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Dec 04, 2014, 06:35 PM
Did I make the A Main?
bill_delong's Avatar
Thread OP
Mini-HowTo

PRIMER: What gearing do I need to run for upgraded electronics in my car?


A temp gun is probably the single most important tool in helping you protect your investment. Let the temps tell you how to gear your car with the following general limits for most electronics on the market:

Battery < 120°
ESC < 140°
Motor < 160°

***Be sure to check the manual for your electronics to see what their specific temp limits are, if none are listed then use the suggested limits listed above.

Anytime you change your battery cell counts or capacity (i.e. from 2S to 3S, or NiMh to LiPo) then you will likely need to re-gear appropriately as well, especially if you increased run time, temps will grow exponentially for sustained duration.

Here are a couple temp guns to consider:
http://www.banggood.com/GM320-Non-Co...166379201304IO
http://www.harborfreight.com/non-con...ter-93983.html

hot battery = replace with higher C rated pack
hot motor + cool ESC = under geared
hot ESC + cool motor = over geared
hot everything = WAY over geared

Start with your stock gearing and then go from there... also keep in mind that driving surface conditions, tires, worn bearings etc all effect your temps... always check your temps just like a 1:1 car has a temp gauge to tell you the overall health of your system.

Remember, a temp gun is the single most important tool to own in this hobby. If you have the money to upgrade your electronics, then you should also include the cost for a temp gun without a doubt

*** For stock racing, here are some tips for using a motor analyzer to get max potential out of a motor

Check out more stuff on My Bookmarks page!
Last edited by bill_delong; Apr 21, 2020 at 09:28 AM.
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Dec 04, 2014, 10:30 PM
Which way did it go?
mckev24's Avatar
Great advice! Definitely plan on purchasing a temp gun now!
Dec 04, 2014, 10:54 PM
Did I make the A Main?
bill_delong's Avatar
Thread OP
good deal... when most brushed motors burn up in a RTR, it's often because folks will install large LiPo battery packs that have 2-3 times the capacity of the original NiMh battery. That means that they will get 2-3 times longer run time, but most folks don't think to check their temps. They might find that their car is over geared if they want to have really long run times when compared to the gearing that was selected for the electronics that the manufacturer had originally provided
Last edited by bill_delong; Dec 05, 2014 at 09:00 AM.
Dec 12, 2014, 08:02 AM
Which way did it go?
mckev24's Avatar
So what exactly do you mean by the gearing? What gears need to be changed?
Dec 12, 2014, 08:53 AM
Did I make the A Main?
bill_delong's Avatar
Thread OP
Short Answer:
Simply change the pinion gear that is on the motor, "gearing up" means installing a larger pinion with more teeth. When you gear up, there will be a trade off between slower acceleration for higher top speed, and in most cases, the more you gear up the warmer your motor temps will get.

When racing, folks are constantly trying to find the sweet spot to achieve the greatest efficiency in their gearing setup to maximize their overall performance of the system.

Long Answer:

FDR (Final Drive Ratio) is used to determine the overall gearing of your system. The smaller the number is the equivalent of "gearing up".

The FDR is the sum of multiplying the IDR (Internal Drive Ratio) with EDR (External Drive Ratio).

The IDR is the number of teeth on the larger Crown (or pulley on belt drive) divided by the internal pinion on the center shaft (or smaller pulley adjacent to spur gear on belt drive). For example, a car with 42T on the crown gear with 17T on shaft pinion = 42/17 = 2.47 IDR

The EDR is the number of teeth on the spur divided by the number of teeth on the motor pinion. For example, a car with 86T on the spur and 30T on the pinion = 86/30 = 2.87 EDR

Now simply multiply IDR x EDR = FDR
2.47 x 2.87 = 7.09 FDR in this example

When tuning the FDR, you typically want to change the EDR gears... start with pinion for major adjustments, then swap out the spur for fine tuning. Sometimes you have no choice but to swap out the spur in order for certain pinions to fit one way or another, this can be tricky for some cars when trying to target a recommended FDR and stock gearing is way off.

Many racers will refer specifically to the FDR which is easier to reference because people will often use different pitch gearing where the finer the pitch used, the more efficient a car will drive. There is also a trade off with using fine pitch gears because the finer the pitch, the more susceptible it will be to stripping gears.

1/8 cars typically use Mod 1 gearing
1/10 off-road typically use 48P (some use 32P or Mod 1 depending on driver preference)
1/10 on-road typically use 64P (some use 48P or 84P depending on driver preference)
Last edited by bill_delong; Dec 12, 2014 at 09:33 AM.
Dec 29, 2014, 01:47 PM
Which way did it go?
mckev24's Avatar
Just wanted to note that I check the temps after every run. Motor got up to 112° one time, usually being in the 90° range. ESC and battery are usually in the 70°-90° range.
Dec 29, 2014, 02:02 PM
Did I make the A Main?
bill_delong's Avatar
Thread OP
That's good... keep in mind that current ambient temps make a big factor too.... so as temps rise in the summer, you'll want to pay closer attention to your temps
Jan 22, 2015, 04:47 PM
King of all monsters.
Godzilla311's Avatar
Great advice Bill! I'm definitely going to pull out the temp gun and check this on our RCs.
I'm very new to the hobby so I'll add my noob experience with this issue as an example.

