RE: Mystery Solved! How to select the proper gearing for your electric RC!

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 ... - 6/28/2005 7:49 PM

jdeez1

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Got this response from NOVAK
Hello,
Are the Super Maxx diffs the one's made by UE?? If so you simply add 3 teeth to the recomended pinion. If you want to "play it safe" add 2 teeth.
That's it really. Those diffs end about "about" 3 teeth less on the pinion gear.

Got this response from U.E.
Rule of thumb is to add 3 to the pinion tooth count to compensate for the
7.5 diffs.
To do this accurately you need to calculate each ratio as it goes thru the
driveline. I'd do it in a spreadsheet if I were you.

In case anyone else was wondering
this would seem to support the post from Traxxas
"A little Razer math:
1st - 2.77:1
2nd - 1.72:1
UE Spyder 6 Diff - 3.31:1

1st (including diffs) - 9.17:1
2nd (including diffs) - 5.69:1

You multiply those by the spur/pinion ratio to find the final drive ratio. (51/15 = 3.4) -
Final drive ratio in 1st - 31.18:1
Final drive ratio in 2nd - 19.35:1 --> Per Novak, do not use"

In which my set-up with 76/15 = 5.06 X 5.69 = 28.82 final (safe by Novaks standards)

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RE: Mystery Solved! How to select the proper gearing ... - 7/1/2005 7:31 PM

jahvajoe

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i am running a stock pede right now, i am putting in a venom fireball 17 double. I am using the stock tires that have a diameter of 4.8. the tranny is the stock 272. using the calculator it says that i should use an 16/89 set up. is this correct? and can i find gears to match. thanks

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RE: Mystery Solved! How to select the proper gearing f... - 7/7/2005 12:40 PM

medunno

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Ok ladies and gentlemen I can read this stuff about the gearing all day but what I see is blahh blah blah, not meaning that twords anyone mean wise , I mean it as in I don't know math like that. Well or at all for the most part so I figured I would just ask all you math guys that do know it. I have a RC10 T2, I have a Novak tempest Pro speed control in it and I just bought a Speed Gems Pro 13 Turn double motor, my tires are 2.2X2.21 and are speed hawgs proline (for street)what size gears should I have on this motor for max speed but not kill the motor and turn it red hot. I am new to this small R/C stuff and I just bought this T2 for $25. Please help in any way any of you can. I want more parts for it too but man their hard to find. I know RPM makes A-arms for it.

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RE: Mystery Solved! How to select the proper gearing fo... - 7/7/2005 1:37 PM

SkrapIron

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I provided you guys with the formula, an explanation of how it works, and even had a calculator script written for it too. Move your cursor up to "RC Community" at the top of this page. Then scroll down to the 'Gear Wizard Calculator' and enter the numbers in the appropriate box. It can't get much simpler than that.

Your truck has 3.5" diameter tires, and a 2.40:1 transmission ratio. Please use the tools provided and figure it out for yourself.

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RE: Mystery Solved! How to select the proper gearing ... - 7/7/2005 1:44 PM

SkrapIron

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quote:

ORIGINAL: jahvajoe

i am running a stock pede right now, i am putting in a venom fireball 17 double. I am using the stock tires that have a diameter of 4.8. the tranny is the stock 272. using the calculator it says that i should use an 16/89 set up. is this correct? and can i find gears to match. thanks

Joe,

90/16 is the most common gear ratio being run in Stampedes. You can get the gears from Tower hobbies, or from your Local Hobby Shop.

The 90 tooth, 48p Spur gear is made by RPM, Kimbroughs, Duratrax, Robinson Racing, HPI, Integy, etc. The 16t pinion gear is made by most of the above manufacturers as well. I personnaly like the Kimbroughs Spur gears, and the Robinson Racing pinions.

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RE: Mystery Solved! How to select the proper gearing ... - 7/7/2005 9:31 PM

jahvajoe

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Thanks alot SkrapIron. I know you probley get tired of all these questions, i really app all the help

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RE: Mystery Solved! How to select the proper gearing fo... - 7/9/2005 10:25 PM

IBrakeForNobody

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SkrapIron, any way to know how to gear my "mystery motor" in my Gold Tub RC10? From what I've read, it has a 1.9:1 tranny ratio, and right now, I'm geared at 84/16 using 48P gears...the stock gears were 32P and it was geared at 54/15 using 32P gears. I call my motor a "mystery motor" because I don't know how many turns it is and it has a sealed endbell (kinda like the Photon Speed motor's endbell, you can axcess the brushes, but not the comm). All I know is it has to be less than 17 turns, because my XL-1 ESC can handle it fine...I am thinking it may be a stock (27 turn) motor because it runs at about the same temperatures as my Monster Stock Pro when running at the same gearing. Right now, at 84/16 using 48P gears, and B4 RTR tires that are 3.25" in diameter, the GearWizard says 0.235. I know that is geared a little toward top end speed but I also know that the number of turns affects how to gear a motor...is that anything I should be concerned about?

