RE: Mystery Solved! How to select the proper gearing for your electric RC!  
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RE: Mystery Solved! How to select the proper gearing fo... - 3/22/2005 4:13 AM   
twostep


 

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Status: offline 		So the pinion/spur combo i get from the formula will, or should work for any motor i choose?

I was always under the impression that i had to change my pinion/spur combo to accomodate lower or higher turn motors.

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RE: Mystery Solved! How to select the proper gearing fo... - 3/22/2005 12:55 PM   
SkrapIron



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Status: offline 		No. keep the same pinion as a baseline for each motor. It may be necessary to move up or down 1-2 teeth either way, depending on your motor, but as a bas setup, use the answer the calculator gives you to start, then fine tweak it from there.

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RE: Mystery Solved! How to select the proper gearing fo... - 3/22/2005 8:28 PM   
twostep


 

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Status: offline 		OOHHH....ok. I see.
Thanks

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RE: Mystery Solved! How to select the proper gearing fo... - 3/30/2005 3:45 PM   
ceverson


 

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Status: offline 		Silly Newbie Question , Are we talking cm's or inches for the measurements in this formula

Thanks

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RE: Mystery Solved! How to select the proper gearing fo... - 3/30/2005 4:51 PM   
IBrakeForNobody



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Status: offline 		Uhh...I got 3.431 with Masher 2000's, 87t spur and 16t pinion and stock 2.2:1 tranny....so, what does that tell me?

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RE: Mystery Solved! How to select the proper gearing fo... - 3/30/2005 4:59 PM   
SkrapIron



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quote:

ORIGINAL: ceverson

Silly Newbie Question , Are we talking cm's or inches for the measurements in this formula

Thanks


It's in inches. I know, Americans, Can't do anything right..

quote:

ORIGINAL: IBrakeForNobody

Uhh...I got 3.431 with Masher 2000's, 87t spur and 16t pinion and stock 2.2:1 tranny....so, what does that tell me?



It tells me that you missed a number or two in your calculation, I Brake. Your Franken-rust-o-pede has a 2.72:1 transmission. Not a 2.2:1 Try putting in the right transmission ratio..... Silly....

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RE: Mystery Solved! How to select the proper gearing fo... - 3/30/2005 5:23 PM   
IBrakeForNobody



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ORIGINAL: SkrapIron

Your Franken-rust-o-pede has a 2.72:1 transmission. Not a 2.2:1 Try putting in the right transmission ratio..... Silly....


I knew that!

EDIT: now it says 0.604. Is that good or bad?

< Message edited by IBrakeForNobody -- 3/30/2005 5:25 PM >

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RE: Mystery Solved! How to select the proper gearing fo... - 3/30/2005 5:36 PM   
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Status: offline 		0.604 means you are geared slightly towards the top end side of the equation. As long as it is less than 1, you should be ok.

Hey Skrap, I intend to try your forumla out on a nitro truck this weekend. A buddy of mine has a XXX-NT RTR, which has a 51t spur and a 4.11:1 internal. I'm making him some tires, which are going to be 3.30". Which means, a 20t clutch bell is in his very near future.


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RE: Mystery Solved! How to select the proper gearing f... - 3/31/2005 3:28 AM   
IBrakeForNobody



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Status: offline 		k thanks...so when I get the BL, would 87/23 be good gearing for the speed hawgs and 87/16 for masher 2000's?

Thanks.

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RE: Mystery Solved! How to select the proper gearing f... - 4/2/2005 4:32 AM   
rustlern4tec


 

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Status: offline 		ok so tell me this in like 2 lines i m to tired to read all of it

i got a rustler and a 4tec what the tran ratio

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RE: Mystery Solved! How to select the proper gearing fo... - 4/2/2005 4:45 AM   
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Status: offline 		Go read the instructions. Anything worth doing is worth reading the instructions, and this is worth doing.


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RE: Mystery Solved! How to select the proper gearing fo... - 4/5/2005 10:17 PM   
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Status: offline 		there has got to be some way someone can plug in motor turns to get a gear ratio that wont fry a motor on the first lap ( i used to like that stock motor) one thing i wanna know, is on my XXX-4 it has 4 wheels to turn, and is single belt drive, will the belt ratio come into play? because by my calculations to get the motor to run on the cool side, id have to run an 18 tooth pinion.

