Written by Sam Theobold
Roto: Unlock additional performance from your printer with Roto. It’s all the extruder you need without unnecessary bulk.
TL;DR: Building upon decades of extrusion system expertise, E3D has produced a featherweight all-in-one extruder that outperforms competitors for power density and thermal efficiency. This enables you to push your printer’s speed without sacrificing quality. Oh, and did we mention the Heatsink is 3D printed in aluminium?!
At E3D we are firm believers that you should not be throttling your hotend’s performance with an extruder that cannot keep up because of insufficient extrusion force. We've seen this happen more and more in the industry as people seek to cut out as much mass from their extruder as possible. So, when we set out to make our next evolution of extruder, we knew this would not be acceptable.
However, required extrusion force cannot simply be summed up to a single number, many factors affect this requirement such as hotend choice, nozzle diameter, filament choice (and how dry it is), poor part cooling system that cool your nozzle, bowden tube drag, spool holder drag, track width/height, (momentary) filament clogs, the list goes on and on. So why not just make an extruder with LOADS of power? Well, if you ever get the chance to drive a supercar round windy Oxfordshire back roads, you’ll soon realise you’re going just as fast as someone in a smaller, lighter sports car. Essentially, don’t carry around unnecessary bulk! As such, E3D has spent a long time evaluating these factors to ensure that we could tailor Roto’s performance to suit. To do this we worked out the critical force for a range of filament and hotend combinations, which we used to build a cloud of data points and then ensure Roto's output covered all the bases.
So, what does this mean in numbers, Roto comes in at 140g whilst outputting 70N+ of extrusion force. Pair that with a 18g Revo hotside and you have the lightest AND most power-dense extruder available. For reference, most X-carriage motors come in around 280g so this is HALF the mass of a single Nema 17 motor (sadly no banana for scale here).
To achieve this, we have paired a small but powerful Nema 14 motor with an 11.262:1 gear ratio. This custom motor provides the Goldilocks balance between performance and mass. The gearing is comprised of a planetary initial stage followed by a spur secondary stage with a dual hobb third stage. This was found to be the optimum pairing while not falling off the end of the stepper motor’s torque-speed curve. Now this might sound like a very high gear ratio, but this brings me onto an important point related to the fact 3D printing is still in its infancy (in the grand scheme of things) and as such there are next to no standard ways of characterising products. The gear ratio of your drivetrain on its own is sadly insufficient as it omits a key aspect: the effective additional ratio from your hobb diameter. What you actually care about is your output filament force, not hobb torque. For example, if you double the size of your hobbs without changing your gearbox or motor, you have halved your output force, which, due to the points made earlier about extrusion force, is not ideal. Therefore, we have coined the term Torque to Force Ratio, or TFR for short so that you can compare apples with apples when evaluating extruders. To calculate this, simply divide the stated gear ratio by half the working diameter of the drive hobb in mm, this gives Roto a TFR of 2.72:1. For reference, Hemera has a TFR of 0.80:1 and Titan has a TFR of 0.84:1.
Roto has also been designed to tend to stall the motor rather than strip the filament, which I’m sure you will appreciate is a much better result if something such as a snag on your filament was to occur – no need to strip and clean your extruder, just resolve the issue and continue extruding. Due to fact that there are thousands of filament types on the market, there are some filaments such as PVA support that are too soft for this to be the case. However, that’s where the ease of maintainability comes into play; three bolts is all it takes to remove your heatsink and entire filament path whilst leaving the body of your extruder mounted in place.
Did someone say 3D-printed Heatsink?
Yep, that’s right. We are 3D printing Roto’s Heatsink from Aluminium, in production and at scale using SLM technology. E3D’s core goal is “changing the way that humanity manufactures goods”, and in the essence of practicing what you preach, we have created the world’s first 3D-printed direct-drive extruder heatsink. Here it is in all its glory.
3D printing gives unparalleled design freedom, which means beyond the obvious cool factor of using this technology, we have been able to highly optimise this design. Minimised wall thicknesses and skeletonised areas mean the Heatsink is as slimmed down as possible. This has not been done at the sacrifice of performance though, in fact this is the most thermally effective heatsink we have ever produced; it’s even been able to print a torture test of back-to-back retractions for 24 hours with PLA while being in an ambient temperature of 40°C!
There are three key aspects to the heatsink design:
When designing an optimised heatsink, one area that can often be overlooked is preventing heat from getting into the heatsink in the first place. This is where the novel AirBreak design comes in. We divert a small amount of air from the fan back around and under the heatsink, which shields it from the brunt of the convective heat transfer from the hotside. There is only a small amount of airflow here so don’t worry, there’s no negative impact on your print/part cooling set ups.
