The last few nights have been spent printing parts for yet another MPCNC build, and while printing I have been scouting for motors and other hardware. I came to think of the dead-weight of the moving parts; what - from what I understand - prompted the Bowden Tube invention.
Would it be possible, or even a good idea, to move the four steppers for the X and Y axis to the four corners instead, and fixing the GT2 belt to the carry? The dual steppers alone contribute to 700g for each axis of weight/inertia that the motors are required to push around.
Am I missing something? Does the extra belt (more or less double the length) add undesirable properties?
If the MPCNC is to be used for CNC milling I don’t think it makes much sense. At the feed rates that work with the stiffness of the MPCNC I don’t think that the mass of the X and Y steppers is an issue. If used as a 3D printer or a laser engraver then it could make a difference. Although looking at the video of Allted’s multi extruder printer I’m not so sure.
I don’t feel power has ever been an issue. Heck I haven’t even optimized the accel, feed rates, driver voltage yet. Honestly there is plenty of power to spare. I think it comes down to length of your z axis, it has the largest effect on anything.
The reason I chose not to use looped belts (motors on the corners) is flex. that makes it twice as hard to dial in belt tension. The only mass that has much effect is the Zmotor getting whipped around (opposite of tool travel, opposite of a mass damper). I have always felt that there should not be any extra z length. the shorter the more rigid, less deflection, less ringing, ect.
Flex of the whole system is the weak point not the mass. $10 rails work really well in my opinion, next step up is at least 10 times the cost for not much improvement. Take a step back and think about the aluminum capabilities for under $500. Compare it to any other system I am very happy with the results but I am also completely biased and have more time than money.
Never know though I could be completely wrong, it is a complex system. Try it out and let us know if it helps.