WW-12 (rev 1.02)
Contents
1. ASCII Ox0A D00000000 lt LF gt V0000 lt LF gt After moving 123 steps at 25 ticks per second the output would look like this D0000007B lt LF gt V0019 lt LF gt WheelWatcher WW 12 Product Manual 10 Command Set The following commands are supported by firmware revisions 1 and 2 of the WW 12 WheelWatcher encoder when in serial mode D lt LF gt Control Distance Output Toggle automatic output of distance on change V lt LF gt Control Velocity Output Toggle automatic output of velocity on change E lt ni gt lt n2 gt lt LF gt Test Interface Echo back the specified nibbles n1 and n2 in reverse order this is used to test the interface The returned data will be E lt n2 gt lt n1l gt lt LF gt For example if you issue E5A lt LF gt You ll receive back EA5 lt LF gt T lt LF gt Request Time This command returns the time since power on of the WW 12 in increments of 10 milliseconds 1 100 of a second resolution For example T lt LF gt T00000352 lt LF gt Means the device has been running for 352H 850 100 8 5 seconds This command can be used to compensate for clock speed variations in each WW 12 which affects the accuracy of the velocity reports M lt LF gt Request Output Mode This command returns the current operating mode which will always be 2 N lt LF gt Request Name and Version This returns the current device name and firmware version same as power up NWw02 lt LF g2. using Timer2 to measure the time between edges of the Clock signals This allows you to tightly control wheel velocity and acceleration despite the low sample rate up to 128 clock changes per second for a 60 RPM wheel speed WheelWatcher WW 12 Product Manual 16 VWVheelVatcher Frequently Asked Questions e 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 S 13 SERIAL INT CONN html e 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 e Where can I buy a WheelWatcher Encoder Acroname acierrabatics e What happens if the codewheel sticker is not centered on the wheel This will result in
3. a repeating wobbling signal pattern for each wheel rotation It would be hard to correct for this in firmware so go slowly and take care when mounting the sticker This won t affect you much if you are only using the WheelWatcher for odometry distance measurement but will affect you if you are using it for velocity control e What do the LEDs mean The YELLOW LED DI is connected to the Direction signal so it turns off when the wheel rotates clockwise CW and on when it rotates counter clock wise CCW The GREEN LED D2 is connected to the ChA signal so it blinks on and off as the wheel turns NOTE For I second after power up the LEDs are set to a pattern to indicate which WheelWatcher WW 12 Product Manual 17 operating mode the WW 12 is in If quadrature mode yellow will be on and green off if sign magnitude yellow will be off and green on and if serial both will be on e How can I clean the codewheel stickers We recommend only gentle cleaning with a tissue or Q Tip moistened with clean warm water Do not use isopropyl rubbing alcohol or other cleaners as they can cloud the silver areas and render them less reflective They could also damage the adhesive e Can I run the WheelWatcher from my 6v or 9v battery pack No The ICs on the board require Vcc to be between 3 3v and 5 5v We recommend the use of a regulated 5v supply e How can I tell how far my robot has travelled This is called odometry As the rob
4. the sticker on the back of the wheel It also depends on reliable maintenance of that alignment by means of the mounting hardware The GM series motor mounting holes are compatible with 2 e g 2 56 or 3 screws The GM 3 and GM 9 mounting holes are compatible with 2 3 or 4 e g 4 40 pan head machine screws WheelWatcher WW 12 Product Manual Installation Step by Step MEN if the motor is already mounted on the robot remove it lower the board over the motor output shaft with the shaft going into the largest hole in the center of the WW 12 making sure the raised alignment pin on the motor housing enters the matching hole on the board Make sure the slightly raised area around the motor shaft fits entirely inside the hole in the circuit board mount the motor and WW 12 to the robot chassis using 2 56 machine screws and 2 56 nuts place insulated washers between the screw heads and the circuit board wire up the cable to your microcontroller see the Connector Pinout for assembly and Interfacing Examples for details For GM 2 or GM 3 motors peel off the adhesive backing then install the optional CS 100 Codewheel Spacer onto the back of the wheel the side into which the motor shaft is inserted being sure to center it then attach the codewheel sticker to the top of the Codewheel Spacer while also ensuring it is centered with the hub For GM 8 or GM 9 motors place the codewheel sticker on the back of the wheel being sure to cente
