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Topic: strange servo behaviour (Read 825 times) previous topic - next topic

Hi Guys,
I need a lot of help with the servos.
I made something similar to robo arm that uses 4 servos.
I tried to use the arduino power and it was working, but I was having problems with the usb so I decided to use external power supply.
The supply has no load voltage-9 and description 3.7V at 375mA
I connected the power supply with common ground to the arduino and the servos and they get mad.
So I did many testings etc.. and I cannot understand why everything is so mad(they are trying to go outside 0-180 degree range).

Then I made a very simple tests that I cannot understand.

I start using just one servo without external dc power supply in order to understand thair behaviour....and

1/ I am connecting the servo to the arduino power pins and everything is working fine.(5v,ground,pwm pin)
2/ I am connectin the servo to the arduino pins trought multimeter(mesuring the current) and the servo is mad again.(the circuit is exactly the same as in case 1/ Only the ampermeter is connected)

I cant understand why adding amp meter is driving the servo mad?
Maybe after understanding why this happens I will understand my other problems?

I am not posting any code because I dont think the code metters for the amp meter problem above.
When I understand the amp meter case  I will use pc power supply (that can supply me with enought current) for my robo arm and If I have problems again I will post code and circuit diagram here.
Now I just need to understand why the servo is going mad when I use amp meter and if I remove the amp meter-its working fine.
Please note that for the amp meter issue I *not* using external power supply -I am using just the arduino power pins.
The servo is TowerPro sg90


Thanks
Anton

MarkT


Hi Guys,
I need a lot of help with the servos.
I made something similar to robo arm that uses 4 servos.
I tried to use the arduino power and it was working, but I was having problems with the usb so I decided to use external power supply.
The supply has no load voltage-9 and description 3.7V at 375mA


Supply sounds very wrong - do you mean no-load voltage 9V and loaded voltage 3.7V???

You need a 5V or 6V _regulated_ supply (or battery pack) capable of 2A or more for the servos.  A separate supply for the Arduino (USB will do) is extremely recommended.

Unless your servos are tiny they will pull more current (over 1A?) than the on-board regulator can handle (and will reset the processor - or even damage it)  4 servos makes the problem 4 times worse.
[ I won't respond to messages, use the forum please ]

kf2qd

Your servos are going nuts because the voltage is too low and the driver circuit inside the servo is not switching properly. Servos NEED a clean 5 - 6 volts.

Thanks for you replays.
So my  other question is why when I wire an ampermeter throught the power wires the servos are going crazy whitout any reason and if I remove the the ampermeter everything is fine.
Something really crazy is going on with those servos.
Yesterday my robo arm was working for more then an hour with pc power supply at 5.1 volts(the PSU shoul provide enought current to supply the servos).

Today I use the same configuration everything is the same I just did some mechanical improovments and new wires and the servos of my arm ar crazy again.They try to go outside 0-180 range.And I still can understand:
1.how the amp meter is changing thair behaiviour
2.why something that yesterday worked for an hour and more with PC power supply is not working today.

I have no idea what is going on.....

And some more info on my issues:

If I connect everything and then power on -my four servos are going crazy(I use ATX PSU to supply them with 5v and enought current)
If I disconnect the servo control wires from arduino,power on everything,and connect the control(yellow) wires while everything is running one by one it is working.

The four servos are connected to 6,9,10,11.Is there any chance that the control pins cannot give enought current to control all four servos in the same moment?

Any ideas?


ok after connecting two 5v channels from my PC ATX PSU it seems that my arm is working.
It seems that 4 micro servos(the cheap ebay 9g model) are draining more then 2(maybe even 3) amps on full load.
Unbelivable how those small things dran so much.
However does anybody have an idea why if I connect one servo to my arduino and use the arduino power to supply it its working.
When I use my multimeter to meassure the current the problems are starting again?
I use relative good multimeter so the resistance should be really small and shouldn't change anything on the circuit

Far-seeker


However does anybody have an idea why if I connect one servo to my arduino and use the arduino power to supply it its working.
When I use my multimeter to meassure the current the problems are starting again?
I use relative good multimeter so the resistance should be really small and shouldn't change anything on the circuit


If I'm reading you correctly, the servo is still connected to the Arduino's power when you are trying to measure it and the problem starts again.  It could be the single servo is getting just barely enough current from the Arduino's power supply, and even the slight additional load of the multimeter is enough to change that.  I admit it's a really unlikely scenario, but the only other thing I can think of, the extra length of the multimeter's cables adding more noise, seems even less probable. 

I don't know how many +5 VDC outputs your ATX PSU has, but could you instead test individual servos on an otherwise unused +5 VDC cable?

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