Dan sent me a Kysan 17HD-B8X300-A, a leadscrew-equipped stepper motor with much higher torque than the Makergear Z axis motor. According to the Kysan description, which is all we have to go on: 4.2 V @ 1.5 A means 2.8 Ω, at which current it produces 5.5 kg·cm = 540 mN·m of torque. I measure 3.2 Ω and 3.5 mH, not that that makes much difference.
I worked out some of the numbers in that post and, if they’re close, then the new motor has twice the torque of the OEM one. What’s more important is that the new motor will work correctly with a microstepping drive and won’t bake while doing so.
The new motor has more metal to it than the old one:
The leadscrew follower nut has unthreaded holes, but, mercifully, has the same OD, fits nicely into the Z stage, and those four holes line up perfectly.
I chopped off most of the wires and spliced a JST plug onto the end; of course, the motor ran backwards. Having foreseen that eventuality, I had not shrunk the tubing over the wires: swap a pair, shrink the tubing, and it’s done:
Some notes from the operation:
- Disconnect all the cables
- Remove HBP + glass plate
- Lay printer on +X side of the chassis
- Remove screws holding Z motor to chassis
- Remove nylock nuts and screws from leadscrew follower nut
- Remove Z axis home switch
- Run Z stage to top of rods
- The leadscrew bearing will probably have fallen out by now
- Loosen Z rod clamp nuts & bolts (top & bottom of rods)
- Push Z rods out using a nut driver, pull with a rag for traction
- Be ready to catch the Z stage when you remove the rods!
- Angle motor & leadscrew out of the chassis
- Angle new motor & leadscrew into the chassis
- Reinstall everything in reverse order
- Recalibrate everything…
The Z rod sliders have little balls inside, but they didn’t fall out during this adventure. I don’t know if that’s reliable information or not.
Now, to see what a better motor can do…