User:Powdermetal
Revision as of 15:08, 3 June 2016 by Powdermetal (talk | contribs)
Release status: Experimental
| Description | Cycloidal gearbox for a lightweight & compact direct drive extruder
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| License | GPL
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Intro
Running a delta printer with a Bowden-style type extruder, many people have been looking into alternatives for a more direct filament-feed response (especially when using flexible materials) while still keeping the dynamics of a lightweight effector system. There are a bunch of options out there and each one has it's specific strengths...
Project Target
- Develop a lightweight, compact and powerful direct driven extruder for drive gears like the MK8
- Utilize a NEMA8/11/14-stepper for weight reasons
- Minimize gearbox package through choosing a cycloidal drive system (gearbox ratio probably between 36:1 and 10:1)
- Potentially setup an attractive alternative to the outphased NMB PG35L-048
Build v0.3
Objective
- Improve heat resistance - previous build failed due to material creep
- Tighten tolerance stackup for better extrusion rate precision
- Squeeze packaging
Design
- To shorten the tolerance stackup, an additional bearing now directly centers the output shaft with the motor shaft
- Tooth clearance reduced from 0.1mm (v0.2) to 0.05mm, aiming for less waviness while keeping printability with FDM machines
- Cleaned a bug in tooth shape formula of v0.1
- Based on v0.2 results, gearbox ratio is changed to 12:1 -> no of teeth: 12, eccentricity: 1.0mm, radius: 18mm, roller radius: 2.0mm
- Some exhaust air from the hotend is directed to the stepper motor for cooling
BOM
- Printed parts
- 1 x StepperOnline Nema 14 .9deg Thin Stepper Motor 12.5mm 0.5A 7Ncm(10oz.in) 14HR05-0504S (50g)
- Same stuff as v0.1
Make & Assemble
- Basicaly like v0.1 - printing and assembly simpler due to larger features and aligning of some of the components' endfaces
- Hint: Cleanup the gears for running smoothly before assembly - remove any blobs and strings carefully
Test & Validate
- Attached to an Azteeg X5, v1.1
- Motor current: 0.45A, 32 microsteps, 10200 steps/mm
- Retract: 0.5mm, 5mm/sec
- Speed: up to 80mm/sec, 0.4mm nozzle, 0.2mm layer height
- Testing: 10x10x5 blocks, Dia30 cylinders, some larger parts, in summary 4 hours printing
Results
- Works basically
- No lost steps while extruding and retracting
- Started to slowly loose steps after 1 hour when printing a larger object - made further tests fail
- Less waivy surface appearance than v0.1, but still worse than Bowden setup
- Motor temperature: approx. 70°C (finger sensor...)
- No specific noise
- After disassembly:
- Excenter and excenter gears lost their press fit with the bearings, probably due to motor-heat induced material creep. This causes locking of the gears and loss of steps
- Some normal surface flattening, small amounts of worn-out particles - seems to be protruding material from the print being removed while in operation
- Weight (drive system + E3D v6 HotEnd): 138g
- v0.2 objectives met
Todo
- Make this thing more robust by using higher temperature resistant material
- Squeeze down packaging
- Try to further tighten tolerances
- Review various issues from poor design
Build v0.3
Objective | Design | BOM | Make & Assemble | Test & Validate | Results
Links
- Wikipedia: Cycloidal drive
- Design of a Planetary-Cyclo-Drive Speed Reducer Cycloid Stage, Geometry, Element Analyses
- Building a Cycloidal Drive with SOLIDWORKS
- Generate DXFs of hypocycloid cams for cycloid drives
- http://forums.reprap.org/read.php?1,617389 (This engineer claims 100 grams direct extruder)
- Build v0.1 album
- Build v0.2 album
