CycloidalExtruderDrive-History
Revision as of 17:15, 3 June 2016 by Powdermetal (talk | contribs)
This page conserves the development-history of the Cycloidal Extruder Drive.
Build v0.1
Objective
Quickly check general feasibility using some existing components:
- StepperOnline Nema 8 Bipolar 0.6A 4Ncm(5.7oz.in) mini stepper motor 8HS15-0604S
- MK8 Drive Gear
- E3D v6 HotEnd - 3mm Direct (12v)
Design
- Gearbox ratio: Some simple engineering calculations based on required feed-forces for 3mm filament and comparisons with existing extruder solutions propose for the 4Ncm stepper a gearbox ratio of approx. 20:1. Having an existing CAD model of a small cycloidal gearbox with a ratio of 36:1, this one was simply adopted.
- STEP-files of the assembly with detailed components, simplified geometry for the core parts (for simplifying mods) and some tools/jigs which help you to assemble this thing: Media:CycloExtruder v01.zip
BOM
- Printed parts
- 1 x StepperOnline Nema 8 Bipolar 0.6A 4Ncm(5.7oz.in) mini stepper motor 8HS15-0604S
- 1 x MK8 Drive Gear
- 1 x E3D v6 HotEnd - 3mm Direct (12v)
- 3 x MR105-ZZ (5x10x4mm) Ball Bearings
- 2 x MR128-ZZ (8x12x3.5mm) Ball Bearings
- 1 x 5mm Stainless Steel Precision Shaft (or a 5mm aluminium shaft from your local hardware store - make sure you go shopping with your caliper: 4.97..4.99mm is sufficient if you are on a hurry)
- 12 x DIN6325 2x10 Steel Dowel Pins
- 4 x DIN912 M2x4 Hex Socket Head Cap Screws (for fixing the stepper)
- 2 x Springs
- Various DIN912 M3 Hex Socket Head Cap Screws
Make & Assemble (not easy...)
- Print the parts: PLA, 2 perimeters, 100% infill, layer height 0.1mm, go slowly for the gears (15mm/sec or less)
- Tune the excenter's bore to make it go gently (!) over the motor shaft and you can remove it gently again (this is a design weakness...)
- Tune the excenter so you can assemble the bearings smoothly
- Press fit the bearings into the excenter gears, push them over the excenter
- Bolt the ring gear with the M2 screws to the stepper
- Mount the excenter/excenter gears over the motor shaft as follows:
- Make the D-shaft look to the left side
- Align the marking dot of the lower gear exactly to the right side
- Align the marking dot of the upper gear exactly to the left side
- Make sure this position is kept, while the excenter gears enter the ring gear
- Press fit the 5mm shaft into the output carrier (using the shaft-mask tool for perpendicular assembly)
- Press fit the 12 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: 0.55A, 32 microsteps, 10500 steps/mm
- Retract: 0.5mm, 5mm/sec
- Speed: up to 80mm/sec, 0.4mm nozzle, 0.2mm layer height
- Did some very basic tests (10x10x5 blocks, Dia30 cylinders), in summary 1 hour printing
Results
- It prints
- No lost steps while extruding and retracting
- Some waivy surface appearance (compared to Bowden setup), probably related to poor tolerances
- Motor temperature: reasonable warm
- No specific noise
- No signs of gear wear after tear down - some normal surface flattening, running without grease
- Works basically - v0.1 objectives met
Todo
- Rethink the assembly process - it's a real pain
- Switch to a more effective 14HR05-0504S stepper recommended by Chri and others
- Evaluate tolerance stackup
- Switch to a hypocycloidal profile - build v0.1 uses arcs
- A lot more...
Build v0.2
Objective
- Gain further weight-saving by using the more effective 14HR05-0504S stepper
- Redesign gearbox for this motor and include some minor improvements
- Keep as many v0.1 components as possible
Design
- From the motor characteristics, a gearbox ratio 12:1 was calculated. However to keep the v0.1 output hub, a ratio of 16:1 is implemented
- No of teeth: 16, eccentricity: 0.8mm, radius: 17mm, roller radius: 1.5mm
- Tooth clearance tightened from 0.2mm (v0.1) to 0.1mm, aiming for less waviness while keeping printability with FDM machines
- STEP-files of the assembly with detailed components and simplified geometry for the core parts (for simplifying mods): Media:CycloExtruder v02.zip
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
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