I bought an Integy i10B for my fiancée's son.
Relevant specs are as follows:
Pre-installed SPECS 430w ESC
Pre-installed SPECS oversized 550 brushed motor w/pinion gear
Weight: (3 lbs. 10.2-oz. (1650g)
4WD Center driveshaft
7.2v NiMH 1800mAh stick pack battery

The included NiMH battery only lasted ~5 minutes the first few runs and was very slow compared to the i10T I bought for my nephew (which has a brushless motor and 2s LiPo). So -- I immediately put the backup battery for the i10T into the i10B, which is a 5000 mAh 25C 2s LiPo, though the specs didn't say it could use a 2s. I figured since the other buggy clones of this model like the Quanum Vandal (although being brushless) call for 3000-4000 mAH 2s it should still be fine to use a 5000 mAH 2s on his brushed; right?

The results were that the i10B now has much quicker acceleration, a much much higher top speed, and could probably last 20 minutes or more though we stop at 15 now.
The issue though, like Bill pointed out, is that we have a heat problem. Midway through the first run in a parking lot where he was doing a lot stop&go and top speed runs, we noticed a smell and saw smoke; and when I picked up the buggy it nearly blistered my fingers (the motor peeks out of the bottom of the chassis where I gripped it). I then noticed melted plastic on the body of the buggy by the motor all warped and wavy (the body is originally very close to the motor). After opening it up, I noticed it had also begun melting some wires close to the motor and it softened the glue holding the ESC down causing it to come loose.

The brushed motor obviously ran far hotter than the i10T's brushless on the 2s and is most likely geared for the NiMH or possibly a lower rated 2s, but not the long runs of the 5000 mAH 2s.

We still run the 5000 mAH 2s on the buggy , but we only run 10-15 minute sessions and I've temporarily modded the body (heat gun) to have a clearance over the motor of more than 1" with more airflow as well as rerouting the wires towards the middle of the chassis and no issues since, but still runs very very hot.

I'll update with temps when I find my gun, but just goes to show what us noobs will do without knowing what we're doing.
Jan 22, 2015, 06:07 PM
Did I make the A Main?
bill_delong's Avatar
Thread OP
thanks for sharing your results, good stuff!
Feb 10, 2015, 05:39 PM
King of all monsters.
Godzilla311's Avatar
Ok... sooo.... I pulled out the temp gun over the weekend and ran a few scans after i10B #2 did a full 15m run.

(This is my temp gun for reference)
http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1

Shockingly, these were the numbers I pulled:
2s LiPo = 95-105 F°
ESC = 130-150
Motor = 135-250 !!!

*note* This was a cool day and it actually started to lightly rain when we were stopping as you can see by the small drops on the infrared thermometer.

As you can see from the attached pics, the 135° is at the bottom of the motor case and the 250° is in the middle where the "heatsink sleeve" is with the sticker of the brand and details of the motor. [I initially thought this 120° difference was due to emissivity as the metal on the bottom is different than the sticker (even though my gun has a setting for both), but the other end of the motor near the gears (which is the same metal casing) was also 200+, so for some reason the very bottom of the motor was cooler]
The ESC was 130° on the heatsink and 150° on the plastic portion.
The battery ranged from 95-105° on different areas.

Again, this just goes to show you what us noobs can do without knowing how different components react to new components.
Last edited by Godzilla311; Feb 10, 2015 at 07:17 PM.
Feb 18, 2015, 02:15 PM
King of all monsters.
Godzilla311's Avatar
Just wanted to update and add what else can cause heat issues--resistance.
I solved a few of the heat issues and although they are still primarily due to the addition of a LiPo battery on an RC that wasn't geared to run one, the issue was exacerbated by wheel/gear/motor resistance. I had tightened down the motor and wheels so tight they were difficult to turn which means the motor was struggling to turn the wheels and overheating more than usual. Fixing these resistance issues dropped my temps down towards 200° F. Adding a heat-sink & fan combo further dropped temps and I'm now down to around 170° on both buggies. Now that I am running more efficient I will be changing pinion gears as Bill suggested.

One question though. If changing gearing can increase/decrease temps as well as acceleration/top speed, would changing to larger diameter wheels have the same effect? This may not be an option as a fix, but it may also cause issues if slapping on wheels without consideration of gearing.
Feb 18, 2015, 02:37 PM
Did I make the A Main?
bill_delong's Avatar
Thread OP
Yes, adjusting the diameter of the wheels will effect what is referred to as "final roll out" , more info here for figuring the final roll out for your cars:

http://scriptasylum.com/rc_speed/rollout_ratio.html
Nov 14, 2015, 12:28 PM
Registered User
Quote:
Originally Posted by bill_delong
hot motor + cool ESC = under geared
hot ESC + cool motor = over geared
Hmm, maybe this is a language issue (I'm not a native english speaker), but shouldn't this be the other way around? I.e.:

- hot motor + cool ESC = too much motor current = too much motor torque = over geared = geared for too high a "ground speed"?

- hot ESC + cool motor = too fast phase switching = too high motor electrical rpm = under geared = motor must turn very fast to give an acceptable "ground speed"?
Jan 12, 2016, 09:30 AM
Did I make the A Main?
bill_delong's Avatar
Thread OP
Yeah it's semantics, I've had the same discussion with other racers at my local race track where we say gearing up actually presents a lower final drive ratio number which is counter intuitive. So with reference to the OP, Gearing up means putting more work on the system.
Aug 07, 2019, 03:46 PM
Registered User
SilbernerSurfer's Avatar
One of the best and helpful threads in my opinion! Thanks Bill!


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