I'm interested in running two circuits from the same battery (on an R/C vehicle) but the motor circuit produces tons of spiky noise that the other circuit won't be able to handle.
Someone mentioned a DC-DC converter package, but I haven't found a good source of information on these, or if a simpler row of a few capacitors and maybe some chokes would end up just as effective for a lot less money.
Weight is an issue, I'd like to stay below 20 grams for power-cleansing if possible, 100 grams is way out of range.
I just weighed the 1100 mAh lipo I use in one of my projects and it only weighs 22 grams, with connector. A separate battery might just be your best solution.
I'm not sure if this DC-DC converter it will fit for your other circuit,
?4.5-14V Input voltage
?0.59V-5.5VDC Regulated output
?6A max output current
and you can add capacitors like 1nF or 470pF, to eliminate high frequency, and a large capacitor with high capacity to absorbe spikes, voltage of capacitor might be 2X your motor voltage.
Depending on what your 2nd circuit is running, and if you can tolerate the voltage drop, I had success on my RC truck using 2 diodes from the battery pack. One diode to the regular circuit, and the the second to my added one. On my circuit I added a 330uF cap to help deal with the voltage drop when you first punch it.
Diode to the original circuit was a 1N4007 and to my circuit was a 1N5818.