control a servo motor

gregory12345

Hi all,

I am working with servo motors and using basic stamp B2sx to program it. I have figured out that it needs a value of 500 to 3000 to get from 0 degrees to 180 degrees. Can anyone help explain to me why 500 to 3000?

$WMc%

Greg

Servos are controlled with a pulse width. Most are 1000uSec for full left, 1500uSec centered,and 2000uSec full right.The pulse width must be updated typically 50 times a Sec. or every 20 milliSec. Different Stamps run at different CLK. speeds So then CON values will vary from one stamp to another

Take a look at experiment#26 pg.146 of the Stamp Works Manuel for more info.

_________$WMc%______

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W9GFO

$WMc% said...
Most are 1000uSec for full left, 1500uSec centered,and 2000uSec full right.

I think that is the more of a standard range than the limits of movement. Most (because I have not tried every one) of my servos respond to values between around .500 mS to 2.500 mS for approximately 180 degrees of total travel.

Rich H

gregory12345

hi! i am using a basic stamp BS2sx, and 1 unit in that stamp is 0.8microseconds. Which means, the value of 500 is 500 * 08microseconds = 0.4ms . and the value of 3000 is 3000 * 0.8micros = 2.4ms. So this means my servo goes from 0 - 180 with 0.4ms-2.4ms pulsewidth instead of 1ms - 2ms?
thx

W9GFO

The pulsewidth where servos hit their stops is not the same for all servos. Be sure not to use a value so high (or low) that the servo is pushing against the stop.

If 1 unit equals .8 uS then,

Center = 1500 uS = 1875 units

LowEnd = 500 uS = 625 units
HighEnd = 2500 uS = 3125 units

NormalHigh = 2000 uS = 2500 units
NormalLow = 1000 uS = 1250 units

So I would say that your servo is behaving pretty much as expected. Remember though, typical range used for servos is much less than 180 degrees even though most can go that far - or even further.

Rich H

Post Edited (W9GFO) : 6/5/2009 4:54:05 AM GMT