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... - 4/28/2005 2:55 PM   
Graystar


 

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quote:

ORIGINAL: ronnerwin
The problem I had is that a scalar value (tire circumference measured exclusively in inches) is subtracted with a constant (final drive ratio) to yield another constant (the tire/gear ratio).
...
Normally, you can’t do this kind of math because the units cannot cancel out to produce a non-scalar result; that is why the “ratio” calculation doesn’t apply to metric units without first converting to imperial. However, just because the math doesn't make sense, doesn’t mean the method doesn’t either.

Exactly. But more importantly, it means that the process isn’t understood. And if you don’t understand something then it can be misapplied, as in the case of touring cars and larger, heavier monster trucks.

quote:

ORIGINAL: ronnerwin
As mentioned in the original post, 1 to 1 (rollout value of 1 inch/rev or 25.4 mm/rev) is ideal.

Why do you say this? Where is this written (other than in this thread?) This assumption is the primary problem with this method. The assumption is only true for stadium trucks with mild modified motors. For buggies and trucks with stock motors, it under-gears the car. For 9 or 7 turn motors, it over-gears the car...possibly to the point of damaging the motor. For a monster truck used for backyard bashing...fine for stock motors but definitely over-gears with modified motors. Basically that means that there’s nothing ideal about the 1-to-1 relationship.

I know that everyone wants a simple formula for gearing but the situation is simply too complex for that. We have different cars of different weights designed for different types of roads running with different motors...there’s simply no way a single formula will account for all these factors. We shouldn’t let our desire to have one formula blind us to the point of accepting something without understanding its limitations.

The formula is just fine for stadium trucks, and won't hurt your buggy. It won't hurt your touring car either, but everyone else will be lapping you. It's fine for a monster truck with stock or mild modified motors. If you understand these limitations, and adjust accordingly, then the formula can serve you well. But if a person doesn't understand the limitations then they're rolling the dice on their motor...expecially expensive low-turn motors.


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RE: Mystery Solved! How to select the proper gearing fo... - 5/9/2005 5:10 AM   
sillared


 

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Status: offline 		Ok.. new here, and not finding this answer easily... Whats the ratio of the tranny of a aftermarket stealth for a RC10 buggy? Thx guys..and gals

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RE: Mystery Solved! How to select the proper gearing fo... - 5/9/2005 7:26 AM   
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RE: Mystery Solved! How to select the proper gearing f... - 5/9/2005 10:55 PM   
jigglebelly


 

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Status: offline 		I'm new to rc and i have an electric rustler. I'm going to get a 19 turn chameleon 2 pro motor and i don't know my transmission ratio. Can anybody help me out with the gearing. I want to gear it for top end speed without overgearing it

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RE: Mystery Solved! How to select the proper gearing f... - 5/9/2005 11:40 PM   
SkrapIron



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Status: offline 		The Transmission ratio for ALL Traxxas Off-road trucks and buggies ( Stampede, Rustler, Bandit) is 2.72:1.

That info is very heavily marketed by the Traxxas folks and " The Tought Magnum 272 Transmission."

Your Rustler with the Chameleon motor will benefit most with an 84t spur gear, and a 21t pinion, if you kept the stock tires. If you change the tires, you will have to adjust the gearing accordingly.

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 1:58 AM   
sillared


 

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Status: offline 		ok.. so I`m running a novak 610 reversible esc... kinwald mod motor with neutral timing.. 13t maybe?? dont remember, O-L-D batteries... they are topping out around 1800 on a pinnacle plus charger... running a gearing of -2.245 or -.8 depending on a 23 or 27 pinion gear.... Motor stays cool to the touch, batteries are cooking by the time they die.... and ESC hits thermal shutdown if I run a couple packs thru in quick succession....
I`m so rusty at this... what does that mean??? ESC cant handle the motor? Would being undergeared overheat the ESC?
Oh yeah.. all in a RC10T collectors item... homeade carbon fiber chassis... bent the old one up too much...

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 2:15 AM   
jigglebelly


 

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Status: offline 		the tire i'm using on my rustler are the road hawg 2s. What should i do for gearing with the chameleon then?

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 2:19 AM   
SkrapIron



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Status: offline 		That's not a gearing issue. That's a problem with garbage batteries. The older they get, the harder it is to get any juice out of them. With the increased resistance, it will build heat in your batteries first, and the ESC second. Your ESC is 1, old, two is being used near it's design limits ( limited to 12t motors).

When selecting your gear choice (23 or 27t pinion), what spur are you running, and what tires? Those a VERY large pinion's, in 48p. Are you using 64p gears in your truck?

The solution? Get youself some new batteries. GP3300's are relatively inexpensive now. Either add some deans connectors yourself, or have your LHS do it for you. Better batteries will help tremendously. Undgergeaing will not cause the problems you are describing.

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 2:22 AM   
SkrapIron



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quote:

ORIGINAL: jigglebelly

the tire i'm using on my rustler are the road hawg 2s. What should i do for gearing with the chameleon then?


The RH II's have a similar roll-out to the stock tires( 3.5" dia., 10.996" roll-out). Your best bet is 84/21.

