has the 40t gear been discontinued?

[Lipko]

okay, i get that. by dispersing the sum force over more contact surface, the gear teeth are able to better withstand the force.

...but you don't get something for nothing, right? the greater the diameter, the more input power required to overcome the torque. wouldn't proportionality come into play?

Power is a different thing than force. If we neglect the friction, then the power is independent of the diameter. Power depends on the torque and the revolution (power=torque*revolution). Or from another viewpoint, power depends on the work and the time it takes to get the work done (power=work/time). The work to be done is given (no matter how you get it done, you have to get it done, for example lifting something to a given height), power is the "intensity" how you do the work. Slower work (more time) means less power, faster work (less time) means more power is needed. If power is given (for example lifting something to a given height with a given time), then more torque means smaller revolution, less torque means bigger revolution is needed. That's why we use gearboxes, to modify the revolution and the torque. But the same power is "transferred" through the system, no matter how many gearboxes are there (again: if we neglect friction, which we can usually, since it's usually small)

So, if we are talking about forces: with larger diameter, a smaller force is enough to overcome the same torque (this force is called tangent force). Think about a lever. The longer it is, the easier to lift with it. I'm talking about same torque, because we are comparing a gear-pair against another gear-pair with the same gear-ratios and the same conditions.

The friction part is a bit more complex, since the force is smaller on each tooth, but the more contacting teeth compensate it. So it seems that the friction torque (friction tangent force multiplied with the diameter/2) is independent from the diameter. But the geometry, flexibility and other crap of the teeth is affecting this, so in the end, f*ck knows how this friction torque coming from the teeth depends on the diameter...

There's another thing comes into play: the friction of the axle in the hole. It does depend on the diameter:

Since the sides of the teeth are angled, radial force also rises between the gears: a force that pushes the gears apart. Since the angle of the teeth is a constant value (maybe 20 degrees, that's quite standard in engineering), this radial force grows as the tangent force grows. So it is inversely proportional to the diameter, just like the tangent force.

The friction torque of the axle is proportional to the radial force (the more you push something against something, the harder to slide them on each other->higher friction). That means a bigger gear have less friction on its axle, so the overall friction is smaller too (I think it's safe to say that this force is affected much more by the diameter, than the friction between the teeth.)

Another and IMHO big advantage of bigger gears: since the precision of Lego parts is given and more or less independent from the size, gearboxes from bigger gears have much less backlash than from smaller gears: more teeth with the same precision means the backlash of two contacting teeth (the gap between them) affects the angle of the gear, thus the backlash angle of the whole gear much less.

So the conclusion: it's almost always better to use bigger wheels. The only situation when smaller wheels are better, is when the space is small. The only disadvantage of bigger gears is the bigger weight, but I don't think it's a bottleneck with Legos. Another drawback is the bigger moment-of-inertia, which means it's harder to accelerate/brake the system, and bigger strain-pikes (shocks) when something changes/stops/whatever. That can affect the lifetime of the parts, especially with the constant speed Lego motors.

I don't know which effect is stronger: shocks but lower constant stain, or smaller shocks but bigger constant strain. I guess it depends on the ABS material.

I would definitely go for bigger gears in non-power-funtcion models.

zzzzz.. zzzzz.. zzzzz..

I think all the info is there, but maybe in not a followable manner. Anyhoo, hope that makes sense

Edited May 3, 2012 by Lipko

[allanp]

I like the 40t gear, it's really ..... erm..... technicy!

[Wiseman_2]

Out of curiosity, when was the last time the 40T was used in a gear train in an official Technic set? I know it's been used on a fair few bikes in the last decade or so but the only set I've seen it in a gear train in lately is the Imperial Shuttle.

[KEvron]

I would definitely go for bigger gears in non-power-funtcion models.

with four or five arbors making up the drive trains for my clocks, the additional friction, due to the additional mass, definitely adds up. i think the application would determine the appropriate sizes.

I think all the info is there, but maybe in not a followable manner. Anyhoo, hope that makes sense

a lot for me to try to get my head around, but thanks much for the info.

