need help with TowerPro MG995 servo

thangngoc

The towerPro MG995 servos can only rotate -90 to +90.
I know the center for the TowerPro MG995 servos is 1500. Is the TowerPro MG995 servos programmable like the continuous rotation servo using Basic Stamp. If so how can I center TowerPro MG995 the servo using basic stamp v2 code? Thanks

Post Edited (thangngoc) : 1/20/2010 8:07:49 PM GMT

kf4ixm

on the bs2 stamp you would do this
PULSOUT 12, 750 ' output of pulse on pin 12

750 is the pulses it would send out on pin 12, the bs2 stamp operates at 2us, so 750 * 2=1500

thangngoc

unlike the continuous rotation servo, I simple use this code PULSOUT 12, 750 and adjust the potentiometer in the servo to center it. But the TowerPro MG995 doen't have the potentiometer. What should I do? When I try the following code
DO
PULSOUT 12 , 1500
PAUSE 20
LOOP

The arm of the servo rotated 180 degree then stop.

kf4ixm

1500 may be too much for the servo, try 1400 1000·or even 1300 900·and see what happens, may be the feedback pot in the servo going bad... 1500 on the bs2·translate to·the servo·to go fully right and there may be some slop in the feedback pot or a bad place in the feedback pot.

Sorry for the misinformation, was being distracted. i have found 1100 to 1300 will max some servos while 1400 to 1500 is fine. this is something you will just have to play with and see where your servo max's out at

Post Edited (kf4ixm) : 1/21/2010 2:14:55 PM GMT

Franklin

Did you try:
PULSOUT 12, 750 ' output of pulse on pin 12
with your servo hooked to pin 12?
If not go back and do that. Most servos that don't rotate all the way around are centered mechanically by removing the horn and setting it where you want it when you are sending the servo code for 'center'

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Stephen

W9GFO

thangngoc said...
unlike the continuous rotation servo, I simple use this code PULSOUT 12, 750 and adjust the potentiometer in the servo to center it. But the TowerPro MG995 doen't have the potentiometer. What should I do? When I try the following code
DO
PULSOUT 12 , 1500
PAUSE 20
LOOP

The arm of the servo rotated 180 degree then stop.

All a servo does is try to seek a position based upon the width of the pulse that it receives.

PULSOUT 12, 1500 is equivalent to a 3.000mS pulse width. That is likely too much. For general operation you want to use pulse widths that range from 1.000ms to 2.000mS.

If you need more movement out of the servo you can go outside that range but you must experiment to find the limits. The extents of a standard servo's range of travel are mechanically limited, if you use a pulse width that the servo can't reach it will be stalled while it pushes against that mechanical limit.

To center your servo, send a pulse width of 1.500mS (PULSOUT 12, 750). There is no adjustment to make. If you need the servo horn to point a different direction, remove it and reinstall in the desired position. Like Franklin said.

Remember each increment of PULSOUT is .002mS.

Rich H

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Simple Servo Tester, a kit from Gadget Gangster.

Post Edited (W9GFO) : 1/21/2010 3:26:34 AM GMT

thangngoc

thanks W9GFO. The servo was center when I tried PULSOUT 12, 750 and this is what I wanted. I tried PULSOUT 12, 1500 and it went beyond the limit of traveling range as you said. Thanks you guys

thangngoc

I tried this code below to initialize the position of the horn of the servo. It did stop as the position where I wanted, but the motor seemed still running inside ( I could hear by the sound inside), perhaps it still took a lot of current. How can I avoid that?

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

DEBUG "Program Running!",CR

counter    VAR    Word

Setup:                   ' Initial position of the servo

FOR counter = 1 TO 10
  PULSOUT 12, 750
  PAUSE 20
NEXT

W9GFO

thangngoc said...
I tried this code below to initialize the position of the horn of the servo. It did stop as the position where I wanted, but the motor seemed still running inside ( I could hear by the sound inside), perhaps it still took a lot of current. How can I avoid that?

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

DEBUG "Program Running!",CR

counter    VAR    Word

Setup:                   ' Initial position of the servo

FOR counter = 1 TO 10
  PULSOUT 12, 750
  PAUSE 20
NEXT

You are only sending the pulses to the servo for 1/5th of a second. 10 times through that FOR..NEXT loop only takes about 200mS. If you increase to (counter = 1 to 100), the servo will get pulses for about two full seconds.

According to what I have read about the TowerPro MG995, the pots are low quality and it exhibits significant overshoot. That may contribute to it being noisy when it's not supposed to be moving.

Rich H

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Simple Servo Tester, a kit from Gadget Gangster.