7 freakin' stepper motors?!  You gotta be kidding me...

7 freakin’ stepper motors?! You gotta be kidding me… /facepalm

Why not 1xNEMA23?

I don’t even see what the top two are coupled to. Looks like just each other?

When you design with labor costs in mind you may make tradeoffs that you might not make when designing for a one-off. The extra motors reduce a lot of mechanical complexity.

Looks like they’ve move to a NEMA14 extruder as well. I’d like to get a closer look at that.

The two x-motors might end up just works against each other, when the mechanical position would require them to be in opposite half-step positions, but electrically, they are in the same position.
With a two-motor configuration, the best thing that can happen is a 100% increase in torque output. Worst case is a 100% decrease. Due to the belt flexing and allowing the two motors to sync up a bit, you’ll end up with pretty much the same torque as with a single motor.
I’ve tried the same thing on my heavy Y-axis. It did not work.

Would their Z-Platform not rock back and forth like a seesaw? I don’t see the LM8UUs being restrained much. Again, i’ve tried a mechanically similar concept on my wide (450mm to be exact) Y-axis where i had a pair of LM12UU at each end and the belt in the center - you could move each end back and forth by a couple millimeters.
Eg. the Ultimaker’s platform works well with just one leadscrew, because the bearings are actually tensioned from the moment the platform itself generates.

Yeah, I was actually thinking that it might work better if one of the pulleys was toothless. With enough belt tension there would still be grip, but even if the teeth don’t slip, they would walk along the surface of that pulley enough to eat any tension that would cause the motors to work against each other.

When one of my printed pulleys broke, i tried out the “toothless pulley”, but merely to have some kind of idler that kept the printer going. I used a ballpen housing epoxy’d onto the motor shaft since that was the only thing i could find that matched the pulley’s diameter. It did work, and i think it still provided some torque, but i’d still say it’s kind of pointless to embrace this concept with two small NEMA 14 motors instead of going for a single short and cheap NEMA 17 with an idler on the other end.

The idea is probably to distribute the mass so that the two Y motors don’t have to deal with different amounts of inertia trying to skew the axis when it changes direction quickly.

Indeed. But again, a single NEMA 17 for Y, this time with an axle (“drive shaft”?) for both pulleys would seem more logical to me. The Ultimaker uses a second belt to get from the motor to the axle, but it would be just as easy to directly couple the axle to the motor shaft.

I was thinking the same thing.