Worm gear

[Mechbuilds]

Hey guys!

Is the new shorter worm gear the same size as the older longer one?


Can the 2 long wormgear be cut in the middle so it will be the same as the shorter one? Or is the shorter one larger in diameter? 

[Gray Gear]

Yes, the newer one is larger in diameter.

[Mechbuilds]

Damn.. So i guess i'll just have to order it.. 

[Zerobricks]

Old one is equivalent to an 8 tooth gear, new one to a 12 tooth one.

Edited May 21, 2020 by Zerobricks

[Didumos69]

2 hours ago, Mechbuilds said:

Is the new shorter worm gear the same size as the older longer one?

No, it's shorter.

[amorti]

Is the increased diameter not just to make it align with modern gears (12,20,etc instead of 8,16,etc) than changing its ratio? 

Edited May 21, 2020 by amorti

[Zerobricks]

31 minutes ago, amorti said:

Is the increased diameter not just to make it align with modern gears (12,20,etc instead of 8,16,etc) than changing its ratio? 

How does one change a ratio of a worm gear?

[amorti]

4 minutes ago, Zerobricks said:

How does one change a ratio of a worm gear?

By putting two threads on it?

I don't believe the diameter of it makes a difference?

@Sariel is usually the expert on gears.

[Mechbuilds]

To change the gear ratio of a worm gear, you thin the gaps between the teeth. 
The increased diameter allows you to spin different gears. 

In my case, i'm trying to spin a 20 tooth gear and i only have 1 stud clearance for a worm gear. 
I thought if both 2 long and 1 long wormgears were the same diameter, i could have just cut one of my wormgears to fit the 1 stud gap. 
But since the diameter is different, i think i should just order and wait a week till the 1 long worm gear arrives. 

[Zerobricks]

12 minutes ago, amorti said:

By putting two threads on it?

I don't believe the diameter of it makes a difference?

@Sariel is usually the expert on gears.

 

7 minutes ago, Mechbuilds said:

To change the gear ratio of a worm gear, you thin the gaps between the teeth. 
The increased diameter allows you to spin different gears. 

In my case, i'm trying to spin a 20 tooth gear and i only have 1 stud clearance for a worm gear. 
I thought if both 2 long and 1 long wormgears were the same diameter, i could have just cut one of my wormgears to fit the 1 stud gap. 
But since the diameter is different, i think i should just order and wait a week till the 1 long worm gear arrives. 

Changing the diameter or the thread gap does not change the gear ratio of the worm gear. My question was rhetorical because you can't change the gear ratio of a worm gear. One rotation will always result in a change of a 1 thread. Gear ratio of an gearbox with a worm gear of is the 1 : to the number of gears of the second gear.

Edited May 21, 2020 by Zerobricks

[amorti]

31 minutes ago, Zerobricks said:

My question was rhetorical because you can't change the gear ratio of a worm gear. One rotation will always result in a change of a 1 thread. 

Like a ball screw, the worm in a worm gear may have a single start or multiple starts – meaning that there are multiple threads, or helicies, on the worm. For a single-start worm, each full turn (360 degrees) of the worm advances the gear by one tooth. So a gear with 24 teeth will provide a gear reduction of 24:1. For a multi-start worm, the gear reduction equals the number of teeth on the gear, divided by the number of starts on the worm.

https://www.motioncontroltips.com/worm-gears-what-are-they-and-where-are-they-used/

[Maaboo the Witch]

Hard to believe the humble worm gear could trigger this much discussion. I'll add some trivia to the pot:

The rarest colour for the standard worm gear is blue. It appeared only once in 8501 Ice Slizer in 1999.

[doug72]

The new worm gear which is 1L which can be hard to mesh with 12, 20, 26 T double bevel gears and usually requires a 1/2 L offset.

There is an earlier topic about various ways to achieve this.

Also this new worm gear has friction on an axle, unlike 2L worm gears are without friction on an axle.

[Mechbuilds]

37 minutes ago, Doug72 said:

The new worm gear which is 1L which can be hard to mesh with 12, 20, 26 T double bevel gears and usually requires a 1/2 L offset.

