Two-Segment Motion Control (Arduino + Nextion)

BEng Course Project — time-constrained motion control with seamless two-segment transition

Goal: drive a small vehicle through two consecutive segments defined by distance and time,
without stopping between segments.

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Project Overview

This project demonstrates a time-constrained motion control system using:

• Arduino (Nano / ATmega328P)
• DC motor + L298N driver
• Optical encoder feedback
• Nextion HMI for input + live telemetry

The system executes two segments back-to-back:

Segment	Distance	Time
1	D1	T1
2	D2	T2

✅ Key requirement: reach the target distance within the given time and transition to segment 2 without pausing.

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What this project does

• Reads motion parameters from a Nextion touchscreen
• Drives a DC motor using PWM
• Measures real speed & distance via optical encoder
• Compensates for non-linear motor behaviour
• Displays live status:
  • progress
  • speed (current / target)
  • distance
  • time
  • voltage
• Smoothly transitions between two motion segments

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Hardware

Current setup:

• Microcontroller: Arduino Nano (ATmega328P)
• Motor driver: L298N H-bridge
• Motor: DC motor (12–24 W, unknown manufacturer)
• Encoder: Optical wheel (10 holes)
• Wheel diameter: 6.1 cm
• Display: Nextion NX3224K024
• Voltage sensing: ADC on A0 (voltage divider)

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Known Limitations

• Motor calibration is hardware-specific
• Speed accuracy depends on encoder alignment
• No closed-loop PID (feed-forward correction only)

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Core Idea

Instead of directly calculating the “correct PWM” from distance and time, the algorithm:

1) Measures real motion

• Distance from encoder pulses
• Speed from Timer1 Input Capture (hardware timing)

2) Continuously recalculates required speed

At every update step:

required_speed = remaining_distance / remaining_time; 

3) Compensates for non-linear motor behaviour

The DC motor does not respond linearly to PWM duty.

Small changes in duty cycle often produce no change in speed, while larger jumps suddenly switch the motor to another stable speed level.

To handle this, a calibration table is used:

• PWM duty → measured real speed
• Values are obtained experimentally using encoder feedback
• The table represents how the motor actually behaves, not how it should behave

This allows the control logic to work in the speed domain, instead of blindly adjusting PWM.

4) Uses duty mixing

Even with calibration, many target speeds lie between two achievable motor speeds.

Instead of forcing the motor to one of them, the system uses duty mixing:

• Two neighbouring PWM duties are selected from the calibration table
• The motor is driven with these two duties in a defined ratio
• The average speed converges to the desired target speed

This approach:

• Avoids oscillations
• Reduces sensitivity to motor dead zones
• Provides smoother motion without complex control theory (PID)

The result is quasi-analog speed control on top of a highly non-linear motor.

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Calibration Mode

A dedicated firmware mode was created to experimentally identify real motor behaviour.

Can be found on this branch: https://github.com/Caelivar/Two-Segment-Motion-Control-Project-Arduino-Nextion/tree/Data-Collection

Calibration procedure:

• Sweep PWM duty values across the usable range
• Measure real speed using the encoder and Timer1
• Display measured speed and duty on the Nextion screen

The resulting data is manually transferred into the motor calibration table used by the main control firmware.

This ensures the control algorithm is based on measured reality, not assumptions.

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Contributing

Contributions are welcome!

You can help by:

• improving documentation
• fixing bugs
• optimizing control logic
• extending UI features

Please:

• keep code style consistent
• describe changes clearly in pull requests

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