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Many consider the Roadster electric vehicle (EV) of Teslamotors as the de facto standard of EV(s).  Likewise, most would agree that the electric motor and generator system (i.e., electric machine system (EMS)) of the Roadster is one of the most optimally designed electric motors available for the EV as  proven by at least application. What else could be a better comparison analysis than showing Synchro-Sym Electric Machine System (SS-EMS) is significantly better than the optimally designed Teslamotors Roadster EMS (T-EMS).  


Online research extrapolated the following specifications for the Roadster EMS suggests:

  • Air cooled, 4 Pole Induction Electric Motor System (T-EMS)

  • T-EMS is strongly assumed to be a radial-flux 3-phase AC electric machine

  • T-EMS Weight 70 lbs (32 Kg)

  • T-EMS average efficiency is 92% with peak power efficiency as 85%

  • T-EMS system efficiency is 88% (i.e., calculates to 95.6% controller efficiency with 92% motor efficiency)

  • 375 volt battery, which is the DC link voltage or PeakToPeak T-EMS AC voltage or 216 peak AC phase volts (i.e., DC Link Volt ÷ 1.73)

  • T-EMS constant-peak-torque is 200 ft-lb (i.e., 270 nm) to 5400 RPM (i.e., 180 Hz), which calculates to 150 kW.

  • T-EMS maximum speed 13000 RPM

  • T-EMS operates at constant-torque to 5400 RPM, after which it enters the constant-horsepower range to 13,000 RPM

  • T-EMS electronic controller supports 900 Ampere (calculates to 205 volts at 185 kW)

  • T-EMS peak power is 185kW @ 200 ft-lb (270 nm) peak torque at 6000 RPM

  • A hand wound performance electric machine to improve winding concentration shows 215kW peak @ 276 ft/lbs (375 nm) to 6000rpm.

  • Transmission ratio is 1 to 8.28 to mate the high speed motor (13000 RPM max.) to the tire speed (1200 RPM max) at 98% efficiency. Tesla transmission won awards for being 98% efficient, which is about average for optimally designed helical gears, anyway.

  • The 17” rim (225/45 R17 tire size) tire has a 29” diameter or 91” (7.6’) circumference, which calculates to 695 RPM @ 60 MPH or 5755 RPM motor with an 8.28 transmission.

  • Tesla mentions 15 KW of power is needed for 60 mph.

  • The Tesla S model seems to utilize two Roadster T-EMS(s) for twice the power [some illustrations show the Model S places the electronic controller in the electric machine end plate (adding about 4” to the length of each T-EMS).

As used herein, T-EMS is the Roadster's Electric Machine (i.e., electric motor) System.


In accordance with the physics of operation, the footprint of any electric motor and generator or electric machine (EM) becomes smaller for a given power rating but with higher operating design speed, the compounded cost, size, and loss of a transmission may be necessary (as in the Roadster, Roadster, Model S and D) to translate the EM speed to the low tire speed.  Figure 1 (derived from online open-sourced images) shows the T-EMS with the larger attached transmission to reduce the 0-13000 RPM speed of the T-EMS to the 0-1200 RPM speed of the Roadster's wheel, which obviously compounds the size, cost, and efficiency of the entire system.  Not shown is the necessary electronic controller for practical variable speed operation, which again further compounds the size, cost, and loss of the entire propulsion system. With an average hand length of about 8” as a gauge (conveniently shown in Figure 1), the Tesla T-EMS is estimated to be approximately 12-13” in diameter x 10-11” long. The same gauge can be used to estimate the compounded size of the transmission. 




                                     Figure 1



Transmissions compound the efficiency of the drive system. Consider the 88% Tesla motor system efficiency compounded with the 98% transmission efficiency shows 86.2% overall system drive efficiency (less wheels, tires, etc.). Furthermore, the Tesla high speed motor (alone) has higher power density and as a result, it will require the cost, size and loss of larger active cooling mechanism.  Without second guessing TeslaMotors, reducing the complexity of the system by removing the transmission, increasing the size of the motor, reducing the high flow cooling system may be a better alternative.



