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Building a custom micro-linear actuator

A project log for TNS 1i

The idea is to create an accesible prosthetic hand that is commercially available in Colombia and doesn't use the classic string system.

giovanni-lealGiovanni Leal 08/30/2016 at 20:430 Comments

So, as the description of the project says, one of the premises of the product is to avoid using those strings that every other open hardware prosthetic hand uses. Yes, we know that the human body uses tendons but we didn't like having a shaky wobbly hand, hence linear actuators. When you search for a linear actuator that fits five in the palm of the hand, all arrows point to the same direction, Firgelli Automations. They are great, not that expensive but... and a big but if you only want to use one battery, they use 12V and where is the fun in buying everything.

So that's why we decided to make our owns. Hasn't been easy.

So, we started by defining the screw where it would glide. The big question was.... and store bought endless screw or a 3D-printed one.

The store bought one implies a 3D-printed adapter and the motor shown there was too weak and too fast also a geared motor with an adapter would be just too long, as shown in the next picture.

To control the DC motor we tried to use a shield with H-bridges to move it forward and backwards. But, tree things, one is that all the shields from Adafruit (Where we buy literally everything) for DC motors require 12V auxiliary power and no. Second is that its bulky and space is not a given. Third how do we know whats the position of each finger. So, we decided to take apart a servo and use de encoder as our controller and the potencio-meter as our sensor. Yes pretty crafty.

So for the "end" result of our custom actuator there is the video at the end.


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