Thanks, and sorry if the post is too long

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RE: Mystery Solved! How to select the proper gearing fo... - 7/11/2005 2:52 PM

bIGmiK

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What is the transmition ratio of an evader st ?

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RE: Mystery Solved! How to select the proper gearing fo... - 7/11/2005 8:22 PM

dirtburglar

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Ok so I actually read the entire thead and believe I have a grasp on why it works the way it does based on the explanations provided. that said, I have a Tamiya King cab that originally had tires with an O.D. of 4.375" or close to and a transmission ratio of 2.5. This yields a tire/gearing ratio of 3.050 when the default 18T pinion is used?? Is this right--why such a high number? Am I still striving to get this number down to 0-1 (14T pinion gets it to -.006) or do i try and preserve the original ratio if new larger tires are to be used (4.75)?

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RE: Mystery Solved! How to select the proper gearing fo... - 7/11/2005 8:54 PM

S.A.E.W.O.T.

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this thread is 2 nuts 4 me man... i jus go with what works

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RE: Mystery Solved! How to select the proper gearing fo... - 7/11/2005 9:38 PM

SkrapIron

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quote:

ORIGINAL: dirtburglar

Ok so I actually read the entire thead and believe I have a grasp on why it works the way it does based on the explanations provided. that said, I have a Tamiya King cab that originally had tires with an O.D. of 4.375" or close to and a transmission ratio of 2.5. This yields a tire/gearing ratio of 3.050 when the default 18T pinion is used?? Is this right--why such a high number? Am I still striving to get this number down to 0-1 (14T pinion gets it to -.006) or do i try and preserve the original ratio if new larger tires are to be used (4.75)?

You have provided 3 parts of the equasion. You have your tire diameter, your transmission ratio, and your pinion size. I can extrapolate that you are running a 77t Spur gear, correct?

Tires that are 4.375" are pretty large, and will require a very high final drive ratio to get moving properly. Going to even larger tires will require a further adjustment in the gear ratio to compensate.

It is common for manufacturers to overgear stock trucks, to make up for poor performing stock motors. Once you get into a modified motor, then you will have to adjust the gear ratio. With 4.375" tires, you want a fina-drive-ratio of around 13.75:1. With the 4.75" tires, you will need a final-drive-ratio of at least 14.93:1.

Running a 77t spur, you will need to run a 14t pinion, MAX, depending on the choice of motor.

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RE: Mystery Solved! How to select the proper gearing fo... - 7/11/2005 9:39 PM

SkrapIron

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The Evader ST has a transmission ratio of 2.667:1.

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RE: Mystery Solved! How to select the proper gearing fo... - 7/12/2005 1:45 AM

dirtburglar

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thanks for that.

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RE: Mystery Solved! How to select the proper gearing fo... - 7/13/2005 4:09 PM

bIGmiK

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ok guys i made a small spread sheet that will tell u all the ratios like the spread sheet at the start of this thread does, but it also works out speed. so all you need to do is change one number and it will tell you the speed increase/decrease. i think someone may have already made one of these.

i renamed the file a .txt so when u download it just change it to a .xls (excel). i hope this helps some of u guys.

by the way, all you need to add into the sheet is: Tire Outer Diameter, Motor Max RPM, Transmition Ratio, Spur and Pinion size.

And guys this will change is u screw with the scripts, and not just change the numbers, id u do muck it up, just download it again. i hope this makes things easy for u guys !

also i added a screen shot of the program, so u guys get some idea of how easy this makes things.

Attachments

Click to see the file in new window.

Click to see fullsize image.

Click for fullsize

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RE: Mystery Solved! How to select the proper gearing fo... - 7/23/2005 12:05 AM

zilla500

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just bought my son a katana rtr. has anyone drove one of these?

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RE: Mystery Solved! How to select the proper gearing fo... - 7/23/2005 5:10 PM

SkrapIron

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Ok, since this thread has gotten REALLY polluted, I've decided to republish the original article at the end of the thread. I am also going to add some additional information that I have learned from other subscribers to help you guys understand how to select the proper gearing for your 1/10 scale Electric RC's.

