ABS Demo Rig using Wheel Speed Sensors

Anti-lock braking is one of the most widely deployed safety systems in automobiles, yet in the classroom it stays an equation: slip ratio curves, friction circles, and a block diagram of "the controller." The physical behavior — pressure modulating many times per second while a wheel hovers on the edge of lockup — is never seen. Commercial ABS test rigs cost lakhs and are out of reach for student labs. This project closes that gap with a bench-scale rig: a DC-motor-driven wheel with a Hall-effect speed sensor on a tone ring, an Arduino that computes slip against a reference speed, and a solenoid brake actuator the controller pulses to keep slip near the 15% design target. Students watch modulation happen live — on the rig's LCD, in the event log, and on the dashboard's wheel-speed traces — and run the classic comparison test: ABS-on stop versus a locked-wheel stop. Because the slip target, modulation rate and reference speed are all configurable in firmware, the rig doubles as a control-theory teaching platform.

1. The DC drive motor spins the wheel to the set reference speed (e.g. 850 rpm); the tone ring rotates with it.
2. Hall-effect sensors count tone-ring teeth 60 times per revolution, giving precise wheel rpm at the Arduino.
3. The firmware computes slip as (reference speed − wheel speed) / reference speed, continuously.
4. When you press the pedal, the Arduino drives the solenoid brake; when slip exceeds the 20% threshold, it releases pressure for ~60 ms, then re-applies.
5. The pulsing keeps slip hovering near the 15% target instead of the wheel locking — visible as the pulsing blue trace on the dashboard.
6. Every modulation event is timestamped to the event log, the LCD and the SD card; the comparison mode records ABS-on and ABS-off traces for the report.
7. The dashboard renders live rpm, slip bars and the traces; the report's test procedure documents how the buyer measures modulation rate and slip behavior on their own rig.

Tech stack:

• Arduino Uno (ATmega328P, Arduino-core firmware with commented slip-control loop)
• Hall-effect wheel speed sensors + 60-tooth tone ring
• DC drive motor with speed controller (reference-speed source)
• Solenoid brake actuator + caliper assembly
• 16x2 LCD (I2C) for on-rig readout; SD card module for test logging
• USB serial telemetry to the dashboard web app
• Single-file HTML/CSS/JS dashboard (live monitor, test-results views)

• [Four-wheel speed sensing] Hall-effect sensors read a 60-tooth tone ring on each driven wheel, giving high-resolution rpm — the same principle real ABS tone rings use, at bench scale.
• [Slip-ratio control loop] The Arduino compares wheel rpm against the reference speed, computes slip continuously, and releases/re-applies brake pressure to hold slip near the configurable 15% design target.
• [Solenoid brake actuator] A solenoid-driven brake caliper provides the fast on/off pressure modulation (~8 Hz design target) that stands in for hydraulic ABS valves.
• [Live rig dashboard] The companion dashboard streams per-wheel rpm, slip bars, brake-pedal pressure, ABS state and a timestamped modulation event log over USB serial.
• [ABS-on vs locked test mode] Record wheel-speed traces with ABS enabled and disabled; the comparison chart shows the modulated stop against the locked-wheel slide — the centerpiece viva demonstration.
• [Configurable firmware] Slip target, modulation rate, reference speed and sensor calibration are all constants in commented firmware, so examiners can probe control-theory understanding live.
• [LCD + SD logging] A 16x2 LCD shows live slip on the rig itself; every braking test logs rpm traces to the SD card for the report's graphs.
• [Complete build docs] Wiring diagram, tone-ring mounting guide, sensor-gap calibration procedure, and firmware with commented control logic.

• Complete Arduino firmware (speed sensing, slip computation, modulation control, logging)
• Rig hardware build guide (frame, motor mount, tone-ring fitting, brake assembly)
• Wiring diagram and sensor-gap calibration procedure
• Live dashboard web app (rig monitor + test-results views)
• Project report PDF (background, control design, test procedure, evaluation method)
• PPT presentation for final review
• Viva Q&A preparation document (slip ratio, ABS theory, Hall sensors, control loops, calibration)
• Setup guide (assembly, first spin-up, first braking test)

• This is a bench-scale demonstrator, not a vehicle braking system: it models one wheel's dynamics with a motor as the "vehicle" — stopping distances are not comparable to real cars, and the report states this explicitly.
• The solenoid actuator stands in for hydraulic valves; pressure modulation is on/off pulsing rather than proportional hydraulic control.
• Slip and modulation figures are design targets and the buyer's own measurements — the report documents the measurement procedure, and no stopping performance is pre-claimed.
• Sensor accuracy depends on correct tone-ring gap setting; the calibration procedure must be run during assembly or rpm readings drift.
• The rig needs a stable bench power supply for the motor and solenoid; brownouts during braking tests corrupt the traces.