By mechanical simplicity alone, an electric motor is considerably more reliable and requires considerably less maintenance than the mechanical complexity of a mechanical transmission. If the real-estate of a larger electric machine system, which includes the electronic controller, reasonably stays within the allotted space and weight constraints of the EV application, opinions suggest a direct drive electric machine system that is without the complexity of a transmission but has the direct drive constant-torque electric motor system is always the better alternative by at least the improvement in reliability and simplified maintenance of the electric motor system itself.  Reasonably assuming the nominal efficiency is similar between the electric machine system (EMS) of a direct-drive versus a transmission-drive system, the larger direct-drive EMS would always show better cooling by at least the increase in electric motor surface area.


Table 1 lists the considerable improvements as a result of the close family replacement between the asymmetrical rotating transformer EMS (T-EMS), which has windings on the rotor and stator, to the symmetrical rotating transformer Synchro-Sym electric machine system (SS-EMS) as calculated with Best Electric Machine Computer Aided Designer tool (BEM-CAD) for both the T-EMS and the SS-EMS. In addition, BEM-CAD uses the same packaging techniques for all contestants, such as the same materials, the same axial flux (or disk shape) footprint (instead of the actual radial-flux footprint), etc.


As verified by Table 1:

  • BEM-CAD calculates nearly the same T-EMS specifications as extrapolated from online (but in an axial-flux (or disk shape) footprint), which conveniently validates BEM-CAD and the assumed optimizing packaging techniques used by T-EMS.

  • SS-EMS (version 1) simply retrofits the T-EMS with an active rotor assembly in accordance with brushless real time control (BRTC) but as a result, the retrofit doubles the Roadster's power and speed performance and quadruples the peak power and torque performance, all while improving efficiency for extended battery life.

  • SS-EMS-500T (version 2) completely replaces the T-EMS and as a result, quadruples the peak power and torque performance within nearly half the package size, all while improving efficiency and weight.

  • SS-EMS-250 (version 3) completely replaces the Roadster's T-EMS and transmission with a direct drive SS-EMS,  all while improving efficiency (no transmission and compounded cost, inefficiency, and size) in a slightly larger package size as the T-EMS.

[Please read the accompanying footnotes for pertinent details of the contestants.]



                                                                      Table  1


TeslaMotors Technology [2]


[Dimensions and Weights

Never Include

Separate Electronic Controller]



SYNCHRO-SYM Technology [4]


[Dimensions and Weights

Always Include

Integrated Electronic Controller]






SS-EMS (v1)[3]

SS-EMS-500T (v2)[5]

SS-EMS-250 (v3)[7]

[Direct Drive]






RMS Battery Voltage (i.e., port voltage)

50-400 v

50-400 v

50-400 v

50-400 v

Winding RMS AC Phase Voltage

205 v

205 v

800[9] v

800[10] v

Constant-HP Range


Excitation Freq.

> 5400 RPM


> 180 Hz

> 10500 RPM


> 180 Hz

> 5400 RPM


> 180 Hz

> 1200 RPM


> 60 Hz

Constant-Torque Range


Excitation Freq.

5400 RPM



180 Hz

10,500[11] RPM



180 Hz

5400 RPM



180 Hz

1200 RPM



60 Hz


Constant- Torque


90 nm

90 nm

200 nm

Power @ Constant-Torque Range

50 kW

100 kW

50 kW

25 kW

Peak Constant-Torque

270 nm

707 nm

707 nm

1593 nm

Peak Power @ Constant Torque

185 kW

800 kW

400 kW

200 kW

Wound-Core Diameter

Not Available

12” (318 mm)

12” (234 mm)

13” (329mm)

Wound-Core Length

Not Available

4.1” (104 mm)

2.3” (53 mm)

2” (50 mm)

Wound-Core Weight

Not Available

66 lb (33 Kg)

27 lb (13 Kg)

44 lb (22 Kg)

Diameter /w frame[13]


12.5” (318 mm)

9.7” (246 mm)

14” (345mm) [19]

Length /w frame



7” (175 mm)

4.9” (126 mm)

4.75” (121 mm) [19]

Weight /w frame

65/70 lb (32 Kg)


87 lb (39.5 Kg)

34 lb

(17 Kg)

65 lb [19]

