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Underwater Robot Competition Workshop Presentation - Motor Control

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					Underwater Robot Competition

Advanced Workshop Part 2 – Motor Control
                Introduction
• The competition has been getting
  more difficult.
• Now more elaborate control of
  the robots is required.
• More sophisticated electronics
  also required to complete the
  required tasks.
                       Today
• We want to help with some ideas.
   Since the propulsion is usually by DC
     motors driving propellers, more
     accurate control can be achieved by
     more precise motor control.
                     DC Motors
• Three types :
   – Stepper Motors.
   – Servo Motors.
   – RC Servo Motors.
          Reversing Motors
• Three methods:
  – Manually switching.
  – Relay switching.
  – “H” bridge.
            Manual Switching




Off / On / Reverse
Relay Switching




        Off & On
Relay Switching




     Reverse
Relay Switching




  Off / On / Reverse
Solid State Switching




        Reverse
H-Bridge Switching




    Off / On / Reverse
H-Bridge Switching




    Off / On / Reverse (More efficient)
           DC Servo Motors
• Off/on by switches or relays.
• Accurate control of speed is usually done
  by:
  – A series connected adjustable resistor.
  – A varying voltage supply.
  – Pulse Width Modulation of a fixed voltage
    supply.
Variable Voltage & Resistors




       This sort of thing gets hot
Variable Voltage & Resistors




       This is a different story
              What is PWM?
• PWM = Pulse Width Modulation.
• It is the switching off and on of a power
  supply for different time periods.

 Slow speed          Faster speed        Full on
                                 So
• The more energy we put into the motor, the faster it will
  rotate.
• Full voltage switching stops the problem of motor stalling
  at low voltages.
• For constant DC supply:
   – Power = volts x amps.

• For PWM :
   – Power = volts x amps x ds
   – Where ds is the duty cycle of on to off time.
           How do we do this?
• Either by discrete electronics.

• Or by microcontrollers.
Discrete Electronics
                Kitsrus DIY Kit 67

                DC Speed Controller

                HK$ 102
                    Kit Notes
• Kit is moderately easy to construct:
   –   Only one direction.
   –   Easy to repair.
   –   Moderate efficiency.
   –   Low voltage 5~16V DC.
   –   Medium current 7.5A.
Discrete Electronics
             Kitsrus DIY Kit 166V2

             DC Speed Controller

             HK$ 145
                      Kit Notes
• Kit is moderately hard to construct:
   –   Two directions on one pot.
   –   Watch the solder bridge between layers.
   –   Easy to repair.
   –   Moderate efficiency.
   –   Low voltage 5~32V DC.
   –   Medium current 5A.
      Microprocessor Control
• Many microcontrollers can be used to
  generate a PWM Signal.
• The Programmable Intelligent Computer
  series from Microchip is quite popular.
• The advantage of using one is a reduction in
  component count and a flexible
  performance curve.
Microprocessor Control
              Oceanway 5A Controller

              DC Speed Controller

              HK$ 160
                     RS232C Control
                     possible




       PIC                            PWM Switching




                                           Direction



Speed Control Pot.
                                              M
             The Tricky Bit
• You need to know how to program the PIC.
• You need to watch for noise on the power
  supply.
• You need some PIC equipment like
  programmers in order to work with them.
                   Advantages
• Really flexible.
• Cheap.
• Remote control possible (RS232C?).
   – Multi-units over a single control cable.
• 8 pin PIC unit suitable.
That’s it


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