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RE: Mystery Solved! How to select the proper gearing fo... - 8/12/2005 4:45 AM   
Speedmunkey



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Status: offline 		Hey Skrap, I wanna clean this thread up.. Do you want me to de-sticky this one, then you post a fresh, un-mutilated one, and I re-sticky and LOCK it? This is good theory in here, and it's far too cluttered to be useful to most people.. Lemme know!


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RE: Mystery Solved! How to select the proper gearing fo... - 8/12/2005 1:14 PM   
SkrapIron



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Status: offline 		Yes, Munkey.

I want to use the re-post on page 9, with an edited second paragraph from page one.

Let me know when you want to do it.

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RE: Mystery Solved! How to select the proper gearing fo... - 8/12/2005 1:56 PM   
Speedmunkey



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Status: offline 		Go ahead and make a new thread. I'll remove this one, then lock and sticky the new one. I could PROBABLY prune this one, but I'd end up killing it cuz I don't know the mod controls yet.


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RE: Mystery Solved! How to select the proper gearing fo... - 8/12/2005 5:01 PM   
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RE: Mystery Solved! How to select the proper gearing fo... - 9/24/2005 12:36 AM   
mnementh


 

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RE: Mystery Solved! How to select the proper gearing fo... - 11/21/2005 3:20 PM   
mwsmith2


 

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Status: offline 		Well, just read through this whole thread (whew!) mainly because I got some HUGE tires for my Emaxx (for some reason, 7.7" tires didn't set off alarm bells in my head) which overgeared the bajeezus out of it. Running the stock 66/18 setup with the 7.7" tires yielded a final ratio of -4.72/6.242. Oy! I knew as soon as I hit 2nd gear that I needed to get my finger off the trigger. After goofing with the proggy, looks like I should be using at 66/13 setup...which would be a real stump-puller at-15.836, and still have decent top end at -0.661, considerably better than that 6.2 I was trying to pull! I could run 66/14, that puts second at 1.114, but I'd like to use the lower torque and speed of the 13t anyway.

So, thanks for all the good info. I like to give back when I've been helped out, and I'm prepared to do the same thing here. I beat on VB during the day, and I'd have no problem writing a VB .exe for you folks. More portable than the web version and sturdier than the spreadsheet. I could even possibly roll versions for pocket pc's if there is interest. Of course this would be a totally free, no strings attached program with unlimited distribution. If you fellers are interested, drop me a note in my PM box.

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RE: Mystery Solved! How to select the proper gearing fo... - 12/3/2005 7:50 AM   
rufus2000


 

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Status: offline 		No Mystery solved. THE FORMULA IS WRONG !!!!!!!!!!

Sorry to crash the party... I don't know were the original poster got the formula from.. or if he tried to figure it out by himself but it's dead wrong... You are supposed to DIVIDE.. not substract the final drive ratio from the tire circumference!!!

What is being referred here as "Tire/ Gearing ration" is actually called "Roll Out" in the racing circles

Roll Out= Tire circumference / Final Gear Ratio

I encourage everyone to read this most excellent article (roll out is explained on page 2 and 3):
http://www.radiocontrolzone.com/cars/fastmath.asp


No wonder I was getting very confusing results once I changed my tires to bigger ones... For regular sized buggy tires, if you substract it seems to work, but that's because the tire circumference is very close to the final ratios, so most of the time you end up between -1 and 1, but change to bigger tires and you get unreasonable results. (Note that for buggies, the result you get by substracting is still not precise... it's close but wrong!)

In my case: My losi xxxt was upgraded to Proline smashers 2000... Those babies are 4.76 inches in diameter and from trial and error I know that the best performance I get is when I use the 87/17 and 87/18.

