Powering Hexapod

I'm currently building a hexapod using an arduino mega with 18 of these servos http://www.amazon.com/HOSSEN®-10pcs-TowerPro-Torgue-Heicopter/dp/B00CCZDJX6/ref=sr_1_1?ie=UTF8&qid=1396490797&sr=8-1&keywords=TowerPro++10. Their operating voltage is 3.0V~7.2V. I've been trying to figure out how to power the thing. I would like to use a rechargeable lipo battery but I'm not sure if I'll need a ubec or not. I currently have an 11.1v 2200 mah lipo battery. The voltage is way to big for the servos but I'm not sure if that is something I need to be concerned about or how to lower the voltage if it is. Can anyone suggest a battery or voltage regulator to use and explain why? Thanks.

I suggest you use one or more 6v UBECs. Closest thing to your servo specs.

Would I use the battery I have in that case? Also for what reason would I need more than one ubec?

Also for what reason would I need more than one ubec?

Look at how much current your servos will consume, and how much current a BEC can provide.

It seems to me that all these servos all carrying weight for a lot of the time are going to use a massive current. Powering them from a LiPo source seems like a reasonable approach, but it needs to be a source that matches the voltage and current requirements of the servos so that you can power them directly. A battery that produces an excessive voltage is not really suitable. The battery you describe would be a three cell battery. A two cell battery would be more appropriate in this case. It's normal for high voltage servos to be designed to run from a two cell LiPo, but check the specs on your specific servos to make sure.

So I'm not sure if these servos are meant to be powered by a 2 cell lipo. I can't find anything that explicitly says so. It is rated for 7.2 volts and since the 7.4 volts from a 2 cell lipo is just an average maybe it will be fine. Perhaps I should use a ubec and a 2 cell lipo just to be safe. What are your thoughts? Also as far as the amperage goes does that mean that if for instance that servo draws 1 amp at max. If I used ubecs that had a 3 amp output and use 18 servos would that mean I would need 6 of these ubecs to safely power all my servos? 1 amp per servo x 18 servos = 18 amps. 18 amps/3 amps per ubec = 6 ubecs? I have a feeling that isn't quite how electricity works.

That's how electricity works - you can just add up the current. However, you need to be aware that the figure of 1A per servo is just a ballpark figure for a typical servo, and you need to know how much your actual servos are going to use. Also, the current drawn by a servo depends how much torque it's generating. If you have some servos that are going to be drawing a lot of current (generating a lot of torque) and some that you expect to be lightly loaded, you can help by sharing the heavily loaded servos out between the BECs.

I suggest that powering the servos directly from a battery of the right voltage is a far better approach to take, though. If you take the BEC approach then roughly a third of the energy in your batteries is going to be wasted as heat, which means you're carrying 50% more battery weight and also have to cope with all the related cooling issues. The direct power approach will give you a lighter and better solution. I think it is almost certain that the 7.2V servos you have are designed to be powered from a 2-cell LiPo but given the potential cost of eighteen servos I would check that rather than assuming it. You should be able to find out from the manufacturer, or the retailer, or user forums with people who use similar servos, for example in RC cars and buggies.

Ok, thanks. So after looking around a bit the best I could find on the tower pro sg90 servos was that their peak current was probably about 250 mA. I may be able to find more info if I spent some more time searching. So it sounds like what I should do is just hook a 7.4v lipo up to the arduino mega? One like this would do the job Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking20390__Turnigy_nano_tech_2200mah_2S_40_80C_Lipo_Pack_TRA2820_Traxxas_1_16_models.html ?

That's the approach I'd suggest, but given the potential cost of eighteen servos I would check that it is safe to power them from a double LiPo rather than assuming it.