Noisy gears

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Trevor Thompson
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Noisy gears

Post by Trevor Thompson » Wed Feb 01, 2023 10:21 am

Using a worm and worm wheel seems to produce a quiet gearbox.

However I have been making gear boxes with spur gears for use in my electrically powered locomotives for a while. They all seem to make a racket. Is it something I am doing wrong or is it the nature of standard MOD 0.5 gears? It doesn't seem to make a difference whether they are plastic or metal gears.

There seem to be plenty of motor/gearboxes available commercially which use spur gears, including expensive ones from Slaters, through to cheap ones on ebay.

Can anyone offer experience of such gearboxes which actually run without making a lot of noise?

I am looking for something to run from 6 volt batteries, giving about 100:1 reduction.

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Re: Noisy gears

Post by Melbournesparks » Thu Feb 02, 2023 1:02 am

I haven't had any real issues with noise in the traction motor gearboxes which use 0.5m nylon gears. It is important that they mesh correctly though, even a small misalignment can make them noisy.

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Re: Noisy gears

Post by GTB » Thu Feb 02, 2023 5:41 am

Trevor Thompson wrote: Wed Feb 01, 2023 10:21 am Using a worm and worm wheel seems to produce a quiet gearbox.
Yes, they can be quieter, but they work by a sliding action, so they absorb more power and wear faster than spur gears.
Trevor Thompson wrote: Wed Feb 01, 2023 10:21 am Can anyone offer experience of such gearboxes which actually run without making a lot of noise?

I am looking for something to run from 6 volt batteries, giving about 100:1 reduction.
Some random thoughts.....

When it comes to gears, cheap and quiet are mutually exclusive. Straight tooth spur gears are cheap to make but are noisy. Helical tooth gears are quieter, but a lot more expensive to make.

0.5 Mod gears are finer and more fragile than say 0.8 Mod, or 1.0 Mod gears, but I've never noticed finer gears to be noisier than coarser ones, all other things being equal. Finer gears are more sensitive to how well they are meshed and that affects the noise level.

High reduction gearboxes are noisier than ones with lower ratios. As I've said before I have never understood why british modellers insist on using very high reduction ratios with small motors screaming their head off at maximum revs. I still remember the much vaunted Portescap drives which were lauded in UK magazines 40+ yrs ago and how I was unimpressed by how noisy they were when I actually heard one running. Fine if you were building a 4mm chaff cutter, or a British diesel, for steam locos not so much.......


You'll see my drive design philosphy for electrically powered models if you do a search for 'TVT' in the electric locomotive section of the forum. There are four recent railmotor models, a steam loco and a large diesel. The large diesel drive is much quieter than the Como based drive in my old Merlin Motor Mule and for that matter it is quieter than the worm drive in the Accucraft Walker railcar. The drive noise in the recent models is masked by the noise from the metal wheels of the train when running outside on the track.

I now use Pololu gearmotors from a local supplier who caters to the robotics hobby. They are about twice the price of a cheap ebay special, but they run smoothly and quietly and the manufacturer has data sheets available showing the dimensions and motor running characteristics needed for designing the drive. Small railmotors use 6V HP micro motor gearboxes which use N20 size motors. Larger models use 12V 20mm, or 12V 25mm motors. The larger motors have closed metal gearboxes, which are quieter than the open gearboxes of the micro motors.

I also buy the final drive mitre gears from the local branch of RS. Again, more expensive, but the quality is consistent and there are data sheets for getting the mesh right when machining gearboxes. I use 0.5 Mod gears for small models where space is tight and 0.8 Mod for heavier and more powerful models.

I find that designing the drive so it runs at the desired scale speed at around half the battery voltage, is a good trade-off between minimum noise and adequate motor torque and speed.

Graeme

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Re: Noisy gears

Post by Phil.P » Thu Feb 02, 2023 12:36 pm

Graeme,
Very interesting, and much to think about. - I hate motor/gear noise!

Do you find any problems, with running the motors at a lower voltage for prolonged periods? - I am wondering if they will tend to run 'hot'?

