Not enough 24 tooth and 8 tooth gears nowdays - or is it just me?

[SM96UK]

feel free to say anything, but i feel lego doesn't use enough of these pieces and instead the often use the 12 tooth and 20 tooth bevel gears often.

[GuiliuG]

I don't really understand your toughs.

Why lego had to put more 8t and 24t if they aren't usefull? You choose the gears for the reductions, not to have the more or the less in one model.

[allanp]

I do find that I have not quite enough 24t gears at times in the newer dark bley colour. Quite what TLG should do about that i'm not sure

[SM96UK]

I don't really understand your toughs.

Why lego had to put more 8t and 24t if they aren't usefull? You choose the gears for the reductions, not to have the more or the less in one model.

i know that 8 tooth gears are not useful because they are weak, but there's not enough like before....

[Plastic Nurak]

i know that 8 tooth gears are not useful because they are weak,

In last years, TLC have reinforced it.

[Splat]

The 8, 24, and 40 tooth gears fit better in the older studded beam constructions, but they don't fit as easily into the newer studless liftarm system. They are just a fraction too big to fit nicely between the liftarms. The 16 and 20 (and 12) tooth gears fit a lot better. Perhaps this is why you don't see as many of the 24 tooth gears these days.

Edited May 3, 2011 by Splat

[Erik Leppen]

I do somewhat agree with SM96UK; there's very few 24t gears in recent sets and I sometimes think this is a pity. I own only five of them in dark gray. I often have to take light gray ones in MOCs.

As Splat, I also think this has a lot to do with the dimensions of the studless system. When building myself I notice this too. I use a lot of 12 and 20 tooth gears. They're very useful to gear up or down without having to save space for it. Also because they work in an angle you can do this nearly without needing extra space at all. And instead of 16 + 16 I take 20 + 12 or 12 + 20. Almost unnoticedly I can generate quite a lot of gearing down or up this way. If you follow the red axles on this image you'll see four times 12 to 20 after one another, to generate a 1 : 8 gear reduction without needing to make extra space for it.

With 24 tooth gears you usually need more space because it's a fraction too big to fit in three studs.

By the way something that is even more missing in recent sets than the 24 gear, is the 24 tooth crown gear. It was ideal in studded constructions, but it has pretty much been replaced by the 20 tooth gears (all types).

The 8 tooth gear is also pretty rare but I can't regret that. I have never liked the 8t gear. Because of the shape of the teeth and the low number of teeth they often don't run very smoothly. They're good for gearing down to 24 or 40 from a fast motor, but gearing up from 24 to 8 is rarely a good idea in my experience. I'd much rather do 20:12 twice, or 36:12. Or a worm.

What I do feel is missing too by the way, are the 36 and 40 tooth gears. I only have three of each, but use them quite often. The additional holes in those are sometimes useful too. The 36 tooth gear fits well in the studless system, and the 40 tooth gear is easy to mesh with a worm generating a 1:40 reduction in one go. Notice there is a 36 tooth gear in the image I linked to for example.

[merman]

I just realize: 8 + 24 = 16 + 16 = 20 + 12 = 32

I never understood why a crown gear is used on a wormgear sometimes....

[SM96UK]

I just realize: 8 + 24 = 16 + 16 = 20 + 12 = 32

I never understood why a crown gear is used on a wormgear sometimes....

ah, now that is because the gears which are a stud apart from each other are directly proportional to each other so if one gear had 18 teeth its partner gear would have 14 teeth, again if a gear had 4 teeth, its partner gear would have 28 teeth so on

[Dutch_EE]

I think that a reason to change to 12-20, is that it doesn't give a nice ratio. It's a strength issue.

When there is a nice ratio like 8:24 = 1:3, a bit of damage on a gear can give serious problems. This is because each tooth of gear 1 always meshes with the same teeth of gear 2. If 1 tooth of gear 1 is damaged, this means that the same teeth of gear 2 will get problems. If there is a ratio of 12:20, each tooth will mesh with different teeth on each revolution.

[Erik Leppen]

I think that a reason to change to 12-20, is that it doesn't give a nice ratio. It's a strength issue.

This is indeed the argument in real mechanics. However this does not really apply to Lego gears. Lego gears are not designed to run flawlessly for years uninterrupted, their primary purpose is that they fit in the dimensions of Lego constructions and give many possibilities with only a few different parts.

But you're right. I believe the two output axles on the RC buggy motor for example have a 17:23 ratio, for exactly this reason.

I just realize: 8 + 24 = 16 + 16 = 20 + 12 = 32

Yes. The sum of the number of teeth = 16 times the distance in studs between the two centers.

This is in fact very natural. The number of teeth is proportional to the gear circumference. The circumference is proportional to its radius. So, twice the radius --> twice the number of teeth. The distance between the axles of two gears is of course the sum of their radii. If this distance is kept the same, the sum of the radii is kept the same, and by proportionality the sum of the numbers of teeth is kept the same. One tooth more on one gear means one less on the other.

So if you can mesh a 20t with a 16t, then you know you can also mesh a 24t with a 12t over the same distance. And if 24t fits with 20t, then you know 36t fits with 8t.

And for Lego it is 8 teeth <-> radius 1/2 <-> circumference 2 * pi * 1/2 = pi.

So each tooth is pi / 8 studs = 0.392 studs.

On gear racks, 10 teeth = 4 studs, so each tooth = 0.400 studs.

I never understood why a crown gear is used on a wormgear sometimes....

My guess: less play? Don't know actually.

[allanp]

I never understood why a crown gear is used on a wormgear sometimes....

I think it's because on a standard gear, the worm gear only touches on a sharp edge of the tooth because the teeth are straight but on a worm they are at an angle. However the 24t crown gear has rounded edges, making for a nicer contact area.