[Please excuse my English]
I really like the popular set-up of 2 servos arduino insects on youtube. When I looked at it, I always remember what BEAM robotic guys did long before that set-up became favorite. These people who are analog robot fanatics did better on the gait due to better angle between the two motors ( microcore / bicore walker , etc).
However, in my opinion, none of those mentioned before look more alive than VBug1.5 (also known as Walkman) created by the founder of beam robotic, Mark Tilden. It’s using 5 motors, therefore it has more maneuverability.
Making a simple BEAM robot is not difficult, but building something as complicated as VBug1.5 could be distressing for an electronic novice like me. So, when I decided to make something like Tilden’s bugs, I had to settled with arduino platform, the easiest choice for non-engineers (or in my case, embarrassingly, an engineer wannabe).
As a result, I made Walter, a 4 legged arduino robot with 5 servos. You may wonder, if I wanted to make a look-alive bug robot then why I didn’t go with 8 or 12 servos instead. Well, I was thinking something simplest I can do to get most maneuverability I can have. I’m talking about using a lot of glue instead of making frames.
Technical Deep-Dive
- 5-Servo Gait & Kinetic Harmonics:
- The VBug-Inspired Propulsion Forensics: Unlike typical 4-servo quadrupeds, WALTER utilizes a $5^{\text{th}}$ servo as a central "Spine" or steering-oscillator. Forensics involve coordinating the leg-sweeps with spinal-flexing to achieve a highly fluid, insectoid gait. The diagnostics manage two primary gait-states: Tripod-Gait for stability and Crawl-Gait for varying-velocity traversal $(3 \text{ discrete speed-tiers})$.
- Hot-Glue Structural Diagnostics: To eliminate the weight of a rigid frame, the servos are bonded directly using high-temperature adhesive forensics. This creates a flexible, vibration-dampening skeleton where the servos act as both the structural members and the kinetic actuators.
- Photovore & Acoustic Navigation Heuristics:
- Photonic Signal-Integrity Analytics: Light-seeking behavior is orchestrated via four photodiodes configured in a quadrant-array. Forensics involve measuring the differential voltage across the $100\text{k}\Omega$ pull-down resistors. The diagnostics identify the luminous-vector $(\vec{L})$, triggering the gait-harmonics to steer the robot toward the highest photonic intensity.
- Triple-ToF Obstacle Forensics: To prevent structural impacts, a 3-sensor ultrasonic array provides a $180^{\circ}$ field-of-vision. Forensics involve calculating the Time-of-Flight $(\mu\text{s})$ for each sensor independently. If a collision-vector is identified $(d < 20\text{cm})$, a random-seed behavioral override $(q)$ is triggered, prompting the robot to execute a reversal-harmonic or a $90^{\circ}$ pivot.
Engineering & Implementation
- Behavioral Logic & Power-Rail Forensics:
- Random-Walk State-Machine Diagnostics: To enhance biological realism, the Arduino Pro Mini executes a random-walk generator. Forensics involve periodic "Rest-Cycles" and gait-shuffling, ensuring that the robot does not enter an infinite-loop state when encountering complex corner-geometries.
- High-Current Power-Bank Orchestration: Managing 5 metal-geared servos requires a stiff current-rail. Diagnostics utilize a $2.1\text{A}$ smartphone power bank to feed the VCC rail, ensuring that the high-torque stall-currents of the MG90S servos do not cause logic-brownouts on the $16\text{MHz}$ Pro Mini.
- Surface-Sensing Limitations:
- The initial implementation attempted to use tactile foot-sensors. Forensics revealed that the low mass $(\approx 300g)$ of the chassis-less frame was insufficient to overcome the activation force $(N)$ of the tact-switches. Future diagnostics involve upgrading to capacitive or analog-potentiometer "Tip-Toe" feedback.
BEHAVIORS
Like many other arduino robots, Walter can avoid obstacles using HC-SR04 ultrasonic sensors. To add character as a bug, Walter also a photovore, means he is attracted to light. Photodiodes are used to detect light. There are random values generated in the arduino sketch to make Walter decides when he wants to stop to rest, and also to randomly changes his gait speed (3 speeds).
When I started, I intended to have tact buttons under each of Walter’s feet so he would have a surface sensors. But the battery (a portable power bank for smartphone) costs the servos to much weight. I know tact buttons weigh almost nothing to worry to add weight, but ironically the weight of the robot is not enough to able to pressed the upside-downed buttons.
I planned to make Walter version 2 with bigger servos and then included these buttons as surface sensors.