More opinion about custom 3D printed Technic parts

[896gerard]

Dear readers, 

For a new project that started a while back (about a year ago), I was investigating a certain track configuration for a tracked vehicle. It pointed out that I needed a lot of ground clearance from the track wheel, but the track wheel could not be two studs wide: the tracked vehicle is only 15 studs wide and a lots of gears, motors and linkages need to be in between. 

As you can see, the standard wheel above is two studs wide due to a ring of 1/2 a stud that supports the track. This ring is not always necessary. In fact, the tracks barely even touch this ring under normal driving. A lot of you will recognize the difficulty with this wheel: it protrudes half a stud to both sides. In many designs, the number of horizontal studs is uneven: an M motor, XL motor, frames, differential, everything has an uneven width when measured in studs. This enables a symmetrical design as Lego Technic has no beams with even lengths (only 3, 5, 7, 9 ..). That's why many Technic designs of this day are an uneven number of studs wide. This is in contrary to the olden days, where all Technic components and widths were even. Check for example the old style liftarms, differential, frames, motors and even battery boxes. 

With this theory lesson over, it is easy to see why this track sprocket introduces a problem: when the wheel is mounted in the uneven Technic system (to get a nice symmetrical design with uneven Technic beams), the wheel size is even! So the wheel can not be connected to a liftarm at the place where the axle connects to the wheel. There needs to be a distance of 1 stud to any supporting liftarm. This is mostly done with a bush or a 3L thick liftarm. This also means that to mount this sprocket very strongly, the minimum width of the structure (when fit in an uneven system) is 5 studs. Then I started thinking: how nice would it be if there would be NO distance to any supporting liftarm? In that case, the sprocket has to be only 1 stud thick and the supporting structure is only 3 studs wide. Also, the support ring has to go. This is an enormous space saver when the maximum width of your vehicle is 15 studs.. 

I decided to draw the part in Solidworks and print it with my own 3D printer. Out of curiosity, I checked GrabCad to check whether someone got the same idea too. To my amazement, somebody had already tried this part,  

with the internals to be the 40 teeth gear. This is done with a reason. A standard 3D printer is generally very bad at printing axle holes. If you draw the outline of a standard Lego Technic part (that has a nice axle hole) into your 3D printed part, the part will be connected firmly inside the model(nice) while the axle is inserted into a Technic part, so no troubles with cracking plastic will occur. In short, I printed that part. It didn't work. (See image below). It turned out that every 3D printer is a little different. A tiny offset can cause a diameter difference, which then will cause friction, because the track doesn't fit around. The wheel needs to be perfect to make the solution work. 

That's why I decided to design my own custom sprocket wheel from scratch.

This was my first 'from scratch' attempt. As you can see, the pin and axle holes do not have great quality. A revised 3D design is in the image below. As you can see, there is a large hole in the middle. This hole fits two 4185 pulley wheels (shown right) very tight. This means the vehicle is connected to a nice and round axle hole, while the 3D printed part is also fit very well to the vehicle. The sprocket diameter is not arbitrary as the number of 'lobes' is fixed: there are no half lobes, otherwise the wheel won't work.. That means that for the same tracks, a limited number of wheel diameters exist.

As you can see, there is a slight ring in the 1 stud wide sprocket wheel, not all track support is gone.

The 3D printed results:

                                                           

I was really happy with the quality of this wheel, the drawbacks from 3D printing don't show up and the wheel is very strong and straight. In the image below, is is visible that the tracks fit very smoothly around without additional friction. It is also visible that the wheel is just as wide as two pulley wheels, so one stud. 

                      

I was so amazed when the 42095 set was launched. There was my not-published-about part, exactly the same size, in a real Technic model! And now there will be 4 DBG ones in the 42100 Liebherr, which will drop the price. There is one 'slight' drawback though. My 3D printed wheel is only one stud wide, needing only a frame of 3 studs wide to support it. The new 42100 sprocket wheel has the 1/2 stud ring protruding out of it on both sides, taking the drawback of the old wheel onto the new wheel. That's a pity. It could have been so nice.  

Then comes the question: why would you 3D print parts? That's cheating. And I agree. It is cheating. I never do this in my models. You are allowed to check my YouTube. I even built of a 3D printed way of getting three axles through a Lego Technic turntable but never used the solution as I do like pure models. Then, why am I doing it now? Because currently, I'm using Lego Technic as a strong platform for a scale model that requires 100% of the quality of Lego Technic, but cannot do without adding custom parts. Even the most skilled builder cannot work his way round sprocket wheels that don't exist. That's why I see it as an engineering project, and from that prospect, creating your own parts (when all else fails or doesn't exist!!) does not show lack of skill but broadness of view.. 