What is the best set-up for my truck? How fast will it go?

These are questions that have haunted me for nearly 10 years. I have been running 1/10 scale R/C trucks off and on, without a real good understanding of how to properly set it up. To me, it was FM ( friggin magic). What pinion should I use? What if I change the spur gear. It was all trial and error, that resulted in several melted motors, blown ESC’s and damaged batteries.

But I have found the answer! And it is good!

Question 1: What size spur gear should I run? What about the pinion gear? Well……. When selecting the spur gear and pinion gear size, you need to understand that there is a ratio between the tire circumference ( refered to as roll-out ) and the final drive ratio. That ratio, in most cases, should be as should be as close to 1 to 1 as possible. 1 to 1? What? By a 1 to 1 ratio, I am referring to the distance traveled by the tire in one revolution to the number of revolutions turned by the motor. In other words, if the motor turns X number or RPM's, the wheel will turn at Y RPM's, which is reduced by the final drive ratio . ( A 32000 rpm motor with a final drive ratio 10.9893, will turn the tire at 2912rpm ). For the sake of efficiency, the vehicle should be geared so that tire should travel approximately the same distace for every revolution of the motor, reduced by the final drive ratio. Here’s how it works. We’ll use my RC10t3 as the example vehicle. The first thing to consider is the diameter of your tire. It is used to calculate the circumference of the tire. Multiply the diameter of the tire by pi. ( Ex: 3.25”xpi=10.2101”) Now, you need to consider the final drive ratio of your drive train. Begin by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear. This will give you your drive ratio. ( Ex: 87/19=4.5789). Now multiply your drive ratio with your transmission gear ratio ( Ex: 2.4x4.5789=10.9893 ). This is your final drive ratio.

Now the magic part. Subtract the final drive ratio from the roll-out of your tire . (Ex: 10.2101-10.9893= -0.77926) That is VERY close to a 0, but is geared a tad to the torque side of the motor ( anything below 0 is always geared towards more torque). Want more speed than torque? Redo your calculation adding another tooth on the pinion : ( Ex: 87/20= 4.35 ( drive ratio )x2.4 ( transmission gear ratio )= 10.44 ( final drive ratio ) Then subtract your final drive ratio ( 10.44 ) from your roll-out ( 10.2101 ) ( Ex: 10.2101-10.44= -0.2299 ) This is your optimum gear ratio, since it is closest to a 0 margin. Any ratio that is greater than 1 will run faster, but will overheat your motor, battery and esc, eventually damaging them.

How do we know this works? We can check out math by multiplying the roll-out of the tire, by the number of RPM's delivered to the tire, via the transmission. (Ex: Vehicle Final Drive Ratio is 10.44:1 and the roll-out of a 3.25" tire is 10.2101 " X 3065 rpm= 31294rpm) The motor's peak RPM is 32000, which means that we have less that 3% loss in efficiency from the motor, through the gear train.

Overgearing a vehicle will add to the speed of the vehicle, but it does so at a tremendous cost. The additional strain placed on the motor by the shorter gearing, will cause tremendous heat build up as the motor struggles to reach it's peak RPM.

While this formula is not absolutely perfect, it does allow you to select a safe, and scientific starting point, to determine what is the best gearing combination for your particular vehicle.
This formula works best with 1/10 scale vehicles running stock to mid-modified motors. ( 27 turn to around 12 turn motors ).
Hotter motors 12 turn and lower will require you to reduce the ratio by as much as -1 or even lower to combat heat build-up.

Happy Racing guys!

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RE: Mystery Solved! How to select the proper gearing fo... - 7/28/2005 9:42 PM

45mph pede

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I got:

Tire Circumference
17.279

Pinion:Spur Ratio
5.625

Gearing Quotient
27

Tire/Gearing Ratio
-9.721

Im running a 12x2 motor at 90/16 with pullers (5.5 high) in my pede (4.8 internal gear ratio). Are those ok numbers? or should I gear up or down. Thanks,
-Wes

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RE: Mystery Solved! How to select the proper gearing fo... - 7/28/2005 10:14 PM

SkrapIron

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Where did you get a 4.8:1 internal gear ratio? The Stampede has a 2.72:1 transmission ratio.

Your equasion should look like this : 90/16x2.72=? The answer is a final drive ratio of 15.3:1.

