The Axial-Flux PMDC Motor Sometime in the mid- to late ‘70s, a gangly young man who’d left school at around age 6 had some interesting ideas about how to build an electric motor… something he’d been fascinated with since picking up a children’s science book describing how to build a motor with a cork and a needle. winding coils around them, strapping it all together He tested out this idea by flattening out tin cans, design, and cobbling it into what was essentially a plywoodin what amounted framed go-cart to a unique for a competition “axial flux” motor hosted by the UK’s Battery Electric Vehicle Association in 1983. The entry got the young man on national television, and started him on his way to designing and manufacturing a remarkably powerful, com- motor that was purpose-built for electric vehicles. Thepact, young lightweight man’s andname efficient is Cedric electric Lynch. motor – a His idea was, in fact, built on concepts that go as far back as the late 1800s, with what are essen- intially the axial-flux early 1940s, designs but essentially (shown in theit’s describingillustration to the left). The design was further refined by GE itsthe coils configuration on the armature, of the magnets spinning in around relation with to the the coils of the armature. A radial flux PMDC motor has outside diameter of the case. The air gap between theoutput armature drive shaft. and the The magnets magnets is areparallel fixed with to the the output shaft. the output shaft, but they extend in a narrow disk, outIn an from axial the flux shaft. motor, The the magnets coils are are also mounted mounted to on the sides of the coils, thus the air gap between the armature and the magnets is perpendicular to the Around 1997, Briggs and Stratton negotiated the drive shaft. This gives the magnetic forces more rights to the Lynch patents and started work de- signing what would soon be a legendary motor in leverage on the rotor – yielding more torque, and a lower powered, much less expensive version of Lynchthus more went power on, in fora few a given years, RPM to devise range. a way to theDIY Lynchrobotics design, and EV re-engineered circles: the Etek. for a mass-producThe Etek was- tion market, but the electric outboard motor proj- assemble motors for sale, which lead to the start of ect was dropped by Briggs and Stratton in only a manufacture the motors more efficiently, to hand- Lynch Motor Company, LTD and the LEMCO motor. EVs.few years. Fiorenza went on to found Mars Electric Within a few years, in 1985, Lynch filed a few of LLC – producing motors of his own design for light his first patents for the design, notably the patent The Etek motors soon became almost unobtain- describing his unique configuration of windings - able through normal channels. Briggs and Strat- and commutator: European patent EP0230759 A1, ton refused sale of the Etek motors to any wheeled German patent DE3679802 D1, United States pat vehicle, period. From Fiorenza: “…ent the 4823039 rotor having A: a current-carrying winding comprising a plurality of circumferentially distrib- “Briggs developed the motor for OEM uses, and did uted winding portions which lie in at least one plane not want the motors to be used on any 2 or three perpendicular to the rotor axis, and extend from a wheeled vehicles, or anything going over 20 mph. If radially inner region to a radially outer region. a customer would come to Briggs and ask for a mo- tor to be used on a vehicle as listed above, then the “A commutator is provided by surfaces of the winding application needed to be reviewed by a special com- portions at the inner region, and the winding is formed from a plurality of conductive sections, each having ends which lie at said outer region, intercon- nections between the winding sections being made only by way of those ends. “Thus, soldered connections made between the winding sections will be remote from the commutator, which is the main source of heat for overheat- ing, and moreover will be at positions where air cooling due to rotor move- ment is greatest. Air gaps between the winding portions at the outer region aid this cooling affect even further.” Stated as simply as possible, the motor was comprised of iron ferrite blocks sandwiched between strips of metal, instead of mittee, and none were ever approved. traditional copper coil windings. “EV enthusiasts found a way to purchase the motors In 1994, interested in this design, a Lynch motor through the Briggs Service Dealers as a service part, was purchased by John Fiorenza, who was working and this started the market and reputation for the with Briggs and Stratton on an electric outboard Etek motor.” - project: the Briggs and Stratton Power Prod ucts Electric Outboard. Fiorenza was impressed. During the production of the LEMCO motor, Lynch