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dangermouse

Gear Ratios

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Hello all

have done some searching and some reading and some pondering

 

I think I understand

 

8t pinion 30t crown = high torque - rally type tracks

10t pinion 24t crown = high speed - tracks with long straights

 

What then is a good middle ratio 9t - 27t ? or 1:3 ?

 

Is it the ratio that matters rather than the number of teeth - ie does an 8t pinion and a 24t crown perform the same as a 9t - 27t ?

I have also discovered that the size of the wheel also impacts on the effective ratio but don't think I will worry too much about that :)

 

thanks

DM

Edited by dangermouse

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its the same ratio but due to the gears being smaller they are not as smooth sometimes (depending on Brand) so i would use 9/27 but others my have different opinions on this


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Taking into account the tyre diameter isnt that hard. Its called rollout.

 

 

Example:

Rollout = [3.14 x (pinion teeth) x (tyre diameter)] / (spur teeth)

 

Rollout for the example above would be

 

Rollout = [3.14 x 10 x 21] / 32 = 20.6mm

 

The other thing to conside is that it takes a certain amount of torque to produce a given speed. Just because you incease the pinion or reduce the spur that is not going to make the car have a higher top end speed. If you aint got the toque to go any faster then changing the ratio is going to do diddly squat.

 

To prove the concept get on your bike and peddle into a head wind. Change the ratio from 3:1 to 2.4:1. Do you really think your gonna go any faster?


cheers

rick1776

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There was a post somewhere about exactly this gear ratio question. some combinations are quieter therefore absorb less energy. Something to do with tooth profile.

 

Did look but can't find it. maybe on a well-known USA forum that I am banned from!


Outside the box looking in.

------------------------------------

You don't own stuff: Stuff owns you!

------------------------------------

Having a cold drink on hot day with a few friends is nice, but having a hot friend on a cold night after a few drinks - PRICELESS.

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FLY - you naughty boy!!!!

 

Prime example of what Rick was saying - put an 11/23 ratio on an NC-1 motor . . . . top speed - not much more - time to get there - "off to make a coffee, call me if the thing starts to accelerate" LOL - Rick, it's "pedal", we is not "peddling" narcotics, sheesh, you smart fellas . . .

 

The gears we mostly use are based AROUND 48 pitch - that's 48 teeth per inch. But think about it - if you have a crown or spur gear at a fixed diameter, and it has say 34 teeth, if you change the number of teeth, you either need a bigger spur to maintain exactly 48 pitch - or you keep the same diameter, and change the pitch a little.

 

These days, most of us use gear sets based nominally around 48 pitch, (called 0.5 modulus by Sloting Plus and some engineering types)

Makers usually hit the 48 pitch at about the centre of their range of ratios, and skew the gears either side of that in pitch, so that the same diameter of gears can be maintained for obvious mechanical reasons.

 

At the "edges" of the range, some of the meshes are a bit marginal. the pitch changes and so does of neccessity the angle of the teeth.

 

Examples are Slot.it's 13 tooth sidewinder 6.5mm pinion and 11 tooth inline 5.5mm pinion. They always sound ratchety. It's a price we pay for keeping life simple with inter-changable parts in common diameters.

 

Gear Ratio Chart in Excel


Walks upright Unaided  *  Ties Own Shoelaces  *  Can Mispronounce Own Name In Five Languages  *  Mostly Aims Rattle Cans Away from Self
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There was a post somewhere about exactly this gear ratio question. some combinations are quieter therefore absorb less energy. Something to do with tooth profile.

 

Did look but can't find it. maybe on a well-known USA forum that I am banned from!

Hi Fly,

Just noticed your city of residence and a beautiful city and country it is. What is the slot car scene like in Thailand? apart from hot and humid. LOL.

 

There is nothing better than a 1 hour foot massage at the MBK after a hard days shopping.

Edited by Bulsara

Gort, Klaatu barada nikto.

 

My poor Krell!

After a million years of shining sanity...

they could hardly have understood what power was destroying them.

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Everything said so far is OK, but discussing pitch and rollout when he asked for a some simple grear ratio advice seem a bit confusing.

 

Back to your questions:

 

8t pinion 30t crown = high torque - rally type tracks

YES

 

10t pinion 24t crown = high speed - tracks with long straights

YES

 

That then is a good middle ratio 9t - 27t ? or 1:3 ?

YES

 

Is it the ratio that matters rather than the number of teeth - ie does an 8t pinion and a 24t crown perform the same as a 9t - 27t?

