Introducing the Hyrel MK2-250 Dual Drive for Flexible Filaments

https://www.youtube.com/watch?v=V_zCytnGvvo

The Hyrel MK2-250 drives flexible filaments from both sides, captured inside a containing tube to avoid misrouting. More at Hyrel3D.com and Hyrel3D.net

lol mine do that with just the one drive cog :-)

It seems like complete overkill at first glance, but the dual motors are great for putting lots of controlled pressure on the filament. This makes for very quick prime and unprime actions and is much better for overcoming friction with materials that have more than the usual amount of swelling as they melt. With single-motor extruders, your pressure on the filament is limited by the stiffness of the idler spring, with the MK2, the only limit is the torque from the steppers themselves, and with the teeth hobbed directly on the shaft, that torque translates to a huge amount of downward force on the filament.

Maybe it is overkill much of the time, but it sure is nice when you need it.