Is the pi 4b with 2g ram enough for the ground unit? Or it needs more ram like 3g, 4g
2GB is fine.
The only difference is the maximum video recording time. 8GB can record for hours.
I have the 2gb 4b and its running at about 20% CPU usage, the ram itself is more than enough and open HD only uses a fraction of it and the remaining ram is used for ground recording.
A 2gb 4b will give you about 12mins of storage for recording with or you can change the setting to record to the SD card instead but I’ve not tried that yet and the wiki says it ‘can’ lead to a performance hit which can cause stuttering and dropped frames and a decent night speed SD car should be used.
I plan to try recording to SD at some point but I have got a HDMI to USB capture device to record footage with the OSB albeit at a slightly lower quality than the direct recording the pi does to ram/SD card.