the ankles, thus balance can only be recovered from a very minor perturbation.
On the right hand side of the TV screen you can see the Centre of Pressure (COP) which is calculated from six ground reaction force sensors and displayed as a normalised red dot. Each line on the grid corresponds to 10%. The robot tries to keep the COP at the point 25% back from the geometric centre of the area of ground contact. This corresponds to a relaxed pose with the weight of the body almost directly over the ankles.
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