User:Powdermetal
Revision as of 16:26, 8 July 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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| Based-on | |
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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 3mm filament with a MK8 drive gear
- 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 v0.4
Objective (see development history)
- Improve robustness: Avoid loosing steps while extruding manually from the printer controller
- Stiffen the hotend clamp - v0.3 shows some visual flexing while extruding hardly
- Improve printability of eccentric
- Make the assembly process less tricky
Design (see development history)
- Gearbox ratio is changed to 16:1 -> no of teeth: 16, eccentricity: 0.8mm, radius: 16mm, roller radius: 1.6mm
- Improve fit of centering bearing on motor shaft: Gain axial space by using bearings without shields
- Make assembly process simpler by adding some axial clearances
- Improve rigidity of hotend clamp by going back to the v0.2 concept
- Add 3 connecting points for bolting the effector
- Replace the two idler springs with O-rings
- Fix a minor bug in the cycloidal curve equation
- STEP-files of the assembly with detailed components and simplified geometry for the core parts (for simplifying mods): Media:CycloExtruder_v04.zip
BOM
- Printed parts from some more heat resistant material than PLA (like ABS/PETG/..., I use ColorFabb's ngen)
- 1 x StepperOnline Nema 14 .9deg Thin Stepper Motor 12.5mm 0.5A 7Ncm(10oz.in) 14HR05-0504S (50g)
- 1 x MK8 Drive Gear
- 1 x E3D v6 HotEnd - 3mm Direct (12v)
- 3 x MR105-ZZ (5x10x4mm) Ball Bearings
- 2 x MR128 (8x12x2.5mm) Ball Bearings
- 1 x MR85 (5x8x2mm) Ball Bearing
- 1 x 5mm aluminium shaft (from your local hardware store - make sure you go shopping with your caliper: 4.97..4.99mm is fine)
- 12 x DIN6325 2x10 Steel Dowel Pins
- 7 x DIN912 M2x8 Hex Socket Head Cap Screws
- 2 x DIN912 M3x8 Hex Socket Head Cap Screws
- 1 x DIN912 M3x10 Hex Socket Head Cap Screw
- 2 x DIN912 M3x16 Hex Socket Head Cap Screws
- 2 x O-Rings 3x1 (ID: 3mm, OD: 5mm)
- Ball Bearing Grease
Make & Assemble (not easy)
- Print the parts: 2 perimeters, 100% infill, layer height 0.1mm, use ABS/PETG, go slowly for the gears (15mm/sec or less)
- Cleanup the gears for running smoothly before assembly - remove any blobs and strings carefully - take your time for precision later on
- Tune the excenter's bore to make it go gently (!) over the motor shaft and remove it gently again (this is still a design weakness...)
- Tune the excenter so you can assemble the MR128-ZZ bearings
- Press fit the MR128-ZZ bearings into the excenter gears, push them over the excenter
- Bolt the ring gear to the stepper motor
- Mount the excenter/excenter gears over the motor shaft as follows:
- Make the flat side of the D-shaft look to the right side
- Align the marking dot of the lower gear exactly to the left side
- Align the marking dot of the upper gear exactly to the right side
- Make sure this position is kept, while the excenter and the excenter gears enter the ring gear
- Push the excenter onto the shaft until the motor shaft is max. 1.2mm above the excenter's endface (when pushing further, the excenter will start to touch the stepper motor inside the gearbox...)
- Add grease to the gears and to the holes for the pins
- Press fit the 5mm shaft into the output carrier (using the shaft-mask tool for perpendicular assembly)
- Press fit the 10 2mm dowel pins into the output carrier (the pin-mask tool and the pin-support-ring tool will help you)
- Assemble all the rest
Test & Validate
- Attached to an Azteeg X5, v1.1
- Motor current: 0.45A, 32 microsteps, 7000 E-Steps (400 steps/rev * 32 microsteps / 21 mm/rev * i=12:1 -> 7.314 steps/mm)
- Retract: 0.5mm, 5mm/sec
- Speed: up to 80mm/sec, 0.4mm nozzle, 0.2mm layer height, material: PLA, temperature: 210°C
- Testing: 10x10x5 blocks, Dia30 cylinders, some larger parts 2-3 hours each, in summary 12 hours printing
Results
- Works - has survived successfully test prints
- No lost steps while extruding and retracting during prints
- Motor temperature: approx. 50°C - the air shield seems to help
- Less waivy surface appearance than v0.2, but still not matching my Bowden setup
- No specific noise
- Loosing steps when manually extruding 5mm from the controller
- After disassembly:
- Grease without any worn-out particles, looks like new
- No wear on teeth, some surface flattening on pin holes but not wear
- Bearings still press fitted on the excenter and inside gears
- The excenter is hard to print, to prepare and to assemble
- v0.3 objectives met
Todo
- Go back to 16:1-ratio for robustness against loosing steps
- Improve fit of centering bearing on motor shaft: Gain axial space by using bearings without shields
- Review various smaller issues
Build v0.4
Objective | Design | BOM | Make & Assemble | Test & Validate | Results
Links
- The development history of the Cycloidal Extruder Drive)
- 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
- RepRap Forum: This engineer claims 100 grams direct extruder
- Build v0.3: Google Album