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Re: Noisy gears

Post by ge_rik » Thu Feb 02, 2023 7:56 pm

Phil.P wrote: Thu Feb 02, 2023 12:36 pm Graeme,
Very interesting, and much to think about. - I hate motor/gear noise!

Do you find any problems, with running the motors at a lower voltage for prolonged periods? - I am wondering if they will tend to run 'hot'?

Phil.P
Hi Phil

I'd have thought they would be more likely to run hot if they were flat out.

Most of my locos use LGB, Piko or Bachmann motor blocks which are designed to run up to 24v. My battery packs are all 3S li ion (nominally 11.1v) and even then I seldom if ever run them over half throttle (6v ish or the PWM equivalent). I've never noticed any of them overheating. I've even run one loco continuously for 12 hours and it was as cool as the legendary cucumber afterwards.

BTW I've just invested in one of MFA Como's more expensive "Noise Attenuated" gearbox motors. The burb says ......

Designed for heavier duty industrial and modelling applications. These units boast a high quality five pole low rpm motor providing
approx 45% more motor torque than the standard RE385 motor with a considerable reduction in motor noise level. The metal gearbox
incorporates sleeve bearings, enabling the high torque transfer from the motor to be transmitted through the gearbox.


I think that means it should be quieter

Rik
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Re: Noisy gears

Post by Trevor Thompson » Thu Feb 02, 2023 8:13 pm

GTB wrote: Thu Feb 02, 2023 5:41 am
Trevor Thompson wrote: Wed Feb 01, 2023 10:21 am Using a worm and worm wheel seems to produce a quiet gearbox.
Yes, they can be quieter, but they work by a sliding action, so they absorb more power and wear faster than spur gears.
Trevor Thompson wrote: Wed Feb 01, 2023 10:21 am Can anyone offer experience of such gearboxes which actually run without making a lot of noise?

I am looking for something to run from 6 volt batteries, giving about 100:1 reduction.
Some random thoughts.....

When it comes to gears, cheap and quiet are mutually exclusive. Straight tooth spur gears are cheap to make but are noisy. Helical tooth gears are quieter, but a lot more expensive to make.

0.5 Mod gears are finer and more fragile than say 0.8 Mod, or 1.0 Mod gears, but I've never noticed finer gears to be noisier than coarser ones, all other things being equal. Finer gears are more sensitive to how well they are meshed and that affects the noise level.

High reduction gearboxes are noisier than ones with lower ratios. As I've said before I have never understood why british modellers insist on using very high reduction ratios with small motors screaming their head off at maximum revs. I still remember the much vaunted Portescap drives which were lauded in UK magazines 40+ yrs ago and how I was unimpressed by how noisy they were when I actually heard one running. Fine if you were building a 4mm chaff cutter, or a British diesel, for steam locos not so much.......


You'll see my drive design philosphy for electrically powered models if you do a search for 'TVT' in the electric locomotive section of the forum. There are four recent railmotor models, a steam loco and a large diesel. The large diesel drive is much quieter than the Como based drive in my old Merlin Motor Mule and for that matter it is quieter than the worm drive in the Accucraft Walker railcar. The drive noise in the recent models is masked by the noise from the metal wheels of the train when running outside on the track.

I now use Pololu gearmotors from a local supplier who caters to the robotics hobby. They are about twice the price of a cheap ebay special, but they run smoothly and quietly and the manufacturer has data sheets available showing the dimensions and motor running characteristics needed for designing the drive. Small railmotors use 6V HP micro motor gearboxes which use N20 size motors. Larger models use 12V 20mm, or 12V 25mm motors. The larger motors have closed metal gearboxes, which are quieter than the open gearboxes of the micro motors.

I also buy the final drive mitre gears from the local branch of RS. Again, more expensive, but the quality is consistent and there are data sheets for getting the mesh right when machining gearboxes. I use 0.5 Mod gears for small models where space is tight and 0.8 Mod for heavier and more powerful models.

I find that designing the drive so it runs at the desired scale speed at around half the battery voltage, is a good trade-off between minimum noise and adequate motor torque and speed.

Graeme
Graeme

Thanks for all of that information. It really is what I was looking for.

