hi , i got a servo thas produces 8kgcm torque with 4 volts supply kai 10 kgcm with 6 volts. Given the 5volt supply of the arduino will i get a smaller torque than the maximum (10kgcm) ? i need for my project the maximum torque possible and i am not sure if i am going to have it with the 5volt supply ... if yes are there any suggestions ?
DON'T
Give the servo its own power supply with the servo GND connected to the Arduino GND.
This applies even for small servos.
...R
Never share a power rail between inductive loads like motors/servos/relays and
digital logic, its asking for expensive damage and disappointment.
Pic attached shows how
ok i got the message , thanks for your answers .. apart from batteries (it has to be a small device-source) is there any other voltage source that i could use ?
Small source of electric power in a portable package? Battery. If there was something better
your phone would use it.
nice thought , thanks a lot ... may i ask for encyclopedic purposes why is it dangerous to give power supply to the servo by using the arduino ?
plt12:
why is it dangerous to give power supply to the servo by using the arduino ?
The Arduino 5V pin can't provide enough current: you should budget 1A per servo, and the Arduino can provide only (from my memory, may be wrong) about 500mA.
MarkT:
Never share a power rail between inductive loads like motors/servos/relays and
digital logic, its asking for expensive damage and disappointment.
Inductive loads have relatively large so called rush-in currents.
Such currents may drop the voltage, which in turn will destabilize your controller and interfere with measuring results.
Switching off these devices may (and very likely will) generate large voltage peaks into its power supply, which are disastrous to the logic level parts connected to the same supply.
So you should use separate power circuits for these inductive devices and your controller (AKA Arduino).
thanks a lot guys
I aslo got the same the problem before so I think Never share a power rail between inductive loads like motors/servos/relays and
digital logic
MarkT:
Never share a power rail between inductive loads like motors/servos/relays and
digital logic, its asking for expensive damage and disappointment.
Does it mean that I should not use some external batteries (let say 4xAAA) to power servos AND the Arduino in this way: V+ of batteries directly to V+ of my servos and to Vin of the arduino ?
As I understand that would be dangerous for the Arduino, is there a way to protect it from the "rush-in" currents then? (with a capacitor?). I'm on a small robot and I don't have space for 2 different power supply. Supplying the Arduino by the jack or USB is not an option, it needs to be free to move.
Hey,
it's the basic "choose 2 from these 3 options" game:
there is "power" - "size" - "price" in your request. you can choose 2 from these to fit together nicely, but all 3 in the same package is not possible.
so there will definitely be a way to get enough power, even with seperate power supplies, and still keep a very small size/weight, but it will become very expensive then.
if it would be possible to put all 3 together to get a powerfull, small and cheap solution, then surely the 4th value will ruin it: it's quality will be crap...
kolia:
Does it mean that I should not use some external batteries (let say 4xAAA) to power servos AND the Arduino in this way: V+ of batteries directly to V+ of my servos and to Vin of the arduino ?
If you split the power wire from the battery so that one leg goes to the Arduino barrel connector and the other goes to a motor there should not be a problem provided the batteries can supply the correct voltage and enough current.
The problems arise when power is fed from the battery to the Arduino and then from the Arduino to the motor. This can look like an attractive option because (say) a 9v wall-wart can power the Arduino and servos could (in theory) be powered from the 5v on the Arduino 5v pin. But the 5v pin cannot provide enough current for motors.
...R
I'm on a small robot and I don't have space for 2 different power supply
You can use a common power supply as long as it is sufficient to keep the arduino from experiencing a low voltage reset. I've never seen anybody report damaging their arduino by directly powering it from the arduino, but it might be possible. Powering the servo from the arduino does account for probably 90% of servo issues reported on the forum due to the servo causing an under voltage reset of the arduino. You might consider using a good RC battery and a UBEC power regulator for the servos. The attached picture shows how I've powered a servo chip and servos from the same power supply in the past.
@zoomkat: so the standard saying:
"always power arduino & motors from seperate power supplies" (which surely is a simple and foolproof solution)
... should be more like this/added:
"and when you are using the same power supply you must have a) added extra hardware/measures to prevent unwanted power drops & peaks ... and b) make sure to still have really enough power for both"
... which is definitely not as easy as simply giving them each their own sources 
yes?
yes?
It depends. If you are using 12v car battery for power, then voltage drops might not be a issue. You just need to understand the hardware power requirements and how they will share the available power if needed.