Overview
BigTreeTech released the BTT-MOT-EXP. It is an adapter that would ordinarily allow 3 more extra drivers to be added to an Fly-Super8.
Connecting the boards
Connect two 10-pin IDC cables between EXP1 and EXP2 on the Fly-Super8 and EXP1 and EXP2 on the BTT EXP-MOT V1.0.
12/24v power should be connected to the BTT-MOT-EXP to power the drivers.
If using the drivers in UART mode, a jumper should be added to the pins underneath the driver as normal.
Fly-Super8 Board.txt configuration
Please edit the stepper.numSmartDrivers in the board.txt file to 11 (assuming you have TMC2208, TMC2009, TMC2225, TMC2226 or TMC5160 drivers in all other sockets).
stepper.numSmartDrivers = 11
Please add the following lines to the board.txt.
stepper.enablePins = { PF_11, PF_14, PG_1, PE_9, PF_2, PC_15, PG_4, PG_7, PG_15, PG_13, PG_14}
stepper.stepPins = { PE_2, PE_3, PE_4, PE_14, PE_15, PE_1, PE_0, PE_6, PA_7, PB_7, PA_6 }
stepper.directionPins = { PC_5, PF_13, PG_0, PE_8, PE_11, PF_0, PG_3, PG_6, PB_6, PA_4, PA_5 }
stepper.TmcUartPins = { PC_4, PF_12, PF_15, PE_7, PE_10, PF_1, PG_2, PG_5, PC_13, PG_8, PE_13 }
Thanks to @o_lampe for the above.
Sensorless Homing
Supported by only the TMC2209, TMC2226 and TMC5160 If using sensorless homing/stall detection on the BTT-MOT-EXP with TMC2209 or TMC2226 the following line must be added to the board.txt file. It is not needed with TMC5160.
stepper.TmcDiagPins = { PG_12, PG_11, PG_10, PG_9, PD_7, PD_6, PA_8, PF_3, PC_14, PB_2, PE_12 }
Please only include the diag pin numbers where you intend to use sensorless homing on that axis.
For example, if you only intend to use sensorless homing/stall detection on driver 0 and driver 1, only include PG_12 and PG_11 in your board.txt file.
For more information about setting up sensorless homing, please read this.
Config.g Modification
The three added drivers would become driver 8, driver 9 and driver 10.
e.g.
M569 P8 S0
M569 P9 S0
M569 P10 S0