The 00str00der is an belt-drive, gear-based, open-source extruder design intended for RepRap 3D Printers. It uses a precision linear drive system to drive a hobbed bolt (or similar drive system which can grip filament/material), which in turn supplies filament to a nozzle used for 3D printing. The inspiration and research for this work was a natural progression based on existing open-source designs and is a result of collaboration between Lee Miller and Terawatt Industries (Colorado, USA). It is based on previous geared-extruder designs such as Wade's Geared Extruder, Adrian's Geared Extruder, and others; as well as Terawatt Industries' experience with miniature linear-drive systems. This design has been tested, revised, and proven on a PrismX 3D Printer.
The designers first shared concepts for the component in 2012, and agreed to collaborate on design and testing in January, 2013. Lee Miller designed the first 00str00der for an H-Bot-style 3D Printer (TBA) with Bowden-style extrusion. Free Beachler of Terawatt Industries revised the design to work with a Prism (TW's PrismX RepRap) by supplying the FlatPlat X-Carriage design. Rev. B is compatible with the for use with H-Bot, Rostock, Prism, MendelMax, Prusa, and other reprap variants. Plans are being discussed to provide variations for 00str00der mounting on other x-carriages where feasible.
The 00str00der is designed to be affordable while offering greater precision, durability, and speed compared to extruder designs based on printed gears. It uses a small closed-loop GT2 belt to transfer power from a NEMA17 motor to a M8 hobbed bolt. GT2 pulleys are used on the NEMA motor and hobbed bolt to achieve an approximately 4:1 gear ratio. PLA and ABS filaments are driven by an M8 hobbed bolt, as is 'traditional' in the related designs mentioned here.
Terawatt Industries has tested and calibrated this component on a PrismX running at infill speeds in excess of 200mm/s and can confidently report that it performs exceptionally well. It was first commissioned on a PrismX on March 13, 2013 and printed for about 200 hours total in March, 2013. I'll say qualitatively: it's difficult to drive a reprap (Prism, MendelMax, whatever) fast or hard enough to stress the extruder's drive system heavily. During prints the nozzle experienced problems before we could drive our machine fast/hard enough to stress the extruder (or frame). During simple extrusion tests we hit speeds in excess of 1500mm/s; as noted before the nozzle shows problems performing at this speed.
The primary advantages to this design approach include:
- The belt-driven system is very smooth, therefore resistance in the drive system is decreased. The positive side-effects from this are several including: faster drive, more accurate drive, potential for smaller/cheaper/lighter motors.
- The belt-driven system can be precisely calibrated. Instead of marking filament and attempting to measure travel inside of the robot's gantry (frame), we can measure the width of the hobbed bolt, and use a calculator for the rest.
- The belt-driven gear system is very durable. Printed gears shed PLA/ABS material within 100 hours of printing. The belts and pulleys are rated for 10's of 1000s of kilometers. In practice, this has been quickly demonstrated by TW's "MendelMax 1.5 Stress Test" and its new PrismX machine.
- Set-screws on the GT2 pulleys work more effectively than most set-screws on printed gears.
Some disadvantages to this system include:
- The gears can't be printed, they must be sourced. This means we can't hack a new kind of herringbone gear and print/test it on an extruder. Purists will note, however, we can print decent GT2 pulleys in certain contexts...
- All the other disadvantages that come with using non-printed parts such as: sourcing suppliers, specifications, availability, lead-time, etc.
