is this flex or backlash?
my z-axis seems to overshoot when going up (second video) however it goes correctly when going down (first video).
any idea how to fix this?
A picture of your printer would help
it is a 300x300 d-bot. so far i did try elastic and rigid couplers (rigid seems worse). i switched to a single motor with belt - pretty much the same result. for today i want to try: a different stepper driver (maybe that skips steps), a anti-backlash nut, moving the low support of z-axis back and forward as it may be not supporting the bed correctly. if all these fails i will buy some linear actuator from openbuilds as i am getting tired of doing and re-re-re-doing the z-axis.
replacedmissing/deleted image from Google+
Is your linear hardware sticking enough that the bed isn’t effectively preloaded by gravity? Could be binding between the rods/rails or screws.
not sure how much it should be sticking - the d-bot tutorial mentions 69 mm for the small version and then it says for larger one it should be more to be close to center of gravity (but no value is mentioned).
couple of things made quite a difference: replaced the bronze nuts with anti-backlash ones made a very big difference but wasnt enough. replacing drv8825 with a4988 solved the remaining issues. now i have a near perfect z-axis…