Ratio, but as mentioned by others, the most extreme combinations are often more noisy.

 

 

Some basic concepts:

Longer gearing = Low numerical ratio (more top speed, less acceleration and brakes)

Shorter gearing = high numerical ratio (less top speed, more accelleration and brakes)

Pinion = gear on motor

Crown = Gear on rear axle used in inline setup

Spur = Gear on rear axle used on sidewinders and anglewinders

Gear ration = teeths on crown or spur divided by teeths on the pinion

Gear ratio example = 27 / 9 = 3.00

9/27 gears means a 9 teeth pinion and a 27 teeth crown gear. This is the most common inline setup and a very good ratio for most RTR cars.

Wheel RPM = Motor RPM / Gear ratio

Wheel RPM example = 20.000 / 3 = 6.666

A standard Scalextric motor usually spin around 20.000 RPM at 12 volt.

Wheel Torque = Motor torque X Gear ratio

Wheel Torque example = 75 X 3 = 225 g*cm

A standard Scalextric motor is estimated to 75 g*cm stall torque at 12 volt.

 

When you know the RPM and Torque in the motor, the weight of the car, and the diameter of the rear wheels, you have the tools you need above.

 

Let's do a simple example, say you have two different motors and need to choose one for your project:

 

Motor 1 = Scalextric "Black stripe" (20.000 RPM and 75 g*cm torque)

Motor 2 = SCX RX-42B (18.000 RPM and 100 g*cm torque)

 

Question 1: What gear ratio does the SCX need to get the same top speed as the std Scalextric?

Answer: 18.000 / 6.666 = 2.7

 

Question 2: Will the SCX with the 2,7 ratio be as strong or accelerate as quick as the std Scalextric?

Answer: YES, it will be stronger

Scalextric = 75 X 3 = 225 g*cm torgue at the wheels

SCX = 100 x 2.7 = 270 g*cm torque at the wheels

 

Question 3: Cool, but wait, isn't the SCX motor about 10 grams heavier than the Scalextric?

Answer: Sure, but it will still be stronger

Scalextric = 225 / 85 = 2.65 g*cm Torque per gram

SCX = 270 / 95 = 2.84 g*cm Torque per gram

 

Hope this makes the gear ratio thing a bit clearer, and let me know when you are ready for the next lesson where we look at Power Curves and wheel power versus car weight and why slower cars are faster :)

Edited by 356speedster

gallery_434_503_9937.jpg

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There was a post somewhere about exactly this gear ratio question. some combinations are quieter therefore absorb less energy. Something to do with tooth profile.

 

Did look but can't find it. maybe on a well-known USA forum that I am banned from!

Hi Fly,

Just noticed your city of residence and a beautiful city and country it is. What is the slot car scene like in Thailand? apart from hot and humid. LOL.

 

There is nothing better than a 1 hour foot massage at the MBK after a hard days shopping.

 

Only two tracks here. One scaley "nextdoor" and one Ninco in Siam Square. No racing so I go next door for beer and laps. He is scaley distributor so I decided to buy one of each make or type or.. So far it worked except for two Fly, two Spirit and two Ninco.

 

I cannot confirm or deny anything to do with massage. :)


Outside the box looking in.

------------------------------------

You don't own stuff: Stuff owns you!

------------------------------------

Having a cold drink on hot day with a few friends is nice, but having a hot friend on a cold night after a few drinks - PRICELESS.

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Some basic concepts:

Longer gearing = Low numerical ratio (more top speed, less acceleration and brakes)

Shorter gearing = high numerical ratio (less top speed, more accelleration and brakes)

 

Have you ever talked to anyone who has this concept the other way round in their mind (ie higher numerical equals higher gearing????)

 

Must be just the dumb Kiwis then ....

 

We sometimes refer to the "longer" gearing as taller or high and the "shorter" gearing as low or geared down.

Maybe this is where the confusion begins.

 

regards


John Warren

Slotcars are my preferred reality

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We mean the same.

 

"Longer", "taller" or "high gearing" means the same = high top speed, which require a low numerical gear ratio like 2.4

 

"Shorter", "low" or "geared down" = low top speed which require a high numerical ratio like 3.5

 

I agree there are many terms that describe this and it's easy to get confused. The reason I like to refer to "longer" or "shorter" is because it's easy to remember when you relate it to a long or short step or long and short legs. A long leg or step gives you more speed :)


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thanks 356

 

power curves and wheel power - is that Gears and Gearing 201?

