Shop OBEX P1 Docs P2 Docs Learn Events
Boe Bot's servos => problem — Parallax Forums

Boe Bot's servos => problem

MysterycatMysterycat Posts: 4
edited 2005-12-29 21:16 in Robotics
Hello
I'm french so sorry if my english is bad,

I just purchase a Boe Bot on Ebay, and i've got a problem with the servos.
In fact, when I run the following program :

DEBUG "Program Running !"

counter         VAR     Word

FOR counter = 1 TO 60
  PULSOUT 13, 850
  PULSOUT 12, 850
  PAUSE 20
NEXT

END



The left servo go to Back direction, and the right to Front, and I don't understand why.
If somebody could help me, it would be very nice.
Thanks

Comments

  • Steve JoblinSteve Joblin Posts: 784
    edited 2005-12-28 18:18
    the motors are both going in the same direction... the problem is that they are not next to each other, they are back to back. You need to run one of them forward and one in reverse to get the BOEbot to move forward or backward.

    I know it sounds funny, but get a friend, stand next to each other and each twirl a string clockwise. Without changing direction of the string, slowly move so you both are standing back to back... look in a mirror and observe which way the two strings are rotating!
  • Steve JoblinSteve Joblin Posts: 784
    edited 2005-12-28 18:20
    Sorry... just realized that I didn't answer your specific question... simply change "pulsout 12, 850" to "pulseout 12, 650"... If the boebot goes backwards, then keep the 12 as 850 and change the 13 to 650.
  • MysterycatMysterycat Posts: 4
    edited 2005-12-28 19:03
    Thank you Steve.
    I knew I could do it by this way but is there a hardware solution ?
  • Steve JoblinSteve Joblin Posts: 784
    edited 2005-12-28 19:47
    sure... switch the + and - wires on one of the motors
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-12-28 19:51
    If you switch the plus (+) and minus (-) wires on a servo you damage it.· Best to follow the directions in the BOE-Bot manual for adjusting the wheel spin.· You can find the BOE-Bot manual in PDF format at the bottom of the following page.

    http://www.parallax.com/detail.asp?product_id=28125

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • Steve JoblinSteve Joblin Posts: 784
    edited 2005-12-28 20:01
    Yes... Chris - thanks to coming to the rescue!!! I was thinking it was a motor, not a servo...
    MysteryCat... the concept I stated is correct... it is just that you need to make the switch of + and - on the motor inside of the servo... you will need to take the entire servo apart, desolder the motor, then solder it backwards. Sorry for the confusion!
  • MysterycatMysterycat Posts: 4
    edited 2005-12-29 13:13
    And, can you tell me where I can buy a new servo (in France) and how much it cost ?
  • John R.John R. Posts: 1,376
    edited 2005-12-29 14:42
    ·
    Steve Joblin said...
    Yes... Chris - thanks to coming to the rescue!!! I was thinking it was a motor, not a servo...
    MysteryCat... the concept I stated is correct... it is just that you need to make the switch of + and - on the motor inside of the servo... you will need to take the entire servo apart, desolder the motor, then solder it backwards. Sorry for the confusion!
    I believe it is more complicated than this.· While reversing the motor would indeed reverse it's direction, I believe that it (the servo) would still be comparing the feedback circuit in the "normal" direction.

    The real way to deal with this is simply to understand that the two servos are installed mirror image.· Clockwise for one is forward, and reverse for the other.· One of the·concepts of having the microcontroller is to have the micorcontroller software deal with these issues, so that you can send it commands like "move forward", and have it take care of sending one servo clockwise and the other counter-clockwise (or anti-clockwise if that is easier to understand for our French friend).

    Servos can probably be found at a hobby shop that sells radio controlled airplanes, cars or boats (not the "cheap toys" but the "real" models).· I'm guessing they should be around 20 Euros or so, but that's based on them being a little under 20 USD here.· I don't know what shipping, differences in volume, VAT and all that good stuff does to the pricing.· There are also instructions available from the Parallax site to convert a "standard" servo (like one you would get from a hobby shop) to a continuous rotation servo (like the ones used to drive the BOE-BOT).· I beleive this is covered in both the BOE-BOT manual and the WAM (What is a Microcontroller) manual.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    John R.

    8 + 8 = 10
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2005-12-29 14:44
    Mysterycat -

    You can check this web page for the Parallax Distributors in France:
    http://www.parallax.com/html_pages/company/distributors/dist_europe.asp

    They should be able to help you, and if they can't they can probably refer you to someone who can.

    Regards,

    Bruce Bates
  • MysterycatMysterycat Posts: 4
    edited 2005-12-29 21:16
    Thank you very much Bruce I will call tomorow, and thank you John for informations !!
Sign In or Register to comment.