problem servomotors power

[haexapodim]

Hello,

I have built a bipedal robot
Each leg is powered with two Hs 755 mg

For this systeme i'm using a 20 m2
and the power supply is a laboratory one which delivers 9v and 1.5 A

During the first 15 seconds all is working but after a very short time servomotors have less and less power
and they stop moving

???

 

[JimPerry]

Do you have a circuit diagram and program listing?

 

[BeanieBots]

Without a diagram it is impossible to help.
9v is too high for most 'hobby' servos, so if your are giving them 9v they are probably dying from stress!
Do they get hot as well?

 

[haexapodim]

Ok
the diagramm isin the attachements
and here the program:

; *******************************
; ***** Sample Header File  *****
; *******************************
;    Filename: 		
;    Date: 			
;    File Version: 	
;    Written by: 		
;    Function:		
;    Last Revision:
;    Target PICAXE:	
; ******************************* 


init:
servo B.4,150
 servo B.3,150
servo B.2,225
 servo B.1,225


main:

for b0 = 70 to 0 step -5
b1= 150 + b0
b2= 225 + b0
pause 10
 servo B.4,b1
 servo B.3,b1
servo B.2,b2
 servo B.1,b2
 pause 50
 next b0
 
 for b0 = 0 to 70 step 5
b1= 80 + b0
b2= 155 + b0
pause 10
 servo B.4,b1
 servo B.3,b1
servo B.2,b2
 servo B.1,b2
 pause 50
 next b0
 
goto main

 

[russbow]

I am not sure it has anything to do with your problem, but all the servo commands in your main program should be changed to servopos.

Manual 2, page 213

 

[haexapodim]

I have ever tried to use servo instead of servopos on an another robot and it's working perfectly
In this case, it looks like, something is wrong on the diagramm circuit

 

[nick12ab]

During the first 15 seconds all is working but after a very short time servomotors have less and less power
and they stop moving

What is this 'laboratory' power supply?

Have you got decoupling capacitors fitted?

 

[haexapodim]

this the power supply :

 

[JimPerry]

Do they start working again after a power cycle - or is the battery pack (4V5 ) dead?

 

[nick12ab]

It looks like one of those cheap crappy power supplies that just select between tap-offs on a transformer. These are unregulated and that power supply could be outputting over 10V on idle even though it's set to 7.5V. It might also has too small a capacitor for the purpose - try adding one of around 470uF. Don't forget 100nF decoupling capacitor on the PICAXE.

 

[boriz]

Try with 4 new AAs (6v) power for the servos. It will help eliminate the PSU as the culprit.

 

[boriz]

Also. Can you monitor the voltage at the servos using a multimeter? Does the voltage drop when the servos slow?

 

[haexapodim]

should i put the 4700 capacitor like in this diagramm?

I don't have multimeter to check the tension but i will try tomorow at work

 

[nick12ab]

should i put the 4700 capacitor like in this diagramm?

Yes that would be fine.

 

[haexapodim]

It's true :
the voltage drop when the servo slow

so i have to find a more powerfull power supply
thank you for help