Power Supply for 32 servos - batteries?

[KMalluc]

Hi all, I'm still incredibly new to electronics, and I've spent the past couple of days reading through forum posts, articles, etc. and trying to fill in the bigger gaps in my knowledge, particularly servos and powering. My terminology might be really incorrect, so please feel free to correct me

I'm having an awful time trying to make sense of this, even after reading similar posts. The end goal is to build an animatronic (Arduino Mega board) that requires 32 servos running simultaneously (going to begin with a smaller prototype using SG90 servos, then moving onto possibly Futaba 3003's). I purchased a couple PCA9685's . Coding is no issue, but I'm struggling with the power supply. Assume each servo requires 6.6V, with a current draw of (worst case) ~1A per servo. If I understand correctly, this means that you'd need a 6.6V 32A power supply to power all of these servos comfortably?

-How would you find such a power supply (that plugs into an outlet) that's up to the job? Searching on Amazon, I found "eTopxizu 12v 30a Dc", is that the right line of thinking for a power supply? Or am I way off base? Do you have any particular product in mind that you'd recommend?

-If that's not possible, and you instead opted to use batteries, how would you set that up? I've read LiPo's are good for powering more servos, but up to 32+? Searching, I found "Zeee 7.4V 6200mAh" which could power 6 servos for an hour or more, but we're interested in 32 servos, so would you purchase 5 of those batteries, connect them in parallel to have a combined capacity of 31000 mAh, and be able to power all 32 servos for about an hour? An hour running time doesn't sound bad at all, but when you're frequently testing and uploading code and revising, an hour goes by quickly. What about recharging? Is it a common workflow to have a stockpile of batteries, with some charging at any given moment, ready swap them out whenever one runs low in your robot?

-If we did use a 6200mAh battery and our load of all the servos combined draws 32A of current, does this mean that a single battery could actually power all 32 servos but for only about 11 minutes (given that 6200mAh/32000mAh = 0.19 hours, or about 11 minutes)? It's a crazy thought but I can't seem to find an answer. Or is there a limit on how much current can be (expelled???) from a battery at any given moment?

-Lastly, though I have no intents of attempting this in the near future, but certainly have interest down the road, how would you instead approach using 48 servos? 64? Even 128?

Again, I'm quite new and still learning, trying to better grasp some of these concepts. Any advice on approaches to powering 32+ servos would be greatly appreciated, thanks!

[slipstick]

I'm not sure where you're getting your information from. Neither SG90s or the old S3003s are rated for 6.6V though they would probably survive at that voltage. The stall current of SG90s is 650mA but the S3003 is nearer 1.5A. But you only see that when the servo is stalled or for a fraction of a second on startup. The normal running current is MUCH lower and when you're working out how long a battery might last you need to work on the average current not the stall current.

It's better to run servos at their rated voltage so perhaps 5V. And that also has the advantage that high current 5V power supplies are relatively easy to find. And of course there's nothing stopping you using two power supplies with half the servos on each (the grounds must be connected together). Similarly you could use several batteries powering the servos in groups.

Lipos are great batteries but their voltages are a problem in this context. 7.4V nominal (8.4V maximum) is too much for servos rated 4.8-6V and it's not easy finding any high power regulators to reduce the voltage.

Steve

[jremington]

A good rule of thumb is to use a 5-6V servo power supply that can easily source 1 Ampere per moving servo, for as many servos as will be moving at the same time.

How likely is it that all 32 servos will be moving at once?

[KMalluc]

Thanks for the info guys!

slipstick:
and it's not easy finding any high power regulators to reduce the voltage.

I haven't gotten far into studying/trying voltage regulators yet, but the ones I've found online so far that do seem capable of dropping 6+ volts down to 5V seem to have a very limited current output. Not too familiar with all of that yet, but that's another topic for another thread when I get there I suppose.

jremington:
How likely is it that all 32 servos will be moving at once?

I've restructured my project a bit so I'll be using less than 32 initially, but I'll be making my way up to 32 eventually. I've written some code to transfer keyframed data/servo positions from Maya to the Arduino and I'm attempting to make smooth, flowing animations play out via the servos - with a single servo it runs wonderfully realtime so far. Since I'm going for overall fluidity, I imagine most of the servos will be moving simultaneously to look less robotic. It's a bit scary to imagine 32 servos running all at the same time and what issues I'll run into like overheating/etc., but I'll get there eventually, all trial and error I suppose!

Thanks again.

[CrossRoads]

Plenty of high current 5V power supplies out there. Pick one or two up.

https://www.mpja.com/5-Volt-Power-Supply/products/534/

(might be some extra characters stuck on the link by the forum)

I found this little 5V/5A, (with +/-15V outputs at lower currents), for example (not necessarilty from MPJA), and use it to power a bunch of stepper motors.