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Blewitt et al. Soft Sci 2024;4:13 https://dx.doi.org/10.20517/ss.2023.49 Page 21 of 26

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Figure 18. Flow chart demonstrating the control system used in the study of Calderón et al. .

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Figure 19. Reprinted with permission from Goldoni et al. . Copyright 2024 American Chemical Society.

earthworm mechanism that consisted of two accelerometers placed on either side of a passive joint. The
passive joint has a potentiometer at the joint to indicate when the robot is passing through a turn. The
posture angle can be calculated by comparing the two accelerometer readings, and hence, the angle of the
pipe turns determined. The robot also had a distance measurement unit that was placed at the entrance to
the pipe which used an encoder to measure the length of cable (attached to the robot) that had travelled in
the pipe. These measurements were used to build a 3D estimation of the pipe the robot had travelled
through. The distance was measured with an uncertainty of 2.6%, whilst the angles of the pipe structure
were measured with uncertainties of up to 50% when the direction of turning was parallel to the direction of
gravity. The angles of measurement perpendicular to gravity were smaller due to the slack of the cable
causing disturbances on the accelerometer when the robot was travelling downwards.