Zero Motorcycles Technology

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When I first researched Zero Motorcycles, the most interesting story that immediately popped out at me was the people who had been a part of their history and rapid rise, through an uncertain and chaotic period during their early years.  There have been many parts and configuration changes over the years, and that is what this article is about, comparing the early Zero’s to what they have now.

Neal Saiki, and the Electricross Drift

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An ex-NASA engineer named Neal Saiki started a company in 2006 called Electricross, and his first product was an electric dirt bike, which I think was a great decision. It was important (at the time) to quickly find out the performance data that he needed in order to make important decisions about the design and also parts supply, and a dirt bike was the fastest way to do that, since it didn’t need to meet Department Of Transportation / DOT street rules, like having lights and turn signals (etc).

Motocross Action Magazine wrote about the “Electricross Drift” in September of 2006, and the first prototype used four lead-acid batteries in series for a nominal 48V. When they went into production, they immediately provided an optional pack made from lithium-Ion cells, which has a more stable voltage throughout its full-to-empty range and also provided more miles of riding. I don’t have any information about the Lithium cells they used from 2006-2008.

The entire dirt bike weighed roughly 140-lbs, and the rolling chassis with no battery was 80-lbs. The base-model retail price was $5500. The stock top-speed on smooth roads was 44-MPH, but that could be changed by simply swapping a sprocket, if you wanted better hill-climbing, and didn’t mind a lower top-speed.

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In 2007, the Electricross company was renamed “Zero”, for zero emissions. The name change was needed because they decided that…the overflowing response from customers, magazines, and potential investors had persuaded them that they needed to also make a street version, and they wanted a new name that was less motocross-specific.

This is the only pic I could find of the 2006 shop, from 3111 Scotts Valley Drive, in the city of Scotts Valley near Santa Cruz, on the central California coast.

The motor was an existing brushed motor in the axial-flux configuration called the Agni, which was designed by Cedric Lynch in the UK. By using a brushed motor, the controller could be fairly simple and affordable. Here is a video of adjusting the timing of the brushes, which also shows the internal configuration.

Here is a video from Jozztek which shows the disassembly and internal configuration of the Agni-R (The R stands for reinforced, so that it can withstand higher RPMs).

The Agni-R motor. In this pic, one of the magnetic side-plates is on the bottom, and the piece above it is the central spinning armature. The opposing magnet-mount side-plate has already been removed at this point.

From the beginning up until the major changes in the 2013 model year, Zero used axial-flux motors. An axial-flux is like plates that are spinning side-by-side, rather than a radial configuration, which is more like a cup spinning inside another cup. In the pic above, an Agni-R is in a vice on its side. With the Agni motors, the permanent magnets that are on the insides of the side-plates are stationary, and the central brushed armature spins.

Zero during 2007-2008

Zero did not begin shipping the Zero-S “Street” model is significant numbers until 2010. So the tenuous 2006-2008 period was focused on the off-road and “dual sport” models.

This is a 2008 Zero-X, founder Neal Saiki.

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Zero 2009-2011

It’s sometimes hard to find information and pics of an older model that is no longer in production, but I stumbled across an unusually good write-up on a 2010 Zero DS (Dual Sport). 2010 is also the year that significant numbers of the Zero-S “Street” version began shipping.

The brushed controller for the 2009-2011 Zeros is the Alltrax AXE4855, and the name indicates that this model has a nominal rating of 48V (it will accept voltages up to 60V), and can provide temporary peaks of up to 500 amps. The controller was later upgraded to the AXE7245.

The 2009 battery was made from cylindrical cells from Emoli / Molicell in the 26700 format (26mm in diameter, 70mm in length), and the pack had twelve cells in series (12S).

A 2010 Zero pack made from Emoli cylindrical cells.

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The world is a better place because of the modern Zero electric motorcycle company, so we are fortunate that these early versions were “good enough” to allow the company to survive. The performance was “as good as could be expected”, but to be honest, there wasn’t a lot of competition during this era. The 44V battery packs that Zero used were reasonable in view of the batteries that were available at that time. However, they do not compare to the exceptional performance of the modern versions. [note, this is 2018, and I recommend that any Zero pack from 2011 or earlier should be immediately retired]

If you know of anyone who has one of these early versions, the Agni motor and Alltrax controller are worth keeping if you only task it with 10-HP / 7.5-kW jobs. The battery is another story. Once it is too worn to continue using, Zero does not make any new legacy battery packs replace them. There is some good news though…you might be able to replace a worn 2009-11 Zero battery with salvaged Nissan Leaf cells (see pic below). Thoroughly research this before attempting it.