5. 8 e Ihave 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 O1 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 WheelWatcher WW 12 Product Manual 20 e What is new about the WW 12 compared to the WW 02 The WW 12 differs in these ways o Spin 0 1 pitch connector rather than 8 pin 2 rows of 4 2mm connector o 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 o sign magnitude mode toggles the clock line on either edge of either quadrature channel rather than the 50us low pu
6. 9 MIN 0 3mm 0 012 TBD MAX 1 7mm 0 067 TBD 12 Sensing Object White Paper 90 reflective IC ON NORMALIZED COLLECTOR CURRENT d DISTANCE mm Figure 9 from datasheet for Fairchild QRE1113 Rev 1 7 0 Copyright 2011 Fairchild Corporation 22 1mm 894 a 17 63 mm 694 14 96 mm 589 23 39 mm l i l 2 54 mm 100 49 89 mm paaa mm KOM 1 964 l 28 52 mm g 1 123 D4 27 mm D168 B2 84 mm 112 17 42 mm 686 Figure 10 board outline WheelWatcher WW 12 Product Manual 13 Detector to CodeWheel spacing MIN 0 3mm MAX 1 7mm 1 00 mm J lt 039 a WheelWatcher PCB HE aa Figure 11 proper spacing WheelWatcher WW 12 Product Manual CodeWheel sticker 1 60 mm 063 Detector top 79mm 031 14 Interfacing Examples Please visit www nubotics com to view and download example code for Atmel AVR Basic and C Microchip PIC Basic and C Kronos Robotics DIOS Motorola 68hc11 Interactive C and Ridgesoft RoboJDE Java Parallax Basic Stamp and Savage Innovations OOPIC controllers Raw Quadrature ChA ChB Onl The ChA ChB signals can be used with motor controllers that accept industrial style incremental encoder signals such as the Acroname BrainStem Moto Savage Innovations OOPIC or Solutions Cubed MiniPID ChA and ChB are 50 duty cycle 90 out of phase signals created by having two photo detector packages spaced at a
7. NUGUT Cs An VV heelV Vatcher Product Manual Incremental quadrature encoder system for gearhead motors 1 02 11 28 2071 1 VU heel Vatcher Features easy installation simple interface preprinted 32 stripe self adhesive reflective codewheel multiple interface modes for easy integration o quadrature ChA ChB o sign magnitude clock direction o 38400 baud serial position velocity e compatible with Solarbotics GM 2 GM 3 GM 8 and GM 9 Gearhead motors e designed for use with standard injection molded robot wheels any color e code examples for common robot controllers available GM 2 and GM 3 motors require the use of the optional CS 100 Codewheel Spacer Description The WW 12 WheelWatcher incremental encoder system enables robot builders to quickly add closed loop control to their robots The WW 12 provides standard ChA ChB raw quadrature outputs 90 phase shift between channels decoded Clock and Direction signals or serial output of distance and velocity The clock signal toggles state at each transition of ChA or ChB providing a 4x increase in resolution compared to the number of stripes 128 clocks per rotation while the direction signal indicates the decoded direction of rotation making it very easy to add to any microcontroller The new serial output mode does all the hard work for you it keeps track of and reports current position a signed 32 bit integer and also measures and reports current
8. W 12 and the inverted signaling will result in unusable data USB Mini b seg USB Stans 3 CTS WCC Status AD t a ae pn la JE of prep w af 5 STA Data In g E Ik p pve a FTN Ja E OW 5RX Data Out Taga a i Pu a til Me prs 5TA Status Blue a AS SRX Status Green i 25 be SE Lad 1 p pe e Figure 7 Acroname USB Serial Connector WAA 1 2 to S527 USB Serial Connections Table 2 connections WW 12Pin _ Name S27Pin 1 Zo ee MCO Y 2 Ls SerMode 0 10K resistor to GND SB SSS O STX Data In 4 RXIn SRX Data Out SoG GND WheelWatcher WW 12 Product Manual Data Format For consistency this serial data format matches the format for our other serial interface product the WC 132 WheelCommander Differential Drive Controller After reset the string NWw02 is displayed indicating the N ame of the product Ww WheelWatcher and the firmware revision 02 NWw02 lt LF gt Once the encoder detects motion it starts outputting distance travelled and velocity of rotation up to 100 times per second where distance a signed 32 bit value is rendered in ASCII characters with its hexadecimal equivalent requiring 8 characters and velocity a signed 16 bit value is also rendered in ASCII hexadecimal requiring 4 characters The letter D precedes the distance value and the letter V precedes the velocity value These values are terminated with a line feed In