360° HeatBreak Cooling
One benefit of more traditional turned heatsinks is that you can get airflow around 360 degrees of the part, giving more surface area close to the interface with the heat spreader and improving cooling performance. The flexibility of the 3D printing process enabled us utilise this same approach in an integrated heatsink. This is a marked improvement over previous integrated extruder heatsink designs where the heat must be moved through the heatsink before its removed through fins or pins - usually from only one side of the heatbreak.
For unwanted heat remaining in the system, we have a skeletonised front structure that the fan blows through. This has the added benefit of keeping the area around the hobbs cooler, which stops the plastic softening and enhances your grip. It also means your system is nice and quiet as there is minimal back pressure.
Ease of Use
Here at E3D we want to make your 3D-printing experience as enjoyable as possible and as such, the products you interact with should be intuitive, simple and designed to remove potential pain points. This is why we came out with the revolutionary Revo ecosystem to remove the tricky hot-tightening process and make swapping nozzles a quick and simple process. Roto is no different, we have spent a lot of time working towards this goal, as you will see below.
Bi-Stable Idler Mechanism
Manual filament changes on extruders with sprung idler mechanisms can be a pain as you have to hold the idler back against the spring force to disengage the hobbs, taking care not to put too much force through your toolhead carriage, and then feed the filament with your free hand. To improve this, we have designed a one-piece idler with a flexible latch that holds the idler out of the way while you swap filaments. But don’t worry, this flexure arm isn’t going to fail on you, we have tested this to over 16,000 cycles with no degradation in function – in fact it managed to outlast the test rig… For perspective, that’s a filament change every day for the next 43.8 years!
To do a filament change you clip the idler over a matching feature on the heatsink, which disengages the idler hobb from the filament. You can then simply pull out any previously loaded filament present and then insert your next spool, all with only one hand. To re-engage the idler hobb you just need to pinch the latch and the main body of the idler together and it will spring back into position. It also makes an incredibly satisfying click to top it off. We have also removed the idler tension adjustment you have seen on our previous extruders, but don’t worry, lots of testing went into this decision (as you would expect from E3D!). One of the most common issues our customer service team encounters is the idler tension being incorrectly set; either way too loose or way too tight. This is not always intuitive for new users getting into FDM. In keeping with the theme of Roto and making the user experience as smooth as possible, we set out to see if we could improve this. What we found through extensive force profiling of Roto was that there was a (relatively) wide band of spring forces that produced the optimum force output. This is due to the trade-off between grip and drivetrain efficiency. The easiest way to visualise this is at the extremes: if you have next to no spring force, you cannot grip the filament and the hobbs slip; if you have excessive spring force, then you have created a highly inefficient drivetrain which creates losses in output force. This knowledge, paired with the manufacturing tolerances we can achieve, meant that we have been able to remove the need to adjust spring force, which was again backed up by further print testing with countless filaments including TPUs.
Roto is compatible with the entire Revo nozzle range meaning you can swap from brass to Obxidian to high flow and everything in between with ease. But that doesn’t mean Roto is locked to the Revo ecosystem, you can throw a bowdaptor on there to use in a short Bowden set up such as in the Stealthburner mount, or with a Hemera heatbreak you can use V6, Volcano or any other compatible hotsides.
We have incorporated a variety of sensor options to pair with Roto to make your printer smarter and more reliable than before. These upgrades give additional avenues for print monitoring and failure detection so you can print with confidence.
3-Wire Tacho Fan
A 3-wire tachometer fan enables your printer to detect if your fan is spinning so that it can automatically pause your print if your fan, wiring, or control board get damaged. This prevents these failures from causing filament jams due to heat-creep.
We have placed a heatsink thermistor right by the filament path so you can get accurate readings for what filament temperature in your hot-end’s cold zone. You want this to stay below the glass transition temperature of your filament otherwise this can lead to extrusion issues. Say you’re printing PLA and forget to leave your printer's doors open, your fan may be spinning but your ambient temperature could creep up and lead to a jam. However, with a heatsink thermistor your printer can detect that the coldside is too hot and automatically pause your print before you see any issues.
We are very happy to announce that we have been working with two great partners to create CAN-FD/USB toolboards which bolt directly to Roto and are compatible with all the integrated sensors mentioned above. Both toolboards feature accelerometers to allow for accurate input shaping calibration.
Duet3D have come up with an option for the RepRap machines out there. Featuring everything you have come to expect from a Duet3D toolboard with additional support for the new Z scanning probe. The board has been designed to take the standard Roto connectors for the motor and fans, plus a Revo HotEnd, making it an easy addition. Further details can be found on Duet3D's website.
LDO motors have come up with an option for the Klipper machines in the form of a USB toolboard. It will have everything needed to connect a Revo Roto with all the additional sensors. More details will be available soon from LDO.