Sooner or later, all EVs (like the Nissan Leaf) will have a few examples become involved in a wreck. If the battery pack is in good shape and has only a few miles on it…there has definitely been a market developing for lithium cells of all types. These Nissan Leaf modules contain 58-Ah, and are capable of 240A continuous, and double that as a temporary peak.

Replacing a 2009-2011 battery pack with modern Nissan Leaf cells. Each Nissan Leaf module has two cells in series (2S), so the 7-module array shown in the middle is a total of 14S, for roughly a nominal 52

Big changes in 2012

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The model year 2012 saw some big changes, and they were significant improvements. The 2012 cells were flat pouch cells made by EIG (Energy Innovations Group) from South Korea and were configured as an 18S pack, which had a nominal voltage of roughly 65V (this is the only year that this voltage was used). From this point forward, Zero has used flat pouch cells. The chemistry was Lithium “Nickel Cobalt Manganese” / NCM. The EIG corporation calls these their 20-Ah “C020” cells. Packs could be made from paralleled modules in 1P / 2P / or 3P, for capacities of 20, 40, and 60 Amp-hours.

However, there is a warranty recall in-place for the 2012 packs, concerning some of the insulation wearing away from vibration. If you have one of these, please contact your closest Zero dealer to have this fixed.

This was also the year for big changes in the motor. The Agni is very efficient and also fairly affordable to manufacture, but hot rodders have stated that it is near its “long term” reliability limits at around 10-HP, and running it at higher power levels reduced its reliability and life-cycle. Customers wanted more power, and the Agni was only an efficient 10-HP scooter-motor. (it could put out 20-HP, but it simply couldn’t last very long when doing that)

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The 2006-2011 Agni axial-flux brushed motor, shown here in a 2010 Zero DS. The brushes are on the left side, and the flex-hose is blowing air onto them to clear dust from brush-wear and then through the motor case for cooling the armature.The Agni brushes on the left, and the commutator that they rub against is on the right. Brushes are a form of rubbing electrical contact. In the pic above, the eight blade-like parts in the left are the brushes. Since they are either charged with the positive or the negative from the controller, this means the Agni has four active electro-magnetic fields that operate it. In order to significantly raise the power, the decision was made that Zero’s next motor was going to be brushless.

The Motenergy ME0913 brushless motor. Two stators, one rotor. The new motor for 2011 was based on the Motenergy ME0913 motor but was made to the exact specifications provided by the Zero Motorcycle engineering team.  There were significant design changes and improvements required by Zero to make a motor that met all their requirements.

When Zero had specified that the new motor must be brushless, it required a more sophisticated controller than the brushed Agni, and a robust unit from Sevcon was selected. This turned out to be a good choice, and Zero’s relationship with Sevcon continues to this day.

A 3-phase motor with a single stator typically has three fat cables mounted to it, but…as you can see in the pic above, this model is identified by the fact that the three electrical mounting posts are split into six cables that are routed to both sides of the motor. This version uses two of the 3-phase stators and a single central permanent-magnet rotor.

Motenergy’s previous name had been “Mars” electric motors, and they are a well-regarded engineering firm, which can provide motor solutions that meet unusual specifications. By having two stators and a central rotor, the hottest parts of this model are placed at the outer sides, where air-cooling can be the most effective when mounted on a motorcycle as an application.

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The new ME0913 motor from Motenergy is still an axial configuration, but it is a brushless design, which helps with several issues. Temporary burst power can be increased without producing a lot of the conductive arc-dust from the brushes that had occasionally caused issues in the Agni. Also, It’s possible to water-proof a ‘brushed’ motor, but by using a brushless style, you can easily have a robust water-proofing along with also having the dramatically improved air-cooling.

These are stators from unrelated industrial 3-phase radial inrunner motors. On the left is a “concentrated” winding, where there is one coil for every stator tooth. The coils on the right are overlapped in a style that is called a “distributed” winding. I’m only posting these examples to explain that the Motenergy stator has three layers of distributed windings with a 66% overlap between each layer. There are various benefits and drawbacks to either style.

Another difference is that the configuration of the Agni had a central spinning armature, which worked with fixed permanent magnets mounted inside the side-plates. The Motenergy has a single central magnetic-rotor, and two stators, with one on each side. The temporary-burst power of a motor is created by increasing the amps to the stators, which causes a lot of heat. By having the stators located on the outer sides of the motor, it was easier to air-cool them in a more effective manner.

The Agni remains a respected motor for modest power applications (due to low cost, ease of manufacture, and high efficiency), but a major difference between the Agni and the Motenergy is that even though armatures and stators have many similarities, the electromagnetic fields that can be turned on and off will only extend outwards a certain distance.

