Why do Power Functions motors need internal gearing

[LiamM32]

I thought that I recalled reading somewhere on the internet a long time ago that Power Functions motors have no internal gearing.

What the?

Well, it looks like that wasn't true. Now that I think of it, I think that I have heard the noise of the internal planetary gears when I run my Emerald Night. I'm just used to the sound, and I may have mistaken it for the buzz of the electric motor.

But I question if it's really a good idea to include internal gearing. Couldn't they have a smaller assembly if there was no internal gearing? Or they could have a larger electric motor inside with more total power-output. I would also expect the motor to be cheaper because of the simpler preassembly. Yes, I am aware of the basic fact that the gears are used to trade speed for strength. Wouldn't it be better if they just let us build that with our Technic gear pieces? Because Technic gears would take more space, maybe a separate preassembled planetary gearbox? I think that there are more Technic models that use gears to increase the speed of the motor than decrease it. It would probably be better if they at-least reduced it to one lair of planetary gears.

I only know the basics of how an electric motor works. But I don't know exactly what determines all the specifications. Is there a way to adjust the balance of speed and strength while the motor is being built? I would expect there to be some way.

[Blakbird]

There's been quite a bit of discussion on this very topic already. Many adult fans agree that it would be more fun to have an unguarded motor and do any adjustments in the model. The older 4.5V and 9V motors were like that. My guess is that Lego is trying to make Technic accessible to a lower age group just like they are doing by making the instructions so simple with 2 parts per step. For example, small models can be directly driven from a motor output using an XL motor.

[750ACE]

Please use search first. Lots of good info here.

http://www.eurobricks.com/forum/index.php?showtopic=78173&view=&hl=&fromsearch=1

[LiamM32]

I tried to use the search, but I didn't really find the results that I wanted. I sometimes just don't type the right words.

There's been quite a bit of discussion on this very topic already. Many adult fans agree that it would be more fun to have an unguarded motor and do any adjustments in the model. The older 4.5V and 9V motors were like that. My guess is that Lego is trying to make Technic accessible to a lower age group just like they are doing by making the instructions so simple with 2 parts per step. For example, small models can be directly driven from a motor output using an XL motor.

Interesting. I haven't found people who have stated that they would really prefer no internal gears, but just a very small amount of opinion-neutral discussion (not reading very deeply into the topics). I was more expecting to get a response to try and justify it.

But a separate planetary-gear preassembly would still be preferable so that it would be optional. But then, the least knowledgeable might not even understand the balance of "speed and strength", so might not even see the need for the gears when building MOCs, and get confused when they don't work. This could easily be solved by including a text-box in the instructions for non-Technic sets explaining it.

Since posting this today, I have made an attempt to quickly slap together my own 2-lair planetary gear set-up after discovering online that there are gear-teeth in the Power Miners drill piece. It would be less specialized, but it is bigger than the set-ups built into the PF motors (about 9L diameter) and has noticably high friction. A worm gear could be another option that would take up less space, which I have not tried yet with Power Functions.

[allanp]

Well I totally agree with you. Having the motor and planetary gear set as two separate parts would be far better. You would get all the pros of both the geared and ungeared motors combined as you can choose which one you have. You would also have a planetary gear set that could be used in many other places. So if you are feeling especially lazy you could stack a number of gear sets onto the end of the motor and it's job done, or you could not use them and have a cool ungeared motor, which means you could use quite, geartrain protecting belt drives, use the white clutch gear more effectively in any situation by choosing where it should be in the gearing down stage, spin those engines fast so they even sound somewhat authentic (I like to have the motor(s) look like an altenator or supercharger, driving the engine via its fan belts!) and so on.

[Zerobricks]

Problem with fast ungeared motors is, they need a lot of additional gearing, and FAST MOTORS TEND TO MELT BRICKS...

[nicjasno]

Badly engineered drivetrains melt bricks. Don't blame it on the motor.

[allanp]

Problem with fast ungeared motors is, they need a lot of additional gearing, and FAST MOTORS TEND TO MELT BRICKS...

There are pros and cons to geared and ungeared motors. All pros and cons considered, apart from the servo motor and a tiny micro motor, I would much rather have the motors be ungeared. However, by having a separate planetary gear reduction unit that can fit directly to an ungeared motor you have both options to choose from, plus the added benefit of a planetary gear reduction hub that can be used anywhere, separate from the motor, even right inside a wheel hub.

[1974]

Ungeared motors need a lot of extra space. It's not possible to design a planetry gear like that with original LEGO parts that don't need as much space as the actual motor. Don't sweat about the internal gears, just think of the XL motor as a motor with low RPM/high torque

The motors TLG uses are NOT available with low torque/high RPM, it's allways the opposite

[Erik Leppen]

Badly engineered drivetrains melt bricks. Don't blame it on the motor.

