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General Questions
WW-01/11 Questions


Designed for
servo motors

WW-02/12 Questions


Designed for
Solarbotics
GM-2/3/8/9 motors

WheelWatcherTM Encoder Frequently Asked Questions

General Questions

WW-01/WW-11 Questions

WW-01
Designed for servo motors
  • Can I hook a WW-11 directly to a PC serial port?
    No. You need to provide an RS-232 level converter between the PC serial port and the WW-11, so that TTL logic levels are used and non inverted data is provided. One product that can do this is the Acroname Serial Interface Connector: http://www.acroname.com/robotics/parts/S13-SERIAL-INT-CONN.html.

  • Can I use a USB to serial adapter to interface with the WW-11, such as a Keyspan USA-19HS?
    No. This type of USB to RS-232 dongle is not directly compatible; you can identify such an incompatible adapter by the presence of a DB-9 connector. To use such an adapter, you must add an RS-232 level converter between it and the WW-11, such as a circuit you make yourself using a Maxim MAX232 chip (http://www.maxim-ic.com/datasheet/index.mvp/id/1798) or the Acroname Serial Interface Connector. A better choice is to use a USB to serial interface that directly provides non-inverted TTL signals, such as the Acroname S27-USB-SERIAL adapter: http://www.acroname.com/robotics/parts/S27-USB-SERIAL.html.

  • Do I need to use the alignment tool?
    Yes, it is highly recommended. If the board's sensors are not aligned well with the codewheel sticker, the timing of the various signals will be strongly affected, to the point that you may end up not getting 128 clock pulses per rotation. Further, the time between each clock pulse will not be consistent, but will instead vary from pulse to pulse, usually with a pattern that repeats every 4 clocks. Severe misalignment may result in ChA and ChB not always being in phase with each other, resulting in inconsistent counts.

  • Do I need to use the adhesive on the back of the board? I might want to remove the WheelWatcher later.
    The adhesive helps prevent the board from falling into misalignment if the mounting screws come loose. We chose a type of adhesive that sticks well to many types of plastic, but not so well that you cannot remove the board if you need to. (This question applies to the WW-01 only; the WW-11 does not provide adhesive).

  • Why am I not getting good counts from the encoders?
    Check the behavior of the LEDs while your servos are turning. Do this either by turning the wheels slowly by hand (rough turning can strip the gears in the servos, so be gentle!) with the power on to the WW-01s but off to the servos, or by using your own test program. The green LEDs should be solid on or off, and should only change state when the direction of wheel rotation changes. The red LEDs should blink on and off, once per stripe -- 32 times on and 32 off for each wheel rotation.

    If the green LED is flashing when it shouldn't be, or if the red LED is not pulsing 32 times per rotation, make sure your wheels are on tight. If the wheels are too high above the WW-01 PCBs, there won't be enough light reflected to the sensors on the boards. It is best to use the screws provided with your servos to hold the wheels in tight.
    If you are still having problems, check the alignment of the PCB with the AL-02 alignment tool with the wheel temporarily removed. Also, check that the codewheel stickers are flat against the wheel, without bubbles under them, and that they are clean.

  • What mounting hardware is provided?
    We provide four 4-40 x 7/8" flat head machine screws, with a 100 degree head angle so that the screw heads will not rub on the wheel. We also provide four 4-40 k-lock nuts, four .25" x .278" #4 custom spacers, and four .25" x .31" #4 spacers. See the product manual for suggested spacers to use with various popular servo models.

  • My robot uses DC motors and hand made wheels. Can I use the WheelWatcher WW-01 with it?
    Maybe. You will need to mount the WW-01 such that it is aligned with your motor's shaft, and place the codewheel sticker on a flat surface (your wheel or something attached to the motor shaft) so that it is parallel to the surface of the WW-01 PCB. The distance between the top of the 2 sensors on the WW-01 and the codewheel sticker must be close to 1.1 mm (0.043") for it to function.

    Beyond that, good luck. We can't support nonstandard motors, wheels, and mounting schemes -- the WW-01 is designed specifically for standard injection molded wheels and standard size RC servos. Let us know how it works for you, though.
     
  • I want to use the WW-11 with a Nubotics WheelCommander differential drive controller.  What settings should I use?
    Let WW-11 pin 4 float or tie it high with a pull-up resistor to select quadrature mode.  For the left WW-11, connect pins 1 and 5 to WheelCommander connector J6 Vdd and ground, and pins 2 and 3 of the WW-11  to J6 ChB / ChA inputs.  Connect the right WW-11 to WheelCommander connector J8 in similar manner.  In the WheelCommander Setup Wizard, Motor and Encoder Settings tab, ensure that the Quadrature Settings checkbox is checked, and that the Encoder Resolution text box says 128.
     
  • I have used the WW-02 encoders for quite a few years and recently purchased a few WW-12 encoders. I am following the instructions and trying to use the WW-12s in sign-magnitude mode, so I am connecting pin#4 to ground, pin#1 to 3.3v, and pin#5 to ground. I am only observing 64 high and low transitions on pin#3 and not the expected 128. Is there something that I am missing?
    The WW-11 and WW-12 use a microcontroller instead of a fixed-function quadrature decoder chip, the LSI LS7084, used in the WW-01 and WW-02.  That chip's clock output generated a very short pulse at each transition of the quadrature sensors.  This short pulse was problematic for some beginners to detect, so when writing the code for the WW-11/WW-12, we decided to make it easier by toggling the clock line on each transition.

