"Gaps" in Parts ... I wish I had

[DrJB]

I took advantage of the long weekend here in the US to sort the mess my kids created ... by mixing NXT/EV3 and all other lego(s). Then, while going through my gears assortment, had a couple of thoughts:

The current gears come in: 8, 12, 16, 20, 24, 36, 40 teeth. Bold have the DB (double-bevel) profile

What is missing from this sequence are of course gears with 28 and 32 teeth. We kind of have the 28 teeth already (mini turntable) but it does not go on an axle. Hence the title of this thread ... 'Gaps'

1. If made available, would such gears be really useful, have you ever needed gears with 28/32 teeth?

2. Would such gears exist (prototypes) but were never officially released?

3. Why TLG has yet to upgrade all gears to DB? Those would use more plastic an thus cost more?

4. Any other GAPS you can think of, as in Liftarms lengths or connectors angles? (I've seen some digital models of 'interesting' connectors).

Of course, the idea here is of parts that would 'increase' the building possibilities, not just a mere combination of anything possible.

Edited December 3, 2013 by DrJB

[Hrafn]

Good topic! In addition, I believe the large Technic turntable has 56 teeth, and of course there are the old, weak 14t single-bevel gears.

1. 28/32 tooth gears wouldn't add much utility, since they wouldn't be that different from 24 and 36 in terms of the ratios you could achieve with other gears. I do wish the 3L differentials had the same number of teeth as existing gears, though - currently they have 28 which can be awkward.

4. As has been brought up in other threads, clutch gears in sizes other than 16t would be nice, probably 20t and 24t. It would be hard to make 8t and 12t work, and 36 and 40 would be too large. The "dogbone" liftarm in the 2014 sets looks promising. I'd like to see more liftarms with holes in more than one direction, like the 5x7 and 5x11 but smaller.

[LegoGBC]

For GBCs, which often require very accurate and specific gear ratios, adding 28t and 32t gears would be great.

I often find myself needing a compact 1:4 gear ratio and with the 8t and 32t gear that could be great.

[Boxerlego]

Size is an issue for gears above 20T. Just look at the new 3L differential and compared that to the old 4L differential where size was seen an issue when it came to building. It is all about proportions. Would the 28/32t gear be like the 4L differential and require a even style of building to mesh with other gears.

[Hrafn]

Size is an issue for gears above 20T. Just look at the new 3L differential and compared that to the old 4L differential where size was seen an issue when it came to building. It is all about proportions. Would the 28/32t gear be like the 4L differential and require a even style of building to mesh with other gears.

I agree with you about size - even 24t can be large in gearboxes.

Spacing, though, should be somewhat less of an issue. We already have gear combinations that don't work with an integer number of Lego units (L) - 8t and 20t, for example. The axle spacing (in mm) required for perfect meshing of two gears is equal to the average of the number of teeth on the two gears. So two 8t gears have an average of 8 teeth and need a spacing of 8mm (which equals 1L). The 28t would mesh easily with the 20t (3L spacing) and the 32t with the 16t (3L). The latter isn't very useful, though - if you need a 2:1 ratio using a 16t/8t is much more compact.

On both size and meshing, 28t seems more useful than 32t.

[DrJB]

Size is an issue for gears above 20T. Just look at the new 3L differential and compared that to the old 4L differential where size was seen an issue when it came to building. It is all about proportions. Would the 28/32t gear be like the 4L differential and require a even style of building to mesh with other gears.

My recollection for the differentials is as follows:

1. The Old 4L wide was useful in studded builds where the width of the car was an even number (xL).

2. For the new liftarm-based cars, where the width tends to be more an 'odd' number, the NEW 3L differential is more appropriate.

[Junpei]

Does the fourth connector down count as a 'gap' ? I've needed that part quite a few times.

[Lakop]

The fourth connector down no longer exists but I wish it did. I've seen it somewhere before.

H

[Junpei]

Have you seen it in a drawing or something else? I'm curious as to where you've seen this piece. Maybe a prototype Technic set?

[Boxerlego]

I found this blog and it brings attention about the 28/32T gears among other very interesting parts idea. http://legodifferent...hat-dont-exist/

@Hrafn Amazing what math and Lego can do, but have a look at this. When you did the math around the 28t and the 20t gear to receive an answer that is 3L spacing. Now here is a spread sheet that is 10 years old showing the spacing and quality of the potential gear mesh, Note: that this spread includes the 28t gear meshing with others gear but not the 32t. The mesh quality between the 28t to the 20t gear defining color is yellow.

