This is an awesome All-Wheel-Drive E-bike, and it is also a folder so that it can be carried onto a train for day-trips to the mountains. It has been designed and built by a brilliant guy named Ben, and we are already quite familiar with him, because…he is also the builder of the the “Dogati” Super E-bike.
Ben has a home in very hilly Taiwan, and in particular there is a hill leading up to his home that is unusually steep. In fact, the inspiration for this bike came from an incident when Ben was riding Dogati up that very hill when returning to his home, and in a brief moment of using too much power…he flipped the bike! While resting from an injury that happened during that fall…he wondered if the extra traction from having an AWD E-bike would help him climb extreme hills.
In the pic below, the desk-top machine in the top left is a CNC mill for cutting the shape of custom metal parts, for those times when Ben has a great idea and doesn’t want to wait for a shop to make a part and ship it to him.
Bens “Dogati” Super Electric Bike, and the his new Duty Cycle AWD.
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FRAME
Once Ben had decided he wanted to build a new AWD project, the next decision he had to consider was, which frame? He enjoys taking day trips to the nearby mountains on the train, and bringing a full-sized E-bike had proven to be problematic in the past, but…the idea occurred to him that maybe a full-sized folding bike might work well.
After a comprehensive search, he settled on the Montague Paratrooper. Most folding frames are not as strong as their one-piece version, but the Paratrooper is the strongest folding frame available anywhere. The strength of this frame was a deciding factor, but it’s also nice that the well-designed folding mechanism allows it to be deployed or stowed in less than 20-seconds without any tools.
Be aware that there are many cheap clones of the Paratrooper frame that are easy to find on the web for purchase. Although they look similar, they will not be as strong as an authentic Montague Paratrooper.
The Montague Paratrooper bicycle in the folded position, with it’s travel bag.
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BATTERY
Bens Duty Cycle AWD is nice enough for us to write about it just as it is, but I am really blown away by his DIY battery. Ben wanted to design and document his take on a DIY pack made from the increasingly popular 18650 format cell. These cylindrical cells (found inside cordless tool batteries), are now available in high current models that are not made from the risky LiPo (which has previously been the popular battery chemistry for high performance).
He chose the excellent NCR18650PD cell from Panasonic, and then settled on a 14S / 7P configuration. If charged to 4.10V per cell, a pack configured of sub-packs (with 14 cell groups each) in Series (14S) would be 57.4V when fully charged.
This Panasonic cell has 2900-mAh per cell, so when the pack is configured with seven cells in each Paralleled group (7P), this surprisingly small pack has an incredible 20.3-Ah. So, 57V X 20-Ah = an awesome 1140-Watt Hours (WH) of capacity. Our experience has shown us that if a rider adds mild pedaling half the time (which is normal), a geared hub E-bike uses about 20-WH per mile.
Using that as a measuring stick, this 1140-WH pack should average 50-miles (80 km/H). That sounds like a pretty outrageous claim for such a small pack, but…this exceptional cell is now the primary cell used by the Tesla Car company, and that should be all the testimonial we would need.
Ben modeled the pack during the design phase using the popular program Solidworks.
Ben used the common black plastic cell-spacers that snap together, and they make forming an odd-shaped pack easier. The thin wires are for balance-charging each 7-cell paralleled sub-pack. The amber colored film is Kapton tape, which is a final layer of non-conductive protection against shorts.
The final touch was adding a hard plastic shell to protect the pack from the minor bumps that are a normal part of life.
Ben knew he wanted a triangle shape for his battery pack, but the dimensions of a triangle can vary widely. The pack size and specific layout of his cells match a specific heavy-duty bag made by Revelate, and it was designed to match frames from Salsa Cycles. This particular bag is the “El Mariachi“.
A triangle frame bag from Revelate, designed for Salsa bicycles.
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ANTI-THEFT PACK LOCK
Ben has been thinking about a battery pack anti-theft lock for a long time. High-end battery packs can cost as much as $1,000, so…theft protection is no small concern. He recently stumbled across a key-locking seat-post clamp during his searches, which was designed to protect bicyclists from having their expensive saddles stolen.
Ben realized that if a cylindrical post-stub (the same diameter as a seat-tube) was bolted under his top-tube, this clamp could be re-purposed to act as a pack lock. He ordered two large 35mm diameter seat-tube clamps to experiment with, and the results worked fantastic!
Here’s a close-up of the key-lock seat-tube clamps which have been re-purposed as battery pack locks.
In the pic on the left, Ben inserted an 8mm Rivnut into the bottom of the top-tube, and he then bolted a 22mm diameter aluminum post onto that Rivnut. In the right pic, Ben made a 22mm to 35mm bushing that is bolted to the battery pack, and the locking seat-post clamp has a side-inserted screw to hold them together. Two sets of these clamps completes a solid battery attachment and anti-theft system.
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FORKS
Ben replaced the stock forks with a Marzocchi DJ1. Since this fork uses a “through-axle”, he just enlarged the slot and made a 20mm adapter sleeve to fit over the 17mm diameter MAC axle. The fork’s axle-clamping bolt is not strong enough to resist the motors’ torque so he added a set-screw through the top. The wheel is still easy to remove for fixing flats and replacing tires, wires and all.
Here’s a close-up of the custom axle-sleeve that allows a stock MAC axle to fit into an upgraded suspension fork that normally takes a heavy-duty “pass-through” axle.
