My OpenCat assembly in a Lego chassis. This was a tough one, using Microbit Servos, which are quite weak (500g/qm), and also that Lego cannot hold stronger forces, without extra support, it can still barely walk. Anyway, i think it looks quite adorable in its new case (:
Your questions are to the point. i was following this guide http://hackster.io/RzLi/petoi-nybble-944867 hence the main chip is arduino pro mini as well @16Mhz clock frequency. SRAM and flash are quite limited on arduino hence one of the less well documented problem was size of sketch because it didn't allow me to upload at first, but i found solution in this forum and remove many Serial and beep calls so i could upload more skills. For battery it uses 260mah 7.4V Lipo cell, but also heavier cell is not a big problem. Lego is also a bit heavy, compared to its stability: the overall weight is 315g. The size should be about the same as orginal Nybble? with a bit bigger legs it wouldn't get up, because servos are weak. also i didn't get it to run well with rubber shoes on. probably due to balance not being perfect, also annoying was i needed to recalibrate servos when it cannot move from too much stress on one of the legs. At least the lego is safe from breaking when applied force is only little haha.