I Built Myself 2 Extra Arms!!

2024-11-21 | By The Hacksmith

Many of life's daily struggles boil down to one key problem: Not having a third hand, and consequently, not having a fourth hand.

We've solved both of these problems.

Hacksmith Industries teamed up with Dave's Armoury to build an extra pair of robotic hands for everyday use. Using Indro Robotics' newly announced Manuvr six-degree-of-freedom robotic arms and a pair of Psyonic Ability Hand prosthetic hands, we built a pair of robots that can be worn on your back to complement your natural dexterity and double your efficiency with household and workplace tasks—for certain definitions of "double".

The two robots are controlled via a VR headset and motion controllers, which can either be worn by the user directly, or worn by a second person to remotely control the robotic backpack. An intuitive control scheme allows for fine and precise manipulation, allowing enough finesse to play chess or eat spaghetti with your second pair of hands.

In those few rare moments of the day where a second pair of hands is not needed, the two robots are safely stowed away behind the wearer's back by a large hobby servo motor rotating the two arms' mounts inwards and back into a safe position. This is driven through an Arduino Nano Every connected to the onboard mini PC. As a bonus, the two arms quickly swinging forward provides a dramatic entrance of the extra limbs!

If comic books have taught us anything, it's that putting robotic arms on your back is a surefire route to having them rise up against you. To quell any robot uprising, a shutoff circuit allows power to be removed from the arms and the stow motor at the press of a button via a high current relay preventing the arms from imperiling the wearer. This exact part is not specifically a safety relay, but in this situation where the risk is limited and loss of life or limb is extremely unlikely, it offers an acceptable level of protection.

Robot Arms Backpack Scheme-it

Powering the Psyonic hands, whose fast and powerful fingers require quite a lot of current during motion, was done with a pair of TDK-Lambda PoL modules which supply up to 20A of 8.4V power from the 24V of the batteries efficiently and compactly - the entire 160W of supply can be fit inside the wrist of the hand. A third one of these supplies powers the mini PC, and by extension the Arduino and the ethernet switch, which are connected over USB.

The final icing on the robotic cake was a custom battery pack built into a Hacksmith shop coat. The 9.6Ahr 6-cell lithium ion battery pack provides hours of stable operation, 3D printed housings provide a cyberpunk-esque aesthetic, and a string of addressable LEDs threaded down the centerline and wired into the Arduino provide a bit of light to really sell the look.

With the extra hands, The Hacksmith was able to wield four lightsabers at once, dress a hotdog with three condiments simultaneously, hold a chainsaw and a plank at the same time, and much more. To see the full adventure, check out the video.

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