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The MOTORS
Ben chose two geared hubs. The MAC geared hub is well-known around ES, and its performance has earned it the right to be the most-often suggested kit for the majority of new E-bike enthusiasts (The nearly identical BMC is very respected too, but costs a little more). Geared hubs are smaller and lighter for a given torque, compared to the slightly less expensive direct-drive (DD) hubs.
For a dual-motor set-up, geared hubs have the feature of a built-in freewheel, and this alleviates several issues that would affect the bike if you used two DD hubs. The fact that these motors are light and they freewheel…it makes it much easier for those times when you will pedal the bike without power.
Now that you’ve decided to use two geared hub-motors, why choose the MAC? The less-expensive Bafang-BPM is one of the most commonly sold geared hubs on the planet, and it is roughly the same diameter as the MAC. However, the BPM’s stator is 17mm wide, while the MAC’s is 22mm wide. This means the MAC is capable of roughly 25% more power, and…even if you run the MAC at a lower power, the larger copper mass of the MAC means it would run cooler than the BPM at the same power levels.
If you want a geared hub in the largest size (like the MAC), you might consider the BMC (which was used by Teklektik for his dual-motor Mundo). Both of those motors are also excellent choices.
Like most modern hubs these days, the MAC allows the use of a large disc brake on the front, which is highly recommended.
Ben initially chose dual 8-Turn (8T) MACs, which provided 60-kph (37-MPH) at 57V. Once he had two of these motors, they didn’t seem to struggle at all with the loads he was putting on them, so he swapped-in two 6T MACs which provide a faster 70-kph (43-MPH). Be aware that a single MAC 6T/8T would struggle on steep hills at 57V, but TWO of them is an entirely different calculation.
The MAC is well-known to survive 1,500W peaks as long as the occasional cruise-phase of about half that wattage allows the motor to cool down between hills. Once you add a second motor to the calculation, your E-bike has the copper mass to be able to use 3,000W of peak power.
And…by going to 57V, Ben can achieve a 3,000W peak from a single battery pack by only drawing 53A. This is an important calculation, because by designing the system to work well at only 53A from each paralleled sub-pack of seven cells (7P), each individual cell only has to provide a temporary peak of 8 amps (these cells are rated for 10A peak). At only 8 amps per cell, Ben was not restricted to using only high current cells, and he was able to choose a high quality cell that provides an awesome 2900-mAh of extra high range per each cell in his parallel sub-packs.
For 3,000W at 57V, the battery must provide 53A, but the MAC motors are only sipping a mere 27A each.
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CONCLUSION
This is the third dual motor build we have featured (the others are the Mental Manno and Teklektiks Mundo), and all three have tried a variety of options…and then evolved into a common configuration. All three use two identical geared hubs. They use a single throttle, a single battery…but they also use dual controllers.
The dual programmable Lyen 12-FET controllers are rated for 40A peaks each, so two of them can handle 80A before controller heat becomes an issue. Under the loads Ben is using, they both stay cool (30A peak each for a total of 60A, and perhaps 10A continuous). This allowed Ben to mount both controllers in a bag behind the seat without any danger of overheating.
This set-up can use a temporary peak of 3,000W, and to equal that performance with a single motor, Nicobie’s eTownie and also Rodgahs Big Hit both used a rear-wheel ventilated Crystalyte H3525 at 100V. Both approaches to achieving a reliable 3,000W of performance have been proven to work, but splitting that amount of power between two motors and two controllers…it can have some benefits that are worthy of consideration.
It’s pretty amazing how much range you can get from these high-quality authentic Panasonic cells. Also, by mounting the batteries weight in the center and putting the motor weight split between two of them at each end, this E-bike has a very balanced feel when riding.
When only pedaling (as rare as that may be with a high-powered E-bike) the geared hubs will freewheel. Also, with the dual motors, you have the option of using a single smaller motor, which can help your range on flat land. One of the biggest benefits is the system redundancy…if one motor or controller ever has an issue, you can power home on the remaining components. This may be a vital characteristic in a very hilly community.
And of course, in wet weather or snow & sand, the added traction of AWD cannot be equaled by a single motor E-bike, no matter how much power it may have.
Ben wrote to me that he recently swapped-in fatter tires: “One day my buddy (ES member: ghettoracer) and I were ripping down a fairly steep mountain when we encountered some slower scooter/car traffic on a narrow road. After miles of slow drafting we saw an opportunity to pass so we gunned it. After the pass, my friend hit the front brakes a little too hard as we were passing over some gravel and his front end slid out.
He was riding the black Duty Cycle AWD with narrower 1.95″ Schwalbe City Jets. I saw him go down in a split-second and immediately stopped and went back to block any oncoming traffic. Luckily he suffered only a few minor scrapes and bruises. After that incident I went out and bought Schwalbe Big Ben 26 X 2.35″ tyres for the bikes.
They are ebike qualified for speeds up to 75-kph (46-MPH). I learned that a good set of “substantial” tyres is a mandatory requirement when you are running this type of high-power AWD setup. Using 50/50% power distribution, the front wheel has a tendency to spin-out. Next on the to-do list for Duty Cycle will be a variable control for altering the front/rear power distribution…” [this is a feature that Teklektik also added to his dual-motor build]
Here is the original build discussion from endless sphere.
Here’s Bens Duty Cycle AWD with the fatter tires, which provide better traction and a softer ride quality.
“Duty Cycle AWD was born from the need for raw utility, and bred for the balance between man and machine”
– Ben Chiu, Benjamin Button Bikes
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Written by Ron/Spinningmagnets, March 2014
