This is the most powerful production mid drive kit that you can run through the bikes gears, and the big surprise is how quiet it is. (edit: as of the spring of 2015, Lightning Rods now has his even MORE powerful “big block” mid drive, which can use twice as many amps as his basic kit, which is what is shown in this article)
We bought the first two production kits before they were even produced. I say that up front to give you an idea of how we feel about this particular mid drive kit. There is quite simply no other kit that you can add to your bike that comes close to what this kit can offer. There are many more mid drive kits available this year, but none are made with the quality or power level that this one will provide.
If you need a simple commuter, this is probably more complex and has a higher price than a 1,200W kit that would satisfy most E-bikers. And, if you want more power than 2,800W…you might be better served by a large hub motor, or a non-hub that drives a left-side chain to the rear wheel. This kit runs through the bicycle gears, and as a result it has all the benefits of letting the motor have more than one speed.
The two user-profiles where this kit will really shine is a heavy cargobike where there are very steep and long uphills…and an off-roader who likes a lot of power, but still wants to be able to crawl slowly around the technical obstacles without overheating the motor….and also taking big jumps.
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Back in August of 2012, electricbike.com was compiling a list of available mid-drive kits, and the new GNG company showed up on a Google search. The drive that they called their 450W unit looked interesting and actually used an impressive 1,000W. Several builders at the endless-sphere.com forum purchased the kit and tried it out.
The reports that were posted showed that it had many weaknesses that needed upgrading, however…it actually was a very powerful kit that could be installed on the majority of available bicycle frames (rather than shopping for an expensive factory-built mid-drive).
A new endless-sphere.com member named Mike Backus (username: LightningRods) began asking about what were the most desirable upgrades, and the following discussions identified those parts that seemed to be the most needed. One by one…he began designing and producing upgraded brackets…and other parts that would make the GNG kit reliable and more powerful.
The general configuration of the drive proved to be useful, and the motor that came with the kit turned out to be unusually well-suited to this job. The motor is just narrow enough to fit between the pedals, and since it is only 4-1/2 inches in diameter (115mm), it can fit onto most bicycle frames. It is an inrunner, so the hot stator coils are bonded to the aluminum housing, which allows this motor to shed heat very well.
And since it is being used as a mid-drive…you can shift the bikes gears when you encounter hills, so the motor can stay up in the higher RPMs. This prevents the motor from producing waste-heat in the first place, due to bogging down and running at low RPM’s, like a hub motor might do (a direct-drive hub spins at the RPMs of the wheel, and geared hubs have a poor heat-shedding path). Also, this motors’ low pole-count is a design feature that allows it to run at high RPMs without experiencing the waste-heat that is usually produced by eddy-currents.
If you raise the systems voltage without changing the motors’ Kv, it will make the motor spin faster. This motor has been verified to work extremely well at voltages between 48V and 72V, although…at 72V and full throttle…the motor will be spinning fast enough that the rider will not be able to pedal along.
This drive provides an impressive mechanical reduction of 33:1 between the motor and the crankset, and having such a high reduction allows the motor to be spinning very fast (with a high tangential magnet speed) compared to the wheel-RPM’s. Lukes “deathbike” racer has very large motor with a small diameter wheel and only needs a modest reduction of 4:1, but that system has very high power that is drawing very high amps from the battery. And don’t forget that Luke’s motor is large and heavy, which is what you would need with a low reduction.
This drive addresses these questions…if we want to design a mid drive system that allows the motor to use the bikes gears, what is the largest reduction that will fit? and then…once the best reduction components are identified, what motor has the most possible copper mass, but is still “just” small enough to fit on a common bicycle frame?
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The Motor
Many cities in China are banning the common 2-stroke gasoline-powered cargo trikes due to smog issues. There are several companies that have put together electric conversion kits that will swap right in to the differential. The motor design needed to be capable of high power, but small enough to fit a variety of trike models.
This need spawned a family of motors with a low pole-count so they have the option of running at high RPMs without excessive eddy-current heat, and it would best for it to be an in-runner so it could shed heat well. Since it is a radial-flux design, a variety of powers can be easily achieved by adding more stator-laminations. This results in motor models with the same diameter, but with a selection of several lengths.
Mike is now ordering these wonderful motors direct from the motor manufacturer, and after they arrive, he swaps-in shafts that have been modded in the USA to his specs. The working end of the shaft has been shaped to a cylindrical 12mm diameter (1/2-inch is equal to 12.7mm), because 12mm still exceeds the strength needed, but is small enough to allow a very low tooth-count on the pulleys and sprockets. This provides the option of very high reductions.
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The Primary Belted Reduction
Belts are quieter than chains, especially at the very high RPMs of a primary reduction. Mike uses a 25mm wide GT2 belt, and the pulley tooth-counts are 90T/18T for a 5.0:1 ratio.