 

My questions probably reveal my humanities background at school. But possibly like many others my only other direct experience with gear ratio is on my bicycle, which are in reverse to slot cars in that the motor (pedals) has the large cog and the wheels the small. Given my understanding of bike gears Rick - if I reduce the ratio as you suggest and if I keep the same RPM then I can't go faster, however it will be easier to pedal hence I may be able to increase my RPM and thus travel faster.

 

I found some other links which may be of use to others..

http://science.howstuffworks.com/gear-ratio1.htm

http://adventure.howstuffworks.com/outdoor...ng/bicycle4.htm

 

DM

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DM,

 

Short answer is yes.

 

This generally gets you close. Choose a gear. If the rear end locks up and you need to dial out some brakes then go to a tall ratio (numerically smaller ratio.) If the car isnt pulling up fast enough and you find yourself say I wish I had more brakes then go for a short ratio (numerically bigger ratio).

 

In the proxy my NC6 had no brakes so I went to a short ratio (numerically bigger ratio). I had good bakes and still had good top end speed.


cheers

rick1776

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Some basic concepts:

Longer gearing = Low numerical ratio (more top speed, less acceleration and brakes)

Shorter gearing = high numerical ratio (less top speed, more accelleration and brakes)

 

Have you ever talked to anyone who has this concept the other way round in their mind (ie higher numerical equals higher gearing????)

 

Must be just the dumb Kiwis then ....

 

We sometimes refer to the "longer" gearing as taller or high and the "shorter" gearing as low or geared down.

Maybe this is where the confusion begins.

 

regards

 

Munter,

 

It is confusing.

 

I usually consider higher gearing to be numerically lower that sounds daft but when driving one changes to a lower gear to go up or down hill and progressively go up the box to get higher cruising speed. So we start in low gear ie. 1 and go "higher" 2,3,4,5,6..........

 

In north america people sometimes use the reverse terminology because they are thinking numerical ratio. So higher gearing would be 3:1 when lower would be 2.4:1. Interestingly though road signs on hills still advise drivers to use low gears when descending hills. Also they use the phrase taller gearing meaning a higher gear with lower ratio.

 

Maybe the words gear and gearing are important here. Gears are thought of as 1,2,3 etc. So higher and lower is understood as gear number , whereas gearing is described in ratio 8/28 (3.5:1) or 9/27 (3:1). So going to a lower ratio generally gives more speed (until the limit is reached). Slot cat people are similar to motorcyclists in this regard talking about 9/27 or 16/42 and the like without doing the math(s).

 

The longer/shorter is new to me, but would usually be used in context so would be clearly understood. "I need more punch out of the corner so we need to change to a shorter rear end'. Even if the "shorter" is not clearly understood the need and solution is. Maybe it is as simple as higher is taller and if you lie things flat taller becomes longer.

 

This is why putting any language in context is important.

 

Phew I need a beer now but alas the sun is not over the yardarm yet.


Outside the box looking in.

------------------------------------

You don't own stuff: Stuff owns you!

------------------------------------

Having a cold drink on hot day with a few friends is nice, but having a hot friend on a cold night after a few drinks - PRICELESS.

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All very interesting reading about gear ratios but at the end of the day it is what works best for a given track, car and driver combination. While we all like to think we are (still) top notch drivers there are variations of ability and three score years and some can have an impact also.

 

From my karting days where there is a large fixed or non-gearbox contingent; at one end we need the ability to pull cleanly out of corners but you want to hit your max. torque (power) down the straight. This applies equally well to slot cars as electric motors have a power band like combustion engines although the characteristics can vary considerably.

 

I also doubt anybody wants to drive a slot car that has no or poor brakes for although you may not have your life in your hands as in the real thing there is nothing quite so demoralising as having to button off only halfway down the straight.

 

My recommendation is therefore to go for good acceleration and braking. Even if the track has a particularly long straight you still need to be able to brake effectively. If acceleration is more important or critical than braking then one of the controllers with variable brakes may be the answer.

 

Food for thought I hope.

