Driving newer turntable with worm gear

[ozacek]

I'm not sure whether this question has been posted before (couldn't find it). Does anyone have a decent way of driving the newer 60-teeth "type 3" large technic turntables with a worm gear?

After spending some time in MLCad trying to align parts based on Sariel's solution with technic bricks, that's the closest match I could come up with:

It's not an exact match, but it seems to work pretty well, although it doesn't leave much space for anything else on the turntable... On the following picture you can see the actual mismatch - the axle is the ideal position.

 

Sariel mentions in his book "it's very difficult to mesh with a worm gear".

Edited May 16, 2019 by ozacek

[Mantarri]

Are you aware of this part, it can be used to mesh with certain beveled gears, including the new turntable AFAIK.

Edited May 16, 2019 by XtremeBuilder

[Mechbuilds]

You could try experimenting with this part: 






You could get the wormgear meshing perfectly singe according to your MLCAD it's only half a stud too high. 

[Erik Leppen]

For gears, the radius is 1/16 times the number of teeth.

• The old turntable has 56 teeth, so has a radius of 56/16 = 3.5.
• The new turntable has 60 teeth, so has a radius of 60/16 = 3.75.

For worms, the radius is as follows:

• The old worm has the same radius as the 8t gear, which is 8/16 = 0.5
• The new worm has the same radius as the 12t gear, which is 12/16 = 0.75

So:

• The old turntable can be driven with the old worm with a distance of 3.5 + 0.5 = 4 studs.
• The new turntable can be driven with the new worm with a distance of 3.75 + 0.75 = 4.5 studs.

Therefore, you need to use a half-stud offset.

Of course, there are other ways. For example you can use a 20t gear (radius 20/16 = 1.25) in between the worm and the turntable. Then, worm-gear is 0.75 + 1.25 = 2, and gear-turntable is 1.25 + 3.75 = 5, both of which are convenient (whole) numbers. However, the 20t then isn't secured and can slide off.

Or you use the bevel ring of the turntable and use new worm-20t and then 12t-turntable in a 90 degree angle. But the 90-degree angle may be slightly weaker too.

 

[Jeroen Ottens]

42 minutes ago, Erik Leppen said:

For gears, the radius is 1/16 times the number of teeth.

• The old turntable has 56 teeth, so has a radius of 56/16 = 3.5.
• The new turntable has 60 teeth, so has a radius of 60/16 = 3.75.

For worms, the radius is as follows:

• The old worm has the same radius as the 8t gear, which is 8/16 = 0.5
• The new worm has the same radius as the 12t gear, which is 12/16 = 0.75

So:

• The old turntable can be driven with the old worm with a distance of 3.5 + 0.5 = 4 studs.
• The new turntable can be driven with the new worm with a distance of 3.75 + 0.75 = 4.5 studs.

Therefore, you need to use a half-stud offset.

Of course, there are other ways. For example you can use a 20t gear (radius 20/16 = 1.25) in between the worm and the turntable. Then, worm-gear is 0.75 + 1.25 = 2, and gear-turntable is 1.25 + 3.75 = 5, both of which are convenient (whole) numbers. However, the 20t then isn't secured and can slide off.

Or you use the bevel ring of the turntable and use new worm-20t and then 12t-turntable in a 90 degree angle. But the 90-degree angle may be slightly weaker too.

 

Excellent explanation Erik.

If you worry about securing the 20T gear you can use the new blue 20T clutch gear and secure it with an axle with stop or a frictionless pin

[ozacek]

1 hour ago, Erik Leppen said:

• The old turntable can be driven with the old worm with a distance of 3.5 + 0.5 = 4 studs.
• The new turntable can be driven with the new worm with a distance of 3.75 + 0.75 = 4.5 studs.

What exactly are the new & old worm gears? I know of type I & II (4716 & 32905), but as far as I know it's only the shape of the axle whole that changes. Thanks!

2 hours ago, Mechbuilds said:

You could get the wormgear meshing perfectly singe according to your MLCAD it's only half a stud too high. 

That's actually much less than 1/2 a stud. The blue axle on that image is 1/2 a stud too high:

Edited May 16, 2019 by ozacek

[doug72]

Perfect gear meshing and ideal for a MOC I am working on.

Edited May 16, 2019 by Doug72

[Erik Leppen]

1 hour ago, ozacek said:

What exactly are the new & old worm gears? I know of type I & II (4716 & 32905), but as far as I know it's only the shape of the axle whole that changes. Thanks!

The old worm is the one you use (that has different types, with different axleholes, indeed).

The new worm is the one @Doug72 uses and @XtremeBuilder linked to.

Edited May 16, 2019 by Erik Leppen

[ozacek]

11 minutes ago, Erik Leppen said:

The old worm is the one you use (that has different types, with different axleholes, indeed).

The new worm is the one @Doug72 uses and @XtremeBuilder linked to.

