A-Z of Gearing with Blinky ESC's
This article explains: Blinky ESC's, Final Drive Ratios, Roll Out, Gearing Charts, Internal Ratios, Spur & Pinion Options, End Bell Timing and Motor Temperature guidelines. Sound complicated? We make it easy.
What is a Blinky ESC?
Background: As the use of brushless motors and electronic speed controllers (ESC) became widespread in Australia, around 2009-2010, the manufacturers looked for ways to make their ESC faster and therefore more popular. They developed dynamic timing software for the ESC which could advance or retard the motor timing based on motor RPM and other factors. ESC’s with dynamic timing (sometimes referred to as “boost” or “turbo”) offer a significant performance advantage but also adds another level of complication to setting up the car to be as fast as possible. It is also easy to over heat a motor which then needs replacing.
Definition: “Blinky” denotes a mode of the ESC with no dynamic timing. This is often indicated by a blinking light on the ESC – hence “Blinky”. Also referred to as “non-timing mode”.
If you are interested in why Blinky ESC's are used then refer to the National Rules FAQ (and search for or scroll down to "Why Blinky?")
Which Blinky ESC should I buy?
Whenever buying something that is new and unfamiliar ask around at your local track and see what is being used. If you need assistance it is always easier to ask someone local. While any Blinky ESC is currently legal we strongly suggest you consider one which is from the ROAR Approved Non-Timing ESC list or the AARCMCC EP Off Road Stock Spec ESC List (which are very similar lists but do have some differences).
Gearing for Final Drive Ratio or Roll Out?
In Australia people will usually discuss Final Drive Ratio (FDR) often called "gear ratio" or "ratio" or "gearing". Although some prefer to use roll out, everyone will know what you mean by FDR and this is what we will discuss. FDR is the number of times the motor must turn in order for the wheels to turn once. Expressed as a ratio eg; 4.0:1 means the motor turns 4 times to rotate the wheels once.
Roll Out is how far the car will move forward with one revolution of the motor. This depends on your FDR and the diameter of the tyres. TQ Racing have an excellent Rollout Calculator.
Final Drive Ratios
FDR's in F1 tend to be lower than in a 4WD car. The F1 is lighter and only two wheel drive which puts less strain on the motor and allows a lower FDR.
Lower FDR's provide higher RPM and therefore faster top end speed but less torque and therefore slower acceleration. Lower means "less than" so 3.0:1 is lower than 4.0:1.
Higher FDR's provide lower RPM and therefore slower top end speed but more torque and therefore greater acceleration. Higher means "greater than" so 4.0:1 is higher than 3.0:1.
Calculating the Final Drive Ratio (FDR)
FDR = Internal Ratio x (Spur / Pinion)
All F1 cars except for the 3 Racing FGX are direct drive ie; the pinion meshes to the spur which drives the rear wheels. There are no other gears in the drive train and therefore the Internal Ratio is 1.0.
The 3 Racing FGX has an Internal Ratio of 2.71.
For example; below are the Gear Ratio Tables from the Tamiya F104 Pro Manual (courtesy of CompetitionX.com):
[table on the left is for the stock 104T spur and on the right is the table for the 93T spur]. Note: 93T = 93 Teeth
Remember our equation:
FDR = Internal Ratio x (Spur / Pinion)
An example from the table above using the 104T spur and 20T pinion:
5.2 = 1.0 x (104 / 20)
The FDR equation works for every type of RC car.
Gear Ratio Charts
It can be handy to make your own gear ratio charts. There are a large number of websites that will create a chart based on a range of spur and pinions you specify. For example; Gear Machine (use the 1:10 Touring menu item).
Check out the Apps page for an excellent iPhone gearing app.
So What FDR should you start with?
|Silver Can Brushed
Many racers will have lower FDR than shown above but the above is a good starting point.
Touring Car drivers warning! - if you have found your way to this page from another site and you drive a 4WD touring car then add 1.0 to the above gear ratios eg; Silver Can Brushed becomes 3.7+1.0=4.7:1. 4WD cars put more strain on the motor and therefore must be geared higher.
Things you should consider when setting your FDR:
- the motor (see table above)
- the track (open with long straight = lower, or short and tight = higher)
- whether you have advanced the end bell motor timing (see below)
- the air temperature (see Motor Temperature below)
Spur and Pinion Options
You can see by the F104 Pro gearing chart above that the lowest FDR that the stock gearing will allow is 3.2:1. For a lower FDR you will need a smaller spur paired with a bigger pinion.
Tamiya use a proprietory gear pitch they call "0.04". It is interchangeable with the industry standard 64 pitch, so you can buy a 64 pitch pinion and use it with a Tamiya spur for example.
If you already run another type of RC car then you may already have a range of spur and pinion gears in the industry standard 48 pitch. There are a couple of ways that these can be used with a Tamiya F103 or F104:
- buy the Tamiya RC Spur Gear Spacer 54215 which fits over the axle and allows industry standard touring car spur gears to be used from manufacturers like Kimbrough
- buy a Kawada spur gear which comes with a spacer similar to the 54215 such as this one
For tips on setting the gap between the spur and pinion gears see this handy tip from RC Tek
More RPM using End Bell Timing
You can increase the RPM of a 21.5, or 17.5, brushless motor by advancing the motor timing. This is often done by loosening the end bell screws and rotating the end bell. You can see in the photo below that the Reedy Sonic 21.5 comes with 20 degrees of end bell timing out of the box (at time of writing). To increase RPM increase the timing eg; to 25 degrees or more. Some notes of caution:
- Increasing the end bell timing will increase your motor temperature (see Motor Temperature below)
- Increasing end bell timing will reduce motor torque. Ie; the motor will have a faster top speed (RPM) but will accelerate slower (torque)
- Never increase motor timing past the last timing mark by the manufacturer (in this case 50 degrees). The motor will not last long - possibly only a few laps.
- To increase motor timing loosen (don't remove) the black screws and rotate the end bell. The silver screws hold the motor together.
Updated 6 June 2013
Ok, so we have the correct starting gearing, the right motor, and a blinky ESC. The car is ok speed wise but we want it to go faster. That's why we like racing! :)
Take the temperature of the motor using an infra red temperature gauge. Some motors are more susceptible to heat than others but as a rule of thumb we want to make sure that our motor is 72 degrees C (162 Fahrenheit) or less at the end of a race. If it is between 72 degrees and 80 degrees C (176F) then decrease the size of the pinion by 1 tooth or decrease the end bell timing by a couple of degrees. The motor can handle 80C occassionally but the motor life will not be as long as motors that live life at 72C (source Novak Electronics). If it is over 80C then unfortunately the motor may well have been damaged.
If it is under 65 degrees C at the end of the race then you can risk lowering the FDR by increasing the size of the pinion by 1 tooth, or increasing the end bell timing by a couple of degrees.
Wait until your motor has cooled down and drive some more laps, this time stopping every 1 minute and taking the temperature.
Repeat the process until the car is as fast as you can make it while coming off the track at 72C (162F) or less.
If on race day the air temperature is hotter than when you carried out your testing then consider raising the FDR or lowering the end bell timing so that you don't over heat the motor.
Over heating the motor melts the solder inside the motor and soon afterwards the motor will probably stop working. It might just go slowly or it might grind to a halt in the middle of a race and start smoking! Motors that have over heated tend to smell (forever).
Tip - An alloy motor mount will assist to dissipate motor heat. As will a motor heat sink and/or fan.