driving in a straight line

[rob nash]

hi all,
I,ve made an observation while running my little bot that i have to keep changing the value of the speed control setting. I set it up with freshly charged battries to go in straight line after a couple of minutes it will start vering left or right is this to be expected

#picaxe28x2
#no_data
#no_table

'               HEADSCAN
'*******************************************************************
symbol pan = b.5
symbol rgt = 225
symbol lft = 85
symbol cen = 152

'*******************************************************************
'           hood control
'*******************************************************************
symbol hood = b.4
symbol openhod = 90
symbol closehod = 172

'*******************************************************************
' servo speed control
'*******************************************************************

symbol l_back_slow = 153
symbol l_back_fast = 215
symbol l_off = 148
symbol l_forward_slow = 137   
symbol l_forward_fast = 75   

symbol r_back_fast = 117
symbol r_back_slow = 137
symbol r_off = 143
symbol r_forward_slow = 153  
symbol r_forward_fast = 171  

symbol r = b.6
symbol l = b.7
symbol counter = b8

 init:
 
servo r, r_off
servo l, l_off
servo pan,cen
servo hood,openhod
'pause 30
'gosub openhood



main:
    
          
          
         
  
       servopos r, r_forward_slow
       servopos l, l_forward_slow
       pause 100
   

       
       
      
       
       goto main
    
       
         
    
    lft90:
         servopos r, r_off
         servopos l, l_off
         pause 100
         servopos l,l_back_slow
         servopos r,r_forward_slow
         pause 1100
      
    return
         
    lft180:
          servopos r, r_off
          servopos l, l_off
          pause 100
          servopos l,l_forward_slow
          servopos r,r_back_slow
          pause 2400
         
       return

         
   
       
    rgt90:
       servopos r, r_off
       servopos l, l_off
       pause 100
       servopos l,l_forward_slow
       servopos r,r_back_slow
       pause 1100
        
     return
                    
   rgt180: 
         servopos r, r_off
         servopos l, l_off
         pause 100
         servopos l,l_forward_slow
         servopos r,r_back_slow
         pause 2400
     return    

    openhood:
       for b6 =closehod to openhod step -2
       servopos hood,b6
       pause 200
       next b6 
       return
      
    closehood:
          servopos r, r_off
          servopos l, l_off
          for b9 =openhod to closehod step 2
          servopos hood,b9
          pause 200
          next b9 
          return

this is the code am using to test drive the bot

could anyone explain what it is that i'm doing wrong

rob

 

[g6ejd]

To me it seems like the servo response rate / power is reducing as the battery voltage depletes. Have you considered this in the various pause commands, that presumably don't allow the Bot to correct its course before it gets too far off line.

 

[cdngunner]

Could be anything from error propagation to one motor being just a little slower/faster then the other one.