Juicer E-bikes, King of the Boardtrackers

January 15, 2016

David Twomey is a custom ebike builder who has a great eye for style, and he has been making ebikes that are reminiscent of the classic boardtrack motorcycles from the turn of the century.



Boardtrack racing” was popular around the world between 1910 and 1930. By having steeply raised corners on the oval tracks, motorcycles did not have to slow down in the turns. This means that the entire race was held at speeds near 100-MPH, which was quite thrilling for both the spectators and riders alike. By making the track surface out of boards, they were more affordable to build, but…they were also very dangerous, because some of the boards always came loose during the race.

I wish I could say the board tracks died out due to safety concerns, and were replaced by asphalt. However, they simply went out of business when the depression hit and spectators could no longer afford to attend. An interesting side note to this is that…the boardtrackers had bicycle pedals as a “starter motor”. The rider would begin pedaling and then “pop the clutch” to start the engine. Then he’d roll up to the starting line.



The beginning of the Juicer

David lives in Southern California, and has posted the progress of his builds over the years in two forums, motorbicycling.com and also endless-sphere.com.

The Headway company makes cylindrical battery cells that are known for three things, they can provide a decent amount current, they use the very safe LiFePO4 chemistry, and…they are large! David visualized a motor and battery combination that evoked the V-twin engines that he was fond of. The model he chose was the 38120, which is 38mm in diameter, and 120mm long. By clustering seven of them in each “cylinder”, the entire pack would be only 14 cells, so he decided he would also need to make a faux “oil tank” just under the seat to hold ten more cells, bringing the total to 24.

A battery made from the LiFePO4 chemistry can be damaged if mis-managed, but this is the chemistry that was known in 2010 to be least likely battery to catch on fire, and it is that safety characteristic that some builders found appealing. Today, NCM and NCA cells in the 18650 format are now considered to be equal in safety to LiFePO4. The 38120 model has 10-Ah of capacity. Davids pack has 12 cells in series, and two cells in parallel (12S / 2P), and that provides a nominal 36V and 20-Ah.

If properly cared for, authentic Headway LiFePO4 cells have been known to last for over 2000 cycles, which is quite good. If you completely drain and charge your pack 5 times a week?…that’s roughly 250 cycles per year, and your pack might last as much as 8 years!












Here, David used wood to mock up the many curves of the very attractive fuel tank, and once he was happy with the result, he made the final metal version. I’ve used wood myself for rapid prototyping. It is fast, easy, and cheap to get your “first-version mistakes” out of the way by using wood.





Juicer II

Not long after he posted the finished project pics of the original “street legal” Juicer, David got the itch to create another custom ebike that looked a little more like the boardtrackers that he loved, and he also wanted to make one that had a lot more power.

Briggs and Stratton used to make a 48V brushed motor with an axial flux configuration called an Etek, and it’s size and power capabilities were perfect for what David had in mind next. If you shop around, you might still find a new one on somebody’s shelf, and used ones are also occasionally found for sale.

He started with a heavy-duty Worksman steel frame.







Many motorcycles from the 1910’s and 20’s had a round crankcase that was mounted in what has become known as a “loop” frame. David found a model of frame that was close to what he needed, and then modified it to fit the motor and jackshaft right where he wanted them.




These cells are still Headway LiFePO4’s, but in this frame he used the larger 40160 format (40mm diameter, and 160mm long). They each have 16-Ah of range, so he would only need one parallel string to the pack configuration. David used 16 of them to make this pack a 48V system (16S / 1P).

I find that the Etek motor is visually perfect for this theme, and its combination with the 40160-format cells is very striking.




Here, David has put together a rough slab-sided boardtracker tank, and is working on the Juicer logo. In the pic below, he found a genuine antique meter that can measure amps and volts. The vintage style of this meter is fantastic, and he knew he had to find a way to blend it into the design of the Juicer.




David lives within driving distance of the Willow Springs track, and he doesn’t just make beautiful ebikes with a classic vintage theme, he actually runs them hard to see what they can do.




Here are a few things that David had to say about the Juicer II,

“I live in the hilly neighborhood near Dodger Stadium, and I am pleased to say that Juicer II, even with the controller limited to 100A, can climb nearly every hill. On the flats, I clocked forty-six on a slight incline…So up to Burbank and back, we went 12.7 miles before the BMS went into protection mode and cut off the juice…I’m sure if I upgraded to a 160A BMS (Yesa?) I’d tap more of the Etek’s potential…”

“…So, the latest additions are a surface-mounted voltmeter and a horn that I mounted in the headlight spot. I bent my own rules on both of these items. First, the voltmeter is an antique, so that violates the Juicer maxim; “No exotic parts I can’t make myself.” Second, the horn is a late thirties Harley design. The horn is 113dB LOUD, and is activated by a momentary button from Radio Shack mounted on the hand-brake clamp…”


Current ebikes from Juicer

36V “Citizen”

The pic just below is the first working version of the Citizen model, but David continued enhancing the design, and…the stunning final results can be seen in the following pics.











