Hi, I am building a quadruped and I need to power 12 servos, each with a stall current of 3.5A at 6V.
To power the servos, I am planning to use a 2S (7.4V) Lipo battery, so a step down converter is needed to get a 6V supply to the servos.
3.5A x 12 = 42A is the maximum current, but then there are no 40A rated buck converters small enough to fit into the robot.
Others seem to build their quadrupeds using converters like this:
which says 300W 20A. Say when I am only outputting at 6V, given that the converter has a power rating of 300W, does it mean 300W / 6V = 50A can be drawn?
If max outputcurrent is told to be 20 amp there is a reason for that. Running at maximum is a bad design.
Build 3 sets, each having its own battery and converter.
Is there a point where you will be drawing max current from all 12 servos at the same time? If I were you, I'd buy a couple dozen cheapo buck converters in bulk from Amazon and make them easy to swap out should you burn one up. I'd think maybe 6 if real estate is an issue, two per: just not two that are doing max work at the same time. If you have space, use 12.
Or you can get one or three of these, although pricey. Castle stuff is great though, been using it in rock crawlers for years.
If you DO choose Castle Creations BEC, purchasing one at your local hobby shop may save you some money since they are set to the desired voltage in software using a dongle called a Castle Link, sold separately. My local shop will set it for you in store for no additional cost using theirs, with purchase of a BEC.
Sure, in a perfect world. What is the project application and how much use will it see, what's the total budget and what else is left to yet purchase, safety, surprises and unexpected results all come into play I think. Are they shooting for perfect design in theory or just good enough? Building an RC heli? Then absolutely I agree with you. Building a Hallowe'en animatronic? Good enough is good enough.
Whatever the decision, it's wise to plan for failure (but not necessarily failure) into the least expensive, most easily accessible parts of a build (fuses, for instance). Cheaper and easier than replacing a servo, I have several in the almost $100 CAD range.
Thank you for all your replies. The application is not that critical, and the buck converter is easily replaceable so I'm fine with replacing it if in the event of failure.
I'm not very familiar how these converters work. If the servos are trying to draw more than 20A, what will happen? Will the current be capped at 20A (and the servos not getting enough current), or will the buck converter just fail and stop working?
For your reference here is a schematic I found online for this converter:
