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Old 06-23-2007, 05:31 PM   #1
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Default GEARING/ROLLOUT QUESTION

Hi Guys,

I am a little confused over gearing and hope someone can set me straight.

below are 2 examples from the rollout charts for a 415MSX.

39 pinion x 83 spur = 42.52 rollout
31 pinion x 66 spur = 42.51 rollout.

can someone please explain the difference in the two ratios ie is one more efficient, will one give more accelaration than the other (Im assuming top speed would be the same with both) or am i wrong.

I am running a "silver can motor" and all I hear is get the comon rollout that guys i am running against are using but it must not be just that simple when you can get the same rollout with two pinions being 8 teeth different.

Which is best and why.

thanks in anticipation

Ross
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Old 06-24-2007, 07:50 AM   #2
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Go here and read this:

http://www.rcuniverse.com/forum/m_3255405/tm.htm

And then read this:

http://www.rcuniverse.com/community/gearwizard.cfm

This should answer all you questions.
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Old 06-24-2007, 12:16 PM   #3
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Thanks Charlie,

However i have entered both examples above (66/31 & 83/39) into the wizard and and the 1. pinion/spur ratio 2. gearing quot. and 3. rollout ratio are the same for both combinations.

I am no mech engineer however have this nagging feeling that they will behave differently in the car.

Maybe I am 100% wrong I just don't know.

Can anyone shed more light on this please.

Thanks
Ross
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Old 06-24-2007, 01:13 PM   #4
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It won't make any difference at all, a gear is a gear. A lot of times people use smaller spur and pinion gears because the larger spur gear won't fit the application. In other words, there isn't room for it, it's too big around. You can fine tune your gearing a little better buy changing your spur gear instead of changing the pinion gear.

It's like the Cyclone. The biggest spur gear that will fit is a 108 tooth. Anything bigger and the spur gear sticks out of the bottom of the chassis and could strike the ground. so you use a smaller pinion gear to achieve the results you want.

The main thing you want to do is get the gearing as close to the 1 to 1 ratio for the "silver can" that you are using. The guys at the track that I run at get some pretty amazing results with that roll-out.

Did you understand the article as what you are trying to achieve?
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Old 06-24-2007, 02:06 PM   #5
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Right, the only real difference in the two different methods of getting that FDR is where the motor sits, with the smaller pinion the motor will likely be sitting a bit more towards the rear of the car, but honestly, I doubt that will have enough of an impact on weight bias to be noticable, so I wouldn't worry about it....
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Old 06-24-2007, 03:06 PM   #6
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bigger pinion/spur combos also provide a better actual "mesh" between the gears.. if they fit..
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Old 06-24-2007, 03:26 PM   #7
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Guys,

There can be a difference between the two, Here's why. If you had a large spur and a large pinion and compared it to a smaller spur and a smaller pinion, but both giving the same ratios you could see a difference with weight in the parts so the heavier spur and pinion would not "spool" up as quick as the smaller parts, but once up to speed the heavier parts would keep their momentum going longer, this is loosely sometimes reffered as a fly wheel affect. I have also been told by machinists and molders years ago, that typically the larger the part the more accurate the part can be.

Someone else mentioned this also that by using different size combinations of spurs and pinions the motor can be moved forward or rearward in the car giving a different handling vehicle.

All that being said the differences that we talking about here on the R/C level are pretty small, and in most cases unless you are competing at the highest levels of racing it may not be worth it to most people.

Steve
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Old 06-25-2007, 11:42 AM   #8
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Thanks guys for the info great as always and Charlie I will be trying thaqt 1:1 ratio. Thanks again
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