Version vom 1. Juni 2016, 06:06 Uhr

Abstract

Ardumower uses two different types of motors (all motors can be purchased via the shop ):

• Two motors (with integrated gearing) for driving (wheel motors) and with integrated encoders (for distance and speed control)
• One motor (with high rotation speed) for mowing (mower motor)

To control the motors, it requires motor drivers. In addition, the motor driver measures the motor current, and allows us to detect obstacles as motor current increases at obstacles. Ardumower uses two dual MC33926 motor drivers, so two channels for left and right motor and two dual channels (connected in parallel) for the mowing motor.

Voltages

As in all modern systems, Ardumower uses 24V motors.

Wheel motors wiring

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  Ardumower gear motor with encoder (8mm diameter, 5900 rpm motor, 0.055 Nm, gear ratio 1/212, output torque 2.45Nm, output rpm 31)

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  Motor wiring

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  Ardumower gear motor curve (motor only)

The two left and right gear motors are controlled independently (aka 'differential driving') to:

• drive the robot forward/backward
• steer the robot left/right

Wheel motor features:

• A rotation speed up to 31 rpm allows to move the robot at sufficient speed (at up to meter/sec = 31rpm/60 * PI * 0.25m = 0.4m/sec using 250mm diameter wheels)
• A high torque (2.45Nm) guarantees that the robot can climb small hills as well (with 2 motors, 0.125 radius wheel, 31rpm = 0.4m/s, acceleration = 0.2 ( 1/2 of nominal speed) see calculator
• Integrated encoders, so it can measure the rotation speed and the distance
• 24V (load current ~1A)

Motor decrease noise

Here's how you can decrease motor noise:

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  Decrease motor noise

• Instructions: Motor-decrease noise REV20150531
• (English comments)

Protector PCB

When quickly tunring motors from forward to backward (or vice versa), high voltage spikes appear. These high voltage spikes could damage the motor driver in the long run. To eliminate high voltage spikes, it is adviced to use a Protector board between motor driver and motor.

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  Protector PCB

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  Protector PCB wiring

• Assembly manual: Protector board (required for safe-use of motor drivers!)

Motor driver assembly (dual MC33926)

Motor driver features: up to 3A with integrated current sensor and thermal shut-down protection

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  PCB and MC33926

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  MC33926 pinout

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  MC33926 schematics

• Video instructions: Dual MC33926

Motor wiring (left motor):

Motor (black)  ==== MC33926 M1OUT1
Motor (red)    ==== MC33926 M1OUT2

For right motor, use MC33926 M2OUT(1,2) accordingly.

Odometry wiring

The Ardumower motors have integrated encoders. These encoders help us to compute speed and traveled distance. Here's how you connect the odometry wires to the PCB.

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  Motor wiring

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  Encoder signal

Motor odometry wiring (left motor):

Motor (brown)  ---- PCB VCC
Motor (green)  ---- PCB GND
Motor (blue)   ---- PCB OdometryLeft (3)
Motor (purple) ---- PCB OdometryLeft (4)

For right motor, use PCB OdometryRight accordingly.

IMPORTANT: PCB v0.5/1.2 are missing pull-up resistors! You need to add them yourself at the PCB:

PCB OdometryLeft(3) --- 4.7k --- 5v
PCB OdometryLeft(4) --- 4.7k --- 5v

Mower motor wiring

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  Ardumower mower motor

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  Ardumower mower motor curve

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  Mower start current

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  Mower blocked, 500ms detection (max), waittime: 5sec (min)

The Ardumower mower motor features:

• Fast enough to cut the lawn (3150 rpm)
• Enough torque (140 mNm / 46 W)
• Quiet mowing (you cannot hear it)
• 24V, load current ~1.0A (L=2.8mH, R=1.9ohm)

Security note: For security reasons, always remove mower blades in your first tests!

Motor wiring (mower motor):

Motor (black)  ==== MC33926 M1OUT1
Motor (red)    ==== MC33926 M1OUT2

Motor controller (PID)

The speed of the motors is controlled by a software PID controller. You can monitor the quality of the motor speed control via pfodApp (Plot->Motor control):

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  Motor speed settings

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