Introducing Lix, the world’s smallest 3D printing pen that allows you to draw plastic structures in 3D. It’s only been on Kickstarter for a few days now, and already it has garnered close to a million dollars in pledges. An astonishing achievement, especially considering we can prove – with math and physics – that it doesn’t work as advertised. However, we’re wondering if it could work at all, so we’re asking the Hackaday community.

The device is powered through a USB 3 port. In the video, the Lix team is using a MacBook Pro. This has a USB port capable of delivering 900 mA at 5 Volts, or 4.5 Watts. Another 3D printing pen, the 3Doodler, uses a 2A, 12V power adapter, equal to 24 Watts. Considering the 3Doodler works, and they both do the same basic thing, there’s something extremely odd going on here.

Just as a comparison, here’s a wirewound resistor commonly found in the heating element or ‘hot end’ of a 3D printer. It’s a 6.8  Ohm resistor powered at 12 Volts. That’s 21 Watts. Here’s a heater cartridge, also found in quite a few hot ends. It sucks down 40 Watts. Once again, the Lix Kickstarter clearly shows the pen extruding filament using only 4.5 Watts of power. Something is really, really fishy here.

Intuition doesn’t hold a candle to math, so let’s figure out exactly why it won’t work.

We’re thinking the easiest way to figure out if 4.5 Watts is enough for a 3D printing pen is from a purely thermodynamic analysis: a specific amount of filament goes in, is heated up to its melting point, and is squeezed out of the nozzle. The equation to calculate how much energy is required for a specific temperature change in a system is Q = cmΔT, where Q is the amount of energy in Joules, c is the specific heat of ABS (1.3 J/g°K, source), m is the mass in grams, and ΔT is the change in temperature. All we need to do now is figure out how fast this pen is extruding, and the mass of that extruded filament.

In this video, starting at 10 seconds in, you see the Lix extruding about 13 centimeters of filament through the 0.6mm nozzle included with the Lix in five seconds. A little bit of math happens (volume of a cylinder with a height of 13cm and a diameter of 0.06 cm), and we can figure out the Lix is extruding 0.038 grams of filament per second (ABS density of 1.04 g/cc, source). This calculation was done by counting pixels and frames, which can be inaccurate, but not by much.

An estimated 0.038 grams of filament extruded per second, a change in temperature of 210°C (20°C room temperature, 230°C extrusion temperature), and a specific heat of ABS of 1.3 J/g°C (source) means 10 Joules are required to extrude one second’s worth of filament from the Lix pen. Since 1 Watt = 1 Joule  for 1 second, about 10 Watts are sucked down whenever the Lix is extruding filament. Once again, the Lix can only draw 4.5 Watts from a USB 3 port. The math simply doesn’t work, and no USB 3 powered device can extrude ABS filament that fast. The math is also generous, as it doesn’t consider the phase change of the filament which would require even more energy. I didn’t include this because I can’t find a reference for the heat of fusion for ABS. The math also doesn’t consider losses to the heater block, the air, and a host of other inefficiencies in any real-world device.

But ABS requires a fairly high temperature to extrude. Even though the Lix team claims the pen works with ABS, let’s say they’re using PLA plastic, extruded at 180°C. Doing the math for a ΔT of 160°C means 7.9 Watts are sucked down from a USB 3 port that can only provide 4.5 Watts. Something is terribly wrong here. That’s why we’re turning to you and asking the rest of the Hackaday community.

The only way we can figure the Lix actually works is if the extrusion rate is really, really slow. Halving the extrusion rate of PLA to 1.3mm/s gets us into the ballpark of what the Lix power supply can do; that only requires about 4 Watts, leaving enough left over to run the motor and electronics inside the pen. This is exceptionally slow for any plastic extruder – RepRaps can extrude plastic about 50 to 100 times faster. There’s a good bit of evidence the video of the Lix has been sped up dramatically, given the disclaimer, “some of video scenes have accelerated speed” appeared on the Kickstarter sometime between the first and second day of the campaign.