Surprisingly, some other minds thought alike and brought a Lego Technic wheel of the same size on the market. Too bad.. Let's start building and stay thinking!

 

 

 

 

Edited June 18, 2019 by 896gerard
added photo's of 3D printed parts

[Toastie]

On ‎6‎/‎17‎/‎2019 at 5:41 PM, 896gerard said:

That's why I see it as an engineering project, and from that prospect, creating your own parts (when all else fails or doesn't exist!!) does not show lack of skill but broadness of view.. 

I fully agree with your thoughts and your approach. TLG is "inventing" parts as >they do see fit for their projects< - uhmm - products. I don't see any reason (at all!) why a skilled individual as you are should not take the exact same route. This is creative. It is the core of the matter. TLG tells us how creative their approach is. Well, you are as well!

Best
Thorsten  

[Roadmonkeytj]

There will always be this debate ... But at the end of the day models that generally keep with the "spirit" of lego are accepted those that do not are generally shunned.  I admire the look of your sprocket.

[896gerard]

2 hours ago, Roadmonkeytj said:

There will always be this debate ... But at the end of the day models that generally keep with the "spirit" of lego are accepted those that do not are generally shunned.  I admire the look of your sprocket.

That's why I posed it as a debate in the first place. Again, it depends on the goal that needs to be achieved with your MOC. For most MOCs, the goal is 'use only Lego pieces'. But why is (for example) the S-brick/ or alternatives so broadly adopted among Technic builders? Because it is a way better solution than any solution that Lego has come up with. I'm currently building a model for which the goal 'use only Lego pieces'  is simply not good enough. The concept of many small pieces to build a working scale model is very strong. Lego pieces have also a very high quality and finish, much better than any 3D printed part. But Lego Technic parts have their limits. And that's why I (a builder who normally finds purity so important) for one single time choose to make a MOC that uses the  'use only Lego pieces'-spirit for 95% of its parts and use much better parts for the remaining 5%. This design philosophy does not disprove, but enforce the Lego Technic platform, as it shows how a very strong concept deserve specific parts that are engineered with much better specifications. 

It is like using non-Lego wheels for offroaders or a custom machined steel turntable for very heavy cranes. Other builders do that. Do they do that because they are non-purists? No. The rest of their machines is mostly impeccably engineered to use 100% Lego parts. They choose it because it lets their machine shine. And shine is what we so hardly need, because other adults (from 'the real world') don't know a thing about Lego Technic building and about parts purity and the lot. They are driven by amazement only, which is not linked to parts purity at all. 

There are much more adults who admire engineering over parts purity. I have that experience in my talks to some companies around me that are convinced of the Lego platform and asked for models! 

[Erik Leppen]

Indeed, those extra half-stud-width rings on both sides of the official sprocket seem to have little function, and your explanation on the disadvantages is very clear. I hope Lego one day adopt your improvement. I'm actualy kind of surprised it works so well with the wedge-belt wheels, since you rely on friction alone there.

Edit: I'm very purist, and I can stand 100% behind your argumentation above.

Edited June 19, 2019 by Erik Leppen

[Lipko]

To the even uneven thing: Old style beams have uneven number of holes too. The new style beams are like old style beams, without studs. So if you look at the holes (which is essentally what Technic is about), you are not right and there was no paradigm shift.

Holes are uneven for a very simple reason: most machines are simmetric and very probably have center shafts somewhere inside.

The even vs uneven problem is only a ""problem"" if you mix studded with studless, for example studded body on a studless chassis.

Edited June 19, 2019 by Lipko

[Lakop]

It's an interesting debate that will always divide opinion. We could look at it in a different way, you are not printing lego parts. You are creating/printing your own parts to assist in building a model with predominantly lego parts. I think as long as the builder/moc creator is honest and shows the parts they have created then its ok by me. I personally like the challenge of using lego parts in different ways and learning. If you make your own gears, sprockets or pneumatic solutions (including LA's) it might be more accepted than if you were making your own bricks (which might get you in court or worse).

Your sprocket is very good so keep at it.