    You will still get 128 transitions per rotation -- you just need to change your code to look for either edge of CLK rather than just one edge.
  • What is new about the WW-11 compared to the WW-01?
    The WW-11 differs in these ways:
    • 5 pin, 0.1" pitch connector rather than 8 pin (2 rows of 4) 2mm connector
    • 3 operating modes which can be selected by selectively pulling down certain connector pins:
      • quadrature (ChA/ChB)
        sign/magnitude (CLK/DIR)
      • serial (38400 baud); outputs distance traveled as well as velocity
    • sign/magnitude mode toggles the clock line on either edge of either quadrature channel, rather than the 50us low pulse on either edge generated on the WW-01
    • thinner board material (0.031" rather than 0.063")
    • no adhesive on back of board

WW-02/WW-12 Questions

WW-02
Designed for Solarbotics GM2, GM3, GM–8, and GM9 motors
  • Can I hook a WW-12 directly to a PC serial port?
    No. You need to provide an RS-232 level converter between the PC serial port and the WW-12, so that TTL logic levels are used and non inverted data is provided. One product that can do this is the Acroname Serial Interface Connector: http://www.acroname.com/robotics/parts/S13-SERIAL-INT-CONN.html.

  • Can I use a USB to serial adapter to interface with the WW-12, such as a Keyspan USA-19HS?
    No. This type of USB to RS-232 dongle is not directly compatible; you can identify such an incompatible adapter by the presence of a DB-9 connector. To use such an adapter, you must add an RS-232 level converter between it and the WW-12, such as a circuit you make yourself using a Maxim MAX232 chip (http://www.maxim-ic.com/datasheet/index.mvp/id/1798) or the Acroname Serial Interface Connector. A better choice is to use a USB to serial interface that directly provides non-inverted TTL signals, such as the Acroname S27-USB-SERIAL adapter: http://www.acroname.com/robotics/parts/S27-USB-SERIAL.html.

  • Why am I not getting good counts from the encoders?
    Check the behavior of the LEDs while your motors are turning. Do this either by turning the wheels slowly by hand (rough turning can strip the gears in the motors, so be gentle!) with the power on to the WW-02s but off to the motors, or by using your own test program. The green LEDs should be solid on or off, and should only change state when the direction of wheel rotation changes. The red LEDs should blink on and off, once per stripe -- 32 times on and 32 off for each wheel rotation.

    If the green LED is flashing when it shouldn't be, or if the red LED is not pulsing 32 times per rotation, make sure your wheels are on tight. If the wheels are too high above the WW-02 PCBs, there won't be enough light reflected to the sensors on the boards. It is best to use screws to hold the wheels in tight.

    If you are still having problems, check that the codewheel stickers are flat against the wheel, without bubbles under them, and that they are clean.

  • What mounting hardware is provided?
    The WW-02 and WW-12 are provided with two insulated #2 washers; two #2 hex nuts; and two 2-56 1" pan head machine screws.

  • My robot uses nonstandard motors and wheels. Can I use the WheelWatcher WW-02 with it?
    Maybe. You will need to mount the WW-02 such that it is aligned with your motor's shaft, and place the codewheel sticker on a flat surface (your wheel or something attached to the motor shaft) so that it is parallel to the surface of the WW-02 PCB. The distance between the top of the 2 sensors on the WW-02 and the codewheel sticker must be close to 1.1 mm (0.043") for it to function.

    Beyond that, good luck. We can't support nonstandard motors, wheels, and mounting schemes -- the WW-02 is designed specifically for standard injection molded wheels and Solarbotics GM-2, GM-3, GM-8, and GM-9 motors. Let us know how it works for you, though.
     
  • I want to use the WW-12 with a Nubotics WheelCommander differential drive controller.  What settings should I use?
    Let WW-12 pin 4 float or tie it high with a pull-up resistor to select quadrature mode.  For the left WW-12, connect pins 1 and 5 to WheelCommander connector J6 Vdd and ground, and pins 2 and 3 of the WW-12  to J6 ChB / ChA inputs.  Connect the right WW-12 to WheelCommander connector J8 in similar manner.  In the WheelCommander Setup Wizard, Motor and Encoder Settings tab, ensure that the Quadrature Settings checkbox is checked, and that the Encoder Resolution text box says 128.
     
  • I have used the WW-02 encoders for quite a few years and recently purchased a few WW-12 encoders. I am following the instructions and trying to use the WW-12s in sign-magnitude mode, so I am connecting pin#4 to ground, pin#1 to 3.3v, and pin#5 to ground. I am only observing 64 high and low transitions on pin#3 and not the expected 128. Is there something that I am missing?
    The WW-12 uses a microcontroller instead of a fixed-function quadrature decoder chip, the LSI LS7084, used in the WW-01 and WW-02.  That chip's clock output generated a very short pulse at each transition of the quadrature sensors.  This short pulse was problematic for some beginners to detect, so when writing the code for the WW-11/WW-12, we decided to make it easier by toggling the clock line on each transition.

    You will still get 128 transitions per rotation -- you just need to change your code to look for either edge of CLK rather than just one edge.
     
  • What is new about the WW-12 compared to the WW-02?
    The WW-12 differs in these ways:
    • 5 pin, 0.1" pitch connector rather than 8 pin (2 rows of 4) 2mm connector
    • 3 operating modes which can be selected by selectively pulling down certain connector pins:
      • quadrature (ChA/ChB)
      • sign/magnitude (CLK/DIR)
      • serial (38400 baud); outputs distance traveled as well as velocity
    • sign/magnitude mode toggles the clock line on either edge of either quadrature channel, rather than the 50us low pulse on either edge generated on the WW-02
    • no 0.1" pitch 2x4 alternate connector area (this was stuffed instead of the 2mm connector for a special build for the Seattle Robotics Society Workshop Robot, level 3

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