Telescopic sliding doors

[Thierry-GearsManiac]

Been amazed by automatic sliding doors mechanisms since I was child, I of course got interest in this subject when it comes to building them in LEGO.
But after some research, until now, I haven't seen yet the telescopic kind (two or more overlapping door panels moving at different speeds in the same direction).

I guess it's because they can hardly be integrated in MOCs because, as I tried to experiment, the mechanism is always bulkier than for symmetric doors (this one is really unbeatable : https://www.youtube.com/watch?v=Wpqx9xFL59c).

However, I find the challenge of reproducing such mechanisms motivating : below are my first prototypes, followed by all the mechanical brainstorming involved :

First, my first prototypes as pictures :

First attempt :Really not terrific (wonky, not strong enough)

Unfortunately, axle guiding reveals too wonky ; studless<->bricks interfacing not terrific, although trying to stay "legal" (no stud -><- Technic hole assembly, avoiding Technic bricks and their holes' tiny vertical offset).

Second attempt :

Large door, traditional bricks, vertical "linear differential" mechanism, use of "door rail" bricks/plates : works well ; possibility to drive the fast door panel from above ; possibility to cascade a third door panel (but at the cost of an overhang in front ; perhaps possible to rebuild this mechanism upside down, eliminating the overhang).

Horizontal and rather compact (still gear-based) linear differential. Could duplicate it symmetrically... but still needs room above for the drive mechanism.

... And now a cable-based linear differential, like on real-world doors. A 3rd panel might be possible, at the expense of some more height for the second linear differential.
(the two bushing-terminated friction pins on the left act like violin keys for adjusting the string tension and mechanical offset between the two panels).

And still a lot of technical recipes combinations to try !...

 

Now comes all the thinking :

• Where to install the mechanism ? Above (like in real world but almost always too bulky) or below (easier to hide but creates a gap in the ground) ?
• Should we drive the slow or the fast panel ? Or even both, eliminating the need of a linear differential ?
• Linear differentials variants : scissor-based (as seen on a GBC module with telescopic stairs), gear-based, string & pulley-based ?
• Orientation of the linear differential mechanism : horizontal or vertical plane ?
• Assembly method : studless, studded, mixed ? (I guess that the door panels themselves will be brick-based, allowing more flexibility for aesthetics)
• Door panel thickness : 1L (more compact but more complex as well) or 2L (much easier but less usable in MOCs) ?
• Door panel mechanical guiding : usually close to the mechanism (prevents pitch backlash that would jam the panel), axle-based or door rail brick-based ? The second gives really excellent results and not too muck yaw backlash.
• Panel drive mechanism : rack & pinion (rack would be too long if on the fast panel) ? String & pulley / chain & gear (compact but needs tension adjustment) ? Leadscrew ? Linkage ? Scotch-Yoke ?
• Even more complex : 3-panel door ? Double (symmetric) 2-panel door ?

(combinatorial explosion, but fortunately a lot of impractical or impossible combinations get discarded at an early stage)

[Mr Jos]

Nice prototypes already. The mechanism to make these kind of movements is a cool one. I made this telescopic fork, for a high bay warehouse crane.

As it has to move in 2 directions, it's a bit bulky, and it needs to support a big weight. When you flip it 90° it could become a door.

 

[MinusAndy]

Have you thought about using a worm drive and a static gear mounted to the door? That could be more compact.

[Thierry-GearsManiac]

@Mr JosImpressive warehouse center (I myself can't achieve such big designs) !
Clever heavy-duty and compact rail design for allowing the intermediate cart and the platform to partially disengage on both sides.
And also clever chain design (crossed chains on both sides) for the linear differential (stroke doubler), so that the stroke can be achieved on both sides. Not counting that chains are a bit hard to work with (matching the axles' distance on a stud pitch, with respect to the chain pitch, in order to get the right tension).

@MinusAndyI don't understand : on which part will the worm gear be mounted, as well as the static gear (probably acting as the "moving nut" of the worm-based linear actuator) ? For which function exactly inside the whole thing ? Driving one of the two panels or moving one with respect to the other ?

 

Meanwhile, I upgraded the cable-based movement to 3 panels (but I reduced the door width to 8L instead of 9 in order to avoid modifying the chassis too much) :

This mechanism could also be easily fit into this big door design from Brick Experiment Channel for achieving a true telescopic movement (and the driving cable is also shared with the linear differential on the "2/3" panel).

[Thierry-GearsManiac]

After building two other variants and upgrading the existing ones, I thought it would be better to show everything in video :

PeerTube link (not yet supported as embedded player) : https://tube.interhacker.space/w/gqKyoBSjnsTPRqCokexgZM

(it is my very first video editing attempt : it was tedious and it's probably far from perfect)

 

[Aurorasaurus]

1 hour ago, Thierry-GearsManiac said:

https://tube.interhacker.space/w/gqKyoBSjnsTPRqCokexgZM

Wow, this is some really fun stuff to watch. The mechanisms are what I would have loved to make for my system builds as a kid. Good work showing the evolution and multiple designs, I liked that.