Prometheus Arm: Latest changes.

In the last few weeks, we have made some improvements in the design of Prometheus arm.
In order to be able to use antagonistic actuation in a simple fashion, it is important that actuation of each degree of freedom remains symmetrical. This means that if you open a finger a little, both inner and outer tensors should be displaced the same length. Initially, a pulley system was our choice for granting this. This iteration was tested in the first version (A3 project) and showd some major inconvenients. Tensors used to degrade quickly and loosed the joints, leading to poor performance of the fingers. In order to solve this issue, we developed a system with adjustable pulleys that allowd tensors to be readjusted.

This moving pulleys are hard to print and require the printer to be very well calibrated. Besides, the teeth degrade rather quickly. Taking into account that, and the fact that fingers were starting to become complex to assemble, this solution didn't seem fitted for anyone to print and assemble at home. A deep redesign was needed.

So we wanted to do three things: Get rid of as many tensors as possible, increase robustness and simplify assembly. The solution is a simple bar actuated mechanism.

Two solid bars link the moving parts of the finger, and keep reduce the number of degrees of freedom to one. This way, the whole finger can be operated from the base and a symmetric mechanism is only needed there. The design is also robust if you choose the right orientation at print time, and the reduced complexity of the features and part count makes it easier to print and assemble. Here is a proof of concept of the finger. The next step is to print a complete finger with the servo adapter, and then test its actuation triggered by electrodes.