Printable Carriage (Truck) with Belt Tension Adjuster

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Printable Carriage (Truck) with Belt Tension Adjuster

Postby bruceg » Fri Apr 20, 2018 2:26 pm

If you have molded carriages and are looking to improve mechanical motion accuracy a little, the Belt Tension Adjust Truck or other eccentric based carriage may be something to consider. The design was inspired by Trick Laser's Trick Truck and including a belt tension feature seemed like a handy thing to do. The truck has a little better clearance to my hexagonal enclosure than the molded carriages had.

After installing a Nimble, i noticed that force created by the arc in the drive cable housing was causing effector platform tilt. While this problem was essentially resolved by mounting the extruder motor on a gimbal, it did cause me to evaluate the mechanical motion components, as the amount of tilt seemed out of proportion to the force imparted by the cable housing. I found that there was quite a bit of play from the molded carriages in both the X-Y plane and the tangential "Z" plane, with the later resulting in significant platform tilt. A very modest amount of finger pressure on the carriages would cause 2-3mm of nozzle motion and visa-versa. I can't recall how how the springs in the molded carriages were when installed a couple of years ago, but they seemed fairly "dead" when taking the carriages apart to investigate.

The plastic "barbells" have a little (0.5-1mm) flex under application of gentle finger pressure to the nozzle. Mine are not particularly true which creates some effector tilt problems and appears to have been the source of large changes in end stop offsets that were occurring when swapping out hotends (identical effector platforms). There also appeared to be a slight amount of flex or motion in the ball cup arms.

After changing the carriages, replacing the plastic barbells with the aluminum ones and installing Trick Laser Carbon Arms there was a subjective improvement in print quality - surface finish was smoother and fine details crisper. I also noticed that captive nut sockets were loose in post upgrade prints (same gcode, filament roll and dimensional calibration process/result/gross print dimensions) presumably as a result of a more accurate shape. Objectively, the hydrostatic pressure test pass rate of a thin (0.25mm) wall X60 tube that i print went from about 40% to (so far) 100%.

The "major" compliance in the system now seems to be axial twisting of the extrusions so that is not very much. Next stop, FSR's and a Duet.

Belt Tension Adjust Truck Exploded Cropped.png

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