Alternative setspeeds() function
Worksheet 12

This page shows how you can make the UKMARS robot read a wider range of positions,
as being over the line rather than fallen off.
This might make drag racers more stable, as the derivative cannot work when fallen off

Below is the graph you get if you slide the drag-racing  robot across the line (from left to right)
after switch-on, but before pressing the button.  pre-race() function. After calibration.
This is the current (old) version.


The code for this is: 
=======================================================================
def setspeeds(ls,rs): # ls and rs are the sensor readings
    global lspeed,rspeed # Python to let this function change speeds
    global error,OldError,mult # to allow changing error

    if (ls >FOlevel and rs >FOlevel): # detect not fallen off
        led.off()
        error = ls-rs # only if on-line,
        myspeed = speed
    else:
        led.on() # Fall-off detected
        # Off-line, so boost error
        if error >0:
            error = FOError
        else:
            error = -FOError
        myspeed = speed * 0.8 # run at fall-off speed

    val = error *mult # adjust steering amount
    # Derivative calculations, using last-time's value
    change = (error - OldError)
    # add in the derivative to val
    val = val + (change * dfactor)/10

    lspeed = myspeed - val # speed of left motor
    rspeed = myspeed + val # speed of right motor
    OldError = error # keep track of this error for later
    return (error)

========================================================================
Here is the graph for the new version (setspeeds2())

You can see that a wider range of positions are used to generate the error. It's a bit wiggly but has an increasing slope
for about 17mm as opposed to the 11mm for the old version.

Here is the code


Const = 2 * FOError         # about 180

def setspeeds2(ls,rs): # ls and rs are the sensor readings
    global lspeed,rspeed # Python to let this function change speeds
    global error,OldError,mult # to allow changing error

    if (ls >FOlevel):                    # left >15
        if (rs >FOlevel):                # right >15
            error = ls-rs                  # central region
        else:
            error = Const - ls        # right of central  region
        led.off()
        myspeed = speed
    else:                                   #(ls <= FOlevel)
        if (rs >FOlevel):              # left of central region
            error = rs - Const
            led.off()
            myspeed = speed
        else:                               # fallen off
            if error >0:
                error = Const - FOlevel  # to the right
            else:
                error = FOlevel - Const  # to the left
            led.on()
            myspeed = speed * 0.8 # run at fall-off speed

    error = error/2   # to give same error when fallen off
    val = error *mult # adjust steering amount
    # Derivative calculations, using last-time's value
    change = (error - OldError)
    # add in the derivative to val
    val = val + (change * dfactor)/10

    lspeed = myspeed - val # speed of left motor
    rspeed = myspeed + val # speed of right motor
    OldError = error # keep track of this error for later
    return (error)

Both setspeeds() and setspeeds2() can be found in this file text version here.