H

[896gerard]

13 minutes ago, Horace T said:

It's an interesting debate that will always divide opinion. We could look at it in a different way, you are not printing lego parts. You are creating/printing your own parts to assist in building a model with predominantly lego parts. I think as long as the builder/moc creator is honest and shows the parts they have created then its ok by me. I personally like the challenge of using lego parts in different ways and learning. If you make your own gears, sprockets or pneumatic solutions (including LA's) it might be more accepted than if you were making your own bricks (which might get you in court or worse).

Your sprocket is very good so keep at it.

H

 I agree, honesty is very important here. That's why I don't want to sell these parts: I have a purist heart and know myself to only use these pieces when nothing else works and know myself to always communicate the use of custom parts. Other builders might not have the same intentions and use the parts only because it needs a lower skill level. That is not my goal. 

[896gerard]

Regarding this debate, I have another question. (Still for the ultimate model I was talking about) I need a crane outtrigger with an extension of 100 millimetres, two studs wide and strong enough for a 2 kg model. The biggest concern to build this with Lego is that there are no gear racks long enough and small enough to fit within a two studs wide outtrigger. Lego Technic has seen this problem and come up with a part, but the extension is too small for my application. Also, the 18940 part requires an axle leading to the top of it for a powered extension. A a very visible axle does not help with getting a nice visually appealing scale model. 

Therefore, I decided to take up the gauntlet and start desiging this part for myself. The tried-and-tested prototype is below. 

 

 

This structure can support 10 kgs of weight (tested) and allows a very smooth extension of >100 mm. A big advantage of designing parts myself is that I can adjust the size anytime I want. And this is the time where I need some opinion on this. Is there a Technic way of doing this? Maybe I didn't think of something. I want to exhaust all options before using a non-Technic part inside a Technic model. 

[powerwindows83]

On 6/19/2019 at 6:06 AM, 896gerard said:

Lego Technic has seen this problem and come up with a part, but the extension is too small for my application. Also, the 18940 part requires an axle leading to the top of it for a powered extension. A a very visible axle does not help with getting a nice visually appealing scale model. 

 

maybe if you put two in a row somehow? also if the axle itself isnt a design issue but the visibility of it is, could you cover the entire exposed length with red axle sleeves to cover everything but the worm gear(s)? just an attempt at keeping to vanilla lego

[896gerard]

I have done a lot of tests on the above outtriggers with linear actuators and the internal clutches kept engaging. Then I tried pneumatics and the air escaped from the hose fittings, while at the same time my tiny onboard compressor couldn't create enough pressure. 

The only solution: an entirely new linear actuator, fully developed in house, made to be fully compatible with Lego Technic electronics. This was a complete new experience for me and I learnt a lot in the process. The cilinder gets SLS printed and has full metal mechanics inside, much higher specced than the usual Lego Technic linear actuator. I'm excited about this new cilinder. Soon, the large actuators from the Lego 42100 Liebherr Excavator will be available. Cannot wait to setup a comparative test! 

 

 

[agrof]

That looks really exciting project, any chance to take a look at the internals? 

[Bartybum]

On 10/2/2019 at 1:27 AM, 896gerard said:

I have done a lot of tests on the above outtriggers with linear actuators and the internal clutches kept engaging. Then I tried pneumatics and the air escaped from the hose fittings, while at the same time my tiny onboard compressor couldn't create enough pressure. 

The only solution: an entirely new linear actuator, fully developed in house, made to be fully compatible with Lego Technic electronics. This was a complete new experience for me and I learnt a lot in the process. The cilinder gets SLS printed and has full metal mechanics inside, much higher specced than the usual Lego Technic linear actuator. I'm excited about this new cilinder. Soon, the large actuators from the Lego 42100 Liebherr Excavator will be available. Cannot wait to setup a comparative test! 

*snip*

Hold up, how do these extend if there's no axle opening at the back? Is there an electric motor inside?

[896gerard]

2 hours ago, Bartybum said:

Hold up, how do these extend if there's no axle opening at the back? Is there an electric motor inside?

You're right. A motor is placed inside the cilinder and also in the same tube, not placed in a box behind it. This gives a smooth finish and a Lego look which is not always achieved.. 

[896gerard]

After a lot of pondering, it sounded like a good idea to me to make a list of criteria for 'allowed' custom or new created Lego Technic parts. Then I will consider some examples. It will be quite a read, but your opinion is appreciated!

