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I'm trying to build a 18 servomotor hexapod robot (6 legs), running from a 11.1 V Li-Po battery supply. I needed to step down the voltage to 5 V for the servos to operate, but the current requirements are very high (approx 10-14 A). I can't build my own high current buck converter right now because the TI chip I was considering for my use is surface mount.

The only buck converter I can get from my area are cheap 5A ones. Can I wire three separate 5A buck converters for a pair of legs each, and connect them to the same battery? If not, is there any other possible solution (different battery source, etc) I could use to power up the servos?

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  • \$\begingroup\$ Is the requirement 10-14A per servo current or the total system +5V current or something else? Would it be practical to have a per-leg buck converter? \$\endgroup\$ – user2943160 Aug 7 '16 at 18:07
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    \$\begingroup\$ This may or may not be relevant for the current project, but you should learn to work with surface mount technology. It's really not as difficult as it first looks, and it's so enabling. \$\endgroup\$ – pericynthion Aug 7 '16 at 18:11
  • \$\begingroup\$ No, it's 10-14 A in total. Each servo consumes 0.35 A no load, and had a maximum stall current of 1.5 A (though obviously it should never reach there). Therefore I estimated the approximate current usage for each pair of legs to be approx 2-5 A. \$\endgroup\$ – P_Lash Aug 7 '16 at 18:13
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You can certainly feed multiple buck converters from a common power source. The problem arises when you want to connect outputs together - one converter will tend to try and supply the full load so, to be safe, use several buck converters and spread the servo motor loads equally on each.

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  • \$\begingroup\$ Thanks a lot for the quick response! So, as long as I keep the outputs (in this case, the legs) separate for each buck converter, I should be safe, right? \$\endgroup\$ – P_Lash Aug 7 '16 at 17:59
  • \$\begingroup\$ You need to treat each buck converter as a circuit in its own right feeding its own output - no cross-mingling of any connections except logic level signals feeding the servo drivers and of course 0V has to be common to make sense from a control standpoint. \$\endgroup\$ – Andy aka Aug 7 '16 at 18:30
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Can I wire three separate 5A buck converters for a pair of legs each, and connect them to the same battery?

Yes you can. In fact this is a good idea anyway as it reduces the maximum current in a fault. If you have one 14 A converter and have a short in a circuit fed by fine wire then you could do some damage. With 5 A converters the risk is reduced because of the lower current limit.

Remember that all negatives will share the battery negative connection. Lay out your scheme logically with motors grouped by power supply. You could also consider keeping one "clean" supply to power all the logic.

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  • \$\begingroup\$ Yes, as of now, I'm maintaining a clean power supply for the logic, and a separate Li-Po supply (with this config) for the servos. I'll have to choose the pairs of legs for each buck in such a way that the load doesn't exceed its capacity. \$\endgroup\$ – P_Lash Aug 7 '16 at 18:09

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