There is an earlier topic about various ways to achieve this.

Also this new worm gear has friction on an axle, unlike 2L worm gears are without friction on an axle.

Here is a comparison. 
Like i said, i only had 1 stud of space in my situation. And also since the diameter is shorter on the 2 long wormgear, it can't be used in this application even if the L beam was removed. 



EDIT:
Speaking of worm gear thread gap.. 
If you have a worm gear that has very large gaps between the teeth, it requires less turns to spin out but if it has a very thin gap, it takes significantly more spins to spin it out. 

You can easily test this when you compare different nuts and bolts cars have which vary in thread sizes. Even if the bolt is a 10MM bolt, if the thread has a thin gap it will require more turns to loosen vs a thread that has a long gap. 
So when you turn the screw you'd think the spiral would push a tooth of a gear faster or slower depending in the gap.. 

Am i completely wrong on this?


EDIT:
I guess it's always one tooth per rib. But the gap would just increase speed but not change the ratio. 

 

Edited May 21, 2020 by Mechbuilds

[amorti]

There are indeed bolts with finer and coarser threads, and the ones with coarser threads will go in and out faster. But that's because the nuts are also coarser threaded. The Lego gears all have teeth at the same pitch.

[doug72]

The gear ratio when using a worm gear is always the same as the number of teeth it is meshing with.

i.e. Worm = 1, / 24 T spur gear = 1:24 reduction etc.

With a two start worm gear that would be 2:24.= 1:12 ( which Lego don,,t make)

 

[ukbajadave]

Mmm, worm gear trivia.

I believe it's also the case that when building for example a brick built linear actuator the old worm gears match up in a line but the new ones don't. 

[Didumos69]

41 minutes ago, ukbajadave said:

Mmm, worm gear trivia.

I believe it's also the case that when building for example a brick built linear actuator the old worm gears match up in a line but the new ones don't. 

What if you rotate every second new worm gear 180 degrees?

Now that we have arrived at the trivia. Obviously you can't make a LEGO worm gear spin with a normal gear. But what if some other power source already spins the axle with the worm gear attached. So the worm gear is already rotating. Now would also applying force with the normal gear that meshes with the worm gear speed up the worm gear, given that the normal gear spins in the right direction?

Edited May 21, 2020 by Didumos69

[pleegwat]

20 minutes ago, Didumos69 said:

Now that we have arrived at the trivia. Obviously you can't make a LEGO worm gear spin with a normal gear. But what if some other power source already spins the axle with the worm gear attached. So the worm gear is already rotating. Now would also applying force with the normal gear that meshes with the worm gear speed up the worm gear, given that the normal gears spins in the right direction?

It would reduce or remove the friction between the two. Whether that speeds up the already-rotating worm gear depends on the nature of the motor rotating it - if that source manages its RPM to a constant rate and has plenty of power, the worm gear probably won't speed up.

[dhc6twinotter]

There is also this worm gear.  For whatever reason, it was only briefly used.  It's the same diameter as the 2L worm gears, but the gear itself is only 1L long.  There are 1L bushings on either side so total length is 3L.

Edited May 22, 2020 by dhc6twinotter

[TechnicRCRacer]

10 minutes ago, dhc6twinotter said:

For whatever reason, it was only briefly used

I heard it was retired because LEGO cited structural problems.

[Didumos69]

8 hours ago, pleegwat said:

It would reduce or remove the friction between the two. Whether that speeds up the already-rotating worm gear depends on the nature of the motor rotating it - if that source manages its RPM to a constant rate and has plenty of power, the worm gear probably won't speed up.

That sound logical! Thanks!

[msk6003]

2 hours ago, TechnicRCRacer said:

I heard it was retired because LEGO cited structural problems.

What kind of structural problems?

[bj51]

10 minutes ago, msk6003 said:

What kind of structural problems?

It broke under load.

[msk6003]

7 minutes ago, bj51 said:

It broke under load.

Oh thanks.