@DrJB Exactly, I want to elaborate a little more on the comparison statement between the new 3L to old 4L differential. We can see that new differential's ring gear has become a half plate bevel gear and the nubs on the ends old differential has been sized down off the design allowing it to fit with in smaller dimensions of studdless design. Overall we can see that the first ever differential gear teeth count has remained exactly the same as the transition from studded to studdless happen along with a significance change in design towards the drive gear.

[Junpei]

I have discovered that before, very interesting that an old style (light grey) diff meshes perfectly with a 20t gear, how could that not be a coincedence? The old-style diff was introduced in 1980, and the 20t was introduced in 1999, which was 19 (!) years later.

[Hrafn]

@Hrafn Amazing what math and Lego can do, but have a look at this. When you did the math around the 28t and the 20t gear to receive an answer that is 3L spacing. Now here is a spread sheet that is 10 years old showing the spacing and quality of the potential gear mesh, Note: that this spread includes the 28t gear meshing with others gear but not the 32t. The mesh quality between the 28t to the 20t gear defining color is yellow.

It's yellow at a meshing distance of 2.968 studs, but green 9 rows down at a distance of 3.000 studs. The rule of thumb I outlined should work for the optimum spacing for any Lego gears (other than the worm) since it's based on the facts that 1) for teeth to mesh, they must be the same size and 2) the number of teeth is proportional to the circumference of the gear, which is also proportional to the radius of the gear.

Of course the rule of thumb doesn't tell you anything about non-optimal spacings that still work reasonably well (with some slop or friction).

[DrJB]

Reading above post reminded me of a 'limitation' in LDD ... does anyone know what 'dimensional' tolerance LDD allows for snapping parts to each other?

Edited December 5, 2013 by DrJB

[Boxerlego]

It's yellow at a meshing distance of 2.968 studs, but green 9 rows down at a distance of 3.000 studs. The rule of thumb I outlined should work for the optimum spacing for any Lego gears (other than the worm) since it's based on the facts that 1) for teeth to mesh, they must be the same size and 2) the number of teeth is proportional to the circumference of the gear, which is also proportional to the radius of the gear.

Of course the rule of thumb doesn't tell you anything about non-optimal spacings that still work reasonably well (with some slop or friction).

I see that green one and I see that the math works... it was just that yellow one and its distance is a hypothetical gap. What if we took some of the yellow and red gear sets and see if some teeth could be added or subtracted to the gear so it can mesh with the other. For example the 14t gear and the 36t gear, just take off two teeth from the 36t gear for a 34t gear and now the new gear set is 14t to 34t and that can fit within the 3 studs distance

[Hrafn]

I see that green one and I see that the math works... it was just that yellow one and its distance is a hypothetical gap. What if we took some of the yellow and red gear sets and see if some teeth could be added or subtracted to the gear so it can mesh with the other. For example the 14t gear and the 36t gear, just take off two teeth from the 36t gear for a 34t gear and now the new gear set is 14t to 34t and that can fit within the 3 studs distance

Ah, I see what you mean now. It's true, having more sizes of gears would allow more combinations of gears at each spacing. Here's hoping we get a 28t double bevel at some point, at least!

[dhc6twinotter]

I'm pretty happy with the current gear selection, however, I do wish there were more idler gear sizes other than the 16t. A 16t clutch gear would be nice too, since the 24t can be a tight fit in places. I would also like a 9L gear rack.

[JM1971]

I've always wanted helical gears for lego, I know they are quieter but are they also stronger?

[Heppeng]

Problem with Helical gears is that they develop side thrust. This could push a lego gear along its axle and out of mesh if the load is high enough.

[DrJB]

That and ... the angle and diameter are tightly related. If you want two gears to mesh, they need to have the same angle, and that leads to diameters that most of the time are not exact multiples of the basic module spacing L/M.

[Moz]

The big issue with helical gears and Lego is that there's a lot of sliding, which is not kind to unlubricated plastic. The current worm gear demonstrates that and the angle issue described by DrJB above. For any high-load application you end up having to put grease on the model.