TPU Printing

Stepper Drivers

DRV 8825 is used for more current on Z. [1]
Initially, one side motor on Z was 44 mm long (17PM-K402-P4V Minebea Motor Mfg Corp, V and A not shown), and the other was 48 mm long (17PM-K402-P5VS, 3.9V 1.3A). *Small motor was easy to stop - pound or 2, whereas larger motor was more like 10lb to stop.

Print volume - 12x12x10 inches - 1440 cu in - or 24 lb max weight of print. Bed can be lowered to attain 12x12x11 or more print volume.

From D3D v20.04 Calculations, bed is 12 lb, and we should be able to lift a total of 40 lb withe the stepper motors - so an additional 25 lb.
Weight of 1/8" steel plate, 8x8" - 2.3 lb. 10 or 11 of these should be held up.
- 3 could be held up reliably. So 7 lb of print mass - 3 spools of filament.
- Up to 6-7 could move up a little, but then they slammed down once the DRV8825 got hot.

Redesigning for 430W each by lengthening 24 ga nichrome to 20' from 14', yielding max 850F temperature of element.

Either more Z motors for better balance - or counterweight - are useful for handling the heavy weight of the bed. Motor skip upon going all the way to the top of bed in Z direction.
Z motors will provide better balance if there are 4 corners of them. This will stabilize print quality.
But also, another option is wider z parts. But this gets away from the natural modularity of the system.
Added cost of 2 motors is about $50 for 2 axes.
Added cost otherwise is a counterweight, which is lower cost.
Less design change is favorable for going with 4 motors - the main case being for stability (larger weight handling is also a plus but secondary)