With the incorrect formula, I would have never tried those gearing combinations... 87/18 gives a "Tire / Gearing ratio" of 3.209.... (way too far away from the "safe" values)
Remember.. it's a ratio, (in this case 3.209:1), so what this is saying is that the tire circumference is more than 3 times the size of the final ratio, which of course is incorrect (In my case the tire circumference is 14.954 vs 11.745 for the final gear ratio)

Applying the formula correctly arrives at the proper "Tire/gearing ration" (roll-out):
14.954 / 11.745 = 1.273
which makes sense because it is telling me that the ratio is (1.273 to 1) (The tire circumference is 1.273 times bigger than the final gear ratio.
You can verify this by multiplying: final gear ration X 1.273
That means... make the final gear ration 27.3% bigger...
The result matches the size of the tire circumference exactly.

Oh, one more thing... Forget about using the 0 as a reference... In roll out, you are looking for the 1, that's the "sweet spot", anything less will give more torque... anything more is more speed... You could ask why is that in my case I arrived at 1.273 as my "optimum" value. Well, it all depends on the motor. I have a Novak ss5800 brushless and it has tons of torque, so even thought 1 is the "sweet spot", a 1.273 gives me the most speed while hardly noticing any decrease in torque.

--- Also, a tire tip I did not want to forget sharing...
When considering tire diameter... consider that with very fast motors (specially brushless) you could get some tires ballooning when accelerating and when reaching top speed (some brands/models/compounds more than others)... This means that the tire diameter will actually be higher than what you measured! So for an ultra precise "roll out", one should be able to consider this increment in tire diameter... I have not tried any "measuring techniques" for that but I would love to hear your comments on how to achieve this. Or you could just experiment and make a wild guess of a 5 to 10% increase in overall tire diameter.

Well, that's it for now.

So update your spreadsheets everyone... and the web calculator too.

Hope this helps to clear things up.

bye.

< Message edited by rcuestas -- 12/3/2005 9:21 AM >

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RE: Mystery Solved! How to select the proper gearing fo... - 3/21/2006 2:11 AM   
bwalker25


 

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Status: offline 		so I should use the formula in the above post Tire Circum/Final Gear = X. So should X be less than 1.0 or more than 1.0? that is my ONLY question, well not really... If less than 1.0 is good assuming it is from the above posts, I should have 4.9" dia tires (masher 2k), 14T double speed gem, xmission ration 2.72 ('pede stock), stock spur gear of 87, that means I should be running something like a 12t pinion to get a 14T hot mod, to run cool and not blow the heck up! haha, i dont wanna cook a motor! that equates to 28mph under optimium conditions

however using the first formula in post #1 from Skrapp, tire cir - fdr = x, I get approx "-4.326" which is WAY under geared from what I have read here, however if I did read this all correctly I should run with the first formula provided in this thread a 90/16.

Bear in mind that I am going to be running stock tires (upgrading to mashers later), these calcs are for the mashers on a 14T motor. woudl I run a 90/16 (spur/pinion), or would I run a 87/12?

someone help me, i read this entire thread and I am more confused than ever! skrapp or munkey where are you!

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RE: Mystery Solved! How to select the proper gearing fo... - 3/21/2006 2:45 AM   
bwalker25


 

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Status: offline 		never mind, I answered my own question just a sec ago! FDR must be as close to 1.0 as possible, sinse I will be running a mod 14T double or lower I can assume that a FDR less than 1.0 is good considering the heat associated with it! I guess I will start with a 12t pinion and go with the 87t spur and I think I will be ok!

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RE: Mystery Solved! How to select the proper gearing fo... - 8/26/2006 10:10 PM   
litljon721


 

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This thread has gotten pretty long. Nobody is posted in this thread for a while. I hope somebody can answer my question. I looked through it little bit. Quite a little.
Does it matter how you hit your ratio?
Does it make a difference if you use for instance, a 13T pinion gear and X spur or a 20T pinion gear and X spur to hit your ratio?
How much above or below the happy spot of one would still be considered acceptable?
The last one would probably be a heat issue I would presume. Maybe?