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RE: Mystery Solved! How to select the proper gearing fo... - 4/7/2005 6:47 PM   
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Status: offline 		I must be missing something, but this all sounds like pseudo-science to me.

First question is – what is the rational behind the 1-to-1 ratio? This statement was made in the original post:

quote:

What size spur gear should I run? Well……. When selecting the spur gear size, you need to keep in mind that the ratio between the tire circumference and the final drive ratio should be 1 to 1.

And it seems to have been accepted as fact throughout the discussion. But why exactly should this be?

I also find it very hard to accept any “formula” that can’t be converted between systems of measurement. It seems like this systems only works for Imperial measure and nothing else.

quote:

Now the magic part.

Magic is right! You’re subtracting a ratio from a distance measurement! I’d just like to know the theory behind it all.


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RE: Mystery Solved! How to select the proper gearing fo... - 4/7/2005 8:08 PM   
Speedmunkey



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Status: offline 		The theory is, it works. Live with it! I don't have an answer for why this works, but it does.

It is easily converted between measurement systems. Take your tire O.D. in MM, and divide by 25.4.. That gives you the O.D. in inches. If that is news to you, then you have no right to question the rest of Skrap's formula


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RE: Mystery Solved! How to select the proper gearing fo... - 4/7/2005 10:03 PM   
Graystar


 

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quote:

The theory is, it works.

But the question is...works for what? I think it only works for stadium trucks.

quote:

It is easily converted between measurement systems. Take your tire O.D. in MM, and divide by 25.4.. That gives you the O.D. in inches. If that is news to you, then you have no right to question the rest of Skrap's formula

You don’t understand what I’m talking about. In physics, equations can always be converted to other forms when there are direct relationships. For example, there are direct relationships between voltage, current, and resistance. Therefore you can express one using the other two. You can say 10 volts or you can say 5 amps divided by .5 ohms...it’s the same thing. As long as there are real relationships, the equations can be restated.

In this particular formula, the equation cannot be restated in other terms. At least, not the way it’s given.

What this formula essentially says is that the car should travel 1 inch for every revolution of the motor. NOW it can be restated as 25.4 mm of travel per revolution, because now we have a relationship.

My initial query remains, however. Why exactly is the 1 rev:1 inch relationship ideal?

Seeing that SkrapIron was referring to blown ESC, melted motors, and other such heat related issues, the primary goal behind the relationship would seem to be limit rolling mass vs. power consumption. A single revolution of the motor represents a certain amount of energy that is available to perform work. SkrapIron has figured out that moving a stadium truck 1 inch forward is about all you would want out of 1 revolution’s worth of energy. If you try to get more work out of that 1 revolution, you overheat the system. This is, in fact, true for stadium trucks, but not heavier trucks. Owners of larger trucks may over-gear their cars and cause damage.


< Message edited by Graystar -- 4/7/2005 10:34 PM >

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RE: Mystery Solved! How to select the proper gearing fo... - 4/7/2005 11:40 PM   
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Status: offline 		Pseudo Science indeed!

The relationship that I found is this. The Ideal ratio is for the motor to turn X number of revolutions to move the tire 1 complete revolution. Whereas X is the diameter of the tire, in inches. So your observation is correct. The motor will THEORETICALLY move the truck/buggy/car 1" for every revolution of the motor. But Why 1 revolution to 1 inch? The answer lies in the pinion's diameter. If you measure the diameter of your pinion gear, and multiply it by Pi, surprise! It has a cirumference of nearly 1". So, every revolution of your motor, the pinion travels more or less 1". It only makes sense to carry over that ratio to the tires.

Our 540 and 550 hobby grade motors generate work, measured in RPM. They are incapable of delivering sufficient torque by themselves to directly drive the axle. We overcome that limitation by dividing the work (RPM) throughout the gear train, giving us our final drive ratio. This division of work, multiplies the torque that would otherwise not be available to us.

As for heavier trucks, such as the E-Maxx, I've already addressed that.

