Converting sensor value to servo movement

Botdocter · 2010-12-03 18:22

I am building a robot containing a Wyse Thin XP system. it uses roborealm and i have setup the serial connection to the propeller. it is working correct. i get back the values that where send by roborealm.

Now i need to convert one of that values to servo movement. or in other words, the value is the camera resolution or a point withing that width.(320px / 2 =160 to -160). That value that is changing constantly, and has to drive the servo to steer the robot.

i attached my main file. it's not working though. all i get is -160 outputted back to roborealm and the servo starts with a quick left then right and then no movement. The servo can't be turned manually. It is still holding steady at ...-160? would be pulsewidth "1300"?

Any help is apreciated!!

RRSerial.spin

W9GFO · 2010-12-03 19:11

Does it work any differently if you use;

SERVO.Set(ServoCh1,Heading,50)
instead of
SERVO.SetRamp(ServoCh1,Heading,50) ?

Rich H

Botdocter · 2010-12-04 05:49

It's the same. Although the the start (left/right twitch) is gone.
If i change the -160 at the bottom of the file, to for example: 162, that is what i get back. So it is not using the value but the -160???

John Abshier · 2010-12-04 08:01

You are starting each of the routines SerialCog Transmitter and WheelAngle in their own cogs and also calling them from main. Try removing the three cognew statements.

John Abshier

Botdocter · 2010-12-04 08:16

i did. it screwed up the output even more than now..

i will try again anyway..

thanx

W9GFO · 2010-12-04 09:04

If you are having a problem with rxVal_1, say it is actually zero, then it will be changed to -160 by WheelAngle before it goes to Transmitter.

Rich H

W9GFO · 2010-12-04 09:19

Also, "scale and offset" would be appropriate for your WheelAngle routine.

You have the values ranging from -160 to 160 that need to correspond to servo pulses of 1,300 to 1,700 with 1,500 being the center.

If you could get by with a pulse range of 1340 to 1660 then it would be super easy;

heading := 1500 + rxVal_1

But to scale the 160 up to 200 you need to multiply it by 1.25. Or multiply it by 125 then divide by 100.

heading := 1500 + ((rxVal_1 *125) / 100)

You should be able to replace your Main loop with this;

repeat
    SerCog
    Transmitter
    heading := 1500 + ((rxVal_1 *125) / 100)    

    SERVO.Set(ServoCh1,Heading,50)

It is of course untested...

Rich H

StefanL38 · 2010-12-04 12:10

Hi Botdocter,

I want to make some comments about your code.

As your methods SerCog, Transmitter and WheelAngle do NOT contain any loop.
The commands cognew start a new cog executes the codeline ONE time and then stops the cog again.

You should get the same results if you just delete the cognew-statements

As you don't have any code below the "elses" INDENTED in the method WheelAngle
you can simply delete the elses

If you meant that the second-ifcondition should only be executed if the first is not true
You would have to indent them.

The following codelines compile but are different from the ones above and below

    IF rxVal_1 := 100
      heading := 1625
    else
    IF rxVal_1 := 120
      heading := 1650
    else
    IF rxVal_1 := 140
      heading := 1675
    else
    IF rxVal_1 := 160
      heading := 1700

I think you wanted to code

    IF rxVal_1 > 100
      heading := 1625
    else
    IF rxVal_1 > 120
      heading := 1650
    else
    IF rxVal_1 > 140
      heading := 1675

IF rxVal_1 := 140

sets rxVal_1 to value 140
and the if-condition will be true as every value <> 0 is true

for the codelines

     IF rxVal_1 > -20
      heading := 1475

I guess you mean value-range -20 to -40
rxVal_1 > -20 is TRUE for -19, -18, -17, -16 etc. etc.
I guess you wanted

rxVal_1 < -20
which is true for -21, -22, -23, etc. etc.

instead of adding a lot of if-conditions you can use
a case-statement

      0..19 : heading := 1500
      
      20..40 :heading := 1525
      
      41..60 : heading := 1550

      61..80 : heading := 1575

      81..100 : heading := 1600

      101..120 : heading := 1625

      121..140 : heading := 1650

      141..160 : heading := 1675

      161..180 : heading := 1700

      -20..-1 : heading := 1500  

      -40..-21 : heading := 1475

      -60..-41 : heading := 1450

      -80..-61 : heading := 1425

      -100..-81 : heading := 1400

      -120..-101 : heading := 1375

      -140..-121 : heading := 1350

      -160..-141 : heading := 1325

      -200..-160 : heading := 1300

from the bugs you made I guess you are pretty new to programming.

My recommendation is to add only 1 to 5 lines of code and then TESTING the code to check if it really does what you expected.
For the testing you should hold anything constant but teh one thing you want to test

example
to test what does the codelines

    IF rxVal_1 > -20
      heading := 1475

you should extract the codelines to a small test-program that only contains

    rxVal_1 := - 22

    IF rxVal_1 > -20
      serial.str(string("rxVal_1 > -20 is true"))
    else  
      serial.str(string("rxVal_1 > -20 is false"))

with this testing code it will be easy to check if your code works as expected and you will be pointed straight forward to a bug
if there is a bug.

You may think uhh so many test-programms?!? This takes too long.
OK it is up to you to do it the fast (but in the long run slowest) way to quickly put together all the code and then start testing with guessing around
is the bug here ore there?

Very old programmers -wisdom: a program does ALWAYS what you have programmed. The only thing is sometime you don't know what you really programmed
because you thought the program should do this but in fact the program does something different. But still EXACTLY what you have programmed.

best regards

Stefan

Ttailspin · 2010-12-04 14:10

Cuz You told it to be -160
I keep falling into this trap Myself...

PUB WheelAngle
    rxVal_1 := rxVal_1 - 160         'Cuz You Told it to be -160
                                                ':= "SETS"  the variable 
 
    IF rxVal_1 < 20                    ' I think You want to use == for Your IF's
      heading := 1500                  'This Line will work to set heading to 1500
    else                                   'This else is not needed 
    IF rxVal_1 > 20        'Once it has decided rxVal is either Greater then or less then 20, 
      heading := 1525               'The remaining IF statements are ignored...
    else                        'Below This Line is not used like You might want them to be 
    IF rxVal_1 > 40
      heading := 1550
    else
    IF rxVal_1 > 60
      heading := 1575
    else
    IF rxVal_1 > 80
      heading := 1600
    else
    IF rxVal_1 := 100
      heading := 1625
    else
    IF rxVal_1 := 120
      heading := 1650
    else

Comments are Your best hope >>> ' <<< Document often, Walk Yourself Thru all Code.
and F9 is your new best friend...

W9GFO · 2010-12-04 14:24

Also, if you're going to use this method;

IF rxVal_1 < 20                   
      heading := 1500                 
                            
    IF rxVal_1 > 20
      heading := 1525

What will happen if the value is 20? Try this instead;

IF rxVal_1 < 21   ' 20 or or lower                
      heading := 1500                 
                            
    IF rxVal_1 > 20         '21 or higher
      heading := 1525

And...

IF rxVal_1 := 140
      heading := 1675

will not work, should be;

IF rxVal_1 == 140
      heading := 1675

Still, I think that this is a much better approach than all those IF statements;

heading := 1500 + ((rxVal_1 *125) / 100)

Rich H

nomad · 2010-12-05 05:15

hi botdocter

here is a new RRserial_1.spin

changed: pst
Servo32.spin
no serial connections

i make a short test (no servo connected) it's run

regards nomad