21 August 2023

LEGO® parts 73763, 73764 & 3863: A worm gear family

Posted by tobymac

Earlier this year LEGO® City 60372 Police Training Academy introduced a new type of worm gear; Technic Worm Gear 6M with Axle Hole in Light Bluish Gray and the accompanying Brick Special 2 x 2 x 1 2/3 with Worm Gear in Black. I always love to see LEGO® Technic parts appear in ‘regular’ sets, so I think a closer look is warranted. 

But what is that kitty doing there?

LEGO part 73763: Worm Gear, 6 Module, W/ Cross Hole

The worm gear is an interesting new part. You could see it as a thicker, sturdier version of Spiral [Fireman] Pole 32L (23421). 

Worm gears are not new in the LEGO universe, as the first was introduced in Technic back in 1985. There are some differences to be discussed. Using 2L axles, the worm gear can easily be extended, while the Technic version slides across an axle. Since an axle has 4 sides, and the new worm gear has 4 threads, you don't have to check the orientation before joining 2 worm gears; they always line up. The Technic version has a single thread, which means 4 orientations are possible, with only 1 lining up with the next one. 

The new gear is also an exact 6 modules wide. The Technic version is just a bit shorter than 2 modules, meaning it has some wiggle-room, causing a lag in the drivetrain. Joining multiples end-to-end can cause issues unless you secure them tightly.

There is another major difference between the new worm gear and the Technic version that is important to take into account with your potential MOCs: the Technic worm gears can't be back-driven. This means the worm gear can spin other gears, but other gears cannot spin the gear worm, and will jam instead. This does not happen with the new worm gear. 

There are several methods of joining other gears to the worm gear. First is to use another of the new worm gear itself: crossing two of them allows for transmission of movement. 

Crossed under a 45deg angle, it's possible to match up a regular gear. This connection allows for back-driving: the worm gear can move the regular gear, but the regular gear can also move the worm gear!

Lastly, after some fiddling, I was able to match a knob gear. There are two drawbacks here though. The knob doesn't fit all the way in the groove and needs to caress the worm gear. With the knobs being far apart from each other, there is a moment in the rotations where there is no contact and the worm gear stops. This also means the direction of transmission can't be reversed: the knob gear can drive the worm gear, but the worm gear can't drive the knob gear. The caressing also means the knob slips easily.

The worm gear can be used in a Great Ball Contraption to transport balls. The angle can't be too high though, or the ball just rolls off. Later in this article there is a video montage to show this better.

LEGO part 73764: Gear Block 2X2X1 2/3

The accompanying gear block has skewed notches on the inside that follow the groove of the gear. Its 5-plate height makes it a perfect cube, allowing for easier integration in your builds in various directions.

When the brick is fixed in its orientation and the worm gear is rotated, the brick slides along, giving a linear motion:

Or, when the gear is stationary, the brick can rotate instead, making it a great carnival ride.

It is possible to move the brick or elevator and make the worm gear spin in turn. This gives new possibilities, but it also means that whenever the elevator is up in the air, there is a constant pressure on the drivetrain when the worm gear is placed vertically. If there is nothing to hold the brick in place, gravity will pull it down. So make sure you build in something to either lock the drivetrain or the brick itself. It will probably also be wise to limit the amount of time the brick is lifted, as the constant pressure can cause gears, axles and other parts to be damaged.

In 60372 Police Training Academy the parts are used for horizontal movement, transporting a rookie along an obstacle course:

Building instructions ©2023 The LEGO Group

The parts also appear in the June set 60366 Ski and Climbing Center, this time going vertically as an elevator. 

Lets see this all in motion:

LEGO part 3863: Gear Block 6X6X5

Having a 4+ age mark, and depicting a show aimed at children of that age, you might have overlooked the LEGO® Gabby’s Dollhouse theme which was released in August 2023. 

The biggest set in the line, 10788 Gabby’s Dollhouse, features an elevator element that is a large, modified version of the Black gear block. However, there is no worm gear included.

The cabin is made out of Brick Special 6 x 5 x 6 with Gear, 3 x 4 Plate with Design ID 3863, and this instance is with Cat Face print in Bright Pink (Element ID 6447176 | Design ID 104593). 

A quick look at the geometry shows a central brick measuring 2 x 4 x 6 modules, with a 4 x 3 plate in front of it. The plate sticks out half a module from the brick, and has half-module wide 'flaps' on the sides. So the total footprint of the part is 5 x 5.5 modules. Only the brick section has some form of clutch power at the underside, but it's not as strong as normal anti-studs.

On the sides of the brick section we find notches that fit in the groove found in elements like Brick Special 1 x 2 x 5 with Groove (88393) or Brick Special 1 x 2 with Groove (4216). Stack a couple of these and you can slide the cabin up and down without much friction.

The most interesting aspect we find in the top: there is a hole that fits the worm gear! The sight of a poor kitten with a drill in its head is a bit disturbing though...