Ideally, the motor should turn 1 revolution for every inch of travel. Remember that the emaxx is using 32 pitch gears ( 66x18 ) and has a 2 speed transmission. It's final drive ratio is 28.9:1 in first gear and 17.9:1 in second gear..... That means, in first gear, the motor is turning almost 2 times for every 1 revolution of the tire. When you select second gear, you now have a 17.9:1 drive ratio. E-Maxx tires are 5.75" tall, and have an overall circumference of 18.06". That means, in top gear the motor is turning the at the magical 1" for 1 revolution.

The weight of the truck precludes it from being able to be geared at the 1:1 ratio. Therefore, it is deliberately undergeared in first, and optimally geared in second gear.

Psuedo Science indeed!

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 2:14 AM   
Graystar


 

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quote:

The Ideal ratio is for the motor to turn X number of revolutions to move the tire 1 complete revolution. Whereas X is the diameter of the tire, in inches.

That’s *a* ratio...not the ideal ratio. Even Novak describes the 12.30 ratio they list as a “starting point”...not some ideal to reach for. The Associated T4 manual lists FDRs in the range of 11.31 to 12.57, depending on the motor...not on what tire you’re using. Obviously, Associated doesn’t share your “ideal” ratio theory.

quote:

So your observation is correct. The motor will THEORETICALLY move the truck/buggy/car 1" for every revolution of the motor. But Why 1 revolution to 1 inch? The answer lies in the pinion's diameter. If you measure the diameter of your pinion gear, and multiply it by Pi, surprise! It has a cirumference of nearly 1". So, every revolution of your motor, the pinion travels more or less 1". It only makes sense to carry over that ratio to the tires
.
If you used 32 pitch gears with the same number of teeth on the pinion and spur, the car would move the same distance per motor revolution even though the pinion is bigger. It has nothing to do with the size of the pinion…it has to do with the gear ratio only.

quote:

As for heavier trucks, such as the E-Maxx, I've already addressed that.

But the E-Maxx has two motors. Obviously something is off if you need twice the power to maintain that “1 to 1” ratio. If you try it on a Stampede you’ll see that the stock gearing ratio is 12.69 while the tire diameter is nearly 15 inches (14.92) There are ratios in the 15 range on Traxxas’s chart, but they seem to be outside the range of normal.

quote:

Ideally, the motor should turn 1 revolution for every inch of travel.

I don’t think there’s anything ideal about it. It’s just another ratio. By following your rule, you’ll simply stay within the range of the manufacturers’ recommended gearing...which is what you should have done in the first place!

But if you try to keep a single gearing and apply it to all different motors, you may still end up burning out a few motors.


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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 2:40 AM   
SkrapIron



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Status: offline 		Look, It is NOT the final answer. Nobody ever said it was. It is a starting point. PERIOD. Use it to get YOUR truck/buggy/car into the BALL PARK. What you select as a final pinion gear depends on YOU and YOUR preferences. The idea is behind it is totake the guess work out of re-gearing a truck/buggy/car when you change to different size tires. You know you cannot run a 24t pinion with Masher 2000's, but you can run it with Road Rage 2.2" buggy tires. Why? The diameter of the tire is crucial in selecting your pinion gear.

It does not matter if you use a 32/48/64 pitch gear. The DIAMETER of the pinion selected will determine it's output RPM. That RPM would be measured from tooth 1 to tooth 1. How far does it travel in that rotation? You want that rotation to be carried over to the drive tire. 1 rotation of the motor equalling 1" should still translate into 1" travelled at the drive tires.


The Stampede/Rustler/Evader are deliberately UNDERGEARRED to compensate for ANEMIC motors. It has nothing to do with performance, other than to mask underperforming motors.


Is it a perfect formula? No. Does it work. Yes. Track tested and race approved.

If you have a better Idea, let's hear it. Until then.............


< Message edited by SkrapIron -- 4/8/2005 2:43 AM >

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 2:45 AM   
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Status: offline 		There may be more science behind this theory than my 15 yr old brain can comprehend, but as and avid and average racer i can only say it has improved my timed, battery/motor temps are down by atleast 20* in 2wd bugy and atleast 40* in 4wd. This formula wrong or right in theory is correct what it has been used for, determining range of gearing before you try it on the track. I have built charts for my xxx4 and my bk2 with every possible gear ratio, although it took a long time it has helped me dearly with gearing as has it helped others at my track. Theorys have been wrong before, and this theory might as well be wrong, but lok at other theorys, E=Mc2, was it though to be right at first? probably not, time will tell if this theory works. I have used it for a month now and i can say i now get the most out of motors and not have them dump in 4 minutes.