I will do some research and read your posts under the electric loco section.

Trevor

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Re: Noisy gears

Post by GTB » Thu Feb 02, 2023 11:33 pm

Phil.P wrote: Thu Feb 02, 2023 12:36 pm Do you find any problems, with running the motors at a lower voltage for prolonged periods? - I am wondering if they will tend to run 'hot'?
No. The gearbox ratio is chosen so that the motor is running at it's maximum efficiency at the rated voltage when the model is running at the desired scale speed. That way heat buildup is minimised.

If the motor is running hot, it is overloaded and running too slow at high voltage. I always make sure with a new model that the drive has enough torque to slip the wheels at the rated voltage. I also fit a suitable PTC fuse (polyswitch?) in the wiring to limit maximum current draw. That way the motor won't be able to stall in normal running and if something causes it to lock up it can't cook itself.

My track is elevated, so is at less risk of something getting into the gearing, but I still fit gear covers to keep debris out of the mech.

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Re: Noisy gears

Post by GTB » Thu Feb 02, 2023 11:50 pm

ge_rik wrote: Thu Feb 02, 2023 7:56 pm BTW I've just invested in one of MFA Como's more expensive "Noise Attenuated" gearbox motors. The burb says ......
That's much the same spec. as the larger Pololu motor gearboxes, they must be feeling the competition.

The Como LN motors only come in 32mm and 35mm sizes. What are you planning that needs that large a motor, a Garratt???

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Re: Noisy gears

Post by ge_rik » Fri Feb 03, 2023 6:41 am

GTB wrote: Thu Feb 02, 2023 11:50 pm
ge_rik wrote: Thu Feb 02, 2023 7:56 pm BTW I've just invested in one of MFA Como's more expensive "Noise Attenuated" gearbox motors. The burb says ......
That's much the same spec. as the larger Pololu motor gearboxes, they must be feeling the competition.

The Como LN motors only come in 32mm and 35mm sizes. What are you planning that needs that large a motor, a Garratt???

Graeme
No, nothing as sophisticated. The GVT tram loco. I tried the bog standard MFA Como gear motor and it was underpowered so I thought I'd try something with a bit more torque. I wasn't aware of the Polulo range of smaller gear motors.

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Re: Noisy gears

Post by Trevor Thompson » Fri Feb 03, 2023 9:34 am

Melbournesparks wrote: Thu Feb 02, 2023 1:02 am I haven't had any real issues with noise in the traction motor gearboxes which use 0.5m nylon gears. It is important that they mesh correctly though, even a small misalignment can make them noisy.

Image
Yes I am sure that half of the problem is getting them to mesh properly. There is no indication of what the pitch circle diameter is when you buy cheap gears - so its difficult to know what the correct mesh should be.

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Re: Noisy gears

Post by philipy » Fri Feb 03, 2023 12:02 pm

Trevor Thompson wrote: Fri Feb 03, 2023 9:34 am so its difficult to know what the correct mesh should be.
Rule of thumb used to be to put a piece of fag paper between the gears and move them together gently until they stop. I'm sure that offends the mechanical experts amongst us but it used to work. :roll:
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Re: Noisy gears

Post by Mamod sterling » Fri Feb 03, 2023 1:26 pm

Phil.P wrote: Thu Feb 02, 2023 12:36 pm Graeme,
Very interesting, and much to think about. - I hate motor/gear noise!

Do you find any problems, with running the motors at a lower voltage for prolonged periods? - I am wondering if they will tend to run 'hot'?

Phil.P
Phil,

In principle, the heat generated (and power consumed) increase by the cube of the speed. so a 10% increase in motor speed, 33% more heat. However it works both ways, so reducing speed from rated, will also reduce heat rejection. Unless you go down to super low percentages of motor rated speed, then the heat starts to crease owing to the load to move the motor from pole to pole, the efficiency drops off and heat generation comes back in.

Thanks
Paul.

P.s. Gears. Worm drive has a cushioning effect which reduces the harshness of the meshing, making it more quiet compared to straight cut spur gears, but the contact time is longer too, increasing friction.

helical cut gears act as a halfway house, part cushion, part efficient transmission.

