Soft Wire-driven Oscillating Tail (TfCD Course, TU Delft)

A technology exploration was executed to determine the possibility to actuate a fish robot with a wire driven active body and floppy compliant tail. We use one material that is both tough to serve as the backbone and flexible, creating an even bending distribution. To create this we used 0.5mm Polypropylene. We aim to oscillate the tail near the eigenfrequency of the material to increase efficiency.

The necessary components are:

1. Arduino UNO

2. Servo

3. Foam

4. Sticks

5. 0.5 mm polypropylene

6. Tiny rope

The importance of “the head” resides in holding the servo in place and raising it to the same high of the tail segments

We cut the tail’s shape from a sheet of 0.5 mm polypropylene. In order to achieve a tail shape, it is recommended to print the tail’s shape on a piece of paper and use it as a template.

Next, you have to build the vertebrates and place them till slightly before half length of the tail. In our case 4 vertebra will be enough. The vertebrae need to have a hole on each side which needs to be aligned with the servo. we used foam with wood sticks (because that sticked better to the PP) for this to test it quickly. But we would recommend using a more rigid material such as wood instead of the foam.

The last vertebra has to be secured a bit better as the rope will pull on this directly. we used wood for this and a nail to secure the rope to.

In order to accomplish the oscillating movement, a tiny unextingable wire is connected from the servo through the holes and be attached to the last vertebra.

We used a simple arduino code to move the servo 12 degrees in either directions with a small delay of 0.3 seconds. This made our tail move near its eigenfrequency. you have to adjust these parameters and possible include speed control to create the same effect in your prototype.