I point this out so that I can say this; to dramatically increase the amps that the motor can use, you must dramatically increase the copper mass. If we simply make the Agni armature fatter (to add more copper) the armatures’ magnetic fields would not be more effective. The Agni only has one armature (in effect, a single spinning “stator”) coupled with two magnet-array plates. The Motenergy uses a single magnetic rotor, with two stators. It has double the copper mass, if not more.

All of these changes result in a motor that is only slightly larger, and yet it can survive a temporary burst of 400A. When using the nominal 65V of their new battery pack (18S), 400A would result in a burst capability of 27-kW / 36-HP for acceleration (although the 2012 battery packs could not actually provide 400A).

Side note: I was curious about the naming system at Motenergy, and John [the owner] told me that the “09” means that this model was designed in 2009, and the “13” meant that it was the thirteenth model-variation they had designed that year.

2013, The Modern Zero is Born

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This was the year that the batteries at Zero took a great leap forward. They use flat pouch cells from Farasis Energy, They raised the voltage to 28S / 102V. Zero designed the new totally enclosed radial flux motor in-house for the 2013 model year, and they chose Motenergy as the supplier for their new design.

The Zero “Z-Force” battery pack.

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From this era forward, each flat pouch cell increased in capacity over time. Starting with 25, then 27, and today finally achieving 29-Ah’s each. They started with a 4C continuous current rate (100A from a 25-Ah cell) and ended up today with 29-Ah cells that can peak at 10C (290A). This means the 2P packs have 58-Ah’s and are capable of a 580A temporary burst.

A polymer-embedded 14S module made from flat Farasis cells (pulled from a wrecked Zero motorcycle). The polymer fill makes this block unrepairable if it ever has an issue, and doing this was only possible by producing a pack that is more reliable than any other on the market. The potting also provides extreme vibration and shock resistance, plus a level of waterproofing that is exceptional. The module is shown still worked.

Farasis Energy Inc has its design headquarters located in Hayward California (in the southern San Francisco Bay), with a manufacturing facility in Guangzhou, China (near Hong Kong). Their CEO Yu Wang has led the company to a recent financing expansion that exceeded $1 billion USD (with a “B”), and I’m certain the success of their Zero battery cell technology has played a major part.

Farasis recently opened a new office in Stuttgart Germany, in preparation for building a new advanced battery pack factory. The Zero battery pack design team was headed-up by CTO Keith Kepler. Other engineers involved in the Farasis cell success are Jackson Edwards (“Farfle”), Chase Nachtmann, and Zero battery specialist Luke Workman (“Live For Physics”).

2017, The Motor Gets An Upgrade to IPM

The new 2013 radial motors from Motenergy worked great, but there was some room for improvement. The permanent magnets found in these types of motors are a solid chunk of metal, which differs from the laminations, which are a stack of many thin silicon-steel plates. Whenever a solid chunk of metal passes rapidly through a magnetic field, it can suffer from eddy-currents, which results in extra heat. The new radial 2013 Zero motor had surface-mount magnets, and even though it performed very well…the 2017 model was upgraded to a configuration using Interior Permanent Magnets / IPM, which allows the motor to run cooler.

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The PM rotor on the left is a very common style on the least expensive motors, with the magnets mounted on the surface of the rotor. The rotor on the right has the magnets embedded into the laminated steel rotor. This is called an “Interior Permanent Magnet” / IPM style.

When you put a permanent magnet next to steel laminations, the steel laminations become magnetized up to a small amount of depth. This means that the magnets can be moved a little farther away from the air-gap between the stator and the rotor, without lowering their magnetic effect on the motor. Doing this reduces the eddy-current heat in the magnets. Permanent magnets can be partially de-magnetized by accident if they get too hot, so magnet-heat is one of the limiting factors in the number of amps and power that a motor like this can survive.

Radial in runners attaches the coils in the stator to the stationary aluminum shell, which does a pretty good job of passively shedding the stator-heat to the ambient air. The engineers at Zero are familiar with all of the known liquid-cooling systems for motors, so this was a conscious choice rather than a compromise. The two biggest reasons I can think of for choosing passive air-cooling is the simplicity, which has a clear element of reliability, and secondly to also to keep the costs affordable.

This is a graphic of the 2017-18 Zero “Z-Force” motor from their website, and this latest 2018 model is called the “75-7”. After tens of thousands of hours of operation, a “rebuild” consists of replacing two shaft-bearings. There are 12 poles on the stator (3-phase), and 10 poles on the rotor

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It’d hard to find pics of these motors while apart, since all motors that are similar to this are so simple and reliable that they rarely need to be torn down. This one had ventilation holes added to the other side to help with racing, and dust plus moisture damaged the bearings. Fortunately, popping-in two new bearings are fairly easy, quick, and affordable. This is a first-gen 75-5 version.

