I think it is an issue, that an half empty battery provides less RPMs to the props,
and that the internal resistance of the battery causes a significant drop of voltage when going full throttle. This has caused a motor-out (or better: a battery-out) on my setup, since my BMS protects the battery by shutting it off, when the minium set voltage has been reached.
What do you think of a circuit that stabilizes the voltage at a set value, such as 50 Volts for example? This would result in always the same Voltage at the input of the ESCs, unrelated to the batterieās actual voltage, and X% Throttle will always give the same result in RPM and thrust.
I was searching online for a step up (or step down) dc-dc converter with a possible output of 60 Volts, but didnāt find anything that would support more than 30Aā¦
If we wanted to always have the same linear relationship between throttle and RPM it would be possible to do this with the new hub PCB in batch 4 that provides telemetry feedback for RPM. The throttle would then intelligently adjust the PWM in order to maintain a consistent RPM.
You could also do this without RPM data (batch < 4 ) and measure the RPM at different voltages relative to the PWM input. Then create a mapping and save it to the throttle to reference pack voltage as well as throttle position when sending PWM.
the problem is the voltage sag.
My Battery is full with 54,6 Volt and empty at 32,5 Volt.
when the battery is at, letās say 38 Volt, I can only go 35% throttle or so, which may not be enough to maintain altitude or even gain altitude.
I would prefer to still be able to go full throttle, to get over an obstacle for example, accepting an even shorter flight time.
the LG HG2 (18650 Li-ion cells) that I have in my system are the ones with the highest discharge rate available (within the 18650 Li-ion models).
I have decided to do just that. I already topped up my capacity from 2,16 kWh to 2,88 kWh
and my plan is to even double that some time towards the end of this year.
that would be good, however the BMS that I have is most likely not compatible with the OpenPPG arduino controller - and still, as mentioned above, Iād prefer to be able to go full throttle at all times during the flight, if needed, rather than only being able to go only 30%throttle towards the end of the battery capacity.
I am definitely in, when it comes to upgrading my equipment to the newest controller, that you guys come up with - however the issue I was referring to is less the linear relationship between RPM and throttle,
but more the ability to still go full throttle when the battery is half empty (the voltage sag prevents me from doing this).
If I understand correctly, you have two problems:
1- BMS shuts off batteries at a low voltage
2- At lower voltages the motors wonāt spin fast enough
Your suggestion may fix option 2 (if there is enough capacitors in that device to handle the load), but it will just increase the amps coming from the batteries which will lower the voltage further causing problem ā1ā to occur even sooner.
Yes, but thatās not a āproblemā in that sense, itās just a fact.
The BMS is designed to do exactly that to protect the individual cells from being damaged.
Yes, at least not as fast as they did with a full battery,
I would not call it a āproblemā either, just an āissueā
Your conclusion is actually the answer to my question, just like @jhair 's conclusion,
so it make sense to top up capacity, rather than adding electronics (which also add weight and cost, and substract efficiency from the equation).
On their larger units, the MGM controllers have a function to correct for voltage sag, and they can be programmed to reduce power at a set voltage. They are expensive thoā¦I tried to upload the manual, but itās a bit too largeā¦