Stack a couple of grooved bricks, link some worm gears, and we have ourselves a functioning elevator.

A downside to this setup is that the stacked grooved bricks need to be placed sturdily, to stay straight and allow for a smooth operation. 

LEGO part 3417: Frame 3X6X6, W/ Reduced Knobs, Cut Out

I’m sure any decent designer of MOCs will have no trouble achieving this, but seeing as we’re finding the element in a 4+ set, LEGO has introduced a new mold to help out the younglings: Door Frame 3 x 6 x 6 with Inside Grooves (3417), found here in a more neutral White (6427520). 

Breaking its geometry down, we can see a 1 x 4 x 6 door frame with two 6-high 1 x 1 bricks flanking it. In front of those 2 bricks are 2x 6-high grooved bricks. The cabin element fits in smoothly.

This entire setup is achievable with existing parts, so you can certainly call this mold a POOP. The same is mostly true of the pink cabin element; although its projecting sections are unique shapes, it’s possible to make a working elevator without these specialized molds, as the elevator in the 60366 Ski and Climbing Center proves. I think these specialized elements are perfect for this 4+ set, however: it’s a quick and easy way for young hands to build a sturdy elevator shaft that is, above all, reliable in heavy play. 

I was a bit disappointed to find Gabby’s Dollhouse not utilizing the worm gear in the elevator, instead leaving the cabin to plummet whenever it is released. My best assumption would be that the designers found in focus group testing that the LEGO Technic aspect was too complicated for the target audience? Hopefully we'll see these bespoke elevator elements being used to their full potential in future sets.

Depending on the scale of your MOC, Gabby's elements could provide the sturdiness required for your aircraft carrier, space station hangar or moving city. 

I wonder how high you could go with linked worm gears before they bend too much, and how much weight the elements can take? 

TobyMac's MOCkup using Technic, Gear Worm Screw 6L

I figured it should be possible to link multiple worm gears together to even the load, making wider platforms possible, so I made a simple MOCkup to test it out. Seeing I only have one kitty-brick at my disposal, I've used 4 of the black 2 x 2 x 2 bricks in the platform.

What are your thoughts on the new worm gear family? Have you used it in your models already, and how did they work out? Have you found alternate connection methods for the molds? Let us know in the comments!
If you're buying one of the sets containing these new elements from LEGO.com, please consider using our affiliate links, we may get a commission:

LEGO® City 60372 Police Training Academy
US$99.99/ £79.99/ 89.99€/ AU$139.99
823 parts
January 2023
USA LEGO Shop | Australia LEGO Shop | UK LEGO Shop

LEGO® City 60366 Ski and Climbing Center
US$119.99/ £94.99/ 104,99€/ AU$169.99
1045 parts
June 2023
USA LEGO Shop | Australia LEGO Shop | UK LEGO Shop

LEGO® 10788 Gabby’s Dollhouse
US$79.99/ £69.99/ 79,99€/ AU$129.99
498 parts
August 2023
| Australia LEGO Shop | UK LEGO Shop

READ MORE: Eero Okkonen visits the Fantastical Tree House of LEGO® DREAMZzz™ set 71461

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  1. I always assumed the inability of the old worm gear to be back-driven was intentional, although I dont know enough about technic to find a way to use that. Its neat that the new one can be used in different ways, and I hope there continues to be space for both parts to co-exist

    1. Yeah, the inability of the old worm gear to be back-driven allowed it to be used to finely position a rotational joint that could support a lot of weight—one set example that comes to mind is the leg joints of the UCS AT-AT. Many of the largest mecha MOCs I've seen take advantage of that for posing as well.

      But for simple "play features" this new worm gear has tons of potential. Can't wait to see it used more for features like elevators—I'd love to see that Gabby's Dollhouse elevator piece with a more basic color and no print, as well.

  2. Great, thanks so much for this article! I was wondering if the worm gear would fit the elevator! Like you I was surprised that Lego didn't use it in Gabby's Dollhouse set. Hope to see this elevator part in more neutral colours and used in their sets as a working elevator!!

  3. Another use for the can't-be-backdriven type is as part of a rope winch on a crane or tow truck, etc. In real life a similar gear is sometimes used in vehicle steering systems, so that when you hit a huge p
    othole it doesn't feed back to the steering wheel and break your thumbs.

  4. I have seen suggestions that the #2 axle (used to join the new worm gears together) is too small for a 4+ set and that's why they didn't use the worm gears in that set.

    1. Doubt it, given the many other smaller parts in that set, like the 1x1 round plate and so on.

    2. But there are other tiny parts as well, so it doesn’t quite make sense.
      It could maybe get a bit to complicated or hard to fit behind the center plate at the top.

  5. Wonder if that could be used to create an elevator for a church.

  6. Just what i was looking for. Can you please share the parts (numbers) needed to create a functional elevator ? Thanks!