Hi all,
I have a problem. When I connect 6 x sg90 servos to my Pololu mini maestro 24 which is powered by 5 x 1.2v AA NiMH cells everything works fine. However, when I try to use any more than that the whole thing goes nuts and collapses. Is this due to lack of amps? I have read that each AA cell can supply upto 700mA so should, in theory, provide 3500 mA.
Can anyone suggest a better power solution for this project? It is for a 350mm high biped robot that needs 12 sg90 servos so I ideally need a small, lightweight power unit or as best possible.
I also have a second question. If I were to supply power to the Pololu board using a 12v adapter would this allow only 5v to go to the servos or would it supply the full 12v? IE will it limit the voltage as desired?
Many thanks. I am quite new to this so really could use some advice.
No, with batteries, voltage adds in series connection, current adds in parallel connection.
For 12 SG-90 servos, you should realistically plan on a 4.8 to 6V power supply capable of supplying at least 10 Amperes. RC battery packs are available that will handle 10A, or you can divide up the servos and power supplies into subgroups. Don’t forget to connect all the grounds.
Finally, be sure to distinguish between battery capacity (mAh) and maximum current rating (mA or A). The “700mA” figure you posted for an NiMH AA battery is probably the battery capacity, 700 mAh. That same battery can actually supply several Amperes, if new and fully charged.
Hello.
As Jim mentioned, all of your servos will receive the same power bus voltage. 12V is almost certainly too much for SG90 servos and would likely damage them.
Jim’s suggestions of an RC battery pack is a good starting point. As he alluded to, if you can’t find an adequate supply to power all of your servos that would work for your project, you can separate the Maestro’s servo power rail into multiple banks and power them from separate power supplies by carefully cutting the trace on the underside of the board. You can find more information in this post by Jon. You might consider splitting the Maestro power rail into multiple banks (or powering the servos separately from the Maestro) even if you power them all from the same supply since the traces are rated for 6A.
Brandon
Many thanks. That sounds like a good option.