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RE: Mystery Solved! How to select the proper gearing fo... - 8/26/2006 10:19 PM   
duneslider


 

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Status: offline 		As long as you hit the ratio or "sweet spot" you are fine. Most seem to think they can only change the pinion so that's all they do.

Duneslider

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RE: Mystery Solved! How to select the proper gearing fo... - 8/26/2006 10:24 PM   
litljon721


 

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quote:

ORIGINAL: duneslider

As long as you hit the ratio or "sweet spot" you are fine. Most seem to think they can only change the pinion so that's all they do.

Duneslider


Thank you very much. Very quick response. Thank you again.


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RE: Mystery Solved! How to select the proper gearing fo... - 8/26/2006 10:33 PM   
duneslider


 

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Status: offline 		Anytime! If you can understand that formula on the gearing selection you should never have problems with gearing. However, don't forget to check engine temps after every change. Always better safe then sorry!

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RE: Mystery Solved! How to select the proper gearing f... - 10/3/2006 12:04 AM   
tomKatsTats


 

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Status: offline 		Hello ,

Help Please ,

I have stock tires on a xxx-t ,with a novak speed control , and a 12 turn motor , it has(pinion) 48 pitch gear ratio with a(Spur) 88 T 48 pitch ratio! ( What is 48 pitch ratio ??? ) I dont see that on my other cars or thucks??I am whanting to know the wright gearing for this I have tryed your caculator ,but could not get it to work!

Thank you so much
TomKat

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RE: Mystery Solved! How to select the proper gearing fo... - 4/17/2007 10:29 AM   
day2dayfun


 

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Status: offline 		I did a lil' number play myself, this is what I got,Using the Rustler tranny, a 86/16 spur&pinion, & Masher2000's. The majic number is -0.76. Don't if it will still burn up the 12T Titan yet. Waiting to them to come in. Thanks...Day

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RE: Mystery Solved! How to select the proper gearing fo... - 4/18/2007 4:59 PM   
IARacer


 

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Status: offline 		Does the gearing calculator apply to other scales besides 1/10? I ran the numbers for my RC18T and it says I should run an 18t pinion to get a 1:1 ratio and that seems like a really tall gearing considering stock gearing is a 12t. Any help would be much appreciated.

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RE: Mystery Solved! How to select the proper gearing fo... - 4/20/2007 3:31 PM   
Marv829


 

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quote:

ORIGINAL: IAMammothST

Does the gearing calculator apply to other scales besides 1/10? I ran the numbers for my RC18T and it says I should run an 18t pinion to get a 1:1 ratio and that seems like a really tall gearing considering stock gearing is a 12t. Any help would be much appreciated.


Hello neighbor, I'm 25mi west of you in Worthington. You do not need a 1:1 ratio to have proper gearing. If your setup works well then calculate what your rollout is. If you ever want to change your tire size and but want to keep the same performance as your present setup then you would try to get as close to your present rollout number as possible through gearing changes with the new tires.

Quote from http://www.radiocontrolzone.com/cars/fastmath2.asp
"A rollout number quantifies exactly the effect of gear ratio and tire-diameter changes. Higher rollout numbers mean an increased load on the engine, which results in slower acceleration and faster top speed. Conversely, lower rollout numbers result in quicker acceleration and lower top speed."

Keep in mind that the rollout calculations do not take into account tire mass. So if you went from 3" tires to 6" tires and were able to get an exact rollout number as your previous setup through gearing changes your performance may not be exactly the same because you increased the total weight of the vehicle.

My Stampede has rollout of 0.876, my Rustler is 0.770 and my E-Tower Terror MT is 2.113. My TT MT runs cooler then the other two and my Rustler is the fastest. They all have different motors and tires (setups) of course. I have a MS Excel spreadsheet to do the math for you here: http://www.freewebs.com/gassmann829/files.htm


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RE: Mystery Solved! How to select the proper gearing fo... - 4/20/2007 4:12 PM   
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Status: offline 		Thanks a lot! I have been running nitro for a while now, but my RC18t is my first electric venture. I'm starting to understand it all now.
Yeah, I'm going to college in Dubuque right now but I was born and raised in Cedar Rapids. Good to see another Iowan on here!

