Worm and sector steering

[Divitis]

As I begun working on MOCing an old car, I wanted to go realistic and integrate worm and sector steering just like the original model.

Worm and sector on Wikipedia

At first glance it feels overdesigned, and it probably is, especially for a Lego model, but ultimately works well and is precise.

The new worm gear piece works like a charm but the main drawback - which admittedly negates one of the advantages of the original design - is that the 6L worm can be backdriven. However, I reckon using the 2L worm would require too much bracing to be integrated in the space I have.

This is the first working prototipe. The main issue has been bracing the worm securely. The amount of force the 'black cube' exerts on the frame is nothing short of impressive, it must be a 45:1 reduction or something!

 

[Jundis]

Never heard of this steering solution, cool to learn something new :-)

For you solution, you used the newer big worm gear. Did you try with a normal worm gear and gear racks or fixed 8 tooth gears first?

[Divitis]

Hey Jundis,

the cube that slides on the new worm gear replicates quite accurately how the actual mechanism goes, so as soon as I saw the schematic as part of the research for my MOC I thought of it and never looked back :)

Connecting the worm gear it to an sliding 8t would probably require a lot of bracing to ensure the movement is smooth, and otherwise using a rack would make the mechanism really redundant, something like this:

 

[2GodBDGlory]

Cool design! It certainly doesn't look practical for Lego, but that was never the point, and I love seeing complex ways of accurately replicating real-life mechanisms!

This is the steering mechanism used on my real-life car, so I'm somewhat familiar with it, and happy to see it in Lego!

[gyenesvi]

Interesting mechanism, but there's something I don't get in the real life version: why is the cube required between the worm gear and the sector gear? Why doesn't the worm gear directly drive the sector gear? That would actually be pretty easy to implement in lego, as done in many models.

One thing I can think of is that this way system may have less slack because of the ball bearings, and that cube that meshes with the sector gear is not rotating, so the system may have less wear as well. Anybody knows that?

[Divitis]

That's a great question @gyenesvi and I couldn't find the answer to that.

In my Lego version I noticed that the 'black cube' is less geared down and moves faster on the worm than brick built actuators. This makes the solution better suited for steering. Maybe it's also the case in real life?

Also, all Lego solutions that I saw using worm screws also include the 24t clutch to stop the steering instead of relying on the C motor auto calibration. I reckon otherwise the worm gear down ratio would break the model. Happy to be proved otherwise of course:)

Meanwhile, I finalized a compact version, properly braced so that the motor calibrates with no issues - it needs a hard stop, if there is play/flex in the mechanism the calibration fails.

Unfortunately I cannot record with my phone and use the app..