A fully enclosed gearbox, with a nice sticky grease that holds between the gear teeth can produce a low noise box. The issue isn't really resolved, its just mitigated.

A really quiet transmission method of course is belt drive.
Mamod SL1 - ripe for modification
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Re: Noisy gears

Post by Phil.P » Fri Feb 03, 2023 3:17 pm

Thanks to all for the extra information..

Being a bit of a luddite, I count teeth, and do the arithmetic! - Mod, means nothing to me! :dontknow:

I don't suppose three-penny motors from across the China Sea help?
When you get a new motor, put the rated voltage on it (no load) and it screams like an injured banshee..
Then you are on a hiding to nothing, before you start.

There is a reason that quality motors, are the size, and price, they are!

Aside:
I was under the impression the 'Como' low-noise motor, was better for 'electrical' noise, as well?


Q2:
Why do very few people use bevel (mitre?) gears?
I understand a worm and worm-wheel can give a large ratio in one stage, but I would have thought transmission through a pair of bevel-gears would be pretty efficient? - Especially as our loads are not excessive.

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Re: Noisy gears

Post by Peter Butler » Fri Feb 03, 2023 9:30 pm

Phil.P wrote: Fri Feb 03, 2023 3:17 pm


Why do very few people use bevel (mitre?) gears?


Phil.P
Please Sir.... I do!
IMG_3068.JPG
IMG_3068.JPG (476.7 KiB) Viewed 4328 times
I have been using nylon bevel gears for some years and they run smoothly and silently.
The best things in life are free.... so why am I doing this?

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Re: Noisy gears

Post by Melbournesparks » Fri Feb 03, 2023 11:56 pm

philipy wrote: Fri Feb 03, 2023 12:02 pm
Trevor Thompson wrote: Fri Feb 03, 2023 9:34 am so its difficult to know what the correct mesh should be.
Rule of thumb used to be to put a piece of fag paper between the gears and move them together gently until they stop. I'm sure that offends the mechanical experts amongst us but it used to work. :roll:
That's pretty much what I did. Measure the spacing with the gears together actually contacting each other, then subtract 0.1mm. It still took a couple of prototypes to fine tune it exactly, but at least with the 3D printed gearbox cases once the process is done they can be easily reproduced.
Phil.P wrote: Fri Feb 03, 2023 3:17 pm Thanks to all for the extra information..

Being a bit of a luddite, I count teeth, and do the arithmetic! - Mod, means nothing to me! :dontknow:

I don't suppose three-penny motors from across the China Sea help?
When you get a new motor, put the rated voltage on it (no load) and it screams like an injured banshee..
Then you are on a hiding to nothing, before you start.

There is a reason that quality motors, are the size, and price, they are!
The modulus is the spacing from the tip of one tooth to the middle of the gap for the opposing tooth. For our small gearboxes there's really only a handful of common ones, the main thing is to just make sure all the gears are the same so they mesh.

You can get motors with high torque and a 12v rated speed of only 4000rpm or so very cheaply now. The wide availability of very strong permanent magnets has made small motors far better than they were in the past needing a lot less gear reduction, but it seems like a lot of UK practice hasn't really caught up with this and gearboxes designed for an input speed of 10,000rpm are still common in rail applications.
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Re: Noisy gears

Post by Phil.P » Sat Feb 04, 2023 11:14 am

Yes, it always seems strange that people talk about 'using 30:1 gear boxes' but no mention of the motor-rpm, or final wheel diameter..

I think many of our models are run very fast (compared to the prototype).

I suppose I need to design/build a 'speed-trap' as well?
:lol:

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Re: Noisy gears

Post by GTB » Fri Feb 17, 2023 3:07 am

Some more technical info to finish this topic, ie. an overview of what is needed to determine the gears needed and to lay them out........

The sort of gears we use in models are what is called involute gears, which refers to the shape of the teeth. The sides of the teeth follow a particular curve so that the tooth to tooth contact is a rolling motion, not a sliding one. Which reduces wear and noise if properly meshed.