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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 10:27 AM   
DarkHorse



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Another Rollout and speed calculator / estimator.

http://dhrc.rchomepage.com/RolloutCalc.htm

RC Car/Truck Power & Setup Calculator

Have a play...

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RE: Mystery Solved! How to select the proper gearing f... - 10/28/2007 2:54 PM   
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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 3:45 PM   
Slo-V Flyer



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Status: offline 		Sorry, but I have a problem with this whole tire/ratio calculation approach.

This whole formula thing doesn't take in to consideration the simple fact that running a 12 turn motor in a Rustler almost always will require the use of 12 tooth pinion because anything taller than that and the motor will burn up... ask me how I know.... Using a 17 turn motor, and you can get away with a 15 or 17 tooth pinion and not be so bad with the temperatures. This while using the same tires. So I really don't think this method of calculating the gearing using just gear ratio and tire roll out is accurate as far as motors and their torque and heating issues are concerned.

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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 4:01 PM   
DarkHorse



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Status: offline 		> Sorry, but I have a problem with this whole tire/ratio calculation approach.
Hey, that's fair enough. My calc just gives you the numbers, I don't care what judgements you make on them or how you implement or draw conclusions from them. Depends on the desired application. Rollout is only one piece of data thrown up of many, some useful some not so useful.

< Message edited by DarkHorse -- 10/28/2007 4:02 PM >

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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 4:27 PM   
Slo-V Flyer



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Status: offline 		Well, my post wasn't aimed at you DH, but this whole method being used. A low turn motor will not work correctly if you keep the same pinion as the higher turn motor in order to keep the same rollout/ratio. Most of us know that you need to gear down for low turn motors, which would therefore change the rollout/gear ratio so that's what I mean that this is not a really good method. If some n00b (no offense noobs) uses this method and replaces his/her old stock 19t or 20t motor and then proceeds to fry their brand spanking new 14 turn motor using this method, then I see that as a problem. They will be confused why their motor is running so hot and not necessarily realize that they would need a smaller pinion for the new 14t motor.

I've read about and seen many newbies who end up running low turn motors with a tall pinion (e.g. using the stock XL-5 Rustler 12t Titan example they'll keep the same 23t pinion when they switch to a standard 15t motor!!!) because they don't know any better and think they will get more speed, only to find out the motor's performing poorly and eventually cook it or nearly do.

Maybe I'm wrong, and maybe this method can be used as a ball park figure, but then again I only see that happening with maybe a stock motor 27 turn or something, where gearing issues won't cook the motor right away.

< Message edited by Slo-V Flyer -- 10/28/2007 4:28 PM >

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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 4:54 PM   
DarkHorse



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Status: offline 		Yes, I see what you mean, good point. Such things as torque and heat issues are not handled in the numbers at all.
In reality I'm a relative noob to these matters anyway , where rollout is just and interesting number to consider at this stage.

> XL-5 Rustler 12t Titan
From what you say about the 14 turn motor, it seems on the margins for a practical solution and falls a bit short on desired performance (gets hot otherwise), so you need to gear accordingly.

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RE: Mystery Solved! How to select the proper gearing fo... - 10/28/2007 4:56 PM   
Access


 

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quote:

ORIGINAL: DarkHorse

I somehow managed to miss this thread .



Another Rollout and speed calculator / estimator.

http://dhrc.rchomepage.com/RolloutCalc.htm

RC Car/Truck Power & Setup Calculator

Have a play...

It's actually a good tool to use, I tried some of my setups and it predicts the max speed within 10-20%, and the runtime figures are in the right ballpark too.

The only problem is that people might actually think rollout matters for something. The 1.0 inch / motor rev. thing is a often a good starting point for 19T or 27T brushed, but just about every other setup needs to be lower and many need to be significantly lower than 1.0.

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