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 10:22 PM   
jigglebelly


 

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Status: offline 		just called traxxas. they said to leave the gearing stock unless the motor gets hot. what do u think of that?

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RE: Mystery Solved! How to select the proper gearing f... - 5/10/2005 10:34 PM   
SkrapIron



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Status: offline 		I think that leaving the stock gearing ( 84t spur, 18t pinion ) will undergear your truck pretty dramatically, and defeat any performance advantage that you gained by switching to a MUCH better motor over the stock Stinger.

Either way, you won't hurt your truck any. But there will be a HUGE difference in performance between the two.

You call.........

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RE: Mystery Solved! How to select the proper gearing f... - 5/11/2005 1:18 PM   
muahaha


 

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Status: offline 		Hi Skrap,

Thou Gray has dun nothing but butchered ur formulae to a million pieces, dun let him get the best of u. All ur sweat and effort has make gearing a much less hasle to most people. But personally for me, thru ur formulae and explaination, i have come to understand some concept of tires diameter vs spur size vs pinion size.

Althou i have been racing for some times now. I did not really have the real understanding of the relation between tire size, spur size and pinion till i have read this thread. In assumptions, most people (like myself) uses rollout formula to determine the 'almost' right pinion to use on any given car/internal drive/tire diameter/spur/motor combo. But here's my problem. I have tried to understand why on any given tc with the SAME ROLLOUT, that same car will have a better acceleration with

a)a smaller tire diameter
b)bigger spur
c)higher internal ratio

and a better top end speed with
i)a bigger tire
ii)a smaller spur
iii)lower internal ratio

With ur formulae i finally understood them to some extend. Now with this knowledge i have gain, i am more deadly then ever at my local track.

Once again, my hats off to you and a whack to ur back (i mean pat :P ).

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RE: Mystery Solved! How to select the proper gearing f... - 5/11/2005 2:47 PM   
Speedmunkey



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Status: offline 		After living with this formula for a few weeks now, I've come to a few conclusions about it.

First, for lower turn mods, it ain't perfect. I bought a Cobalt 8x1 and I tried gearing it using this forumla. I checked after 5 laps, and knew it wasn't right when I BBQ'd my finger. This wasn't entirely unexpected, which is why I've told people since day 1 to check the temp frequently until you know it's ok..

The way I've started using it is more of a guideline. What I do, is figure out the best "rating" for a motor and then gear according to that. For example, I know my SS5800's FLY when I run them with a final number of 1.500ish.. So, I aim for that when I switch tires. I have a matrix made up showing all my different tire sizes and the gearing it takes to make them all come out as a 1.500 or close to it. It's similar to the concept of roll-out, but easier to wrap my brain around. I also do it for my brushed motors. The Cobalt, for example, want's a -3.335! So I know, as long as I gear it for that number, things are going to be ok and perform well.

I'm still a believer in this formula, it gives me a scientific, mathematical way to follow the power from the motor to the tires. But I use it a little differently than Skrap intended.


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RE: Mystery Solved! How to select the proper gearing f... - 5/11/2005 3:06 PM   
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Status: offline 		dang! now i don't have to buy a radar gun or what ever u call those.thanx!
dave

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RE: Mystery Solved! How to select the proper gearing f... - 5/11/2005 4:43 PM   
jaejw1


 

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Status: offline 		i dont understand why you guys just dont use a smaller spur gear,, and start from there,, find out what the stock ratio is,, and the smallest spur you can use,, use it,, and then use gearing around the original ratio,, ... the only thing is that,, there is less mass to turn,, look at it this way..

ratio 5:1
180/36
120/24
110/22
100/20
90/18
80/16
75/15
70/14


looking at this,, you tell me which gearing would be faster,, and give more torque... .. if you look carfeully,, they all have the same ratio,, but as the gears get smaller,, the speed and torque go up.. and you can use the smallest with a 48pitch,, i use 48p in my rc18t and my gearing is 51/10 it was 55/11... and my micro rs4 is 58/26... ... .. like i said find the smallest spur that will fit your ride,, and go with the same stock ratio,, and start from there,, and only change the pinion,, one i takes less time and effort,, and while at the track time is everything.. .. so take my car for example,,, stock gearing is 87/18 which is a ratio of 4.833:1.. the smallest spur i can use is 78t.. and keeping the same ratio i would go with a 16t pinion,,,, and from there i could go up or down,, .. but i currently run a 81 spur,,, and i have geared it to 81/20 and im loving it,, cant see using a 93/23 gearing,, just too much metal and plastic to spin..


this is my take on things,, and i may be wrong,, but it is working for me...

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RE: Mystery Solved! How to select the proper gearing f... - 5/11/2005 5:21 PM   
Speedmunkey



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Status: offline 		My reasoning for not going with smaller gears is simply making them reach each other. Take my Cobalt motor for example. It uses a 16t pinion.. That's a pretty small pinion. Ok, now let's say I drop my 86t spur to a 78t spur (the smallest Kevlar spur made in 487p..) I'd then need a 14t pinion to make a ratio that was close to the original.. You ever tried making those 2 gears mesh on a XXX-T? They don't get close to each other. It's a design flaw in the Losi, but it's something you gotta live with.

