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Sidewinder Gear Ratios For The Bwa Nc1 Motor

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#1 terry

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Posted 12 July 2017 - 10:42 PM

I'm about to build up a Sports Sedan, probably using the Aston Martin DBR9 body or the Jaguar XKR GT3 body from Airfix, I'm thinking I will be using the SlotIt HRS chassis or maybe a scratch build in wire and brass, but using a Slotit motor pod, sidewinder.

Trouble is that although I've used the BWA NC1 motor in many cars, nearly all of them are inline, and for that setup I use a 10:24 or 25 gear set up.

I have little understanding of how that ratio converts to a sidewinder, can anyone help me in converting a 10:25 inline setup to the same type of performance in a sidewinder?

Silly thing is that I should know this, but no, I'm a bit lost here :huh:

Thanks for any help,


Edited by terry, 12 July 2017 - 10:44 PM.

#2 kalbfellp

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Posted 13 July 2017 - 12:50 AM

13:32 is about the closest.

#3 terry

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Posted 13 July 2017 - 07:26 AM

Thanks Phil,

for some reason I was under the impression that the ratio used in the inline setup was not the same as sidewinder, I know the gear sizes are bigger in side and angle winder but from what you have given me the ratio are as close as they can be.

Thanks again

#4 ZeGas


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Posted 13 July 2017 - 07:54 AM

Not sure a BWA NC1 would power a brass chassis all that well.

#5 lenny broke

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Posted 13 July 2017 - 08:22 AM

Hi Terry,
Divide the spur/ crown wheel teeth count by the pinion teeth eg: 27/9 = 3 so ratio is 3 to 1
or 32/11 = 2.99 or for every 2.99 rotations of the pinion the spur will rotate once.

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#6 difinity


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Posted 13 July 2017 - 09:37 AM

Your 2.4:1 or 2.5:1 ratio can be achieved by using either
32/12 or 32/13.
You might find 28 or 32/11 a better ratio though. (Gives better braking, is a bit quicker of the mark and may allow you to drive harder into each corner.)

I find that while gear ratios are important and a good guide, getting the balance for the chassis and between rpm and brakes more helpful. The other thing is that the rear wheel rpm and actual speed needs to account for motor rpm at load, and tyre circumference.

It may be better to run a shorter ratio (better motor brakes) and a slightly taller tyre, or the opposite...


#7 shadow_rusty

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Posted 13 July 2017 - 09:42 AM

Remember, gear ratio isn't everything.
You must also consider the tyre diameter as it's a crucial part of the overall gearing of the car.

Here is a Rollout (how far the car travels for each rotation of the motor) Calculator for a 1/12 Pan Car which uses the same gearing style (pinion / spur / tyre size) as our slotcars...
Rollout Calculator - http://store.ontrack..._page=page&id=3
As you can see, 9/27 gearing with 21mm tyres works out to be the same rollout as 9/23 gearing with 18mm tyres, which will equal similar on track performance...

So, if you have an inline car that works how you like, measure it's tyres, enter the values into the calculator, make note of the rollout, enter the new cars tyres, and play with the values till you get the rollout the same.

Note: It won't be perfect however, as most slot car gears are cut to a size, not to a pitch, and as such, a 13 tooth inline pinion is not as efficient as a 9 tooth one, even if you change the spur to create the same ratio (i.e. 13/30 vs 9/21), but it will get you in the ball park...

ps. BWA's are great motors for small tracks... I even had one in a 120g truck at one stage.
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#8 ZeGas


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Posted 13 July 2017 - 02:11 PM

What SR said.

I few years back I created a simple spreadsheet to work out what gear ratios for tyre diameter and motor size.
You, and anyone else is welcome to use it.
I use it all the time for setting up and testing cars.

Download from HERE

Down the bottom I have added in Tall / Short gear examples to help clarify if you need it.
Think of a bicycle is the easiest way, to go up hill small chain ring big sprocket downhill big chain ring small sprocket.

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