Etek. - had contracted with a German company, Cupex, soonlater knownrecognize as Permas a pattern Motor GmbH,of intellectual and now property oper practicesating under pretty Heinzmann much industry-wide, GmbH & Co. InCupex what appar we’ll - Mars, ultimately renamed Motenergy, went on to ently made the decision to design and market their work with OEM companies like Zero Motorcycles own motor using what they’d learned in working to help produce some of their earliest PMAC earlybrushless bikes. motors – one of their first steps away motor reportedly infringed on several of Lynch’s from the PMDC brushed Agni motors used in their patents.with Lynch, The and company in the productioncontinued to of manufacture the Perm 132 Stories are somewhat vague and vary in who tells them as to what happened in the formation and the motor in spite of several challenges. Of the three, the LEMCO (Agni), Etek and Perm132, the late ‘90s developments at Lynch Motors, Ltd, but original LEMCO/Agni design remains the most in 2002 Cedric took his design to a partnership powerful for weight and size, and most efficient. with Arvind Rabadia of Agni Motors to product the Agni 95 and 95R… (reinforced). John Fiorenza, as Mars Electric LLC, continued to If you were designing and build- ing an electric motorcycle with an interest in getting the best performance in power and ef- wereficiency looking in the at period the Agni between mo- 2002 and on into 2009, you versions,tor or the and Lynch Brammo design. used Zero the Motorcycles used Agni in early models. Perm 132 in their early Enertia Before this design became available there were no viable commercially produced electric produce motors designed for use in light electric motorcycles, and most garage-built bikes were vehicles but abandoned the proprietary issues of designed around re-purposed industrial motors These motors were fully half the weight and bulk working with the Lynch design. Mars committed – most typically from 48V forklifts and golf-carts. - to a more typical, and arguably more reliable (yet tor, a detail that’s of crucial importance to a pow- weresomewhat tagged less with efficient the Etek and moniker, power-dense) as in the radial- “Etek er-to-weight,of an industrial performance radial-flux permanentsensitive vehicle magnet like mo flux design. Though several of the Mars motors a motorcycle. Since the motors could be driven StrattonR” and “Etek Etek RT”, design, these and motors the use were of the significantly term was time-proven in industrial applications, applying adifferent violation than of Briggs the original and Stratton axial-flux copyright. Briggs and The R productswith a standard from Alltrax, PMDC Curtiscontroller, and Sevconwell, known was an and - ostensiblyand RT tags to came paint from the motors a few of as Mars’ replacements resellers (refor Virtuallyeasy jump any – even motorcycle in high-load claiming applications. to be a perfor- theferring now to discontinued, the ME0708 and ME0709,fast becoming respectively), legendary mance electric bike was running Agni motors – as warping to one side or the other. - were all the top contenders for the first-year TTXGP It soon became apparent that cooling was re- astonishingIsle of Man races three-motor in 2009. chain Most mounted of them wereunder run the quired, as well as simply bigger, more powerful batteryning two, modules. and the first-year The challenges MotoCzysz of teaming bike had mul an- become apparent. andmotors easily-integrateded – both significant liquid design cooling challenges systems, for tiple PMDC axial-flux motors, however, would soon the LEMCO/Agni layout. PMAC, with no brushes - depending on the operating conditions and whose ever,as well this as didn’t higher change voltages the and advantage higher RPM of the limits, Lynch specsA single you Agni believe. 95R is To rated get to at the around performance 16-20kW, of a design.soon supplanted PMDC brushed motors. How typical 600cc sport bike, the goal is around 100kW, so it’s simple math and modeling to get to the con- clusion that more power is needed. Even with the powerful, most compact electric motor avail- The axial flux design remains the lightest, most - butthree far motors short ofthe anything MotoCzysz that bike would proposed, compete they’re with a tionable. primarily YASA, Emrax, for an and industry even industry that has giantseven more like gasoline-poweredworking with only race60kW bike. – remarkable for the day, Seimens are all adopting the axial flux configura Unlike other motor types such - liablyas series in a DC, dual-motor a PMDC brushed high-load array.motor Evenis very if difficultthe motors to run are re perfectly matched, it’s nearly im- possible to drive them without one motor being under-driven leading to the over-loading of - - ergica)the twin.