9. cc to ensure it definitely goes into quadrature mode If you pull down pin 4 the encoder goes into sign magnitude mode In this mode the direction line is logic high when the wheel rotates clockwise and low when it rotates counter clockwise The clock line toggles on every change of either sensor resulting in an alternating pattern of 128 high and low values for each wheel rotation NOTE this ts different from the behavior of the clock line in the WW 01 and WW 02 WheelWatcher encoders in those older products the clock WheelWatcher WW 12 Product Manual 8 line would pulse low briefly on each edge If you pull down pin 2 instead of pin 4 the encoder goes into serial mode In serial mode data will be output from the Serial TX Out pin pin 3 at 38400 baud 8 data bits no parity 1 stop bit commands can be issued to the WW 12 using Serial RX In pin pin 4 Again the TX and RX lines expect normal TTL signaling with non inverted data This is what one would obtain from the serial interface coming directly out of most common off the shelf microcontrollers such as PIC or ATMEGA the Arduino TX RX pins usually digital pins 0 and 1 and or from a USB to serial converter such as the Acroname S27 USB SERIAL http www acroname com robotics parts S27 USB SERIAL html see figure below NOTE Do not connect the WW 12 directly to a USB to RS 232 converter nor to a standard PC serial port the high voltages present can damage the W
10. g terrain is called a PID loop which stands for Proportional Integral Differential Much has been written about this technique and Google is your friend See the Example Code area of the Nubotics website for examples of P and PI loops using the WheelWatcher for various robot platforms e 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 12s but off to the motors or by using your own test program The yellow LED should be solid on or off and should only change state when the direction of wheel rotation changes The green LED should blink on and off once per stripe 32 times on and 32 off for each wheel rotation If the yellow LED is flashing when it shouldn t be or if the green LED is not pulsing 32 times per rotation make sure your wheels are on tight If the wheels are too high above the WW 12 PCBs there won t be enough light reflected to the sensors on the boards It is best to use the screws provided with your motors to hold the wheels in tight If you are still having problems check the alignment of the PCB with the motor shaft Also check that the codewheel stickers are flat against the wheel without bubbles under them and that they are clean e What mounting hardware is provided The WW 02 and WW 12 are provided with tw
11. gs such that the retention bump on the pin engages with the Small opening on the side of the connector WheelWatcher WW 12 Product Manual Figure 5 Inserting Pins 8 your cable assembly is now complete Figure 6 Complete WheelWatcher WW 12 Product Manual Connector Pinout The color suggestions based on cable assembly photos below We provide two different colors of ribbon cable indicated below as Color Set A and Color Set B Choice of color is up to the distributor Table 1 connector pinout Jn ereen Quadrature Mode Sign Magnitude Serial Mode Mode Set A Set B po Red Violet a_i O eee tee A ChAT Clock 4 M__ QuadMode 1 SMMode 0 RXin SK Green Black _ 5l o Ghd Blue Brow Mode Selection As hinted at in the connector pinout you can select the desired operating mode of the encoder by holding specific pins high or low at reset In firmware revisions 2 and later this is sampled 50ms after reset revision 1 firmware would sample immediately after reset You can accomplish this by using a pull up or pull down resistor anything up to 10K ohm would work to either Gnd for logic low 0 or Vcc for logic high 1 depending on the mode required If you do not pull down any pins the encoder defaults to quadrature outputs ChA ChB These signals are square waves which are 90 degrees out of phase with respect to each other NOTE it can be helpful to tie pin 4 high with a resistor to V
12. lse on either edge generated on the WW 02 WheelWatcher WW 12 Product Manual 21 Errata Firmware Rev 1 The power up states of pins 2 and 4 were sampled immediately after the microcontroller exited reset this is too fast for slow rising power supplies Revision 2 and later now delay 50ms after reset before sampling pins 2 and 4 ensuring proper mode selection Noetic Design released firmware revision 2 on 6 21 2011 For more information visit www nubotics com Produced by Noetic Design Inc 25 NW 23 PL STE 6 PMB 181 Portland OR 97210 Copyright 2004 2011 Noetic Design Inc All rights reserved WheelWatcher WW 12 Product Manual 22
