Technic Worm Gear 3L with Bush Ends

[Phantom59]

I read that the new worm gear is beaning drop from production.

http://www.eurobricks.com/forum/index.php?showtopic=97020 *

[jantjeuh]

I wonder why?

[jorgeopesi]

I wonder why?

Me too , I preffer the old one but the new one is good too for other uses.

[TechnicHead41]

I think why they have disappeared, its because they

slip to easy on the gears no matter how much you keep bracing them.

Have already tried them in a vehicle and they just keep slipping and they break easy to...

[Zerobricks]

I think why they have disappeared, its because they

slip to easy on the gears no matter how much you keep bracing them.

Have already tried them in a vehicle and they just keep slipping and they break easy to...

Wow...Than why did they even bother to make them? Didnt they test them?

[Paul Boratko]

If there was a new part that should have been pulled and redone, it should have been the hubs from the 42000...

I think that new worm gear is fantastic...I used 2 of them in a door opening mechanism in a new project that I am working on...

I think why they have disappeared, its because they

slip to easy on the gears no matter how much you keep bracing them.

Have already tried them in a vehicle and they just keep slipping and they break easy to...

I am assuming this is uder moderate to heavy torque..? The screw seems to be about as thick as the older one...

[Phantom59]

If there was a new part that should have been pulled and redone, it should have been the hubs from the 42000...

I think that new worm gear is fantastic...I used 2 of them in a door opening mechanism in a new project that I am working on...

I am assuming this is uder moderate to heavy torque..? The screw seems to be about as thick as the older one...

But I do not think it's as strong as the old one with the axle running all the way through it, I don't know why they (TLG) change it any way ?

Edited June 28, 2014 by Phantom59

[Paul Boratko]

But I do not think it's as strong as the old one.

It very well might not be...

When you look at both of them, the old one just looks like it could take more abuse...

[merman]

I tried to make a Skid Steer Loader with the new worm gears but they are terrible. The axles kept popping out because of the tension. The axles holes/bushes should have had better friction.

[Superkalle]

From an engineering perspective, the new worm screw has a serious design flaw in that it doesn't allow a cross-axle to pass through. This will create bending forces and play inside the worm as the gear rotates when a force is applied/generated.

Also, there are only 1,5 turns of threads on the new screw, which seems quite few and doesn't seem enough to completely engage the threads in all possible sized cogwheels. Normally you want as many threads as possible to engage with the worm to get maximum distribution of forces and a smooth engagement. Compare to pics below.

True, the old worm screw did have an issue that it's length was out of system (required two extra half-bushings), and I think that is what they wanted to fix with the new one. Unfortunately they introduced some other much more severe problems.

EDIT: Oh, and third issue with the new part: TLG calls it WORM GEAR....when I believe a more correct term is a WORM SCREW or just WORM.

[SNIPE]

I like the old worm gear better because it slides over the axle freely however lets say theres two liftarms with a 3L gap, and 1L under this is an 8 tooth spur gear spur gear,

Now a normal worm gear would only be able to support one liftarm assuming it is used with an axle .w stop, where as with the new worm gear you can put an axle to pin connector in both ends of the worm gear and that will support both liftarms.

Most of the time you can just support the liftarms externally but not always.

Edited June 28, 2014 by SNIPE

[Erik Leppen]

much more severe

That depends on what you want to do. For the purposes TLG has in mind, the new one is probably better because it is easier to fit in, and the forces won't be as high. The force limit is only a problem if you're gonig to exert a lot of force on the part - something that won't be done in official sets because playing with official sets should never induce part damage.

Also, there would only be an issue if the old worm will disappear. If the old worm stays, the new part only gives more options. :)

[Superkalle]

That depends on what you want to do. For the purposes TLG has in mind, the new one is probably better because it is easier to fit in, and the forces won't be as high. The force limit is only a problem if you're gonig to exert a lot of force on the part - something that won't be done in official sets because playing with official sets should never induce part damage.

Also, there would only be an issue if the old worm will disappear. If the old worm stays, the new part only gives more options. :)

Well, I guess you are right in one sense - for light loads and simple applications, the new worm screw is sufficient. The thing is that LEGO elements are supposed to be designed for use in many different kinds of applications. The forces in the the large sets can be pretty massive (with XL-motors and all) and the new worm gear is (was) not good for that. I think the fact that TLG pulled the part from even existing sets and re-made all building instructions is evidence enough that it was (and is) a bad design. At least that's my guess.

[Anio]

Normally you want as many threads as possible to engage with the worm to get maximum distribution of forces and a smooth engagement. Compare to pics below.

True to some extent : more teeth of a gear (24t, for example) in the worm gear lead to more friction. In some case, this may not be recommended.

the old worm screw did have an issue that it's length was out of system

True and wrong.

Yes it is not 2L long but a bit less.

However, make it precisely 2L long and then put 2 of these new worm gears on the same axle : the spirals of the 2 worm gears don't match anymore.

That depends on what you want to do. For the purposes TLG has in mind, the new one is probably better because it is easier to fit in, and the forces won't be as high. The force limit is only a problem if you're gonig to exert a lot of force on the part - something that won't be done in official sets because playing with official sets should never induce part damage.

This is a curious reasonning.

The part can not support high forces => official sets do not damage parts => the worm gear will not be damaged => the part is ok for TLG.

You consider a limited use of the part to conclude that it is well designed. :-S

I would rather say :

The part can not support high forces => TLG can not use it in sets where high forces are involved => the part is not very well designed.

