Lecture Alternate Assignment

Summary and critique of the article by Professor Wood and his colleagues

Seitz, Benedikt F., et al,  “Bio-inspired mechanisms for inclined locomotion in a legged insect-scale robot.” Harvard Microrobotics Laboratory. 14 December, 2014.

The development of insect-scale robots has made a lot of progress in flat surface movements. However, locomotion of the insect-scale robots on slanted surfaces has not been as successful. This paper explores the use of different adhesion and alignment mechanisms on the Harvard Ambulatory Microrobot (HAMR), the model insect-scale robot for this experiment. The legs of the robot must exert enough peak and normal forces on the surface to prevent slipping. Therefore, the different adhesion methods must be tested for a degree of stability.

The components to of the HAMR were carefully analyzed and tested to ensure the best performance of the robot. The design of the actuator of the HAMR was selected after testing different thicknesses of the various actuators. The 2-ply actuator was determined to have the best mechanical advantage. Also the transmission performance of the legs of the HAMR was tested. The locomotion of the legs was then analyzed; it was found that the motion of the legs as they took steps was not ideal for climbing inclined planes, as the robot rocked back and forth on the legs that were in contact with the ground as the other legs were moving. In order to compensate for this unwanted motion, a passive tail was added to the HAMR so that its motion would be more stable.

There were three types of adhesion methods that were tested: electroadhesion, micro-spine adhesion, and gecko-like dry adhesion. The HAMR’s performance using these adhesion methods was recorded.

In testing the three methods, the HAMR was programmed to simulate walking on a flat surface. The peak shear force (x-direction) and peak normal force (z-direction) were recorded for each adhesion method. The directional gecko adhesive resulted in the highest average shear force, while the electro-adhesive material resulted in the highest average normal force.

Then, the adhesion methods were tested in a climbing test. Each adhesive was tested for the maximum incline and decline angle for which slipping would not occur. The gecko dry adhesive, h = 100um, resulted in the greatest angle for incline and decline – 22 and 45 degrees, respectively.          

The paper presents an exploration of ways to design locomotion on inclined planes for insect-scale robots. By comparing the performances of the three adhesion methods, the experiment clearly showed why one was more effective than the other. The data and conclusions agree with each other – the gecko dry adhesive had the largest maximum angle without slipping. The data and conclusions address the limitations of certain aspects of the experiment, as well. The micro-spine feet have a limited trajectory, and thus the trajectory must be adjusted to create an adhesive force. This acknowledgement is thorough and provides room for improvement in future experiments. Also, the analysis of the original HAMR and corrections to its mechanics, such as adding the tail, was very important to the overall experiment.

Possible future experiments include using a combination of different adhesives to achieve maximum attachment to inclined surfaces. I would also suggest that future experiments include the same peak/normal force test and climbing test, but with slightly different specifics – for example, alter the h value for the gecko dry adhesive. I found it very interesting and helpful to see an example of hybrid adhesion systems in nature – the Oecophylla smaragdina ant’s foot. This shows that the idea of the insect-scale robot’s hybrid adhesion systems is modeled after something found in the natural world.