Ah well look at that! Surely that makes things easier, I didn't know that part existed. Like the Genie says in Aladdin, I feel sheeepish :)

I guess I should change the question to "Does anyone have a better way of driving a new large turntable with an old worm gear" then.

[Ngoc Nguyen]

@Doug72 And how would you mesh a 1/2-stud-offset axle with an axle on the grid?

[doug72]

35 minutes ago, ozacek said:

Ah well look at that! Surely that makes things easier, I didn't know that part existed. Like the Genie says in Aladdin, I feel sheeepish :)

I guess I should change the question to "Does anyone have a better way of driving a new large turntable with an old worm gear" then.

It can be done - see photo BUT its not Lego legal !

 

Old style worm designed for Z56 turntable.
New style worm designed for Z60 turnatble and are not readilly interchanged.

8 minutes ago, Ngoc Nguyen said:

@Doug72 And how would you mesh a 1/2-stud-offset axle with an axle on the grid?

Not sure what you mean ?

Edited May 16, 2019 by Doug72

[Ngoc Nguyen]

Just now, Doug72 said:

Not sure what you mean ?

In your picture, the axle that drives the worm gear is offset 1/2 stud from the alignment of other studs (I call that the grid). So in case you need to mesh that axle with another axle that aligns with the grid, how would you do it?

[doug72]

Use offset gears as per image 24T / 20T gears also 12T/16T gears do the same thing and you are back on  grid.

Or use universal couplings if room.

Edited May 16, 2019 by Doug72

[pleegwat]

If you're exactly half a stud off, 8T/16T or 12T/12T are also options. Or you can always use a perpendicular axle.

[Mechbuilds]

Doug showed the exact way to mesh it that i had in my mind. 

[doug72]

Alternative arrangment for Z60 Turntable and new worm gear - Not as strong but OK for light loads.

Edited May 17, 2019 by Doug72

[Maaboo the Witch]

Odd that this worm part has fallen out of use for this year so far. You'd think TLG would jump on every chance they had to use it. 

[Saberwing40k]

16 hours ago, Maaboo35 said:

Odd that this worm part has fallen out of use for this year so far. You'd think TLG would jump on every chance they had to use it. 

Actually, not really. Lego, at least now, wants functions to slip in case a child manipulates the mechanism by hand.

[doug72]

4 hours ago, Saberwing40k said:

Actually, not really. Lego, at least now, wants functions to slip in case a child manipulates the mechanism by hand.

There are other ways to introduce slip other than allowing gears to skip, which damages them.

Children & others learn by making mistakes.

I learnt when I was very young not to poke keys into a electric socket , never done is again !

Edited May 18, 2019 by Doug72

[ozacek]

23 hours ago, Doug72 said:

Alternative arrangment for Z60 Turntable and new worm gear - Not as strong but OK for light loads.

Thanks Doug for all the pictures. It's so much easier to understand than with a description.

[doug72]

2 hours ago, ozacek said:

Thanks Doug for all the pictures. It's so much easier to understand than with a description.

A picture saves a thousand words.

[SNIPE]

Here is one way that I think will work, The trick is to lower the old worm gear down by half in order for it to work with any double bevel gear. or turntable (does not work with single bevel gears)

LXF file

[doug72]

9 hours ago, SNIPE said:

Here is one way that I think will work, The trick is to lower the old worm gear down by half in order for it to work with any double bevel gear. or turntable (does not work with single bevel gears)

Now built your suggestion using your LXF file, but it doesn’t work., the worm gear only engages with the edge of the turntable gear ring.

Supports for worm gear axle don’t align and nothing to stop frame for worm axle rotating like a hinge.

Added bracing to kept things in the same plane, see last image.

See photos.

 

Mis-alignment:

Hinge effect:

3L beam added to keep worm meshed, but stiil slight mis-alignment and more worm gear friction. 

 

Solution: Use the correct worm with each type of turntable or gear.
i.e 2L worm with Z56 t/t and 1L worm with Z60 t/t.

 

Edited May 20, 2019 by Doug72

[Sariel]

On 5/16/2019 at 1:36 AM, ozacek said:

Sariel mentions in his book "it's very difficult to mesh with a worm gear".

Actual internal dialogue I had back when writing this book:
Me: I don't see any way to mesh this. OK, let's say this turntable doesn't mesh with the worm gear.
Also me: Wait, somebody will eventually figure out some wild way to mesh it and will make you and your book look stupid.
Me: Let's play it safe... "very difficult to mesh with a worm gear". 

:)

[ozacek]

27 minutes ago, Sariel said:

Also me: Wait, somebody will eventually figure out some wild way to mesh it and will make you and your book look stupid.
Me: Let's play it safe... "very difficult to mesh with a worm gear". 

haha :)

Actually in the end I like my approach of meshing it. Maybe it's not 100% ideal, but it holds very well, supports some torque without slipping, doesn't cause pressure in the gears, and the support liftarms can be moved on the outside if one needs the inner part of the turntable free.