LEGO's target age group is not educated in engineering drivetrains.

[andythenorth]

Eh? There is no way a compact planetary mechanism could be built from standard technic gear parts. No planetary = no RC bulldozer, no rock crawler, no excavator, no...the list goes on. So Lego have traded playable functions against trying to teach the detail of how the gear train works. I have no problems with that.

When I was a kid, building gear trains got boring fast: "yeah ratios, ok I get it now, I can do maths, but I'm trying to build a racing car / dump truck / lift / lock gate / turntable / bulldozer, and these ABS gears are too big / too weak / too high friction to make decent gear trains".

Separate planetary part - that is an interesting idea. These existed for 4.5v / 9v motors and were useful. They could be stacked inline too for more reduction. More recently there was a cage part for making a strong compact worm gear drive - it's useful.

Edited August 18, 2013 by andythenorth

[rm8]

Nothing to add cause guys already answered

Use buggy motors

...even in Emerald night

Edited August 18, 2013 by rm8

[Nike 2101]

Nothing to add cause guys already answered

Use buggy motors

...even in Emerald night

Good idea!

[LiamM32]

Eh? There is no way a compact planetary mechanism could be built from standard technic gear parts. No planetary = no RC bulldozer, no rock crawler, no excavator, no...the list goes on. So Lego have traded playable functions against trying to teach the detail of how the gear train works. I have no problems with that.

Separate planetary part - that is an interesting idea. These existed for 4.5v / 9v motors and were useful. They could be stacked inline too for more reduction. More recently there was a cage part for making a strong compact worm gear drive - it's useful.

I can agree that most current Technic sets that would want to use motors suite the lower gear ratios, mostly being large land vehicles. There are still many land vehicles that would gear it back up slightly. But most of the official Technic sets that use motors are very large vehicles with full RC. I would like to see smaller vehicles with more minimalistic use of Power Functions, which would be able to use the motor at a faster speed. But then there is even more potential for fast but weak motorization if you look forward to expansion to things that use air turbines such as desk fans, rotary pneumatic compressors, and a slight chance of helicopters.

But it is good that we can agree that it would be better to split the motor and the planetary gears into 2 separate preassemblies. There is hardly-any argument against that (apposed to what the motors already are). I am rarely an advocate for Lego preassemblies, but it would save space from standard-gears. But I could not find the old planetary gearbox on Bricklink, so could you please give a link?

You also implied to like the cage that held a worm gear connection (with regular gear-pieces). That can easily be achieved without the cage piece. How is the worm with friction (at high speed)? I would expect it to be much better than the other options for down-gearing.

As for the friction problem; Maybe The Lego Group should change the plastic material in Technic gears to a lower-friction plastic. It appears that the internal gears in the PF motors are made of a plastic, which I recall seeing in gears in other toys. Could that one work? The problem with that that I can see is that it would slide around the axle too much. But maybe they could try co-injecting with the current plastic in the center, and the low-friction plastic around the teeth. There could easily be problems with this idea that I am unaware of though.

[clarkdef]

There are pros and cons to geared and ungeared motors. All pros and cons considered, apart from the servo motor and a tiny micro motor, I would much rather have the motors be ungeared. However, by having a separate planetary gear reduction unit that can fit directly to an ungeared motor you have both options to choose from, plus the added benefit of a planetary gear reduction hub that can be used anywhere, separate from the motor, even right inside a wheel hub.

This! One of the best Ideas I have heard in a while.

[andythenorth]

But I could not find the old planetary gearbox on Bricklink, so could you please give a link? (...snip...) You also implied to like the cage that held a worm gear connection (with regular gear-pieces). That can easily be achieved without the cage piece.

I think I mis-remembered the planetary; I think it was actually a worm drive with 90' between input and output. http://www.bricklink...gItem.asp?P=768 It's more than 20 years ago, but I was sure that education motor sets had a reduction gear with same angle input / output. Bad memory I guess.

Worm cage part is this http://www.bricklink...D=136&catType=P

Building a worm cage can be achieved with regular parts. Building a compact worm cage that doesn't come apart under torque loading is hard. Worm drives generate high torque, both when rotating, and if they are prone to a shock load when stopping (e.g. moving steering arms, extending a crane arm etc).

There is yet another worm drive as a preassembled gearbox: http://www.bricklink.com/catalogItem.asp?P=46220 marginally less flexible in mounting options (studs only). This gearbox shipped in a set that also included a couple of 90' 1:1 gearboxes http://www.bricklink....asp?P=46217c01

It appears that the internal gears in the PF motors are made of a plastic, which I recall seeing in gears in other toys. Could that one work?

