Boe-Bot troubles (turning on the beginning of the program)

roksraka

I programmed my Boe-Bot to make a tone and then drive forward for 10s. However, before the piezo speaker turns on, the entire robot turns left slightly. (Right servo turns a bit. When it starts to drive forward it drives slightly RIGHT (but that's not the problem).

Do you happen to know what causes this problem and how could I fix it? If you know anything please REPLY!

Thanks for help!
roksraka

Post Edited By Moderator (Chris Savage (Parallax)) : 8/20/2008 8:02:09 PM GMT

SRLM

Could you post your code? Without that it's very difficult to help and the best that we can do is theorize. My guess is that your BS2 is sending out a pulse or series of pulses to the servo. However, this is all hypothetical without the code.

Mike Green

Servo motors, particularly when modified for continuous motion (as in the BoeBot wheel servos), are not exact things. There's some slippage and no feedback. The closest thing to a "fix" is to get and install wheel encoders that provide wheel position feedback to the Stamp (www.parallax.com/Store/Microcontrollers/BASICStampModules/tabid/134/List/1/ProductID/80/Default.aspx?txtSearch=wheel+encoder&SortField=ProductName%2cProductName). These still don't account for wheel slippage where one wheel slips on the floor ever so slightly and the other does not. The wheel encoders also require additional code in your program to track the wheel position.

roksraka

' Robotics with the Boe-Bot - BoeBotForwardTenSeconds.bs2
' Make the Boe-Bot roll forward for three seconds.

' {$STAMP BS2}
' {$PBASIC 2.5}

counter VAR Word

FREQOUT 4, 2000, 3000

FOR counter = 1 TO 407

PULSOUT 13, 850
PULSOUT 12, 650
PAUSE 20

NEXT

END

Phil Pilgrim (PhiPi)

Try inserting the following code in your program just before the FREQOUT:

LOW 12 : LOW 13

This will make sure that both P12 and P13 are low and not floating while the speaker is sounding. Without this, the servo may be getting some noise through its input. Also, be aware that servos often twitch a little when first powered up. This may also be what you're seeing.

-Phil

roksraka

Thanks for your help! By the way, I forgot to mention one thing - this servo movement only occur averytime when the robot is turned on. If the programm ends and you reset, I won't happen.

Phil Pilgrim (PhiPi)

In that case, what you're seeing is the normal power-on servo twitching. There's not much you can do about it. We all have to live with it!

-Phil