Out of curiosity, when was the last time the 40T was used in a gear train in an official Technic set? I know it's been used on a fair few bikes in the last decade or so but the only set I've seen it in a gear train in lately is the Imperial Shuttle.

'04, 8439 front end loader. otherwise, it's appeared in a few creator sets, nxt and supplementals.

KEvron

Edited May 3, 2012 by KEvron

[rgbrown]

[re: larger diameters give less friction] ah, i wasn't aware of this. could you explain?

KEvron

What I was thinking of is that the sliding friction should be less because the teeth are more parallel over the duration of contact. This presumably depends heavily on the tooth profile.

My impression of technic gears is that bevel gears have much greater friction than spur gears, but I've never actually tested this. I keep intending to do some proper measurements, but never quite manage to find the time!

[Brickthus]

I have always liked the 40T gear. It is great for taking a gear train sideways by a large amount. This is especially useful when connecting to a motor. I have used it noth as 5:1 reduction from a motor and for 1:1 sideways transmission when using multiple motors to increase the torque on a high-speed axle. Gearing up by 5:1 for a faster axle is best with these too, since TLG don't have a 4000rpm motor available in the current range. This is useful for my flight experiments:

The 40T gear has been superseded in the crawler track role to some extent by the new sprockets and 5-wide links. It looked like TLG were trying to phase out the older chain links (e.g. sets 856, 8851) but AFOLs stepped in to order more of them. May there always be a motorbike to use that system.

Yes, the trend towards heavier, higher-friction gear trains is bad. Bad for AFOLs and bad for children learning about basic mechanisms. If all the friction is taken by the double bevel gears, less power is left for the wheels of each super-fast car that every young lad wants to make.

It was a travesty when the crankshaft axle holes were removed from the 24T gear. That lost us a unique offset, which is in fact very useful for driving a crankshaft with small pneumatic cylinders, whose travel is less than 2M. We can hope that TLG would update the design of the cylinder in line with the compressor in Unimog 8110, so that small cylinders could be used with 2M half beams as the crank pieces. With the 24T gear hole removal in mind, I sincerely hope that TLG will never tamper with the 40T gear design.

The 40T cog has also been the best one for large steam engines whose wheels are suspended off the rails, till the model team 62mm wheel hubs came along. The latter are smoother but need modification for use in that role.

Mark

[KEvron]

What I was thinking of is that the sliding friction should be less because the teeth are more parallel over the duration of contact.

ah, again! that makes sense. still, more contact surface.

you'd think a thing like friction would be more intuitive. just when i think i've got my head around a thing, reality deals me a slap.

I keep intending to do some proper measurements, but never quite manage to find the time!

keep us posted.

Gearing up by 5:1 for a faster axle is best with these too, since TLG don't have a 4000rpm motor available in the current range.

you should think about acquiring the 5292 motors that came with the rc vehicles a few years ago:

they don't have quite the rpm's that the train motors do, but they've got double the torque. they're beasts!

and 5:1 brings up another gripe: the ratios which the bevels offer are irregular. 3:1 is the only straight ratio which they provide. i get that they're very useful for transmissions, where the range of the ratios is the critical factor, as opposed to specific specific ratios, but outside of that, who really has use for a 7:3 or 9:5 ratio?

It was a travesty when the crankshaft axle holes were removed from the 24T gear.

i believe they changed the design because the original was prone to structural failure. regardless, i ordered several from bricklink, just to make sure i have some on hand.

KEvron

Edited May 5, 2012 by KEvron

[CP5670]

This gear has been used sparsely for a long time. Even in the 90s, I can only think of two or three Technic sets that included it. It was more common in the 80s and in Mindstorms and Lego Education sets.

I've got a bunch of them but rarely use them. You can usually get similar or higher gear ratios in a smaller space by stacking two sets of smaller gears together, like 12/20 and 8/24.

[Brickthus]

...

you should think about acquiring the 5292 motors that came with the rc vehicles a few years ago:

they don't have quite the rpm's that the train motors do, but they've got double the torque. they're beasts!

...