13. o insulated 2 washers two 2 hex nuts and two 2 56 I pan head machine screws WheelWatcher WW 12 Product Manual 19 e My robot uses nonstandard motors and wheels Can I use the WheelWatcher with it Maybe You will need to mount the WW 12 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 12 PCB the CS 100 Codewheel Spacer is useful for this The distance between the top of the 2 sensors on the WW 12 and the codewheel sticker must be close to 1 1 mm 0 43 for it to function Beyond that good luck We can t support nonstandard motors wheels and mounting schemes the WW 12 is designed specifically for standard injection molded wheels and Solarbotics GM series motors Let us know how it works for you though e 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 I 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 JS 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 12
14. ontrol loop bandwidth in control theory language will be slow Another method is to measure the time using your microcontroller s hardware timers between each Clock edge or ChA or ChB edge then take the inverse 1 T to get counts per unit time At 6ORPM you could update your servo control pulse value or PWM value every amp ms instead of every second and have much better resolution too WheelWatcher WW 12 Product Manual 18 However regardless of how well aligned the board is and well centered the sticker is manufacturing error and alignment error will still result in some time variation from clock to clock so we recommend that your firmware calculates a running average of the time between the 4 most recent pulses when using this method e How can I control the velocity of the wheel This is an area of engineering known as control systems theory There are many methods for using feedback to control velocity of a motor In the simplest method one measures the actual velocity of the wheel calculates an error signal by subtracting the actual velocity from the commanded or goal velocity multiplies that by a constant then feeds that value to the motor Thus if the wheel is spinning too slowly the motor is told to speed up and vice versa What I just described is known as a P loop proportional control loop since the only error term is proportional to the difference in velocity One common technique that works better for varyin
15. ot moves simply count up edges of ChA CB or Clock signals or use the serial mode and decode the D distance string See the next question for clues as to how to convert these counts to real world distance units Note that wheel slippage or uneven terrain will result in inaccurate distance measurements no matter what encoder system you use this is the bane of dead reckoning e How can I measure the velocity of the wheel Two methods are commonly employed The easiest is to count the number of clock transitions N or changes to ChA and or ChB over a certain interval of time T Velocity V N T in terms of counts per unit time If T is too small you sometimes won t get any counts even if the wheel is still turning The standard injection molded wheel used with the WheelWatcher is 2 75 in diameter for O ring wheels Pi D gives a circumference of 8 64 If you are using the Clock signal the counts per rotation C 128 That gives C PI D 128 8 64 14 8 clocks per inch of linear travel So if you measured N using Clock and T in seconds then V N T pi D C in terms of inches per second The limitation with this method is that you can only update your servo control pulse width or PWM value every T seconds For a normal servo the highest rotation speed is usually around 60 RPM which is one rotation per second or 128 CLK transitions per second at slower speeds you will get fewer transitions per second Your update rate or c
16. r it with the hub the back of the wheel is the side into which the motor shaft is inserted the raised hub fits inside the sticker s center hole Figure 1 CS 100 Sold Separately WheelWatcher WW 12 Product Manual Cable Assembly The WW 12 kit contains a length of ribbon cable 5 female Molex crimp pins and a matching white Molex header You will need to assemble this cable by performing the following steps 1 2 3 4 separate about 0 75 of the ribbon cable into individual wires strip off approximately 1 8 of insulation from the separated wires twist the ends of each wire so that the individual fine wires are not frayed do not connect the 5 wires to each other just tighten each one separately notice that each crimp pin once crimped to a wire will grab the bare wire with one set of crimped tabs and will grab the insulated area adjacent to the bare area with another set of crimped tabs Figure 2 Ready to Crimp using a crimping tool or needle nose pliers crimp the pins one at a time to each separate wire being sure to crimp both the insulated and uninsulated sections it must be crimped tightly so that the pin can fit into the connector housing WheelWatcher WW 12 Product Manual Figure 3 Crimping Figure 4 One Crimped 6 optional solder the crimped bare section for a more reliable connection 7 insert the crimp pins one at a time into the end of the connector housing with the larger openin
