Electromagnets
Soft robotics
Interesting topic called Soft robotics. Shape changing, regenerating
Instead of a spring you can use a fishing line (Science, 21 Feb 2014, Vol 343, Issue 6173, pp. 868-872). Just twist the fishing line and will swirl into thin spring. If you apply heat it will contract. If you wind up a copper whire around the fishing line first then it can dissipate heat when electricity is applied to the wire.
- Illustration https://www.youtube.com/watch?v=i8mjU3i3QWE
- How to twist https://www.youtube.com/watch?v=UbvNW7ONiTc
- All together as one arm https://www.youtube.com/watch?v=i8mjU3i3QWE
Pneumatic muscle actuators
- Tetrahedral locomotion - three legs-tentacles and a neck, but it can swap them interchangeably https://www.youtube.com/watch?v=qAkJws7VEcI
- Soft quadruped video, article
- Tetrahedral kinematics explained https://arxiv.org/pdf/2303.05454.pdf
- 3D print molds for silicone, connect air tubes (see some steps in the video)
- PAM fabrication with pictures
Pump
https://www.youtube.com/watch?v=wHYL4cFTAY0
Memory alloy actuator
- Just watch videos for this article: Chasing biomimetic locomotion speeds: Creating untethered soft robots with shape memory alloy actuators