This paper presents the design, development, and basic operation of MinIAQ, an origami-inspired, foldable, untethered, miniature quadruped robot. Instead of employing multilayer composite structures similar to most microrobotic fabrication techniques, MinIAQ is fabricated from a single sheet of thin A4-sized PET film. Its legs are designed based on a simple four-bar locomotion mechanism that is embedded within its planar design. Each leg is actuated and controlled individually by separate DC motors enabling gait modification and higher degree of freedom on controlling the motion. The origami-inspired fabrication technique is a fast and inexpensive method to make complex 3D robotic structures through successive-folding of laser-machined sheets. However, there is still a need for improvement in modulating and extending the design standards of origami robots. In an effort to addressing this need, the primitive foldable design patterns of MinIAQ for higher structural integrity and rigidity are presented in detail. The current robot takes less than two hours to be cut and assembled and weighs about 23 grams where 3.5 grams is the weight of its body, 7.5 grams is its motors and encoders, 5 grams is its battery, and about 7 grams is its current on-board electronics and sensors. The robot is capable of running about 30 minutes on a single fully charged 150mAh single cell LiPo battery. Using the feedback signals from the custom encoders, MinIAQ can perform a trot gait with a speed of approximately 0.65 Bodylengths/sec, or equivalently 7.5 cm/s.

Origami has long been renowned as a simple yet creative form of art and its folding techniques have recently inspired advances in design and fabrication of miniature robots. In this work, we present the design and fabrication novelties, enhancements, and performance improvements on MinIAQ (Miniature Independently Actuated-legged Quadruped), an origami-inspired, foldable, miniature quadruped robot with individually actuated legs. The resulting robot, MinIAQ-II, has a trajectory-optimized leg actuation mechanism with longer stride, improved traction, less flexure joint bending, and smaller leg lift resulting in faster and smoother walking, better maneuverability, and higher durability and joint life. In order to maximize the joint fatigue life while keeping the leg design simple, the initial four-bar mechanism is optimized by manipulating the joint locations and changing the leg link into a non-straight knee shape with a fixed-angle lock. Despite having a 1 cm longer frame to embed its new actuation mechanism, the overall weight and dimensions are similar to its first version as its legs are no longer extended beyond its frame. As a result, MinIAQ-II is 12-cm-long, 6-cm-wide, 4.5-cm-high and weighs 23 grams. The test results demonstrate the improvement in speed over its predecessor from 0.65 to more than 0.8 bodylengths/s at 3 Hz, and an approximate decrease in body's roll ±21 • to ±9 • and pitch from 0 • -11 • to 0 • -7 • . The independent actuation and control over each leg enables such a robot to be used for gait studies in miniature scale, as is the next direction in our research.

C-Quad is an origami-inspired, foldable, miniature robot whose legs and body are all machined from one PET sheet each. The already famous compliant legs are modified such that they can be manufactured from a flat PET sheet and folded into the C-shape wanted. The compliant legs enable the miniature robot to run fast and scale obstacles with ease due to the geometry of the legs. C-Quad has four legs that are manufactured separately from the main body frame, which is also manufactured from a single PET sheet. All of its legs are actuated individually with a total of four DC motors. Despite the thin PET film, the structural rigidity and robustness of the body frame is increased by using specialized folds and locks. The manufacturing and assembly of the robot takes approximately 2.5 hours. C-Quad carries a battery, an Arduino Pro Micro control board, a bluetooth communication module, custom made encoders and commercially available IR sensors for motor speed control and motor drivers, all of which weighs 38 grams. By using very simple control strategies, it can achieve the speed of 2.7 Bodylengths/sec, can perform in-place turns and can climb over obstacles more than half of its height.

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