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The Secondary #219 Chain Reduction
Mike chose #219 Kart chain and sprockets for the secondary reduction. These affordable parts are designed for 2-stroke gasoline racers using 20-HP at 10,000-RPMs, and due to the quality of the steel, I suspect that this part of the drive will last the longest, when it comes to replacing worn parts. Also, the small pitch (distance between the pins), means that an 11T sprocket for #219 will be much smaller than an 11T sprocket for bicycle chain (11T is the smallest tooth-count to avoid the high noise of the “polygonal effect”).
It is not recommended make to any changes to the primary belted side (in order to dial in the drive to suit a particular application). The majority of any adjustment should be made with the sprocket tooth-counts of the secondary reduction. The stock reduction is a 12T drive sprocket and an 80T driven chainring, both of which are easily changed to a different size, or for replacing a worn part.
There is no need to shop for expensive custom-cut parts. The stock secondary is 80T/12T = 6.66:1, but by using only off-the-shelf parts, the tooth-counts can be changed from a high of 11T/93T (8.45:1 ratio) all the way down to 18T/64T (3.55:1 ratio). Since the primary reduction is fixed at 5.00:1, the options are:
17.7:1 Minimum reduction (for highest top speed)
33.0:1 Stock reduction
42.2:1 Max possible reduction (lowest speed, highest torque)
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Freewheeling Crankset with Three Chainrings
This kit has a freewheeling crankset that uses an interface that will accept two well-known replacement freewheels. You can use the stock ACS-Crossfire flanged freewheel, or the White Industries ENO flanged freewheel.
Also, rather than using proprietary drive sprockets, the 48T and 32T bicycle chainrings on this kit use the common 4-arm 104-BCD interface. A gear-change or replacing a worn chainring is easy and affordable.
The #219 80T chainring shown on the right (made for 20-HP and 10,000-RPMs) is also an off-the-shelf item.
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Recommended Controller?
This motor really shines at 30A, and at that power level…it can take a frequent pounding without much concern for heat build-up. However, if you give the motor an occasional cruise-phase to let it cool down some…several builders have dialed-in 40A, which is exceptional for a mid drive.
Using between 30A and 40A leads us to the programmable Lyen 12-FET as our top choice for a controller. If you are certain you will only use 65V or less, you can specify the efficient and cool-running 3077 FET. If you think you might want to try 72V someday, make sure to specify the 4110 FET, which can be run up to 100V (although the 4110 FET does run slightly warmer than the 3077 at all voltages).
Lyen personally hand-assembles each 12-FET controller. He uses only genuine name-brand FETs and ensures that each FET is properly bonded to the robust heat sink, so the controller will shed heat as designed. The no-name controllers use cheaper generic FETs, which run hotter, and if even ONE of the FETs is not properly mounted…it will fail from too much localized heat at the poor connection, and then the cascading effect will cause the entire controller to fail.
48V X 30A = 1,440W
72V X 40A = 2,880W
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140mm wide ISIS Crankset
To install the extra-wide bottom-bracket (pedal-axle), you might not be able to tighten down the cartridge end-cap with a conventional socket. Tightening down the BB cartridge shown above may require a tool similar to the “Pedros” brand wrench.
The standard Shimano 8-spline bearing cup is tightened down with the socket shown on the right. The Lightning Rods bottom-bracket cartridge may need to be tightened down using a wrench like the “Pedro’s” brand shown on the left.
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Cycle Analyst, V2.3 and V3.0
If you only want a watt-meter, or a battery pack voltage meter…there are many affordable options. However, the Cycle Analyst is quite simply the best E-bike computer available.
The V2.3 Cycle Analyst is a comprehensive electric vehicle display showing your battery voltage, amp-hours used per trip along with all your speed and distance stats. The V3 has all the functionality of the V2.3 , and also adds…the ability to let you control your E-bike, such advanced throttle adjustments and optional pedelec modes (when coupled with torque sensor). The standout feature of the V3 is the temperature sensor input, which allows extreme users to keep their components safewhen setting up their systems for very high performance.
The temp input can be used for either the motor or the controller, whichever runs warmer due to the users setting and riding style. The V3 not only indicates the temperatures, you can program-in a “roll back” limit, where the heat producing amps are automatically limited when the system gets too warm. Then, after the E-bike cools down a little…full amps are automatically re-enabled. We recommend 160F (71C) as the amp-limiting point, and 200F (93C) as a power cut-off.
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What Battery?
Any battery that can provide the voltage and current that you want to use will work, and we suspect some users will choose a home-built LiPo pack. However, our top pick for a battery is made from quality name-brand 18650 cells from the vendor em3ev.com.
