Modular soft robots_1

PART 1 of 4

For PART 2 click here
For PART 3 click here
For PART 4 click here


For my finals for soft robotics class I want to make a system of modular soft actuators which can be combined together to perform different functions.

The soft modular system is an effort to create a plug and play system with soft robotics which is a very fabrication intensive process. I am also thinking of this system as working like an educational tool or toy to introduce kids and adults to the field of soft robotics. This will be to soft robotics, what K’nex is to mechanics or Little Bits is to electronics. Ideally, these blocks should also be compliant with other forms of robotics where they can be easily integrated.

Examples of similar systems

Modular soft robots by EPFL

The modular body

Modular robotic cubes



I had two approaches ahead of me

  1. Multiple modules for a common function
    This approach required me to fabricate multiple modules which would come together to carry out a single function. Like putting together the pieces of a puzzle.
  2. Same module, Multiple functions
    In this case I will make multiples of the same module which can perform differently with simple modifications or combinations. I found this approach to be more interesting and feasible, given the time frame of 3 weeks


The image below demonstrates my idea of a kit with different modular components.

The kit mainly comprises of linear silicone actuators, internal restraints, wheels, end caps, etc.


The different components can be fit together to create different robots or mechanisms as shown in the animation below.


clockwise from top left : Rope climbing robot, gripper, CG wheel, crawling robot.


The chart below explains the motivations and rationale behind the project.

Untitled presentation (2)


Most common actuation methods used in soft robotics are linear (forward and backward) and bending. I realized I need only design a linear actuator and use a mix of external and internal constraints to achieve different kinds of motions. So the actuator module remains same but the variety of motions is brought about by modular restraints.

Update : April 3rd

To test out the idea I designed a mold in Rhino to cast a basic actuator. I also wanted to test the coupler design which would enable the modularity and interfacing between different modules.

mould design.PNG
Dark grey part is the actuator and the light grey covering is a cross section of the mold design
mould design 2.PNG
Final molding assembly file ready for 3D printing



Shown in red in the image above is the coupler in hard plastic which is assembled with the actuator. The coupler has 4 arms which serve as hooks for different restraints. The coupler is slightly oversized to achieve a tight fit with the silicone actuator. In the final design the coupler should be in-molded with the silicone part. The 4 holes seen on the silicone part at the corners is the channel for the internal restraint to pass through.

Update : April 7th



Main body of the cast is ready for molding. I inserted two sticks in each half to form the channel for the restraint.



I also made small holes to let the air out and get the silicone moving more freely.


One half of the mold assembly. The green stick in the center forms the central inner air cavity.



Unfortunately the silicone started leaking from the bottom due to increasing pressure. I decided to let it sit and re-cast it the next day.

Update : April 8th


Was happy to see at least half of the actuator was casted. If anything it was a good run for testing the quality of the cast. Also gave me a much better idea for dis-assembly.


After de-molding, I reassembled the mold and plugged the holes and the edges with hot glue this time.



Parallely I cleaned up the half casted actuator for early testing of the actuation.


Tested assembling the coupler for fit.


I decided to plug one end of the actuator with more silicone and set it aside for casting.


3 hours later…

The actuator is sealed from one end

On the side, I injected more silicone into the mold which was still curing, to fill it up completely and compensate for some of the silicone which leaked at the bottom.


Update : April 9th


Final casted actuator. The red cable demonstrates the restraint mechanism. (6).gif
I was able to achieve some linear actuation but not without overall inflation.



For PART 2 click here
For PART 3 click here
For PART 4 click here

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