Your Imex tires are 5.5" diameter, so your roll-out is 17.28" per revolution.

Roll out - final drive ratio = efficiency ratio.

17.28-15.3=1.98. Your truck is overgeared. Your best gearing choice would be a 96/15 Spur/pinion. Your motor is probably getting very toasty with the 90/16 setup. With those tires, and the 96/15 setup, you should see about 35mph out of your truck.

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RE: Mystery Solved! How to select the proper gearing fo... - 7/29/2005 2:22 AM

45mph pede

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96! oh boy...

Never seen one of those, hopefully my LHS has a 96'r that will fit my pede

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RE: Mystery Solved! How to select the proper gearing fo... - 7/30/2005 5:51 AM

jkrustchinsky

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this is crazy, this thread is still alive after this long

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RE: Mystery Solved! How to select the proper gearing f... - 7/31/2005 6:02 AM

lokie

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Just wanted to thank skrapiron speedmunky and rcuniverse for the gear chart.....it proved usefull!!!

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RE: Mystery Solved! How to select the proper gearing f... - 8/1/2005 2:55 AM

WRXTC

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LOL

. According to that Chart, xls document my car does 11 KMH

. I havea Mission S1 carbon with a 15 Turn motor in it and am running a 92 spur and 24 Tooth pinion. I am just a little slower than the dudes that race Mod at our track and they have been clocked at between 75-85KMH down the main straight. How can I only be doing 11KMH

?

Oh and this gearing information is fantastic. But bear in mind that when racing most races are only 5-6 mins in length. Therefore strictly for racing you can change the gearing a lot to obtain max power, speed etc..As you will not cook a motor in that amount of time.

Just keep a constant check on the temp of the motor. Mind you most cars that are running a 9-13 turn motor won't get much more than 6 mins from a 3300 MAH pack.

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RE: Mystery Solved! How to select the proper gearing fo... - 8/2/2005 4:45 AM

MBX5T Maniac

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cool. thanks skrap.

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RE: Mystery Solved! How to select the proper gearing fo... - 8/3/2005 8:43 PM

B Boy

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see if this simplifys Skrapirons's philosophy:

Get wheel's diameter (in inches), divide diameter by rc's transmission ratio <<not FDR>> and get your "magic number" for those particular tires. Multiply your cars "magic number" (for those particular tires) by whatever size pinion you have (or want to use) for the perect spur gear size, or divide a spur you have by your "magic number" for the perfect pinion. Round up or down to approach torque or speed based gearing.

Skrap, you are the truth for this one!

< Message edited by B Boy -- 8/3/2005 8:47 PM >

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RE: Mystery Solved! How to select the proper gearing f... - 8/12/2005 2:45 AM

jaejw1

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quote:

ORIGINAL: WRXTC

LOL . According to that Chart, xls document my car does 11 KMH . I havea Mission S1 carbon with a 15 Turn motor in it and am running a 92 spur and 24 Tooth pinion. I am just a little slower than the dudes that race Mod at our track and they have been clocked at between 75-85KMH down the main straight. How can I only be doing 11KMH ?

Oh and this gearing information is fantastic. But bear in mind that when racing most races are only 5-6 mins in length. Therefore strictly for racing you can change the gearing a lot to obtain max power, speed etc..As you will not cook a motor in that amount of time. Just keep a constant check on the temp of the motor. Mind you most cars that are running a 9-13 turn motor won't get much more than 6 mins from a 3300 MAH pack.

with that said,, what should the gearing be for motors with such low turns,, i have been told that the lower the turns,, the less torque you have,, so shouldnt the tire/gear ratio be more in the negative for a 10t than say a 19t or stock motor,, ... im burning up too many motors.. 2 14t motors have died so far,, and im not sure if it was because of the gearing,, for both motors i had in the positive side of things,, t/g ratio= 2.356 i guess just because the motor can do it doesnt mean that it should,, not for a tight track where you are gunning every few seconds to clear jumps and for a short straight.....

my goal here is to find the best ratio for my 4wd buggy which is a motor killer,, motors get extremely hot after every pack,, my initial t/g ratio was 0.585,, which in a 2wd buggy or truck might be fine,, but not in my 4wd buggy,,, motors were smoking... so im guessing that if i go to an extreme low on the t/g then i will be ok and the buggy should run/jump better.. i was thinking a t/g of -1.437 or even a t/g of -2.165 if the the motor will mesh correctly..

< Message edited by jaejw1 -- 8/12/2005 2:50 AM >

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