I think it's probably nylon, but not sure. Edited August 19, 2013 by andythenorth

[LiamM32]

Maybe The Lego Group should change the plastic material in Technic gears to a lower-friction plastic. It appears that the internal gears in the PF motors are made of a plastic, which I recall seeing in gears in other toys. Could that one work? The problem with that that I can see is that it would slide around the axle too much. But maybe they could try co-injecting with the current plastic in the center, and the low-friction plastic around the teeth. There could easily be problems with this idea that I am unaware of though.

I think it's probably nylon, but not sure.

That is probably the right material. I just looked at the nylon Wikipedia page. It stated that nylon is used for gears in low or medium-stress applications.

The article stated that nylon is durable, abrasion-resistant (scratch-proof), and has other desirable properties listed. It is a moldable thermoplastic, just like ABS. I didn't find this stated clearly on Wikipedia, but some Google search results appear to imply that it is low-friction, which is the main reason why I am suggesting it.

I found an old preassembled bevel gearbox today in my house, which I believe is from an old Star Wars X-Wing set. The bevel gears inside appear to be nylon (judging by the nylon gears I looked at on Google images). I put an axle into the hole (which is part of the gear), and it is held nicely. It spins smoothly with low friction inside. Maybe they oil the internal gears in the factory. But if not that, then the combination of low-friction at the teeth and good grip at the axle makes it a suitable material for Technic gears.

I also tried to test the friction of the worm gear. It appears to be better than the connection of 2 spur or bevel gears, and it could reduce friction even more overall because it can give a great reduction with just one connection. It was not such an accurate test, but it appears that this would be the best way with current gear parts to give a high reduction in a compact size, but I should find an ungeared motor to test this.

Now about the nylon again; It appears that this is a very suitable material for Lego Technic gears. I think that they should replace the plastic used in their standard Technic gear pieces with nylon. Durable, moldable, low-friction at the teeth while having good grip in the axle-hole. They shouldn't worry much about the more special parts that have gear-teeth on them, such as the Power Miners drill or Technic turnables.

[Blakbird]

Nylon gears are perfect for this application. Metallic gears would have much higher friction and be noisier.

[LiamM32]

It is nice to see that we have generated a few ideas in my topic. As we don't suggest new product concepts on this site as often as I would like. It would be nice to test the hypothesis, but gearing-down an electric motor could be practical with the worm gear idea. The Emerald Night would work well with that. Maybe this topic should be moved to the embassy to suggest the ideas, or I could start a new topic.

Now it's nice to see a bit of agreement to the theory that nylon could be a more suitable material for Technic gears. I still have some questions though;

How much do gears currently cost? How much would they be if they were nylon?

Should the molds be changed so that we can tell between the old (current) and new nylon gears, or should they look the same?

Would they be broken by stress in cases when the current gears would not?

I think that the Lego company should first change their spur gears (in the 4 smallest cross-axle sizes) to nylon. They could then replace other types later.

The worm gear could be next in line, as it could reduce friction when pushing against the holder.

I am unsure about the double-bevel gears though; It could solve friction problems with them, but it seems to be the gears that they use in system playsets. I want to see more gears in playsets, but they could become less common if nylon is more expensive.

I'm not sure about the differential. I don't know how easy would be to give nylon such a complex mold. Maybe a different low-friction plastic. Unlike most gears, it doesn't need to grip the axles.

The knob gears should be kept the way they are. Same goes for non-dedicated gears such as Power Miners drill.

Like I said, I could post on the embassy to propose ungeared motors and nylon gears.

[Junpei]

You could always use the 2838 motors, they are cheap as dirt and look like they would fit well into a train too.

[Lipko]

To the neylon idea: can it be painted just like ABS? I would vomit of pale-white, or just slighty off color gears all around inside a Technic model.

Maybe that's the main reason for ABS

[Technyk32231]

To the neylon idea: can it be painted just like ABS? I would vomit of pale-white, or just slighty off color gears all around inside a Technic model.

Maybe that's the main reason for ABS

So you also hate the white in mindstorms?

[Junpei]

That's a different type of white. Take apart an m-motor and you'll see. It would look gross in a technic model.

[allanp]

Yeah, the colour isn't so nice, but you can still have ungeared motors and the same planetary gears used in the geared motors by having a separate planetay gear reduction preassembly, so when you put the two together it is basically the same as having a geared motor like we have now but the benefit is that you also have the option to have an ungeared motor as well as a planetary gear reduction preassembly that could be used anywhere in the geartrain and as many times as you like, so it would be much more versatile. I really think this is the best way forward.

Edited August 26, 2013 by allanp

[Junpei]

The 4.5V motor is ungeared and has a 1:20 gear block attachment, and ends up just being 1 stud longer than the m-motor because of the plugs which lego can now get rid of.

What? The 4.5V motor is being deleted from bricklink?