Stepper Drivers and Motors
Because of the gearing inside the Flex3Drive, the stepper motor on the extruder axis will need to run at higher speeds compared to traditional lower geared extruders.
For optimal performance a stepper motor with a low inductance is required. Generally speaking these will be motors with a lower peak torque, but are able to run at higher speeds.
The reason for this is due to the way the magnetic fields collapse within the motor when being driven at higher speeds. A higher inductance motor can generally drive a higher torque, and is designed to handle a higher electrical current to achieve this higher torque output.
However this higher current means there is more energy in the magnetic field, and this can take longer to collapse as a result of the increased back EMF that occurs when the magnetic fields are switched.
When setting up a Flex3Drive it is required to run with a low motor current setting, typically around 400mA. This reduced motor current allows the motor to generate enough torque to power the Flex3Drive, but crucially, the reduced motor current allows faster dissipation of the magnetic fields within.
It is quite possible your existing motor will be sufficient but you will have to confirm this by checking the data sheet for the inductance value. The lower the value the better. If you have a long-can motor with an inductance value above 10mH it is advised to replace the motor when you install a Flex3Drive.
Ideally you want a motor with the inductance value below 10mH. The majority of mid and short can (pancake) motors will have an inductance value of around 6mH or lower.
NEMA17 motors that have been tested include:
NEMA17 mid-can motors
NEMA17 short-can motors
The gearing within the extruder means the stepper motor will have to run at higher speeds. Even more so during retraction. To this end we setup stepper drivers accordingly.
Depending on the electronic controller board you are using will determine to some extent which stepper drivers you will use but the approach to setup will generally be the same.
One thing however that should be noted is that it is not required to use a TMC style driver in a high resolution mode, rather the settings required will essentially detuned to achieve maximum possible speeds, as the gearing within the extruder takes care of the resolution, rather than having to fine microstep with interpolated 256 steps.
If you are running a RAMPs Arduino board, it is not necessary to swap out a standard pololu driver for a TMC variant.
There is more info in the firmware setup regarding the settings for the drivers based on the electronics used.