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 2:53 AM   
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Status: offline 		Nick, don't sweat the 15 year old mind thing, I'm a 30 year old mechanical designer and the intricacies of this theory escape my mind too =) I agree though, while I may not GET why it works, the bootm line is that it does work. I'm faster than I've ever been and my packs are lasting longer.. I believe in ya Skrappy, ignore the non-believers!


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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 3:42 AM   
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quote:

Look, It is NOT the final answer. Nobody ever said it was.

Hmmm...that’s not what the word “ideal” suggests...

quote:

The DIAMETER of the pinion selected will determine it's output RPM.

If the diameter of the pinion is so important, then why isn’t it accounted for in the formula? Before relating the ratio to the tire circumference, the only thing you’ve worked with are tooth counts. The size of the pinion means nothing. It is the relationship of the tooth counts that matters.

quote:

The Stampede/Rustler/Evader are deliberately UNDERGEARRED to compensate for ANEMIC motors.

Look again. The recommend ratios for the Stampede are *lower* than what you recommend. Tire is 14.92”, ratio is 12.69...using your formula, that’s a *positive* 2.23! That is, you get more than 1 inch of forward movement per revolution of the motor. Traxxas expects this level of car to be used with stock or mild motors, and that level of gearing is appropriate for those types of motor.

quote:

I'm a 30 year old mechanical designer and the intricacies of this theory escape my mind too

That’s because there are no intricacies. The formula gets you somewhere near the manufacturer’s recommendations. Just save yourself a step and check the manufacturer’s recommendations!

quote:

I have used it for a month now and i can say i now get the most out of motors and not have them dump in 4 minutes.

For buggies the formula under-gears the car. If you’re running a modified 10 turn motor then you’re probably right at Losi’s recommendation. Otherwise, you’re probably under-geared. That would explain your temps and longer runtimes. If you haven’t noticed a difference in top speed, then you were probably over-geared to begin with. Get out the manual and compare your current and past gearing with Losi’s recommendations.


quote:

If you have a better Idea, let's hear it.

Follow the manufacturer's recommended gearing. They know more about their car than anyone.

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 3:51 AM   
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Status: offline 		I've got an Idea. Take a T4. with an 85t spur. Take off the stock M3 Hole shot tires. Put on, say some masher 2000's. You are running a Novak SS 4300 motor. What pinion will you use? Hmm? Nothing in this list is stock. What pinion do you use, wise guy?


Come on, I want an answer, and an explaination of why.........

< Message edited by SkrapIron -- 4/8/2005 4:02 AM >

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 4:16 AM   
SkrapIron



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Manufacturer recommended final drive ratio's are based on 1 really BIG assumption. They assume that You are NOT going to change your spur gear or the size of your tires. In a perfect world, all 2.2" tires would be 3.5" in diameter. That would make selecting a pinion fool proof.

But it's not. With all of the aftermarket parts available, the variables are incalculable. So, when they publish a list, it's assuming you will never stray away from the stock tire and the stock spur gear.

In the real world, things are very fluid. You can buy 2.2" truck tires that are as small as 3.0" tall, up to 5.5" tall. What pinion gear will you choose to run these tires?


Final Drive Ratio -- The transmission ratio determined by combining the internal drive ratio and the spur/pinion combination with this formula:

spur gear tooth count divided by pinion gear tooth count multiplied by the internal drive ratio
or
spur / pinion * internal drive ratio = final drive ratio


Manufacturer recommendation says that you need to maintain an 12.30:1 final drive ratio ( Novak SS). Well, if I'm running Road hawg 1 tires ( 9.425" circumference) on my T4, I have to run an 87t spur with an 18t pinion to get close to the 12.30:1 ratio. But, anyone who has run the really itty bitty racing tires will tell you, the motor will rev like there is no tomorrow, but the truck is slow. Why? Same senario, only this time we are putting Masher 2000's on the same truck. We keep the same 12.30:1 final drive ratio ( manufacturer recommnedation) It runs like a bat out of hell for 5 mins, and then the motor goes into thermal shutdown. Well, why'd that happen? Why can I fry an egg on my ESC? I followed the manufactureres recommendation???? Why do I know this? Because the plastic on my Chameleon 2 melted when I ran Stampede tires on my T3. My manufacturer recommended ratio said that I could run a 19t pinion. I ran a 21t pinion. Then I changed the size of the tires and everything went wrong after that. Why? Answer me that, smart guy!