KEvron

Yes, I have 4 of those. Having tried 4 PF M-motors, I'm about to try all 4 5292 motors at once on my compressor, which uses 16-cylinder dual crankshaft V-formation and is driving a pneumatic stepper motor. The PF M-motors managed enough air for 85rpm at 1.2 Amps with the hose disconnected, 1.8 Amps whilst pressurised, so it will be interesting to see whether the stepper motor driver speed can be increased - need more M-motors to drive that faster. The potential move towards more powerful motors (e.g. RS-380) gathers motivation! I think my car tyre air compressor might use an RS-540 or similar.

Having seen a couple in YouTube, I will see whether it's possible to drive a pneumatic steam engine without any tether to mains air or power. It's looking like one carriage for the compressor, one for the batteries! Whether it will still use 40-tooth cogs for driving wheels I don't know yet.

...

You can usually get similar or higher gear ratios in a smaller space by stacking two sets of smaller gears together, like 12/20 and 8/24.

Yes, albeit with greater friction. I don't like the amount of friction in the double bevel gears. It's the softer compound that causes some of it. That was a hangover from the z24 contrate gear. One thing that's better is that the bevel gears are more rigid than the contrate gear, which was redesigned at least twice over the years in order to stop the face bending relative to the axle support.

Also I actually like the fact that a 20-tooth gear can slide on an axle. I used it in the gearbox of my rail crane:

The pic shows the worm and one of the 8-tooth gears that engages with it so that the worm can move the 3x3 frame left and right. The 20-tooth gear slides by 4M, meshing with each of 4 12-tooth gears in turn, or two at once if you stop in the right place. This drives two winches, jib raising and turntable functions. Folder here.

I agree that sliding is not often so useful. I had to file a helicopter 8-lobe CV joint gear to allow it to slide for my Apache's full rotor control.

Mark

[DarkShadow73]

Geez, never realized there was so much controversy over this gear, the only sets I have them in are the Front-End Loaders and there were just there for articulation of the front and rear sections of that model...wow guess I better hang on to them...

with four or five arbors making up the drive trains for my clocks, the additional friction, due to the additional mass, definitely adds up. i think the application would determine the appropriate sizes.

a lot for me to try to get my head around, but thanks much for the info.

'04, 8439 front end loader. otherwise, it's appeared in a few creator sets, nxt and supplementals.

KEvron

Do indeed miss the motor, much larger and more torquier than the current PF motors...still have 3 of them but you have to use the old battery boxes, either the large bulky one or the smaller PF type one but with the 2 stud power connector cable with them...

Yes, I have 4 of those. Having tried 4 PF M-motors, I'm about to try all 4 5292 motors at once on my compressor, which uses 16-cylinder dual crankshaft V-formation and is driving a pneumatic stepper motor. The PF M-motors managed enough air for 85rpm at 1.2 Amps with the hose disconnected, 1.8 Amps whilst pressurised, so it will be interesting to see whether the stepper motor driver speed can be increased - need more M-motors to drive that faster. The potential move towards more powerful motors (e.g. RS-380) gathers motivation! I think my car tyre air compressor might use an RS-540 or similar.

Having seen a couple in YouTube, I will see whether it's possible to drive a pneumatic steam engine without any tether to mains air or power. It's looking like one carriage for the compressor, one for the batteries! Whether it will still use 40-tooth cogs for driving wheels I don't know yet.

Yes, albeit with greater friction. I don't like the amount of friction in the double bevel gears. It's the softer compound that causes some of it. That was a hangover from the z24 contrate gear. One thing that's better is that the bevel gears are more rigid than the contrate gear, which was redesigned at least twice over the years in order to stop the face bending relative to the axle support.

Also I actually like the fact that a 20-tooth gear can slide on an axle. I used it in the gearbox of my rail crane:

The pic shows the worm and one of the 8-tooth gears that engages with it so that the worm can move the 3x3 frame left and right. The 20-tooth gear slides by 4M, meshing with each of 4 12-tooth gears in turn, or two at once if you stop in the right place. This drives two winches, jib raising and turntable functions. Folder here.

I agree that sliding is not often so useful. I had to file a helicopter 8-lobe CV joint gear to allow it to slide for my Apache's full rotor control.

Mark

[KEvron]

I'm about to try all 4 5292 motors at once on my compressor

two words: safety goggles.

KEvron