Quote Originally Posted by Rapidrory View Post
If you're going opto, may as well go with a proper opto isolator to avoid joining ground planes through the RX; I've had signal issues when joining up non opto isolated high power ESCs.

Also, the HSOF packages ideally need thermal vias and to be heatsunk through the board. You can heatsink the case but it's not as efficient. Without a heatsink you'll likely get about 160A cont from 4 of those FETs, so to get to 300A you'll need to dump a lot of heat.
I have added an opto isolator for the reciever input.

For the current design it works out about 110W of dissipation, which should be fine. It will run quite hot 120oC at 300A continuous load. The heatsink is in contact with all power components on both sides of the pcb and some of the board itself next to the fets. Board is probably going to be 2-4 layer with 4oz - 6oz copper and copper bus bars for each phase and power input.

The heatsink is going to be around 1oC/W or better and will form a custom two part machined aluminium case.