Hi,
I want to buy a robotic arm from Aliexpress that has 6 MG996R servos, and of course I have to use the pca9685.
In this system I know that I have to use separate voltage sources, one to power the Arduino and other non-heavy parts or modules, and the second one to power the servos throw the pca9685.
My question, which is the best power module to use with this module powering 6x servos ? and which voltage level ?
A power supply giving the voltage and current needed for the servos. Just read the datasheets for the servos. Likely a power converter can convert the voltage of that power supply into what the controller needs.
Why " of course " ? You can use the PCA9685, but you don't have to. An Arduino can easily control 6 servos directly. If you want to move the servos slowly, it is easier to do it directly than with a PCA9685.
But this is independent of the fact that the servos need their own power source.
If all servos can operate at the same time, ideally the locked horn current times 6 will be the current needed.
If one servo needs 2A, then you need a 12A supply.
These servos work well a 5v supply.
Hence 5v @ 12A.
This is from the datasheet.
Operating voltage:
I think I won't run all the servos in stall stress at the same time to draw 2.5A for all the 6 servos.
It is just a college project for demonstration project of controlling a robot arm through a TFT control GUI.
I think I have to buy a 5V power supply with 5-6 ampere rating.
Thank you all for the support.
Yep, that should work.
But also as you mentioned in #4, if the servos draw at full stall stress 2.5A, then the optimal power supply for this setup would be 5V/15A.
And also since as I said there won't be a stress for all the servos at the same time to draw all the 15A for the 6 servos.
I learned something about choosing the power supply, which is when I know the real maximum current the system would draw, and the average current in normal condition.
Like, the computer power supply, if it's rated for; e.g. 500W then that doesn't mean the computer is drawing this wattage all the time, and that is just depends on the power conditions and if the CPU is running at full speed with full load ... etc.
At servo start to move time, you draw the maximum current, as it moves the current draw reduces dramatically.
High amperage power supplies usually can provide considerably more current for a short time than their continuous current rating.
This makes a perfect marriage; one needs lots of current for a short time, the other can supply lots of current for a short time.
If there is a possibility of the horn lock on a servo, you need a stronger servo or adjust the connecting rod closer to the centre.
This is true. Start time is also a problem because often, ALL servos are away from the "start position" at "start", and therefore all servos begin to move simultaneously; it's not generally at power up, but rather at the moment when the initialization enables the servo driver. For example, when a PCA9685 board is set up, and all of the servos jump to the 90 degree position from wherever they ended up previously.
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Should I use any kind of capacitors for the whole robot arm system ?
For example, in case of running 6 servos with a good power supply 5V/15A, the power supply of course should supply the required current, but in this case, is it necessary to use capacitors to maintain the voltage levels or the power supply already have enough capacitors at the output rails ?
So you mean here the importance of having a power supply with enough current rating ?
For the case you mentioned at the start up when the system requires to set all servos to certain position, in that case the servos will drain a lot of current.
It’s usually a good idea to add a reservoir capacitor near the servo connectors, ex. 220 to 470uF.
In case of 6 servos, how many capacitors should I use ?
Start out with one or two.
Edit:
If you are using the PCA9685 there is a capacitor on it.
What if I used high value capacitors ? Like, 2200uF or 1000uF to have more voltage to supply.
Are you are using the PCA9685, start with the capacitor on the board.
Yep, got you.
I should start with the one on the board, then if it's not enough, I should add some capacitors and measure the voltage balance and stability 
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