When laying out the gears for a chassis or gearbox, the relevant dimensions needed are tooth number (sets the reduction ratio), PCD ( pitch circle diameter which determines the spacing of the gears) and either MOD (module) or DP (diametral pitch) which determines the tooth size and compatibility with other gears. These are the only dimensions that we need to be worried about when choosing commercial gears for a model, the other dimensions are only relevant to making the gears from scratch.

MOD is used to describe metric gears. The formula used is MOD = PCD x no. of teeth.

DP is used to describe gears made in english units and is still used in the US. The formula is DP = PCD/no. of teeth.

Standard commercial gears are usually made in a limited range of MOD/DP and tooth numbers, which keeps cost down.

Contrary to what you may read in the descriptions of cheap gears sold on Ebay, etc. metric unit gears and english unit gears are NOT compatible. As an example I recently bought some gears made for the gearbox of an r/c car that were claimed to be 42 DP. Being made in China I doubted that and when they arrived, as expected they were 0.6 MOD, which is equivalent to 42.333 DP. It didn't matter to me in this case, I wanted metric gears for my application anyway....... :roll:

If you do the calculations, for obvious reasons when converting from mm to inches there can be no exact equivalents between MOD and DP gears. It would be easy to make a gear with some multiple of 42.3 teeth by screwing up the indexing, but getting it to work would be interesting........

Since I much prefer to use reference books than online sources, my usual reference source when working with gears is the first half of 'Gears and Gearcutting' by Ivan Law. Aimed at model engineers, This is no. 17 in the Workshop Practice Series published by Special Interest Model Books in the UK and is still in print (and a lot cheaper than a copy of Machinery's Handbook :shock: ).

Yes, I have read the section on gear cutting in Ivan Law's book and no, I'm not planning on taking it up any time soon. :study:

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Re: Noisy gears

Post by GTB » Fri Feb 17, 2023 3:35 am

Phil.P wrote: Sat Feb 04, 2023 11:14 am I suppose I need to design/build a 'speed-trap' as well?
If you like fiddling with electronics go for it......

I just use a cheap timer and a calculator, or a mobile phone could do it. The mainline loop on my track is 120 ft long and if a model takes about 1 min 20 secs to travel back to the starting point it will be doing around 20 scale mph.

Which just happens to be the maximum speed the VR allowed on the ng lines.

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Re: Noisy gears

Post by ge_rik » Fri Feb 17, 2023 7:50 am

That's a really interesting and helpful summary Graeme.

When I was trying to find replacements for the large diameter worms on my early Bachmann Lyn motor block, I discovered a website which calculated the MOD if I entered the worm wheel diameter and the number of teeth. Of course, even with a digital micrometer it was tricky trying to measure the diameter and a difference of even a few hundredths of a mm made quite a difference to the MOD. I sent off for replacement worms which were as near as I could find to the average of calculated MOD values and, inevitably, they didn't mesh. I see now that I should have been calculating DP, as Bachmann is a US company; though, probably, I still would have struggled to find an exact match.

In the end, I discovered that the worms from a different (and redundant) Bachmann loco were the same, as was the motor, and so used that.

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Re: Noisy gears

Post by GTB » Fri Feb 17, 2023 11:42 am

ge_rik wrote: Fri Feb 17, 2023 7:50 am I see now that I should have been calculating DP, as Bachmann is a US company; though, probably, I still would have struggled to find an exact match.
Bachmann used to be American, but for a long time has been a subsidiary of the Kader group, which is Chinese owned. More importantly the factories and design offices are in China, so their gears are more likely to be metric. I wouldn't be surprised though if that strange worm gear arrangement they used in the early Lyn was a unique MOD size.

I've avoided worm gearing in garden scale and know just enough about them to be dangerous. I think they use an involute tooth form, but a properly made worm wheel and a spur gear aren't interchangeable, even if they are the same MOD or DP.

One of the 'fun' things about using gears is that the critical dimension is the PCD and that can't actually be measured, it can only be calculated from the other parameters. Which is why I pay the extra and use gears where the manufacturer specs. are available.

Graeme

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