Quadruped Spider Robot with Servo Gait Control

Wheeled robots are easy; legged robots are where robotics gets interesting. A quadruped has to coordinate eight servos in precise phase relationships just to stand, let alone walk — and when students get the timing right, the machine genuinely walks. This project builds a spider-style quadruped: four legs, two servos per leg (hip and knee), an Arduino with a servo driver board generating the PWM signals, and an ultrasonic sensor for obstacle detection. The firmware implements proper gait patterns — a stable wave gait for careful walking and a faster trot — plus turning by differential leg phasing. Bluetooth remote control from a phone app makes it demonstrable and fun, while the engineering underneath (gait tables, servo current budgets, center-of-gravity management) is serious robotics.

1. The Arduino boots the servo driver and moves all eight servos to the neutral standing pose, establishing the robot's balance baseline.
2. The selected gait table (wave or trot) defines each servo's angle as a function of the gait phase; the firmware steps the phase forward at the gait frequency.
3. In wave gait, legs lift and plant one at a time for maximum stability; in trot, diagonal pairs move together for speed.
4. The ultrasonic sensor scans ahead continuously; when an obstacle is within the stop distance, the robot halts and executes a turn sequence.
5. Bluetooth commands from the phone override autonomy: walk forward/back, turn left/right, switch gait, or stand at attention.
6. A dedicated 5–6 V high-current supply feeds the servos separately from the logic, preventing the brownouts that plague servo projects.
7. Students tune stride and timing parameters on their own build using the gait tuning guide, documenting the final gait in the report.

Tech stack:

• Arduino Uno + 16-channel servo driver
• 8x SG90/MG996R-class servos
• Aluminium leg linkages + chassis
• Ultrasonic distance sensor
• HC-05 Bluetooth module
• Phone control app
• 5–6 V high-current servo supply
• Gait sequencing firmware

• [Programmed walk gaits] Wave gait for stable walking and trot gait for speed, implemented as phase-timed servo sequences — real legged locomotion, not random leg wiggling.
• [8-servo leg mechanics] Four legs with hip and knee servos on aluminium linkages, giving the 8-DOF platform that makes gait study meaningful.
• [Ultrasonic obstacle avoidance] Front-mounted ultrasonic sensor triggers stop-and-turn behavior, demonstrating sensor-driven autonomy.
• [Bluetooth remote control] Phone app control for walk, turn, gait select and stop — the standard live-demo interface.
• [Turning by differential phasing] The robot steers by phasing the left and right leg pairs differently, teaching the legged equivalent of differential drive.
• [Servo power design] A dedicated high-current servo supply with the current budget documented, addressing the number-one failure mode of servo robots (brownouts).
• [Gait tuning guide] Step-by-step procedure for adjusting stride length, lift height and phase timing on the student's own build.

• Quadruped spider robot (assembled: chassis, 8 servos, linkages)
• Arduino + servo driver electronics (programmed)
• Complete gait firmware source code with tuning guide
• Phone control app setup guide
• Wiring diagram and mechanical assembly guide
• Servo power and current-budget document
• Project report PDF (background, gait theory, firmware, results)
• PPT presentation for final review
• Viva Q&A preparation document (gaits, servo control, power design)

• This is a servo-driven hobby quadruped, not a dynamic running robot — gaits are quasi-static and speeds are modest, stated honestly.
• Servo quality varies; the tuning guide expects the student to calibrate on their own build rather than trusting nominal angles.
• Battery life is approximately 20–30 minutes of walking (expected); continuous demo needs the supply or spare packs.
• The ultrasonic sensor sees only straight ahead; side and rear obstacles are out of scope.
• Rough or slippery surfaces degrade gait performance — the report documents tested surfaces honestly.
• Bluetooth range is approximately 10 m line-of-sight; walls and interference shorten it.