Multistepper

This short ARDUINO sketch allows controlling multiple stepper motors at once. It is set up for 28BYJ-48 stepper motors.

I needed a program that allows the control of more than one motor simultaneously to use the cheap steppers I got (28BYJ-48) with the LEGO-compatible housing for a LEGO technic robot arm that I built with my son.

The requirements were:

• multiple motors move simultaneously with one command (comparable to 3D-printer G1 command)
• feeding of new commands to the arduino via serial/USB (to later add a raspberry with user interface)
• as flexible as possible with as little code as possible

Hardware

• Stepper motors 28BYJ-48 with ULN2003 driver boards
• Arduino UNO or MEGA (these I tested)
• jumper wires

optional:

• LEGO housings for the motors
• zillions of LEGO technic sets 😄

Install

• just load the myStepper.ino into your arduino board
• connect the driver boards to the arduino and to a power source If you did not change the sample code from line 632 you need to connect the first 3 motors as follows:
  • Mot1: Pins 4,5,6,7
  • Mot2: Pins 8,9,10,11
  • Mot3: Pins 22,23,24,25 (Arduino MEGA only)
    You are free to change the pins as needed!

Usage

Open the serial monitor. Set the line break to new line and the speed to 9600 baud

If you did not remove the sample code the printout will look like

Motor A
Motor B
Motor C
clearMove()
PowerOff

after uploading the sketch.

commands

The serial interface allows the following command to be send to the multistepper:

MD Letter pin1 pin2 pin3 pin4 [homeSwitchPin]
Motor Definition: Adds a new motor to the multistepper

ML
Motor List: Prints a list of the known motors

GA Letter Position [Letter2 Position2 ...] [FD StepsPerSecond]
Go Absolute: Defines a motion and starts it. The motor movements are synchronized to start and finish synchronously.

MOFF
Motors Off: Switches off all motor coils. The 28BYJ-48 tends to heat up very quickly so switching the magnetic coils off is recommended. For small (lego) models the gear ratio (~1:64) is large enough for the self-locking of the gear to hold the position.

APO 0/1
Auto Power Off after Motion: Shuts down the coil current after completion of each GA command

examples

Motor List
Enter ML and press

ML
Parsing command ML
Info Motor 0 [A]:
 Coil Pins: 4 5 6 7
 No End stop (home) pin.
 Current position: 0
Info Motor 1 [B]:
 Coil Pins: 8 9 10 11
 No End stop (home) pin.
 Current position: 0
Info Motor 2 [C]:
 Coil Pins: 22 23 24 25
 No End stop (home) pin.
 Current position: 0
OK

Adding a new (4th) motor: I connected a fourth motor to the pins 34..37, and want it to be known as motor "D":
MD D 34 35 36 37

MD D 34 35 36 37
Parsing command MD D 34 35 36 37
Info: No home pin defined pin.
OK

now ML prints:

ML
Parsing command ML
Info Motor 0 [A]:
 Coil Pins: 4 5 6 7
 No End stop (home) pin.
 Current position: 0
Info Motor 1 [B]:
 Coil Pins: 8 9 10 11
 No End stop (home) pin.
 Current position: 0
Info Motor 2 [C]:
 Coil Pins: 22 23 24 25
 No End stop (home) pin.
 Current position: 0
Info Motor 3 [D]:
 Coil Pins: 34 35 36 37
 No End stop (home) pin.
 Current position: 0
OK

Coordinated motion of two motors: In this example, A and C motors are to be moved, and they started both at position 0.

GA A 1000 C 2000
Parsing command GA A 1000 C 2000
OK: motor A is motor #0
OK: position 1000
Motor 0
OK: motor C is motor #2
OK: position 2000
Motor 2
0: Steps 1000
1: Steps 0
2: Steps 2000
3: Steps 0
0 done: 1000
2 done: 2000
OK

Work in progress

• home switches (end stops)
• precision with large numbers of steps. The floating point arithmetic currently used is not precise enough. Sometimes a motor has to make some steps after the others have finished to reach its final position.

DISCLAIMER

This is a) work in progress b) comes with absolutely no warranty in any way, to the extend legally possible.