The case is a small hard pressed alu type, easy to drill holes.
The function of this discharger auto switch, is an electronic controlled switch using a FET to turn on/off an external load.
This load can be a bulb or resistors or a motor or whatever you like.
A wattmeter with mA/hr counter in combination with bulbs seems to be a perfect solution to see the remaining capacity/time left after flying.
When the battery voltage goes under a presat value, it will switch off the load current and STAY off even if the battery voltage rise.
The motivation for this unit is the lack of fast/hi discharge levels in the most modern chargers we have.
We wanted to know the remain power shortly after landing using a cheap homemade device.
This discharger can handle from zero to 30Amps loading using one cheap FET, just use two in parallel to get 60Amps if needed.
If you fly hi performance F5B er similar using NIMH cells, it is an advantage to empty the cells after flying and store them empty.
When you charge them just before flying, they will be hotter and have a higher internal pressure this gives lower internal resistance in the battery
and more power to the motor, this is the way to go for best performance at competitions.
The inside stuff on the first prototype
The 5V regulator is only used for the refferance voltage, a 5V zener could be used for cost reduction.
I used a rail to rail cmos opamp, I guess you can use almost all types you have on stock.
no values are critical, good luck have fun..