 

Regards

 

Chas Le Breton

New Plymouth

New Zealand

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Some good info here and 356 speedsters info was terrific. Not being an engineering type my experience is just from an observational racers point of view. Slot cars are a one geared item so matching a ratio to a motor type is pretty simple really. High torque motors like King evos and slot it boxer 2 motors need to push a big gear or else they become very hard to drive out of corners (too much torque on the rear tyres) and brake in ridiculously short distances I use a ratio around 2.4 to 1 as a starting point. Low torque motors like scalextric need an easy gear. Even with 11/36 = 3.27 to 1 gears scaley cars don't brake particularly well and changing from a higher torque ninco nc5 car to a scaley on a wood track always requires a different driving approach. Dial the brake out a little on the Ninco. Full brake and a bit more please with the scaley. changing the gearing down to 10/36 on a scaley motor works well on a technical track and some drivers prefer this ratio anyway for the better punch out of corners and better brakes. Its that whole rpm+ torque that gives you the total power of the motor. Knowing what style of motor you are working with and the track type plus how much brake you like as a driver can give you a pretty good indication of what gear you should run.

Edited by first corner crash

4x national champion 6x national runner up. I come second most often but my girlfriends happy.

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FCC seems correct to my mind as well as most of the slotcar experience i've had...............

HOWEVER, there's always an exception to the rule........on the higher voltage (13.8 vs 12.0) i raced on in Perth (on wooden routered tracks) smaller pinions and larger spur/crown gears almost always made cars more drivable. EG: a ratio of 8:30 made a proslot GT1 toyota "zent" (extremely fast car) much more drivable than a ration of 10:24. The main track used in Perth was quite big for 1/32 track.

Go figure..........seems to defy logic, but it worked!


i hope all of your racing is enjoyed

slot on!

:)

 

www.slotcaraustralia.com

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FCC seems correct to my mind as well as most of the slotcar experience i've had...............

HOWEVER, there's always an exception to the rule........on the higher voltage (13.8 vs 12.0) i raced on in Perth (on wooden routered tracks) smaller pinions and larger spur/crown gears almost always made cars more drivable. EG: a ratio of 8:30 made a proslot GT1 toyota "zent" (extremely fast car) much more drivable than a ration of 10:24. The main track used in Perth was quite big for 1/32 track.

Go figure..........seems to defy logic, but it worked!

Alot had to do with all the corners on DN's track as you know what may have worked there didn't alway work as well as on mine!

West Australian Slot Car Racing Group

web: www.waslotcarracinggroup.com

email: syd.miller@outlook.com scott.kendal@bigpond.com

mob: Syd 0413 020 421 or Chris 0435086304

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exactly

 

PS: have you broken my track record? If so, what with?


i hope all of your racing is enjoyed

slot on!

:)

 

www.slotcaraustralia.com

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cool, i'll line you up against Trevor when u come over here!


i hope all of your racing is enjoyed

slot on!

:)

 

www.slotcaraustralia.com

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FCC seems correct to my mind as well as most of the slotcar experience i've had...............

HOWEVER, there's always an exception to the rule........on the higher voltage (13.8 vs 12.0) i raced on in Perth (on wooden routered tracks) smaller pinions and larger spur/crown gears almost always made cars more drivable. EG: a ratio of 8:30 made a proslot GT1 toyota "zent" (extremely fast car) much more drivable than a ration of 10:24. The main track used in Perth was quite big for 1/32 track.

Go figure..........seems to defy logic, but it worked!

 

Actually mate it makes complete sense. Think about whats happening here you have the same motor but you are feeding it more power so by giving it an easier gear it will have plenty of top end but it will brake in an acceptable distance. Kim from the valley told me as a rule when you go up in rpm a standard is to make the gear ratio easier so the cars actually stop but that was for the old time motors that revved well but had little torque compared to some of the monster motors we have now. You have seen my gt one with only a 23k mb slot motor but it pushes an 11/26 gear goes like stink and stops to. If you put a low torque scaleauto or scalextric type motor you would need to increase the rev level and make the gear easier for the same level of performance.


4x national champion 6x national runner up. I come second most often but my girlfriends happy.

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Speaking of dragging old dead threads. Since this was here, I'll drag it out of a shallow grave and use it.

This is a gear ratios chart I did some time back, just updated for a few new pinions.

It was based around what Slot.it gears are available, as that is what I use most, but the numbers are the same regardless of brand.

 

Feel free to grab and save. It just saves having to engage the brain sometimes.

gearratios.jpg


Walks upright Unaided  *  Ties Own Shoelaces  *  Can Mispronounce Own Name In Five Languages  *  Mostly Aims Rattle Cans Away from Self
 My Track Oakland Raceway V2     Our Club  HMBRC     

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