it is possible to install 2 motors on a single axis but you will require another driver and motor, but wire it directly to the same pins on your breakout board. Also the orientation of your motor since it is opposite side of the original so getting it to move accordingly to the original motor it will need to be orientated correctly. The slight shift could be the cause of the rod not being completely flat where the set screws are suppose to tighten the sprocket to the rod, so sanding it to a flatter surface might fix the shift in directions.
Currently do not have a kit or schematic available.
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My X-axis on the Blacktoe cannot run above ~40 ipm. I've checked all connections,tensions, sprocket locks, etc. All is fine. Can the 425 OZ stepping motor be replaced with a bigger motor, or could a second 425 OZ stepper be added to increase torque?