Day 14 - Humanoid Robot Arm Endurance Testing - Open Source stl files @therobotstudio Hackady.io

An open source 3d printed humanoid robot arm undergoing endurance testing especially of the wiring which all runs internally.

The joints motors are series elastic actuators SEA which means a physical spring is inserted between the output of the gearmotor and the structure of the arm.

This allows the storage and release of kinetic energy to achieve a more dynamic style of action than traditional robots.

The movements are selected randomly via the LSB noise on a spare ADC and occasionally interact in a chaotic fashion.



The stl files are available on Thingiverse and Hackaday.io

CAD as parasolids on Onshape.com

All free, all under @therobotstudio




Failure modes of this arm so far are:

1. 30hrs - Wire pinched during assembly failed by fatigue - Replaced section of wire
2. 40hrs - Elbow and Pitch Rocker Bar screws loose - Retightened with Loctite
3. 50hrs+ - Glitch on node 1 - cause still unknown...found it! Single fractured strand of encoder ribbon cable - obvious really - always start with the physical layer! Is it plugged in, duh? The cable is multi-strand hence the intermittent nature - the motor controller detects this as a Sensor Position Breach error (error code 0x7830 in section 7.2 maxonmotor EPOS4 firmware specification) which causes a shutdown event that the embedded code automatically tries to recover from before it registers in the EPOS Studio GUI. Additionally, if this occurs once the arm is already in motion it allows the nominal zero position of the gearmotor to change. This was erroneously investigated initially as a power issue. Breakage fixed by digging into the encoder casing and soldering a wire to the remaining stump of wire. Strain relief by epoxy resin added to the entire ribbon cable attachment area. Additional strain relief has been added by securing the woven cable sheave that protects the encoder and other motor cables as they pass through the armpit and humeral rotation to one of the M4 assembly screws in the shoulder structure.
4. 65hrs - Pitch Rocker Bar screws loose again. Stripped the assembly down fully and found that previous loctite had not penetrated. Reassembled with all pieces loctited including directly to the motorshaft.

Тэги:

#robot #compliant #humanoid #build #your #own #self #DIY

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