So my configuration is like this 2x 3.7 2200 mAh batteries in series doing 7.4 V in total --> Lithium Battery Charge module (its connected to a solar panel and yes the output its 7.4 V from it)--> Step Up Buck that takes the 7.4 V to exactly 11.7 V --> motor driver L9110s ---> Arduino Nano which also has a HC-05 connected to the 5 V of the Arduino Nano and I suspect there is a drop in voltage that makes the arduino reset itself when I start up the motors. Arduino Nano works fine like all the modules on it while on VIN and Bluetooth but when I start the motors it resets itself. What should I do to fix this issue ? Thanks ! (also sorry for not posting a schematic but only through text cause its morning and I am really tired and I am not on my home computer).
The schematic is always best. Simply measure the battery voltage during start up, you may have to use a scope depending on your meter. The Arduino a Power Supply it is NOT!
During start up its 3.40 V
What is 3.4V during start up of what?
Complete schematic is needed, plus detailed specs of your motors (ideally in the form of a link to the datasheet).
The clear blunder is not comprehending what the "Vin" or "RAW" terminal is. The regulator on the Arduino UNO/ Nano/ Pro Mini/ Mega2560/ Leonardo/ Pro Micro has very little heatsink, so will not pass very much current (depending on the input voltage and thus, how much voltage it has to drop) before it overheats and (hopefully reversibly) shuts down. It is essentially a novelty provided in the very beginning of the Arduino project when "9V" power packs were common and this was a practical way to power a lone Arduino board for initial demonstration purposes. And even then it was limited because an unloaded 9 V transformer-rectifier-capacitor supply would generally provide over 12 V which the regulator could barely handle.
Nowadays, 5 V regulated switchmode packs are arguably the most readily available in the form of "Phone chargers" and switchmode "buck" regulators to regulate down from 12 V or other available voltages are cheap on eBay so these can be fed into the USB connector or (more appropriately) 5 V pin to provide adequate power for most applications. Unfortunately, many tutorials or "instructables" are seriously outdated or misleading and have not been updated to reflect the contemporary situation.
If powering directly from batteries, as long as the battery pack cannot exceed 5.5 V, this must be connected to the 5 V pin.
I agree with you Paul, it seems from your post I understood my issue and resolved it accordingly thanks !