Problems with gears in the Crocodile 10277

[Lebostein]

In the Crocodile 10277 is a gear combination like the screenshot below. A black "12 Tooth Double Bevel" (32270) and a tan "20 Tooth Double Bevel" (32269) between two technic bricks separated by two plates. My problem: it seems that gear combination don't work smooth. It it keeps stalling, it rattles and it runs very stiffly (high friction). I have tried the same gears from other sets, but the problem remains (sometimes worse, sometimes less bad).

What is going on? Are these gears ar not made to use it in this combination? Or is the design of the teeths wrong for this wheels? https://en.wikipedia.org/wiki/Gear#Nomenclature

[Zerobricks]

Check here:

https://www.eurobricks.com/forum/index.php?/forums/topic/173683-anyone-having-problems-with-tan-bevel-gear-in-recent-sets/

[Lebostein]

It seems this is a design bug by LEGO. Maybe LEGO should have asked a mechanical engineer before designing new gears. The design of tooth profiles was compulsory in our basic studies: https://en.wikipedia.org/wiki/Involute_gear

The old gray gears from my Technic Sets from 1990 have involute gears. Very smooth and almost frictionless...

Edited July 28, 2020 by Lebostein

[howitzer]

It's not about tooth profile design, there appears to be a manufacturing defect in some of these tan 20-tooth double bevel gears. Many people have experienced problems and for others they work fine so it might be an issue with the moulds from a certain factory. You can ask for a replacement from Lego customer service. In the topic linked by Zerobricks you can find more discussion about the problem.

[kbalage]

My sample had no issues with this gear combination, tried with several different motors and power sources

[Captainowie]

Two axleholes in bricks separated by two plates in the vertical direction are the same distance apart as two axleholes separated by one axlehole in the horizontal direction. Given that that's the spacing of that gear pairing, there really shouldn't be any problem with the setup you posted.

[Polarlicht]

Is it possible to use 2 grey gears (the "medium" ones which are rougly 2 studs in diameter and have 4 bar sized holes, forgot how much tooth they have) with a chain in this case?

[howitzer]

33 minutes ago, Coolusername said:

Is it possible to use 2 grey gears (the "medium" ones which are rougly 2 studs in diameter and have 4 bar sized holes, forgot how much tooth they have) with a chain in this case?

If you're talking about 16T gears, they mesh as do the pictured 12+20T gears, so chain is not an option. Chain would also make the gears turn in the same direction, unlike two meshing gears. Other than that, two 16T gears could be used, assuming there's enough clearance around the 12T gear and the change in gearing ratio doesn't become a problem.

[Polarlicht]

Yeah, but the croc has 3 gears doesn't it so motor turns in the same direction as the wheels.

[Lebostein]

On 7/28/2020 at 9:56 PM, kbalage said:

My sample had no issues with this gear combination, tried with several different motors and power sources

No! With a motor you can not feel the friction. The motor has enough power to rotate the wheels. But you can feel the massive friction if you turn the gears by hand!

[kbalage]

1 hour ago, Lebostein said:

No! With a motor you can not feel the friction. The motor has enough power to rotate the wheels. But you can feel the massive friction if you turn the gears by hand!

Nope, no any "massive" friction even if I turn it by hand. Btw if there's a higher than usual friction then you will also see it on the motors' performance.

[Rudivdk]

@Lebostein although I do not have this specific set, I did have the same issue with this gear combination in other sets. It's a production flaw for SOME of the tan 20t double bevel gears in the last few years.

These gears also exist in black and have also been produced in light (bluish) grey. The grey ones are the oldest, and most smooth ones. Try if you can get a hold of a different colored version and your problems are almost certainly over. 

And of course as howitzer mentioned before, contact LEGO customer support for a replacement tan gear, they provide them without issue. From what I have read around here, the replacements are (almost) always better quality than the flawed ones in the set.

[doug72]

You might get more answers on the Train Tech Forum.