The servos I ordered for my biped project never arrived, so I got my money back and ordered new ones, which probably will not arrive before december. *sigh* Not to get bored I did some reading about powering a walking robot. Quite a surprising subject.
As a lot of hobbyist do I also ordered Towerpro MG966R servos, because they're cheap and quite powerful. The drawback is that they use quite a bit of juice, 500 - 900mA under load and 2,5A stall current. Or that's what Towerpro says, it wouldn't surprise me if the clones are less efficient... With that knowledge in mind I started figuring out how much the average current draw of a robot would be and more important the maximum current draw.
And then it got confusing... not only because there isn't much info available on this subject, but the info that I did found was contradicting. I for example found Badji's hexapod here and learned that he fried one of his two 8A Ubecs and needed three of them. That did make sense. 18 996R servos take a lot of juice. But, to my surprise I did find a nice biped on the net called Rofi, which uses 12 996Rs and only uses a 6v 5A volt regulator! And it does work without blue smoke!
Anyway, I'm a firm believer in Murphy's law so I bought two 10A continues buck converters, which apperently can deliver 15A continue if you add ventilators, if not the peak current is 15A and it even has a current limiter as protection, so I should be safe with 14 996R's running at 6v. Ok, those are Chinese specifications so it probably is a bit less great as it sounds.
Now that that problem is "solved" I turned my attention to Lipos. What a wonderful batteries: you charge them, get a whole lot of power out of them and then it's guessing when they are empty. Apparently no one knows for sure what a safe minimum voltage is for these things! Some people say it's ok to go under 3 volts under load while others claim that 3,7 volt should be the minimum.
This is quite a dilemma. 2s Lipos are more efficient in combination with buck converters, but 7v will be the absolute minimum to avoid a brownout of my bucks. If a Lipo at 3,5v still has plenty of juice in them 2s Lipos are a bit wasteful. 3s Lipos on the other hand are less efficient and a bit more expensive (and bulkier). And then there is of course the weight issue. 5000mA batteries are nice, but quite a bit heavier than a battery with lower capacity and do I really need it? Again the unknown average current draw question.
So, what's the average running time and power consumption of your robot? And what batteries do you use to power your robot?