A well design force would support high forces. 2L worm gear does.

[Lipko]

Yes it is not 2L long but a bit less.

However, make it precisely 2L long and then put 2 of these new worm gears on the same axle : the spirals of the 2 worm gears don't match anymore.

I don't understand this. You are saying that the the spirals wouldn't match with 2L length. But gear racks (10 teeth distributed over 4 studs) are in system (match perfectly) and they (should) have the same profile as the worm gear since they are in the same gear system (same modulus).

EDIT: now that I think about it, the gear racks and worm gears cannot be made with the same modulus as the gears have, just approximately, since gears roll on racks, so PI comes into play

With a 8t gear, one revolution means 3,2 studs of gear rack movement (8t/10t*4studs) in the Lego system.

While with realistic teeth the rack should move 3,14 studs (since the 8t gear has 1-stud pitch diameter)

Okay Lipko, thanks

Edited June 28, 2014 by Lipko

[Superkalle]

True to some extent : more teeth of a gear (24t, for example) in the worm gear lead to more friction. In some case, this may not be recommended.

I'm not sure what you mean. You want to distribute the force over as large area as possible to lower contact point pressure, so opposite of what you say.

Also, with only 1,5 threads, the end of the 1,5 threads will chop into the gear edges of the wheel so there will not be a smooth transition between gear cogs. The LEGO design goes against all rules for worm screw design. 1,5 threads is just too little. Here is Google image search

True and wrong.

Yes it is not 2L long but a bit less.

However, make it precisely 2L long and then put 2 of these new worm gears on the same axle : the spirals of the 2 worm gears don't match anymore.

Not sure what you mean here either I'm afraid. Maybe I was a bit vague in my wordings though, but what I meant is that 2L worm gear is "out of system" in terms of standard modern Technic design. In the old Technic days, 2L was good. But modern Technic is based on odd modules (1, 3, 5 etc), That is what I meant.

[Anio]

Not sure what you mean here either I'm afraid.

Pretty hard to explain that in English. I will try.

A worm gear is about 1,9L. So, when you put 2 worm gears side by side on the same, the spiral of the 2 worm gear match. There is no "interruption" in the spiral.

Now, imagine a 2L worm gear. Each worm gear will "more" spiral. And if you put 2 of them side by side on the same axle, the whole spiral weel have an interruption.

Because on the axle, you can turn the worm gear only by 90°.

But I see that you had odd length in mind when you said out of the system.

It is true that 2L is out of the system in that regard (studless).

However, I am not sure a 1L worm gear is relevant (it might not even work with 24t and 40t).

And if you want to use a 3L worm gear, a regular 2L worm gear + technic bush is fine. And this is what we see in many Technic models.

[Superkalle]

However, I am not sure a 1L worm gear is relevant (it might not even work with 24t and 40t).

And if you want to use a 3L worm gear, a regular 2L worm gear + technic bush is fine. And this is what we see in many Technic models.

A 1L worm screw is actually a good proposal If the number of gears in engagement are sufficient given the LEGO gear geometry, it should work fine. But it might be too tight though to fit supportive beams on the sides.

A 3L worm screw would be good if they just allowed the axle to pass through and it had more threads .

A 2L worm is OK like you say - only that you always need bushings to make it 3L => extra parts needed in the set and extra steps in building process.

[Anio]

Yes, 1L works with nothing on both side.

But add a connector like 42003 or 32068 on each side. Maybe there will be a collision between the connector and the teeth. Dunno.

[Blakbird]

Just because the new worm gear was pulled from a set does not mean that it has been discontinued. Perhaps it did not work out well in this particular application. I would guess we will see it again it some sets next year used in different ways.

[Captainowie]

However, make it precisely 2L long and then put 2 of these new worm gears on the same axle : the spirals of the 2 worm gears don't match anymore.

Surely if you're going to make it precisely 2L long, then you're also going to change the pitch of the thread such that this isn't an issue??

[1974]

Just because the new worm gear was pulled from a set does not mean that it has been discontinued. Perhaps it did not work out well in this particular application. I would guess we will see it again it some sets next year used in different ways.

TLG does not do something this unless there's something seriously wrong. It's very costly to alter designs/sets/packaging this late

If it doesn't work out well in this application it probably won't work well at all. Major fail in product development/testing, I'd say

I would guess we'll never see it again unless redesigned

[Doc_Brown]

oh man I just got 2 of these. Looking at them they do look a little weak.

[Blakbird]

TLG does not do something this unless there's something seriously wrong. It's very costly to alter designs/sets/packaging this late

This is certainly true, but the converse is also true. TLG doesn't invest in a new part and new molds unless they have a use for it and have done lots of testing to prove it will work. I don't see them abandoning a part after one set. I guess time will tell.

My point was that this thread starts by saying "I read that the new worm gear is beaning (sic) drop from production" but there is nothing in either this thread or the referenced thread that actually shows the part is being dropped from production. We just don't know that. All we know is that it was replaced in one set.

[Anio]

Surely if you're going to make it precisely 2L long, then you're also going to change the pitch of the thread such that this isn't an issue??

The pitch was orginally designed/chosen so that it works at its best with the teeth of regular gears (mainly 24t and 40t, at the time ; worm gear + 8t was introduced with studless)

If you change the pitch, I am pretty sure that the worm gear will not work as good. More friction, mainly. And a good worm gear already makes a lot of friction. :-s