|1||extruder idler block||RP|
|1||65T Plastic GT2 Pulley, 8mm bore, 2mm pitch, 6mm width||Drive System||8mm bore for hobbed bolt; metal pulleys also work|
|1||17T Plastic GT2 Pulley, 5mm bore, 2mm pitch, 6mm width||Drive System||5mm bore for NEMA motor; metal pulleys also work|
|1||GT2 Belt, 98T, 198mm length, 2mm pitch, 6mm width||Drive System||+/- 1 tooth works OK|
|2||608 bearings, skateboard bearings||Bearings|
|1||M8×55 bolt (50mm works)||Fastener||to be hobbed, M8×60 has a longer smooth part, allows a second lock-nut, and may be easier to find|
|1||M8 nylock nut||Fastener||Nyloc works better, but a pair of nuts will also work|
|4-5||M8 washers||Fastener||to space the large gear clear of the motor retaining bolt heads|
|1||608 bearing, skateboard bearing||Bearings|
|1||M3×30 socket-head cap screw||Fastener||mount idler arm to extruder block|
|2||M3×50 or M3×45 socket-head cap screws||Fastener|
|3||M3 nuts||Fastener||one (1) for block mount|
|5||M3 Fender washers||Fastener||one (1) for block mount; standard washers will work|
|2||~4mm ID springs||Spring||Sized to fit over an M3/M4 bolt, unsprung length of 10-12mm, each spring providing 25-35N load. For a given filament drive force, you'll need about twice the spring force - i.e., if you want 100N of filament drive, your springs need to push with about 50N each.|
|NOTE: Some users have their extruders working without springs, but springs are recommended. A good source for these springs is in the cloth-cabinet on spring loaded skirt-hangers or trouser-hangers. Just cut the right length off the springs.||'Hotend Mount|
|NOTE: The only current tested hotend mount is the j-head style mount reflected in the SCAD/STL files for the extruder block.|
|Stepper Motor Mount|
|2||M3×12 bolts||Fastener||Low profile bolt heads might work better here|
|2||M3 Fender washers||Fastener||std. washers will work|
|2||M3 lock washers||Fastener||optional - resists vibration|
|1||NEMA 17 bipolar stepper motors||Stepper||0.49 Nm (69 ozf*in) works well. We've been using the Stepper Motors from Terawatt Industries and it appears to be much more force than necessary. Should be capable of creating a holding torque of at least 0.4Nm (56.6 ozf*in), at the very least.|
|3||M4×20 bolts||Fastener||The FlatPlat X-Carriage has a three-point mounting system for this extruder.|
|3||M4 nuts||Fastener||x-carriage mount|
|3||M4 washers||Fastener||x-carriage mount|
|3||M4 lock washers||Fastener||optional - x-carriage mount|
How to make the hobbed bolt
I've been using the Terawatt Industries hobbed bolt for testing on this component, which is a M8x50mm bolt hobbed at 30mm from the head. It works OK; however 55mm+ works slightly better with the current (Rev. B) extruder block design. We're considering a few options around modifying this, including using a non-threaded M8 rod or other machined options; but currently the 'traditional' hobbed bolt works.
If you don't want to purchase a hobbed bolt then [Wade%27s_Geared_Extruder] describes how to make your own.
- Rev. A: for use with h-bot
- Rev. B: for use with Prism/MendelMax machine; 3-point attachment to FlatPlat x-carriage
- Rev. C: planned: for use with M4x50mm bolts on idler; potential revision around threaded hobbed bolt
3D CAD Files
The design files for the latest version can be found on Github at (link).
The formula to calibrate the 00str00der is as follows:
- Measure the O.D. of the knurled (hobbed) area of the M8 hobbed bolt, preferably with digital calipers. The exact OD will depend on things like manufacturer and batch.
- Calculate the gear ratio between small and larger gear.
- Find the step angle for the motor - most common NEMA17 motors are 200 steps per revolution.
- Find the microstepping value supported by your stepper drivers. This usually depends on brand of driver and type of control electronics.
- Use the following formula:
steps_per_mm = (gear_ratio / (hobbed_bolt_OD * Pi)) * ((360 / motor_step_size) * (1 / driver_microstepping))
- A hobbed bolt where the knurled bolt measures 7.52mm in outer-diameter (O.D.)
- The gear ratio for a 17-to-65-tooth gear system is ~3.8235. In other words, ~3.8235 revolutions of the smaller gear equal one revolution of the larger gear.
- NEMA17 motors are common with 1.8 step angle and RAMPS 1.4 with pololu drivers supports 1/16 microstepping.
steps_per_mm = (3.8235 / (7.52 * 3.1416)) * (360 / 1.8) * (1 / 1/16) = 517.8957 ~= 517.9
You should be able to use [] to drive this extruder.