Robot Construction Test
In order to see if the Hot Glue Kit can actually be used to build robots within minutes, we decided to roll the camera and put ourselves and the Hot Glue Kit to a test. Below is the video that shows the recording of this test.
We used 2 actuation modules, a glue gun, 5 glue sticks and a scalpel to build our robot. The robot is inspired from a caterpillar with both actuation modules are placed at the head and tail of the robot. The idea is that both of these modules are pulling their tendons which are attached to the opposite side of the body, therefore bending the soft robot like a caterpillar to move forward.
Following this idea, we managed to build the 1st robot prototype within 6 minutes. When we commanded the actuators to pull the tendons, we noticed that the body was bending as desired however there was not forward motion. After investigating the behavior of the robot with the table surface, we noticed that a "directional friction" is required to move forward.
Therefore we decided to add a glue stick piece at the tail of the robot hoping that it would stop the robot body going backward when it is fully bent. The second part of the video shows that this improvement to the 2nd prototype took 2 more minutes.
When we actuated the modules again with the 2nd prototype, we noticed that the robot was steering to the right, which was improvement compared to the previous case. In order to see what would happen when the modules are commanded to pull with a less amplitude, we changed the target turn for the motors and commanded from the PC. With this, we managed to get a forward motion. All of this process was recorded live and it is shown that a functional soft robot can be built, improved and actuated within 15 minutes.
After the tendon wire is attached to the robot, it is possible for it to get loose. This is not due the tendon wire as the chosen Dyneema line is a non-stretchable strong braided wire. It is mostly due to the plasticity of the robot structure. In such cases, the actuation module needs to be commanded with the direct pose command to turn small steps until the wire is tight again. After that module should be switched off and switched on again to reset the resting position of the motor. As there are no non-volatile memory to store the initial motor position right after the fabrication, switching off and on the system resets the resting motor position.
The current and voltage limitations in the system allow the motor to pull up to 11N of load. Considering the module is only 60g, the weight-to-power ratio of the module is more than sufficient to actuate robots that can be built with hot glue. However, if there is a heavier load on the tendon or the motion is being stopped with a strong interrupt, the module will stop pulling, reset its behavior parameters and send the overload response “L!”. In this case, reconfigure the module from the start and run it again.
When the module is commanded to actuate in an alternate mode with no load, a full battery lasts approximately 8 hours. If there is a load smaller than the maximum value, the battery lasts around 5 hours. When the battery runs out, take out the battery and use a 1S LiPo charger to recharge.