I measured three GC controllers' 5V lines when rumbling. Results:
Original Nintendo: 36 mA
Smash Ultimate (released 2018 Dec): 32 mA
3rd party, GameStop brand: 40 mA
This confirms the only other result on the entire internet,
https://github.com/NicoHood/Nintendo/wiki/Gamecube that reported 30 mA. Much less than other consoles' controllers, and should be well within N64 spec for one or two controllers.
My only concerns are...
1- The N64 doesn't provide 5V, but instead only provides 3.3V.
2- A 5V motor provided with 3.3V will only run at half the power (3.3²÷5² = 43%). Torque in a brushed DC motor is a function of current, the lower available peak torque here could cause it to stall. A boost converter could be added, but then you'd need 150% the current at 3.3V to provide the same power output.
These may well work regardless.
Yeah I have a small step-up converter for that. It's a miniaturized proper converter apparently, advertised as high efficiency. Hope to get the cables hooked up soon to test things.
I searched again for the N64 rumble pack power draw, and found none. Would be good to know how much that took, even if it used batteries, but I don't have one, and too much trouble to buy just for that.
I would also check if the vibration was still acceptable at 3.3V... who knows, it might be.
I found a source that measured the DC resistance (i.e. stall current) of the N64's vibration motor to be 9 ohms, and I just measured my GC's vibration motor to be 35 ohms. At 3V and 5V, that would be 330mA and 140mA in stall current respectively, although in practice back-EMF means the actual current drawn will be much lower. (Apparently by a factor of 4 on the GC vibration motor, but I don't think this has any predictive power at all...)
It might work for original controllers, but reportedly there are third-party controllers that require 5V just to work, using it for more than rumble. I'd want to be compatible with those, so the step-up would be necessary.
So 3.88x? Assuming it can be extrapolated. There's plenty of reports of mods where people put two original N64 rumble paks in one controller, meaning four GC controllers rumbling at once would be within the power budget.
Oh, this is part of a almost-passive adapter to use gamecube controllers on an N64? Sounds good to me, then.
I might still be tempted to look into adding a USB B jack for external power, or something that taps +12V from the EXP port and bucks that down, but both might only count as backup plans.
Ah yeah, the first post could definitely be read as putting a GC rumble motor into a N64 controller.
I suck at soldering, but finally managed to get the cables into shape, and it was a 100% success. With a simple straight-through cable, no microcontrollers like Raphnet's, just the small step-up converter for the 5V line, everything works. Rumble, two sticks, analog triggers, everything.
With the availability of two sticks for proper controls, one step closer to great N64 games