While we know the video is an outright misrepresentation of what any USB 3 powered device can do, We can’t figure out if the Lix is a viable product. We’re turning to you. Can you figure out if the Lix pen actually works? All we know is the Lix pen has a 4.5 Watt power supply from a USB 3 port. It’s possible for a USB 3 powered 3D printing pen to work, albeit slowly, but the engineering is difficult and we don’t know if the Lix team has the chops.

* For the hardware heads out there, yes, I know there is a USB 3 spec  – the USB Power Delivery Specification – out there that will supply up to 100 Watts through a USB port. Apple does not support this spec in any of their products, and the Lix Kickstarter video uses a MacBook Pro for power. The maximum amount of current the Lix can draw from a MacBook is 900mA, and the Lix has a power budget of 4.5 Watts. There really is no arguing that fact.
As an aside, this post has inspired us to consider a column on Kickstarters that seem to defy the laws of physics. We’re thinking about calling it Kickherder, as the vast majority of Kickstarter backers for these types of projects are mindless sheep. If you have a better name, leave it in the comments.

## 281 thoughts on “Ask Hackaday: Can The Lix 3D Printing Pen Actually Work?”

1. HighSpeed_LowDrag says:

This thread was emailed to me to see if it made sense, and I feel I need to point something out.

Has anyone checked the math?? if you extrude 13cm in 1 second and using all the values listed in this thread, then the math checks out and you would need roughly 10.5 Watts to power this device. However, since it was claimed that the device extruded 13cm “in 5 seconds” ( you see the Lix extruding about 13 centimeters of filament through the 0.6mm nozzle included with the Lix in five seconds) then you would take that length and divide it by the time to get the approximate extrusion speed which would be 2.6 cm/s. Using this value and the Specific Heat and Density in this thread, one obtains that the device only needs 2.08 Watts of power which is definitely capable from a USB port.

However, recently the LIX creators stated (in the comments section on their kick starter page) that their device currently extrudes at 6mm/s. Using this extrusion speed and the maximum density (1.08 g/cc) and specific heat (1.675 J/(g*K)) from the sources provided in this thread (as margin); then one easily obtains a mass flow rate of 0.001832 grams/second. This equates to a power draw of only 0.6444 Watts!!! Using the USB port at maximum 900mA rating means that only a 0.716 voltage would be required.

Clearly this device can work off a USB outlet.

2. Meisam says:

As it can be seen in DSC curves of ABS analysis, fusion enthalpy of ABS polymers are negligible. Because, they usually are amorphous and do not contain any crystalline part to have a exact melting temperature and correspondingly heat exchange in form of fusion enthalpy.

http://www.sciencedirect.com/science/article/pii/004060319180242B

Given how long this post is I’m sure this has been mentioned but I’ll say it anyway.

2 methods to make this device work are:
1. Preheat all the filament to near melting.
2. Don’t actually get the plastic to melt, just get it near the transition temp where it’s gooey and flexible. A second button for melting would allow you to extrude small ammounts of melted plastic to weld joints.

4. JoeM55 says:

The way the video looked to me is it was a time lapse, can see shifts of the hand and pen.

5. Guest says:

“Lix has a hot-end nozzle that is power supplied from wall charger. “

1. Dougmsbbs says:

They added the ‘supplied from a wall charger’ after this discussion was started. Before that all they had was that it was powered from a USB port for maximum portability. It’s a shifting target…

6. It could work with black heatglue, but even the smallest heatgun uses 10W.

7. jake says:

Besides the power supply problem could anyone tell me if the pen would be possible if it was powered by something a little more heavy duty (whether it uses a USB or not doesn’t really matter much from my point of view)
This video is showing a previous version of LIX PEN
Beside new video of LIX PEN presented and it is available on lixpen.com
New demo video of this product will be available soon

Could anyone also tell me if it’s possible for a heated extruder and a speed regulator to fit into a regular pen body and if a printed filament could actually become solid in the time that’s shown in the video or if the video is maybe sped up?
would appreciate any feed back, even if its just direction to another comment/post as i haven’t read all the comments above either.

P.s. could someone translate this for me please:

Disclaimer at start of the LIX PEN ad