The Seven Golden Criteria of custom/new Lego Technic parts:

1. The part must have a general Lego Technic look, so all shapes and curves should look like typical Technic shapes and curves.
2. The part must be fully compatible with Lego Technic: all dimensions have to fit in a 4mm or 8mm system.
3. The part should enable something in Lego Technic that was not achievable before with combining pure-Lego parts: its function should be new and clear.
4. The part must be connected to other parts with only Lego parts. Connecting to other 3D printed parts using non-Lego methods is not allowed.
5. The look and strength of the part must adhere to the same high-quality standards as general Technic parts.
6. Possible electronics must work with Lego Technic electronics and adhere to the same safety standards as pure-Lego parts.
7. The part may not be a slight alteration of an existing Lego part.

Based on these rules: what IS NOT a valid custom Lego* Technic part? 

• Mindsensors sensor additions for EV3 and Mindstorms NXT
• L12 EV3 Linear actuators
• Cutting or gluing parts together
• The underpinnings of the life size Lego Technic Bugatti Chiron

Based on these rules: what IS a valid custom Lego* Technic part? 

• Wheel covers, GoPro mount, pneumatic cylinder bracket (here)
• Bigger sprocket design for Technic tracks
• Custom frames that look alike real Technic
• Torsen differential, really useful
• Custom aluminum turntable

I'm really curious whether you find these rules acceptable. Do you know of more examples of either kind of parts? Thanks in advance!

Edited December 16, 2019 by 896gerard

[emielroumen]

On 10/1/2019 at 5:27 PM, 896gerard said:

The only solution: an entirely new linear actuator, fully developed in house, made to be fully compatible with Lego Technic electronics.

 

@896gerard: were you able to put the actuator to use on the Liebherr? Any pictures you can share?

[TeamThrifty]

On 12/13/2019 at 3:05 PM, 896gerard said:

I'm really curious whether you find these rules acceptable

Rules? Its a toy....  I totally get the Pure vs Not Pure. I have no problem with that at all, i love 3rd wheels and tyres as they provide options not available in lego. But i fully understand why some people prefer purity, so there's zero argument from me on that. Each to their own within this glorious sub-culture that is Lego....

But drawing up a list of rules is taking it a bit far in my opinion... rules without a threat are simply a suggestion, so are the rule breakers going to be punished in someway?! When i was 12 and axles didn't have end-stops i used to glue bushes on to stop wheels falling off. Seemed reasonable then, still does now!

There are no rules.. its a toy. Some build purist, some don't.. its that simple. (or should be!)

[896gerard]

On 12/15/2019 at 11:43 AM, TeamThrifty said:

Rules? Its a toy....  I totally get the Pure vs Not Pure. I have no problem with that at all, i love 3rd wheels and tyres as they provide options not available in lego. But i fully understand why some people prefer purity, so there's zero argument from me on that. Each to their own within this glorious sub-culture that is Lego....

But drawing up a list of rules is taking it a bit far in my opinion... rules without a threat are simply a suggestion, so are the rule breakers going to be punished in someway?! When i was 12 and axles didn't have end-stops i used to glue bushes on to stop wheels falling off. Seemed reasonable then, still does now!

There are no rules.. its a toy. Some build purist, some don't.. its that simple. (or should be!)

Thank you. I also get the pure vs not pure, meaning that building with Lego should be some kind of a challenge: you don't have the shape or parts you need but build it with Lego. Using a custom part can remove the challenge of building, i.e. a suspension can be fully 3D printed OR carefully engineered from pure Technic parts. 

This is kind of unfair, because designing parts for a specific function is much easier than using general non-specific parts for a specific function. To make it 'fair' again, I created this list. This pushes the challenge back into making 3rd party parts!

Maybe then the name should not be 'rules', but 'guidelines'. Whatever. Thanks for your opinion!

On 12/14/2019 at 10:48 PM, emielroumen said:

@896gerard: were you able to put the actuator to use on the Liebherr? Any pictures you can share?

I'm planning a full length comparison video with the new XL type linear actuator. Stay tuned!

[Toastie]

2 hours ago, 896gerard said:

This is kind of unfair, because designing parts for a specific function is much easier than using general non-specific parts for a specific function.

But that means that TLG is playing unfair all the time. In case you see them as the "giving entity" then it is not. But I love creativity not stopped by such an entity - provided you can do it on your own.

Best
Thorsten 

 

 

[Gray Gear]

I would not like people to print like bodypanels and other stuff because its hard to make that shape from normal bricks...Wheels, rims, gears and other stuff that is impossible to do with normal bricks is fine with me tho. I'd like to print some 5 spoke rims myself, because the Porsche wheels arn't that great tbh