Besides, what you are suggesting has been argued endlessly over the years and the eventual conclusion is that it doesn't make enough difference to matter. The mass differences in an 86t plastic spur and a 78t plastic spur are tiny. The mass differences in a 16t steel pinion and a 14t steel pinion are even smaller. Maybe on a small truck, like an 1/18 scale, it would matter, but not on a 1/10 scale vehicle.


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RE: Mystery Solved! How to select the proper gearing f... - 5/14/2005 10:34 PM   
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Status: offline 		On post #14 I can't figure out how to get speedmunkey's spreadsheetvsaved. How do you save it and read it.


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RE: Mystery Solved! How to select the proper gearing f... - 5/14/2005 11:46 PM   
Speedmunkey



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Status: offline 		You right click it, then save it as a .txt file.. You then go rename it to a .xls file. It requires Microsoft Excel to be installed on your system. If you don't have that, go to the community link that RCU posted. Works the same, just less portable.


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RE: Mystery Solved! How to select the proper gearing f... - 5/20/2005 10:22 AM   
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Status: offline 		hey guys I just was wondering if the motor timming will affect in any way Skrappy's gear calculator...

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RE: Mystery Solved! How to select the proper gearing f... - 5/20/2005 1:39 PM   
Speedmunkey



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Status: offline 		Advancing the timing will make the motor pull more power. That, in turn, will make more heat. So yes, and no. The formula still works to get you in the ballpark, but you'll need to check the temperature frequently the first few runs to make sure it isn't overheating. As has been stated, this isn't a fool-proof, dead on the money formula for every motor. But it gets you very close.


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RE: Mystery Solved! How to select the proper gearing f... - 5/21/2005 3:56 PM   
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Status: offline 		OK, so i have the spreed sheet, the desire to speed up my elect pede. I am really new to RC and the first thing i am going to do is change to a new motor. the 272 tranny will support down to a 17 turn, was thinking of dropping to a 19 turn, not sure which yet. and sticking with he stock 2.2 wheels. using the formula i come out with a -6.235 ratio with the stock 20 turn motor. where should i go from here to bring this more in line with the 20t and what should i look forward to doing to line out the 19t. thanks allot.

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RE: Mystery Solved! How to select the proper gearing f... - 5/21/2005 4:01 PM   
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Status: offline 		i forgot i am running 18/87 pinon/spur set up

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RE: Mystery Solved! How to select the proper gearing f... - 5/21/2005 5:34 PM   
jahvajoe


 

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Status: offline 		ok, so i have been told that i used the wrong measurment for the tire size, after remeasure, things look a bit more correct. according to the formula if i re-gear to a 16/87 set up it ges me around a .5 or so. Does this sound do-able and will it work with a 20t or a 19t motor.

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RE: Mystery Solved! How to select the proper gearing f... - 5/23/2005 7:14 AM   
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Status: offline 		This is pretty darn cool, i'm new to all this and bought a Tamiya TT-01. Right now i'm using a stock 61T spur gear and a stock 19T pinion gear. If these calculations are correct, my stock top end speed is about 15.03mph. If i upgrade to the Tamiya Sport Tuned Motor and switch to a 58-22 Spur to Pinion i can get up to 22.6. If i even get more crazy and go to an motor pulling 37500RPM (11turn?) with that same pinion set i can get up to 40.3 mph.

I guesstimated my tire diameter at 2.5 and transmission ratio 2.6. Hopefully that's right or it's back to the drawing board.

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RE: Mystery Solved! How to select the proper gearing f... - 5/24/2005 9:52 AM   
jaejw1


 

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Status: offline 		well i just saw the conversion calulator and found out that my new masher 2000 tires require a 90/16 = .769 or 93/16 = .281 either one would work i guess,,, i currently am using a 90/18= 2.394 and before that i was using 84/18= 3.26 i guess this is why my packs werent lasting long,,,

as far as my proline holeshots are concerned the magic gearing would be 90/20=.081 when before i was using 81/20 = 1.251

so i will report in the morning on what i think about my new 90/16 gearing,,,

one thing i did notice with the masher 2000 that with the 84/18 the top end was ther,, but took time to get there and the 90/18 lost the top end but the wheels just spun all the way down the track,,, so i dont know what to expect with the 90/16 i know the wheels will spin more,, and i will loose more top end but if this will allow for more runtime and greater fun factor,, then im sold,, i guess i will have to get a faster motor...



dont know if this has been discussed, but i dont think this calculator works fo 18th scale cars,, according to the calculator my rc18t is on a real severe side of things,, 60/15= -3.324
if i were to gear it to equal 0 1:1 or anything close to it,, the motor for sure would over heat or the esc would shut down,,, already things get pretty warm,, according to the calculator the best thing to use is a 60/20 gearing which equals -0.824 which is way too high ,, but that is just my opinion

i dont think they make pinions that large for lil tiny shafts like on the mamba


< Message edited by jaejw1 -- 5/24/2005 10:16 AM >

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