17. t Synchronize If you issue a single period character the unit will flush its buffers and issue back its own period character This is useful to ensure communication synchronization between the unit and your controller WheelWatcher WW 12 Product Manual 11 Timing Diagram The following diagram illustrates the behavior of the ChA ChB Direction and Clock Signals as the wheel slows down and changes direction then speeds back up Figure 8 WW 12 Timing Specifications e Supply Voltage Vcc 3 3v to 5 5v e Supply Current Icc 34mA TYP 42mA MAX when Vcc 5v e DC Input Voltage low 0 5v to 0 3 Vcc e DC Input Voltage high 0 6 Vcc to Vcc 0 5v e DC Output Voltage low 0 6v e DC Output Voltage high 4 1v if Vcc 5v 2 5v if Vcc 3 3v e DC Output Current pins 2 4 20mA e Mode Sample Time 50ms after reset firmware rev 2 and later e Radial misalignment TBD e Tangential misalignment TBD e Angular misalignment TBD e Codewheel tilt TBD e Phase error TBD e Encoder Resolution Per Rev 128 32 stripes e Maximum Encoder Ticks Second TBD e PCB center shaft hole diameter NOM 9 22mm 0 363 e PCB width NOM 22 71mm 0 894 e PCB length NOM 49 89mm 1 964 e PCB thickness NOM 0 79mm 0 031 e Detector height 1 50mm 0 059 MIN 1 70mm 0 067 MAX See figure 11 below e Detector top to codewheel See figure 9 below WheelWatcher WW 12 Product Manual from top to PCB NOM 0 5mm 0 020 1 0mm 0 03
18. velocity in encoder ticks per second Serial data is output only when encoder ticks occur up to a rate of 100 updates per second at 38400 baud 8N1 Serial data is non inverted TTL logic level not RS 232 which is by definition inverted logic and gt 5v signal levels See the Mode Selection section below as well as the FAQ at the end of this document for more details WheelWatcher WW 12 Product Manual W VV 1 2 Parts List printed circuit board preassembled self adhesive codewheel 6 five lead color coded ribbon cable two insulated washers two 2 56 hex nuts two 2 56 1 pan head machine screws Ov o1 B WN Ft Installation Proper spacing between the photodetectors and codewheel as well as alignment of the photodetectors to the codewheel is essential to proper operation Proper spacing depends on the board being held tightly against the top of the motor using appropriate mounting hardware and also depends on the use of standard injection molded wheels designed for the GM 2 GM 3 GM 8 and GM 9 gearhead motors It is possible to use the WheelWatcher system with other commercial wheels custom wheels or even to give feedback on the rate of rotation or relative position of a leg or arm joint However details of such use is up to the end user Noetic Design Inc does not provide support for such custom applications Accurate alignment of the photodetectors to the codewheel depends on accurate placement of
19. very specific angle with respect to each other at a specific radius from the center of the axis of rotation and expect to be used with a 32 stripe codewheel with a 50 silver 50 black radial stripe pattern Decoded Quadrature Clock Direction Only The decoded outputs Clock and Direction are useful when interfacing the WheelWatcher to the Parallax BasicStamp IT Microchip Technologies PIC midrange family or other microcontrollers with hardware counter inputs or external interrupt pins The clock line changes state toggles upon each transition of either ChA or ChB The direction line is high when the wheel rotates one way and low when it rotates the opposite way For example on a Basic Stamp II the PulsIn command operating on a Clock signal results in a direct measurement of the period of rotation of a wheel Use that value to calculate a new servo pulse period to maintain a desired velocity On a PIC 16F877 tie the Clock signals to TOCKI and T1CKI then tie the Direction signals to B4 and B5 which can issue an interrupt on change WheelWatcher WW 12 Product Manual 15 Whenever B4 or B5 change read the timer value add or subtract it from a running position value based on the last direction value since the counts in the counter were from previous motion before the direction changed save the new direction value then reset the hardware counter Accurate relatively high bandwidth measurements of wheel velocity can be taken by
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