It's because the manufacturers setup was based on a stock 3.25-3.5" tire. Changing that throws it all into a tizzy. The optimum final drive ratio is COMPLETELY dependent on the circumfernece of the tire that you are running. A 12.30:1 drive is intended to turn a 12.30" circumference tire. If you change the size or your tire, your final drive ratio needs to change as well!!!!!!!!!!!!!

As for the Stampede and Rustler and Evader, I mis Typed. They are OVERGEARED to compensate for their rather pathetic motors.


I'm not going to argue whether it works, or even why it works. It does. Case closed. You cannot deny results!

< Message edited by SkrapIron -- 4/8/2005 4:45 AM >

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 5:07 AM   
Graystar


 

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quote:

I've got an Idea. Take a T4. with an 85t spur. Take off the stock M3 Hole shot tires. Put on, say some masher 2000's. You are running a Novak SS 4300 motor. What pinion will you use? Hmm? Nothing in this list is stock. What pinion do you use, wise guy?

Come on, I want an answer, and an explaination of why.........

No prob...

I would increase the spur/pinion ratio by the increase in tire size.

from the tire specs...
M3 diameter = 3.75"
2000 diameter = 4.9"

Increase in tire diameter = 4.9/3.75 = 1.3067 or 30.67%


From Novak specs: "the SS4300 Brushless Motor provides performance similar to a 27-turn racing stock brushed motor."

So, from the T4 manual...stock motor = 87T spur/19T pinion

ratio = 87/19 = 4.5789

just multiply by the increase...

4.5789 x 1.3067 = 5.98324863

That's my new spur/pinion ratio

Finally, I divide 85 by 5.98324863 and get a pinion size of 14.


The formula is:

[Actual Spur] / (( [new tire dia.] / [stock tire dia.]) X ([sugg. spur] / [sugg. pinion])) = actual pinion needed


< Message edited by Graystar -- 4/8/2005 6:25 AM >

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RE: Mystery Solved! How to select the proper gearing fo... - 4/8/2005 6:46 AM   
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quote:

Manufacturer recommended final drive ratio's are based on 1 really BIG assumption. They assume that You are NOT going to change your spur gear or the size of your tires.

That’s all they *can* assume.

quote:

With all of the aftermarket parts available, the variables are incalculable.

I think I just demonstrated that it’s pretty easy to calculate.

quote:

Manufacturer recommendation says that you need to maintain an 12.30:1 final drive ratio ( Novak SS). Well, if I'm running Road hawg 1 tires ( 9.425" circumference) on my T4,...

Novak is making the same assumptions that the manufacturers are making with regards to gearing. They even say…
quote:

We are currently working with the vehicle manufacturers to offer a Gearing Chart that will be more specific.

Their gearing ratios are base on manufacturers’ specs. Of course they’re going to be off when you install odd sized tires!

quote:

As for the Stampede and Rustler and Evader, I mis Typed. They are OVERGEARED to compensate for their rather pathetic motors.

This is where you are wrong, and why I question the premise of your entire system. The gearing is appropriate for the type of motor typically used in those vehicles. And THAT is the point that I’m making. Different motors require different gearing. There is no “one fits all” gear.

If you follow my formula you can properly scale the manufacturers’ recommended gearing for any motor to any size tire. With your method you’re making a gearing presumption that may or may not be correct. I think that in most cases your method under-gears the car.

quote:

You cannot deny results!

The only results I see so far is that you solved overheating problems by under-gearing. When your gearing systems starts winning races, then I’ll believe. Until then I’ll use my simple formula.


< Message edited by Graystar -- 4/8/2005 6:50 AM >

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(in reply to SkrapIron)
       Post #: 125

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