Hi, I am creating a robotic arm using the Arduino. The amperage from the 5v power supply on the arduino uno board is not enough to power my 4 servos. To solve that, I plan on using an external power source. I was thinking a 5v 2-amp wall wart charger. Would this work? Also, how do I do this while staying safe from shocking myself?
What kind of servo motors are they ? Can you give a link to them ?
The very cheap servo motors might already need peak current of 500mA.
A 5V 100A power supply will be the same as 5V 0.5A power supply when touching it. You might feel something at 40V, but not with 5V.
Please don't buy the cheapest power supply. Stay safe, and buy one that is certified to be used in your country.
Oh, and the servos that I am using are the MG995's here is a link:
Amazon.com: 4PCS Servo Motor MG995 Control Angle180 Metal Gear Servo 20KG Digital High Speed Torque Servo Motor for Smart Car Robot Boat RC Helicopter : Toys & Games
It's even worse than that. Not one single amp is available there.
I wouldn't go for that wall wart charger. Post links to the servo datasheet.
These are the specs I could find:
Specification:
Gear Type: All Metal Gears
Connector Wire :11.81 inch (300mm),
signal wire/PWM--Yellow;
positive Pole(+)--Red;
negative Pole/GND(-)—Brown
Item Dimension:40.719.742.9mm(1.600.781.69inch)
Servo Weight: 55g
Positioning speed at 4.8V without load0.17s / 60 degrees; 6.0V without load 0.13s / 60 degrees
Dead Band Width: 4us
Plug Specification: JR FUTABA, Hitec,Sanwa, GWS are universal
Operation Voltage: 3.0V - 7.2V
Stall torque: 6V 12kg/cm, 7.2V 13kg/cm.
Temperature range: -30 to +60deg
Applicable models: biped robot / robot / remote control car, suitable for50-90 methanol fixed-wing aircraft and
26cc-50ccgasoline fixed-wing aircraft and other models
Accessories; steering wheel, fixing screws, rubber sleeves and aluminumsleeves.
Suitable for most receiver connector: Futaba, Hitec, Sanwa, GWS etc
Great for truck, Boat, Racing Car,Helicopter and Airplane.
Thanks for the try but all You show is from a sales site, no data about current consumption, average as well as stall current.
Google "MG995 stall current". The first hit says it's 1500mA (1.5Amp).
One servo is already way beyond the ~400mA capabilities of an Uno.
For 4 servos you need a 5volt supply that can deliver more than 6Amp.
A "PCA9685 breakout board" is an easy way to connect servos to an Arduino.
It has a screw terminal for power, and pinheaders for the servo connectors.
Leo..
Great Thanks. I didn't know about stall current, and I just looked it up and now understand it.
I don't fully understand what you are saying here. I thought it was amperage which determines how dangerous a circuit is. I guess voltage is also taken into account.
The voltage determines how dangerous it is to a human.
However, if a voltage is very high, but very low amps, then it might be safe because there is not enough amps to cause any trouble. There are ionizers that are at a few thousand Volts. If they are touched, then that voltage will do no harm, because there is almost no current (no power) with it.
A 9V battery is safe (it can deliver maybe 150mA) and a large 12V battery is safe (even if it can deliver hundreds of amps).
The danger with a strong power supplies is that wires can start to glow and burn. You should also keep strong currents away from the Arduino board.
Suppose you have two power supplies. One is 12V 1A, and the other is 12V with one million amps. They have the same effect when touching it, you won't feel it.
Ok I really appreciate the explanation! I saw online that below 40 volts a circuit is generally considered safe for humans
I did more research and found what power supply I want to use. There are 5-volt options that have either 5, 7, 8, 12, or 40 amps. Now I might hook another servo up to my circuit which means a maximum stall current of 7.5 amps. That leaves me with three options: 8, 40 or 12 amps. Is there an issue with having a power supply that has an amperage greater than what is being drawn? For example, if I got the 40-amp power supply would that cause issues or fry something? Would that behave any different than if I were to get the 12 or 8-amp power supply?
As noted, there simply is no 5 V power supply of any sort on the Arduino UNO board.
Connect your 5 V supply to the "5V" and "GND" terminals on the UNO to power it, as well as to the servos. But disconnect just the "5V" terminal when you plug the USB jack into a PC for any reason.
No issues. The power supply will only deliver what the things it's powering need. If the power supply COULD provide a lot more that's generally a good thing. No risk of overloading the power supply.
Steve
I am using 5 MG995 servos for my robotic arm. I will be using the PCA9685 driver module as well. Now the MG995 servos range from a current draw of 170mA to 1200mA depending on the load. That means that the combined 5 servos will draw between 850 mA and 6000 mA. Where in that range should the amperage of my power supply fall? I have seen many people use 2 amps for their builds.
All servo motors drink a lot of current when they start from zero.
If all servos might get started at the same time, within the same second, I suggest a power supply of 10 Amps to be safe.
Know that even a short, very short, moment of current overload makes the power supply to cut off.
If You use Chinese made power supplies You should preferably go for even higher current ratings. One metric, or Imperial Amp, often calls for 2 Chinese Amps.
The important quantity is the start/stall current, which is 1.5 Amperes for the MG995. The servo draws that every time it starts to move.
Thus, your power supply should be capable of easily providing at least 5x1.5 = 7.5 Amperes. As stated above, 10 A would be good.
Great thanks!
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