Hi! I am completely new to this field and wanted advice on my setup. I have a motor controller with an RS-485 Interface that I'm hoping to connect to an Arduino Mega to control the speed of the motor. Also, I have two motors that run alternatively, so I have two motor drivers and two RS-485s. I attached my circuit and code below, but I am not too sure if it's correct. If anyone can check it out and lmk that would be great!
Code so far:
/*
Dual UMC1BDS32 Motor Control via RS485 (Modbus RTU)
---------------------------------------------------
Hardware setup (Arduino Mega):
- MAX485 #1 → Motor 1 (UMC #1) using Serial1 (TX1=18, RX1=19)
- MAX485 #2 → Motor 2 (UMC #2) using Serial2 (TX2=16, RX2=17)
- Each MAX485 has its own DE+RE control pin
- STO bypassed (J502) on both UMC boards
- Each UMC powered separately (12–48 V)
Serial Monitor @ 9600 baud:
Type:
M1 <Enter> → select Motor 1
M2 <Enter> → select Motor 2
<number> → set RPM (e.g. 50, -50, or 0 to stop)
*/
#include <ModbusMaster.h>
// === RS-485 driver enable pins ===
#define MAX485_1_DE_RE 4 // for Motor 1 (Serial1)
#define MAX485_2_DE_RE 5 // for Motor 2 (Serial2)
// Create Modbus objects for each motor
ModbusMaster motor1;
ModbusMaster motor2;
int selectedMotor = 1; // Start with motor 1
// RS-485 control functions for Motor 1
void preTransmission1() { digitalWrite(MAX485_1_DE_RE, HIGH); }
void postTransmission1() { digitalWrite(MAX485_1_DE_RE, LOW); }
// RS-485 control functions for Motor 2
void preTransmission2() { digitalWrite(MAX485_2_DE_RE, HIGH); }
void postTransmission2() { digitalWrite(MAX485_2_DE_RE, LOW); }
void setup() {
pinMode(MAX485_1_DE_RE, OUTPUT);
pinMode(MAX485_2_DE_RE, OUTPUT);
digitalWrite(MAX485_1_DE_RE, LOW);
digitalWrite(MAX485_2_DE_RE, LOW);
Serial.begin(9600);
Serial.println("=== Dual UMC Motor Control (Mega + Dual RS485) ===");
Serial.println("Commands:");
Serial.println(" M1 → select Motor 1");
Serial.println(" M2 → select Motor 2");
Serial.println(" [number] → set RPM (e.g. 50, -50, 0)");
Serial.println("------------------------------------------");
// Initialize both serial ports for RS485
Serial1.begin(9600); // MAX485 #1 (Motor 1)
Serial2.begin(9600); // MAX485 #2 (Motor 2)
// Assign Modbus ports
motor1.begin(1, Serial1); // ID can be 1 for both, since separate lines
motor2.begin(1, Serial2);
motor1.preTransmission(preTransmission1);
motor1.postTransmission(postTransmission1);
motor2.preTransmission(preTransmission2);
motor2.postTransmission(postTransmission2);
delay(300);
// Set both drives to velocity mode
motor1.writeSingleRegister(0x6060, 2);
motor2.writeSingleRegister(0x6060, 2);
// Disable both initially
motor1.writeSingleRegister(0x6040, 0x0000);
motor2.writeSingleRegister(0x6040, 0x0000);
}
void enableMotor(ModbusMaster &m) {
m.writeSingleRegister(0x6040, 0x0006); delay(20);
m.writeSingleRegister(0x6040, 0x0007); delay(20);
}
void disableMotor(ModbusMaster &m) {
m.writeSingleRegister(0x6040, 0x0000);
m.writeSingleRegister(0x6042, 0); // stop motion
}
void setSpeed(ModbusMaster &m, int rpm) {
int targetValue = rpm * 10; // adjust scaling factor if needed
m.writeSingleRegister(0x6042, targetValue);
}
void loop() {
if (Serial.available()) {
String cmd = Serial.readStringUntil('\n');
cmd.trim();
cmd.toUpperCase();
if (cmd == "M1") {
selectedMotor = 1;
disableMotor(motor2);
enableMotor(motor1);
Serial.println("✅ Motor 1 selected and enabled.");
}
else if (cmd == "M2") {
selectedMotor = 2;
disableMotor(motor1);
enableMotor(motor2);
Serial.println("✅ Motor 2 selected and enabled.");
}
else {
int rpm = cmd.toInt();
if (selectedMotor == 1) {
disableMotor(motor2);
enableMotor(motor1);
setSpeed(motor1, rpm);
Serial.print("Motor 1 → "); Serial.print(rpm); Serial.println(" RPM");
} else {
disableMotor(motor1);
enableMotor(motor2);
setSpeed(motor2, rpm);
Serial.print("Motor 2 → "); Serial.print(rpm); Serial.println(" RPM");
}
}
}
delay(100);
}