The original Lightning Rods kit was the most powerful mid drive available when we wrote about it back in December of 2014. But now, he has produced an even more powerful kit that he is calling his “big block”. It is wide enough that it fits between the pedals on extra-wide bottom brackets, like those found on some downhill bikes, the recently popular fatbikes, some cargobikes, and the Qulbix Raptor.
You can find our article on the original kit here. Mike at Lightning Rods Industries identified the widest motor that was the same width as a common 68mm wide bottom bracket shell, and designed his original kit to fit in that space. Almost immediately, some customers asked about a kit that had a wider motor that could fit between the pedals on a bike with a 100mm wide bottom bracket, due to that size often being found on high-end downhill bicycles.
Mike began importing a wider motor from the same family as his successful original drive, and the additional copper mass allows customers to use twice as many amps. This worked quite well, because batteries exist that can provide very high amps, but if Mike had chosen a design a power system that needed more volts, the battery would need to be larger in order to include more cells, and…riders had found that any bicycle frame volume that was available to carry a battery pack…was already tight on available frame space.
The original motor and the new larger motor both have the same diameter, which turned out to be a very good size to fit onto a bicycle frame as a mid drive kit. Due to the two motor volume differences, he began calling the original unit the “small block” and the new motor the “big block”, which is a tribute to his enthusiasm for performance V8 hot rods, which had developed when he was a young man in Southern California.
So far, I haven’t heard of any builders complaining that the small block is not powerful enough, but…some customers were insistent that if a bigger motor would fit, then that is what they wanted. Mike is also developing this big block kit to address customer desires concerning fully-loaded cargobikes on a steep hill, the recently popular fatbikes, and also the Qulbix Raptor.
For those who are not familiar with the Qulbix Raptor, it is a frame kit, where the customer gets to choose and purchase the forks, shock, wheels, and motor as separate items, in order to better suit the exact customers needs. Like several other frame kits, the Raptor has a very large central battery compartment in order to house and protect the battery pack and any other electronics mounted inside this frame.
The thing about the Raptor that makes it such a wonderful off-road E-bike, is the same reason the Lightning Rods big block is such a good match. This frame allows the builder to mount the weight of the large battery pack near the center and fairly low. Anyone who has experience riding gasoline dirt-bikes knows exactly what I’m talking about.
Up until now, almost every Raptor I’ve seen was using a very large and heavy rear hub motor, like the Monster Cromotor and also the MXUS 3000 V2. Doing that allowed the frame to remain completely free to house the largest battery possible. Sometimes that large battery volume was used to run higher volts (anywhere from 72V up to 100V), and sometimes it was used to have the maximum possible volume of Amp-hours (Ah), to allow the fun to last as long as possible between charges.
Here is the reason that this is an important development. Direct Drive (DD) hubmotors turn at the speed of the wheel (obviously), but…that is a compromise to allow huge amps and watts to be chosen by the customer (a big hub can take 6,000W because it doesn’t pass its power through the bicycle chain and sprockets). A common 26-inch wheel traveling 26-MPH is only turning 336-RPMs. This is why high-performance hubmotors require high amps…which also causes high heat in the motor, controller, and also the battery.
Using Mikes big block not only moves the weight of the motor from the rear wheel to a low position in the middle of the frame…his dual-reduction jackshaft configuration provides a very high tangential magnet speed, whether you are running a chain through the bikes gears, or a single-chain “one speed” electric drive. This means you can get an unusually high amount of torque from a lower system voltage and lower amp-draws.
Let’s do some math
The diameter of this motors rotor is 80mm, so the rotor circumference is 251mm. With the Lightning Rods massive 33:1 dual-reduction, the unloaded motors’ RPM at 48V (with a Kv of 67) is 3216, resulting in roughly 90-RPMs at the pedals, and the magnet speed is 251mm times 3216 revolutions, per minute, or…13,400mm per second.
To put that into perspective, the Cromotor and MXUS 3000 V2 have a stator airgap diameter of 200mm, so their working circumference is 628mm. The popular “4 turn” versions have a Kv of 9.0 RPMs per volt, so at their designed voltage of 72V, their unloaded RPMs are 648. This makes their magnet speed 406,944mm per minute, or…6,780mm per second. This means that the magnets in the Lightning Rods motors are traveling over twice as fast at only 2/3rds the voltage. And that means you will get the same torque applied to the rear wheel from a lower input wattage to the motor, when using a mid drive that has a high magnet speed.
Benefits of a mid drive over a hubmotor?
That’s only half the story…you could mount the large hubmotors in several different sizes of wheel (19-inch dirt-bike tires are the most popular for an off-road Raptor) to make a small change in its diameter to affect the bikes torque/top-speed, but… If we compare the motors’ magnet speed to the length of tire distance traveled, the Lightning Rods kit gets even better. The magnet speed of a DD hubmotor has a direct 1:1 ratio with the distance traveled by the tire per revolution, but…the LR kit still has two distinct advantages.
First, if you run the LR motor through the bikes gears, you can downshift the bikes “transmission” so that…even when you are traveling very slowly on a steep uphill technical portion of a trail…the motor is still running at very high RPMs (and not overheating). The second major advantage is that by simply changing a readily available $20 Kart sprocket or chain-ring on the drive reduction, the builder can adjust the entire power range of the bike’s torque curve, from one day to the next.
Both sizes of Lightning Rods kits use only high-performance #219 Kart racing chain. These chains, sprockets, and chain-rings are designed to handle 10,000-RPM gasoline 2-stroke engines. Mike partially chose this format of chain because they are much stronger than needed for these kits, but also…because a selection of these sprockets and chains are readily available at affordable prices. Even under severe abuse, these chains and sprockets will last a very long time, but…it is reassuring to know that when they eventually wear out, you can get replacements without needing to special-order proprietary components.
Fitting many different frames
A key feature of the Lightning Rods kit family is that, right from the beginning…Mike wanted his kits to be able to fit to the widest variety of frames possible. The common bottom bracket (BB) widths are 68mm, 73mm, 83mm, and 100mm wide.
After much research, Mike chose the 8-spline Shimano ISIS crank interface. Quality BB cartridges are available that would satisfy his kit requirements, and by custom-machining his own adapters, Mike was able to adapt a 148mm long spindle that is available to fit into the ISIS bearing cups,which allows his big block kit to fit into the four different bottom bracket shells that he needed.
Due to the depth of the bearing cups and locking rings on the cartridges that Mike supplies, you will need a wrench similar to the “Pedro’s” wrench shown below, since the common socket (shown just to the right) will not seat deeply enough to reach it.
Mike is in the process of adapting the big block kit onto several frame types, including the Surly Big Dummy longtail cargobike. The pic below is a sneak peek at the Luna longtail fatbike with the big block kit configured in a vertical arrangement behind the seat tube.
Here are videos of customers riding their Lightning Rods driven E-bikes (videos courtesy of endless-sphere.com member Föppel):
Here is a pic from the latest customer, Henrik from Norway
Where to order one?
Here is the Lightning Rods Facebook page.
Here is the Lightning Rods home website.
Written by Ron/spinningmagnets, June 2015