1 - Main motorization
I found on youtube a video of a guy who motorized the set : https://www.youtube.com/watch?v=87gg9RwA3EU (LEGO Technic Porsche GT3 RS (42056) with Power Functions & Remote Control ) but I think he bypassed the gearbox,
so I made my own motorization using two XL motors (Power Function) too, but in a different way....
@ the begining : have to disassemble the back of the car body
I'm sorry to not have made the whole MOD documentation but I fine-tuned while building/testing it, hope the photograph & a bit of imagination will allow you to make something better than me :)
For information : my car is now 1 brick longer than the original, so I had to adapt some bloc hooks...
The efficiency of my MOD is limited but I can use the gearbox on sereval ratios, I think it should be better if I could lock more my motor bloc.
Anyway, it works...
next step is : plug my motors to the L298 dual H bridge controller ...
As each L298 boards are brushed differently, I let you google your own model.
But for the most number of those : use Vcc to 9v, GND to GND, +5 to regulated +5 (to let you use PWM signal ~as voltage comparator) then SEL 1&2 to control the motor direction & brake + PWM line for the speed of motor (0 to 255).
Here's a try with an Arduino micro & a smaller LEGO motor
How to wire a LEGO Power Function Motor :
keep only the two middle wires for the motor : it can be used in both direction.
keep only two external wires for the power supply (on another cable !).
putting all together : contoller + Hbridge + battery + motors... ( 1st try ;) )
Finally, I removed the passenger chair to use the original LEGO battery box...