Engeneering question: Variable Gearbox

[HectorMB]

Hi everyone, 

I have been struggling with setting up a variable gearbox, based in two differentials, suitable for heavy models (>2 kgs). In these gearboxes, the power coming from the motors is distributed between the two differentials, depending on the resistance found on each differential. With the adequate gearing between the two differentials, one can set the max and min torque and speed at will. The "issue" is that, because the high torque is going to always offer less resistance than the low torque, the power is going to be always through the differential with the highest torque and lowest speed. To solve this, one can add some resistance to the "high torque" differential (as seen, for example in @nico71's model https://rebrickable.com/mocs/MOC-92756/Nico71/truck-with-continuously-variable-transmission/#details). But, obviously, increasing the resistance in this way also increases the power loss of the whole system... but I think this is kind of unavoidable, no?. The question that I have comes to the following: the strength of this resistance will depend on:
a) The weight of the model
b) The difference in torque between both differentials. 

Although I though it would  depend on both aspects, now I think that it should be only depending on B. What do you think?

Edited November 21, 2021 by HectorMB
Thinking a bit more about it...