When using batteries with high voltage swings, like LiPo or LiFePO4, the swing in voltage from high to low can cause trouble. Either you exceed rated voltages at the high end, or you get no torque at the low end. This is a problem even with NiMH batteries to some extent, and certainly a problem with LiPo and LiFePO4.
Pololu has some nice switching voltage regulators – especially the new buck/boost controller with over 90% efficiency is very nice! But too low current to be useful for power hungry servos and motors.
Digi-key has some nice parts, too – I like the GE/Lineage raptor, for example, for generating 6V at 10A from a 3S LiPo: digikey.com/scripts/DkSearch … =0&cur=USD (this needs a few additional capacitors and some hookup to make a finished product.)
Building these kinds of things yourself is hard, because none of the low-volume “prototype” board houses do more than 1 oz copper plating on their boards, and high-power boards need 2 or even 3 oz thickness for traces.
Wouldn’t it be great if Pololu had hobby robotics regulators designed to take, say anything from 2S to 4S LiPo, and output something like 12V / 25A? Or, if buck/boost for this amount of current is too hard to solve, a buck-only converter that takes 4S LiPo in and outputs an even 12V / 25A would be good, too.
You can buy things like this, but they are built on heavy steel frames, and cost many hundreds if not thousands of dollars, and are based on older designs. With modern chips and parallel MOSFET switchers, I bet these could be built to sell for, say, $50 each as bare boards.
Another hole in the availability spectrum is battery cell controllers. Places like all-battery sell LiPo and LiFePO4 cells, as well as the necessary battery management circuitry to turn those cells into “safe” battery packs, with overcharge and underdischarge protection. However, those boards typically top out at 10A to 15A. A hungry robot may want to draw 50A or more. A battery protection/management board for hobby robotics with those kinds of amperage ratings would be sweet! Again, you can buy BMS-es that do this, intended for scooters or cars, that are way too heavy and way too expensive for hobby robots.