What motor should I buy? One of the most common questions...
The answer is ... Whatever suits your purpose.
The purposes are...
Surface Grip Level?
These are repeating themes in RC Drift . So basically... as you get into the hobby more and more, you will buy a range of motors. They will suit more purposes. As usual, talk to the guys you drift with, because matching your friends for tandem will bring the best results.
I am going to ignore brushed motors in this description as 99% of motors these days are brush-less.
FAST = The Highest Grip Surface + the Softest Tyre.
to Slide on this surface with a soft tyre... you need the HIGHEST RPM to burst past the grip level and keep the wheels spinning.
A lower turn "T" motor allows more RPM. Another measurement is KV (kilowatts per Volt.)
The higher KV = More RPM
This KV number x Volts (7.4) with more at full charge can give you an approximate MAX RPM without load.You can check approximate values below.
7.5T = about 4600 KV x 8.4V = 38640RPM
So RPM can range with different motors from 21.5T(10000 RPM) to about 4.5T(50000 RPM), which equates to a HUGE difference in how an RC car behaves. That's why people have many for different situations.
SLOW = The Lowest Grip Surface + the Hardest Tyre (within reason).
21.5T = about 1600 KV x 8.4V = 13440RPM
If you are getting into the hobby a 13.5T is a good middle of the range motor and gearing can change the behavior.
...but you can't talk motor with out the full picture.
So which is best....?
These machines have 7.5 through 21.5 and are used on high grip carpet at ludicrous speed and slippery polished concrete with differing tyres for different results.
Combine the motor with the Final Drive ratio and throttle response add to the equations among other concerns. Why do I have the smallest pinion and the largest spur here? Response is lower at 5.2:1
Response here is less than 3.8:1 giving you less control over the RPM... but in some situations this is exactly what you need. Instant power Spool Up and higher top end. Differential settings and other considerations also come into play.
You need to experiment and get a feel for what you like and what works.
Personally, I love free spinning high rpm motors, but I only need about 60% of the RPM on my surface.
So I use the ESC to de-tune the forward power setting. I end up with the low RPM of a Higher turn motor with the instant response of a high RPM motor. I also try to go for a lower FDR (12:1) to give me control. This is a real issue in RWD machines where a few RPM the wrong way can make a big difference.
I never use CURVE to confuse the linear settings and give predictable behavior. TURBO can be an advantage in certain conditions.
Sometimes it's this FEEL and CONTROL that contributes more to the way your RC drift chassis handles.
There are other reasons for motor choice too.
How about Scale Speed?
How do you want to drive this 800+HP 2.8L 6 cylinder turbo 2JZ Powered JZX100?
I can guarantee the answer is aggressively.Even in the real car, you don't need FULL 800hp to spin the tyres so you will find that throttle modulation becomes more important.
How do you want to drive this 86 with 180hp 4AGE 4Cylinder Motor.
You may want to mash the throttle most of the time, so it shouldn't really be the same end result as the MARK II. The real cars are not the same, so the RC result may not be the same..The 86 will run out of wheelspin ability. The Mark II never will.
FRD with 17.5T Motor and with lower final drive gear ratio of leaves max wheel RPM around 1000 only.
the below is a way of comparing wheel speeds. Don't forget your finger controls the RPM from ZERO to 100% so this is the best way to control RPM
USE YOUR FINGER. IF you are using only FULL THROTTLE or ZERO, you are never going to have control.
Throttle modulation is probably the most neglected skill in RC.
ALSO remember as car speed rises you will need more RPM to overcome the loaded and geared wheels so you need some reserve RPM.
Sample calculations for wheel speed. If you build a spreadsheet you can calculate the Variables entered in the blue section.
|Battery Volt||8.4||8.4||8.4||8.4||8.4||8.4||8.4||100% Charged|
|Adjust RPM||MAX||13674||16800||21778||28000||30947||39200||MAX RPM - Adjusted %|
|Response||4.09||4.09||4.09||4.09||4.09||4.09||Spur / Pinion|
|Shaft RPM||3343||4107||5323||6844||7565||9582||Adjusted RPM / Response|
|Rear Pulley / Diff Crown||42||42||42||42||42||42||42|
|Centre Pulley / Drive Pinion||13||13||13||13||13||13||13|
|Rear Drive Ratio||3.23||3.23||3.23||3.23||3.23||3.23||Rear Pulley / Center Pulley|
|Final Drive Ratio||13.22||13.22||13.22||13.22||13.22||13.22||Shaft RPM x Response|
|Rear Wheel RPM||MAX||1035||1271||1648||2119||2342||2966||Rear Wheel RPM / Final Drive Ratio|
|Tyre Grip will lose RPM|
|LOAD LOSS %||20||828||1017||1318||1695||1873||2373||Rear Wheel RPM - %|
|WHEEL RPM by Throttle Percentage
AT THE FINGER!!!
Input values in blue
Here are two distinctly different setups achieving a similar result... but the feel and control are far from similar.
|Battery Volt||8.4||8.4||Full charge||Battery Volt||6.9||6.9||Low BAttery|
|Max RPM||MAX||13674||Max RPM||MAX||32200|
|ESC FWD||100||100||ESC FWD||100||100|
|Adjust RPM||MAX||13674||Adjust RPM||MAX||19320|
|Shaft RPM||5128||Shaft RPM||4942|
|Rear Pulley||40||40||Rear Pulley||40||40|
|Centre Pulley||17||17||Centre Pulley||17||17|
|Rear Drive Ratio||2.35||Rear Drive Ratio||2.35|
|Final Drive Ratio||6.27||Final Drive Ratio||9.20|
|Rear Wheel RPM||MAX||2179||Rear Wheel RPM||MAX||2100|
|Tyre Grip will lose RPM||Tyre Grip will lose RPM|
|LOAD LOSS %||20||1743||LOAD LOSS %||20||1680|
|WHEEL RPM by Throttle Percentage||WHEEL RPM by Throttle Percentage|