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Old 11-08-2007, 06:32 AM   #1
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Default Drivetrain ratio theory.

I am Stock racer, then want to purchase TRF416 or HBCyclone.
Due the FDR it's limited in the rules, maybe should i change 18T from these cars to 16T, if i am not necessary to have lower FDR, then i don't need to have big spurgear?
What are the main difference about these 2 situations?

- Same FDR, same differential pulley, different center pulley.
- Same FDR, different differential pulley, same center pulley.
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Old 11-08-2007, 06:58 AM   #2
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guys correct me if i'm wrong.
but here's my theory about bigger and smaller pulleys.

i will set an example (principles of wheelchair)
for example if you are sitting on a wheelchair and if you want to accelerate from rest position and then you rotate the wheels. the outer part of the wheels will be much easier to rotate than the inside part of the wheelchair(center part of the wheel).

when applied to RC. I think the rc will move much freely and easily when using larger pulleys compared to smaller pulleys.
i hope you understand my explanation.
try to imagine your sitting on a wheelchair and you are rotating the wheels. of course the outer part of the wheels will be much easier to move than the inside part of the wheel chair.


look at the pic (the hand of the man is holding the outer part of the wheelchair).

not only the acceleration will be affected but also when the car is running it operates much better so it means much more effecient = much faster.
also when using larger pulleys the belts will hold/clamp the pulley much better so it means the drivetrain loss will be lessen.


guys correct me if im wrong..
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Old 11-08-2007, 07:06 AM   #3
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That's why Off roads has bigger's?
But why the new chassis should use 18T center pulley for BL, if need big FDR then make lower ratio for it for avoid ESC overheat?

Last edited by mac853; 11-08-2007 at 08:54 AM.
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Old 11-08-2007, 10:55 AM   #4
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I'd keep the 18T/37T pulleys for the 416, and just switch the spur and pinion gears..

A larger middle pulley results in more belt teeth contacting the pulley at once so you can afford to have less tension in the belts. This is important for stock racing where every bit counts.

Going from 16T to 18T in the middle is a 12.5% increase in surface area. Increasing the diff pulley size from 35T or 36T to 37T is a 5.7% and 2.7% increase respectively, so you're better off with a larger middle pulley.

I switched my 16T/35T MSX to the 18T/36T wide-pitch setup, and I can run the belts noticeably looser without slippage.. plus, cleaning the bearings once in a while will help too..

Plus, I doubt you'd be able to go 16T with the 416, there'd be too much slack to make up in the belts..

I think brushless setups on average end up using a lower rollout than their brushed equivalents, so instead of buying even larger pinions and smaller spurs that reach each other to accomodate them, the internal ratio change allows us to use the same gears we had before..
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Old 11-08-2007, 11:24 AM   #5
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Quote:
Originally Posted by nikkiesteban View Post
guys correct me if i'm wrong.
but here's my theory about bigger and smaller pulleys.

i will set an example (principles of wheelchair)
for example if you are sitting on a wheelchair and if you want to accelerate from rest position and then you rotate the wheels. the outer part of the wheels will be much easier to rotate than the inside part of the wheelchair(center part of the wheel).

when applied to RC. I think the rc will move much freely and easily when using larger pulleys compared to smaller pulleys.
i hope you understand my explanation.
try to imagine your sitting on a wheelchair and you are rotating the wheels. of course the outer part of the wheels will be much easier to move than the inside part of the wheel chair.


look at the pic (the hand of the man is holding the outer part of the wheelchair).

not only the acceleration will be affected but also when the car is running it operates much better so it means much more effecient = much faster.
also when using larger pulleys the belts will hold/clamp the pulley much better so it means the drivetrain loss will be lessen.


guys correct me if im wrong..
Your wheelchair theory is inaccurate. When you use the outside of the wheel you are in effect using a larger ratio and when you use the inner part of the wheel you are using a smaller ratio. An FDR is an FDR, doenst matter if you use large or small pulleys.

The change comes in the radius you are trying to kink the belt. The tighter the circle the more effort it takes, more drivetrain drag. Bigger pulleys are much freer and require less belt tension since they have more teeth engaged in the pulley at one time.

Same thing with gears, larger gears are more efficient since the teeth have less angle wrapping around a bigger circle.
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Old 11-08-2007, 12:00 PM   #6
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Quote:
Originally Posted by mac853 View Post
I am Stock racer, then want to purchase TRF416 or HBCyclone.
Due the FDR it's limited in the rules, maybe should i change 18T from these cars to 16T, if i am not necessary to have lower FDR, then i don't need to have big spurgear?
What are the main difference about these 2 situations?

- Same FDR, same differential pulley, different center pulley.
- Same FDR, different differential pulley, same center pulley.
I just compare new TRF416 and T2 008 drivetrain ratio

Tamiya TRF416 is 2.0 and earlier it was 2.25
x-ray T2 008 is 2.3 and earlier it was 1.77

Why x-ray change there rubber car to the bigger ratio? Any thoughs..
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Old 11-08-2007, 12:19 PM   #7
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1) bigger pulleys for greater drivetrain efficiency
2) to make it easier to gear 4.5 and 3.5 brushless motors without using tiny pinions for greater drivetrain efficiency

Notice the foam spec didnt change the ratio since the tires are smaller and you can get the ratios you want easily.
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Old 11-08-2007, 01:04 PM   #8
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The lower internal ratio will almost always be more efficient than a car with higher internal ratio. even if you gear them with identical FDR just because the belt speed and pulley speed is reduced on the cars with Lower internal ratio.
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