The 18650 cell (cylindrical, 18mm diameter, 65mm long), might be best-known from their use in laptop computers, however…the high-performance cells in the 18650 format were developed for the global cordless tool market. Paul at em3ev.com only uses quality name-brand cells, and over the past few years he has worked hard to develop a reputation for quality and great customer service.
He carries a variety of sizes of packs in the common rectangular format (of course), but Paul is also the only vendor I know of who sells triangle packs right now (in several sizes), and this is a very helpful option. There are hundreds of vendors making packs that can safely provide 20A, but Pauls battery packs provide 30A to 40A (depending on the size of the pack, and which cell is chosen). The 30A to 40A capability of em3ev.com’s battery packs is perfect for this drive.
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Wide Bottom Brackets
If you’ve seen our article on mid drive kits, it may be frustrating for some customers who want one, but…their favorite bike doesn’t have the common 68mm wide Bottom Bracket (BB).
The 68mm wide BB is by far the most common, but an increasing number of off-road bicycle models have a 73mm wide BB. There are a few models that have an 83mm wide BB, and many of the new Fat Bikes (with 3-to-4 inch wide tires) have a 100mm wide BB.
lectriccycles.com has adapted the Bafang BBS02 to a fat bike (which have an extra-wide BB), which is available to the public, but…that is only a 750W mid drive. So…what’s a high-powered enthusiast with an odd-sized BB to do? Mike decided that before the first kit is sold…he wanted heavy-duty steel brackets available to fit all four of these BB widths.
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Stretch Brackets
Some popular down-hill (DH) bicycle frame designs, now have an “S” shaped bend in the downtube. If you attach a standard Lightning Rods mounting bracket to such a frame, the entire drive would be rotated downwards, and decrease the bikes ability to crawl over obstacles. From the very beginning, Mike designed optional “stretch” versions of every width of mounting bracket, and this allows frames like this to be able to use this drive.
Each of the four widths of mounting bracket has a “stretch” version, that allows the drive to be mounted onto a frame with an “S” shaped downtube.
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Here is a four-part video instructional about how to properly install a Lightning Rods mid drive kit.
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Comparable Drives
Our list of mid drive kits can be found here. The majority of them are made for low power in places like the European Union, which has a 250W limit. The higher powered kits on that list are not quite as powerful as this one, they are noisier, and…they are more expensive.
The only kits that are truly comparable are the custom-order kits from Schumaker Technologies. We have been fans of Matts drives from his beginning. We have written about three of the custom builds that have used his drives. Matts Monster yellow trike, the beautiful Roys eCortina, and also Deecanios Astro mid drive from 2008.
Matts drives are CNC-cut from billet aluminum, based on his own designs. They are works of art, and Matt was an early pioneer in the development of adapting large RC motors to electric bike use. He uses the high-quality Astro Flight motor, and their tiny controllers. Matts drives are smaller than the Lightning Rods kit, but…to get this level of high power, the smaller Astro motor has to typically run at 6,000+ RPMs.
The Astro uses high-temperature SmCo magnets, because they know the motor will get very hot. Both motors are inrunners, and that configuration sheds heat much better than the more common RC outrunner. However, the motor in the Lightning Rods kit has more copper mass to absorb and shed heat spikes, and its lower Kv of 67 provides 3216-RPMs (when unloaded at 48V).
The Lightning Rods kit runs very quietly (but admittedly it is not silent), and the Astro has a turbine-like sound. Although some builders wish the Astro was quieter, others actually like the sound. Both motors are powerful enough to break the bicycle components if managed without the proper care, so…which one is the winner? I don’t think there is a clear winner so much as…these two drives are like two wonderful flavors. Both have the benefits of mid drives…but:
Astro: smaller, lighter, tiny controller, billet aluminum machinist art, however…more expensive and louder.
Lightning Rods: Runs more quietly, costs less, lower-Kv motor and higher reduction means you can pedal along with the motor. Larger motor has more mass, can absorb and shed lots of heat, off-the-shelf Kart sprockets means you can easily change the reduction whenever you want. Lower price leaves more money for the bike and battery.
I would be proud to have a bike with the premium Astro drive on it, but…I actually own the first production Lightning Rods drive. I was watching the discussion on endless-sphere.com as it was being designed, and decided that when it became available…this was the drive for me.
“Lightning Rods is a design service dedicated to bringing the philosophy of hot rodding to electric vehicles. Driving an EV should not be either an embarrassment or a punishment“
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A more powerful kit?
If you really like this kit, but…you actually want more power? You are in luck, Mike has recently begun producing a very similar kit with a wider motor called his “big block”, and the extra copper mass allows you to use roughly twice the amps!
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Written by Ron/Spinningmagnets, December 2014