Here’s part of a discussion that I found interesting from a technical standpoint…

“I just noticed that the Zero S and SR have the same motor Z-Force 75-7 and that motor is rated 40-kW in the Zero-S but 50-kW in the Zero-SR. Previously, I said “Zero-S power is limited by the motor, not the controller or pack” but that’s not correct. Actually, Zero-S power is limited by the controller, not the motor or pack.

Here’s my reasoning: The same motor model–the Z-Force 75-7–appears in the Zero S and SR. In the Zero SR, the 75-7 motor is rated 50-kW, so we know the motor can handle 50,000W / 102 V = 490 A. But the Zero-S specs state that the Zero-S controller can deliver 420A (no more). Or in terms of power, the Zero-S controller can handle 102V x 420A = 42-kW (no more).

To recap, the Zero S has a 50-kW motor, 42-kW controller, and a 57-kW (102 V x 567 A) battery pack. I.e. Zero-S power is limited by the controller, not the motor or pack. When you choose a Zero SR over a Zero S, you’re getting a more powerful controller and a larger battery pack that can support the Z-Force 75-7 motor at 50-kW”

“As of 2016, a reliable source indicated that Zero was producing 17 electric motorcycles a day”

If you already own a Zero and are interested in a couple of upgrades, you can change one of the pulleys to enhance the low-speed torque. Doing this also lowers the top speed a bit, but many feel it is worth it. Another easy option is to upgrade the rear shock absorber.

The Sevcon Gen4 Size-6 that is currently being used by Zero.

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Below is a pic of the battery pack mounting-slots in a 2016 FXS. You can use a large single 102V 7.2-kWh monoblock pack (which is the less-expensive option), or two smaller 102V 3.6-kWh sub-packs (in parallel). The smaller packs are lighter and easier to swap-out. Being able to quickly and easily swap battery packs was one of the features desired by the military and law enforcement agencies. You can run an FX / FXS on just one of the smaller packs, but you will not get the full amps that the system is capable of unless you are using both of the small packs or the full-sized monoblock.

The battery pack slots for a 2016 Zero FXs.

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A 2017 Zero FX.

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The closest Zero dealer to me was Letko Cycles, near Kansas City, on the Kansas side…which can be found at 12535 Rogers Rd, in the city of Olathe. They are a very experienced dealer of Zero and KTM motorcycles, and I’d like to thank them for their help, and also for the test rides..

I am 6-foot tall, and about 200-lbs, and I am including that info so you can compare the proportions in these pics.

I am very impressed by the 2018 Zero SR

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The physical size and performance of the Zero SR have been compared by others to the current crop of high-performance 600cc sportbikes. I’ve never ridden a 600cc, but I have owned a 1981 750cc sportbike, and the 0-60 acceleration torque from the SR felt the same to me. Here’s a quote I found: “67-HP and 106 ft/lbs at the motor. Acceleration is 0-60 in 3.3 seconds. Top speed of 102 mph. The range is 171 miles with the 2.8-kWh Power-Tank option”

If you are already a fan of EV’s I don’t have to emphasize how eerie it is to be riding something this powerful, but the motor and belt-drive only emits a faint whine. The tire contact on the asphalt was as loud as any other noise coming from the bike.

As much as I also like vintage motorcycles, I once owned a motorcycle with spokes that could loosen, and tubes in the tires that were easily flattened…and I never will again. The SR I tested has tubeless tires, cast wheels, and a low maintenance belt-drive. If you’ve ever had to clean, lube, and tension a chain to help it last as long as possible…you know what that means.

No more changing engine-oil, oil-filters, and fuel-filters. No more cleaning out clogged jets and adjusting the carburetor. No more clogged fuel injector nozzles. I recall years ago when I removed a gas tank and dumped the gasoline into a bucket through a T-shirt to filter out the rust flakes. When I was young, I liked fiddling with antiques, but now…I like my antiques on display at a museum.

Sine Cycles is a custom builder that is proud to be using a completely stock Zero drivetrain. I can see jet skis and snowmobiles starting to do this soon too…
The Transform Cafe Racer. I am fairly certain they are using a complete Zero “plug and play” drive system. After all of my research, this was a very smart move.

Let’s wrap it up

I wrote this article for me, but I hope some of our readers were curious about the same things I like to find out. If you like this sort of thing, stop by again once in a while, and I will try to write some more…

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