The 00str00der is a belt-driven, 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 that grips 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 RepRap drive systems.
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 Sheliak X-Carriage design. Both designs are being converged (rev. C) and a mounting plate has been added to attach this extruder to carriages like [http://www.thingiverse.com/thing:18657].
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 up to 400mm/s. The 00str00der was first tested and proven on a PrismX 3D Printer in March, 2013 by Terawatt Industries. In April 2013 tests with the 00str00der on an h-bot in Bowden configuration were performed by Lee Miller. It performs exceptionally well in both configurations. On the PrismX it printed approx. 250+ hours total in March-April 2013.
I'll say qualitatively: it's difficult to drive a reprap (Prism, MendelMax, whatever) fast or hard enough to stress the 00str00der's drive system noticeably. During prints the nozzle experienced problems before we could drive our machine fast enough to stress the 00str00der 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 such as NEMA14.
- 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 1000s of kilometers and more.
- Set-screws on the GT2 pulleys work more effectively than most set-screws on printed gears. Last longer too.
- The ratio of gears can be adjusted. One-to-one (direct-drive) can be achieved with a set of 36T GT2 pulleys.
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: finding suppliers, specifications, availability, lead-time, etc.
|1||extruder idler block||RP|
We need to write specific assembly instructions. For now the best we have are some assembly guies based on earlier ancestors:
How to make the hobbed bolt
We've been using Terawatt Industries hobbed bolts for testing on this component, which is a M8x60mm bolt hobbed at 30mm from the head. 65mm+ 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 great.
If you don't want to purchase a hobbed bolt then Wade's_Geared_Extruder describes how to make your own.
- Rev. A: for use with h-bot in Bowden configuration
- Rev. B: for use with Prism/MendelMax machine; 3-point attachment to Sheliak x-carriage
- Rev. C: converges rev.A + B; testing started: for use with M4x50mm bolts on idler; potential revision on hobbed bolt and/or mount
3D CAD Files
The procedure 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 can use community-tested electronics to drive this extruder. Experimental electronics like 4Pi should work OK also.