Boe-Bot servo problem

Comments

• Mike Green Posts: 23,101

  2012-04-13 12:34 edited 2012-04-13 12:34

  Servos are not precise mechanisms. It's certainly possible that one servo could continue running for a short time after another, but a second or two is a bit long. It's impossible to tell you why without a listing of your program and a description of the circumstances involved.
• Never4ever Posts: 2

  2012-04-13 13:07 edited 2012-04-13 13:07

  Thanks for your quick reply.
  
  I took another look and concluded that I judged the lag to be longer than it is. It might be just around 10 ms. So I'll just have to live with the minor twitch the robot makes when it stops. That turned the problem into a little issue!
• xanadu Posts: 3,347

  2012-04-14 13:54 edited 2012-04-14 13:54

  I'm not sure if anyone else does this but for continuous rotation servo's the trim pot always has a little null zone which makes it easy to tune but at the same time it can also lead to steering issues. If you really want to fine tune it you could do something like this:
  

   {$STAMP BS2}
  ' {$PBASIC 2.5}
  '
  'Continuous Servo Super Centering
  '
  'My servo's null range is min 748 max 752. The min value must be equal
  'distance from max value and always centered on 750.
  '
  'Center your servo using pulsout 750. Then:
  '
  'You should setup the null zone for your servo by testing one pulsout
  'at a time until you cover the range of values that do not move the
  'servo. Once you have that range, you adjust it so the center of your
  'range is based on pulsout 750. Pulsout all the positions in the null
  'zone and then adjust potentiometer. You may want to delete the highest
  'and lowest pulsout to make it a little easier.
  
  
  servo    CON 12      'set this to servo pin
  
  DO
  
   PULSOUT servo, 748
   PAUSE 20
   PULSOUT servo, 749
   PAUSE 20
   PULSOUT servo, 750
   PAUSE 20
   PULSOUT servo, 751
   PAUSE 20
   PULSOUT servo, 752
   PAUSE 20
  
  LOOP
  
• erco Posts: 20,261

  2012-04-14 22:20 edited 2012-04-14 22:20

  CR servos can be finnicky on stopping. Note that there are two different ways to stop:
  
  1) Coasting: Just stop sending pulsouts to the servos and they'll coast a little while as they stop.
  2) Braking: Continuing to send a stream of PULSOUT 750's to both servos applies dynamic braking for faster stopping.
  
  Try both approaches and see which works best for your situation.