(32.2 Kg)

Motor Efficiency



Motor & BRTC are integral

Motor & BRTC are integral

Motor & BRTC are integral

Electronic controller Efficiency



Motor & BRTC are integral

Motor & BRTC are integral

Motor & BRTC are integral

System Efficiency [20]








[1] In accordance with BEM-CAD, the original radial-flux footprint was calculated within an axial-flux (or disk shape) footprint with expected improvements (Theoretical considerations by Polard [Zahra Nasiri-Gheidari, Hamid Lesani,”A Survey on Axial Flux Induction Motors,” PRZEGLAD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R.88 NR 2/2012] show the axial-flux electric machine can reduce copper utilization by 13-14% and iron utilization by 21.5-32.5% compared to the traditional radial-flux electric machine. Furthermore, amorphous metal can reduce core loss, which is 15% of the total loss of any electric machine, by up to 80%, but show properties that make manufacturing difficult (e.g., no practical amorphous metal EMS is available to date).

[2] Dimensions do not include the compounded size of the electronic controller.

[3] Retrofit the T-EMS with SS-EMS technology by replacing the “passive” rotor with an “active” rotor provided by Brushless Real-time Control (BRTC), which doubles the constant torque speed range (and power) in the same size package.

[4] Dimension of the SS-EMS always include the proprietary and integral brushless real time controller (BRTC).

[5] SS-EMS is designed to the same constant-torque speed range as the T-EMS (i.e., 5400 RPM/8poles).

[7] SS-EMS is designed as a direct drive high torque motor/generator (i.e., up to 1200 RPM tire speed) to eliminate the compounded size, weight, and cost of a transmission.

[9] SS-EMS has a compact inherent position-dependent-flux high frequency transformer provided by Brushless Real Time Control, which can be a step-up transformer, and as always SS-EMS dimensions always include BRTC.

[10] SS-EMS has a compact inherent position-dependent-flux high frequency transformer provided by Brushless Real Time Control, which can be a step-up transformer, and as always SS-EMS dimensions always include BRTC.

[11] SS-EMS is only electric machine system technology with twice the constant torque speed range for a given frequency of excitation in the same size package. For an T-EMS replacement, the transmission must be geared to twice the 8.28 to 1 or 16.56 to 1 but the power and efficiency improvement are undeniable.

[12] Commonly understood, the Induction electric machine can achieve peak torque of up to 3x “design torque” before core saturation because of the asymmetrical (i.e., single port) transformer topology, and as a result, the “design constant-torque” is predicted to be 90nm (or 270 nm÷3 = 90 nm).

[13] Unlike Tesla’s T-EMS, all SS-EMS dimensions include electronic controller (but no dimensions include the transmission)

[14] To be fair, BEM-CAD calculated the Tesla T-EMS with an Axial-Flux (AF) footprint but included the actual Radial-Flux (RF) specs provided by the online research (e.g., AF/RF). As expected, the dimensions of the AF form for the T-EMS is slightly better.

[15] BEM-CAD calculated the electronic controller efficiency but with a reported combined system efficiency of 88% and a reported electric machine efficiency of 92%, the Tesla electronic controller efficiency calculates to 95.6% efficiency. However, BEM-CAD calculated a lower system efficiency and any unknown packaging technique (such as better semiconductors) used by TeslaMotors to improve performance can likewise, be entered into the BEM-CAD to equally improve the efficiency of all contestants.

[16] SS-EMS BRTC technology offers full bi-directional control without harmonic content.

[17] SS-EMS BRTC technology offers full bi-directional control without harmonic content.

[18] SS-EMS BRTC technology offers full bi-directional control without harmonic content.

[19] SS-EMS direct drive technology eliminates the compounded size, weight, loss, cost and complexity of the transmission but the just-in-time non-optimized frame must be reinforced for the massive peak torque.

[20] Efficiency of the EMS with the compounded efficiency of the electronic controller, together.

[Just The Facts For Comparisons]

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Note: The Radial Flux prototyping of the Advanced Brushless Wound-Rotor Synchronous Doubly-Fed Electric Motor Or Generator System is shown as our Icon, which predates the axial-flux SS-EMS Technology. 


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