Free fall Z Axis - Back porting fix from mkIII to mkII

Hi in mkII Cetus had to use a friction bearing to stop the z axis from free falling into bed after powered off (or you issued M84 to turn off motors). But that puts lot of extra pressure on z stepper. Given the steppers (Moons Stepping Motor 17HT4003) used by Cetus are not even mentioned on Moons website, we will in big trouble if stepper fails.

Now in mk3 they seems to have figured out a way to keep Z axis at given height without power or friction block. DO you know if that can be back ported to mk2 models? If its a simple fix, can Tiertime release an upgrade kit (like how Prusa released upgrade kits for mk2 to mk2.5)? I am not asking for a free of cost solution, but a fix at cost.

Mk3 uses a plastic piece at he bottom of Z rail that surrounds the axel and you tighten the screw to add friction. Same i’ve seen on thingiverse for mk2 and is likely to reduce motor life too on mk3.

Hmm… I was watching Makers Muses review of mk3 and at 15 minute mark, he talks about regen braking. He did point about it still using the brace, but said about the slow fall. If you have mk3 can you loosen the brace screw and try once if it drops like a rock?

Stepper motors are available from Cetus, I have extra two of them. I own a Mk3…

What do you mean “listen to the brace screw?”

and i commented there mine just drops like a brick, as supplied Mk3 from Cetus, dont forget Angus and other reviewers do not get the version customers get. Often its been tested at factory first so they dont encounter all the little issues buyers get. I’m not stupid enough to apply fixes because someone on a forum says so if my product doesnt have the issue the fix is for.

Ah… Sorry typo… I mean loosen the screw, auto corrected to listen :man_facepalming: I did not know about the replacement steppers. Thank you for that pointer.

Your claim about reviewers not getting the same thing the customers does is not true. Many reviewers have pointed out how the Z axis will fall on power off. I am well aware of this “characteristic” before I bought my Cetus.

On my Mk3, the is a “grip” that’s adjustable by screw to prevent a free-fall. But as other have pointed out, “it may affect” the longevity of the motor. The motor has more torque that what the grip has, so I’m not concerned about it.

Either way I was wrong to assume what Angus said… Any way if it’s same friction cup then mk2 and mk3 are same… I have since moved my mk2 to TinyFab and with the option to turn off all motors at the end of print is nice. But this makes it hit or miss… Every few weeks it becomes lose and might ruin the print. Leaving it on means the motors are in hold pattern for long time.

wel i would have been quiet if adarsha didnt imply i hadnt tried my mk3 without tightening the brace.

My reviewers claim is completely true. if youve watched Angus’s videos you’ve heard him say his review copy on something was previously used by another reviewer and serviced before he got it. he’s also stated when he requests review copies that he wants a random one from the production line that customers get. Specifically so it hasnt been tweaked first. Hes not the only reviewer whose done this clearly in their videos. I’ve experienced this myself in the past as a tester and reviewer in several industries. I dont care what you or anyone thinks, i’m not a youtube fanboi, none of this is new and the process of reviewing is the same in all industries and always has been. Anyone who has bought a mk3 themselves and if familiar with Angus’s process would immediately see he didn’t mention all the issues a buyer has to deal with which showsthey were addressed before he experienced them. He is very careful to note such issues as the cetus was placed as a pefect beginners printer but the mk3 steps backwards and requires research and prior knowledge/experience as there is no single instructions set that gets a new buyer from sealed box to first working print. I speak from decades of experience with such manufacturers, if your printer came with better instruction than mine did then good for you, but mine was missing steps and nothing about various spare parts i was left with. I can only comment on my experience and try to help others with a familiar problem.

Chill out… I didn’t mean to imply anything… As I said in OP I have a mk2, and just wanted some real world feedback after seeing it in Makers Muse. As I said above I was wrong to assume Tier Time has actually fixed it. I am thinking about adding my own solution and before going down the rabbit hole wanted to check their solution.

Druing free fall, The MK3’s mainboard has a circuit to collect the power generate from free fall to become reverse current to the motor to counter the free fall. We still use the one-way bearing and brace to prevent the nozzle to dip into print if electricity is cut off suddenly.

Thanks for the clarification Jason. So going back to my original question, is there a way we can get that feature in mk2? Or can TierTime share the circuit so if someone like me try to implement it for mk2?

You can convert your machine to MK3, by change the mainboard and add limit switch. We are working on MK3 conversion kit now.

Several Z axis clamp designs are available for printing on thingiverse.

I designed this one because the outside surface of my one-way bearing was not axially concentric when slipped over the stepper motor shaft. This causes lots of grief.


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