The Citizen model has a small Currie brushed motor, and it is in a “Basman” style frame that has been modified. The new California DMV definition of a “Motorized Bicycle” or “Moped” now limits Wattage to 1000W. This gets you out of the yearly registration/insurance hassles attendant to motorcycle ownership. David takes the long-view when he chose his components, so like Juicer I, the “Citizen” redux has a Currie-type 1000W motor, and it is a tough little powerplant that is likely to be available for years to come.


48V Ranger

David really got a lot of attention when he began showing the Juicer II, and quite a few people asked him if he would ever make them for sale. He decided to make a few modifications to the design so it would be more production-ready, and the result was the Juicer III (which he now calls the “48V Ranger“). It has a smaller controller, a bigger BMS, a strengthened springer fork that weighs less than the previous fork he used, and an improved rider posture.




The original controller in particular was very oversized (capable of 400A), and as a result had a lower efficiency that what was possible. A similar model was found that was more size-appropriate, and the higher efficiency from that unit provided a much better range from the same battery pack (up to 30-miles, with typical riding).



For the newest model he was visualizing, David decided that he needed to make the frame from scratch, so he could have complete control over the strength, shape, and style of the finished product. 








For David’s “3kw” (the name means 3000-watts), he chose a Lynch motor, the LEM 130-95. It is the more efficient variant of their smallest motor, and it just so happens to be rated at 3.02 kW continuous. It’s the perfect size for the new four-horse California legal “moped” power-limit.






Here, David used 3D printing to make caps for the cell-bundles, and in the pic below, a DC/DC converter (located inside the faux fuel tank) takes the pack voltage and drops it to 12V to supply the street-legal headlights, tail-lights, horn, and also…an accessory socket for charging your smart-phone or GPS.






Although the main reason for mounting the batteries and motor in a V-twin configuration is for the engaging style, this central location is the absolute best place to install the weight of the drive system, so…this is one ebike that will actually handle well at its top-speed.

If you want to ride a California street-legal moped, and you also want to travel in style, the Juicer 3kw is a stunningly beautiful example of the vintage motorcycle theme. Here, it is shown in front of the Eastern Columbia building, an authentic “art deco” structure in Los Angeles, built in 1930.


An interview with David

As an eBike builder, why do you call your electrics “motorbicycles”?

To me the distinction lies in the chain-lines.  Today’s motorbicycles, like mopeds and early motorcycles have two chains that lead to the rear wheel.  I’m not going to say that this is the only way to do things, but it has some advantages.  One, it separates motor power from human power.  This allows each power source to be set to its most efficient cruising-speed gear ratio.  Also, it prevents the motor from overloading a drive-train engineered to only withstand one-human-power level stresses.

What is your approach to designing bikes?

In 2010 when I built the first Juicer, eBikes seemed to have been designed the cheapest way possible, namely, put the motor in the rear hub and the battery on the rear rack.  Often the sales pitch stressed how hidden the power elements were, as if to reassure the rider that “no one will know you’re cheating.”  To me, that approach was ludicrous.  First, the weight distribution was a disaster, and second, why shouldn’t an eBiker be proud of what his ride is made of?  In my mind, the answer was to find the beauty in the electro-motive materials and to come up with a time-tested design with integrity that showcased the power-plant.  Subscribing to the notion that form follows function suggested putting the heaviest elements (the motor/batteries) low and between the wheels, and the lightest elements (electronics) higher.  Today we see that the best performing electric bikes are mid-drive rides with packs either along the down-tube or the seat-post tube, or both, in the case of Juicer.

Isn’t the “EV-Twin” a gimmick?

I won’t deny that I enjoy the resemblance of my power-plants to early v-twin gas engines, but it is not sufficient to say that I do it that way to copy the v-twin look.  The battery-pack is perhaps the most critical part of an electric vehicle.  There are good reasons to split the pack, one of which is serviceability.  It is typical of BMS systems of 48v or more to break the sense-wire array into two plugs.  It follows naturally to have those lead (ahem) to distinct locations to enable easier cell-removal.   Also, mounting pack-halves is easier than a larger whole.    Back in the early 1900’s when they first started putting two-cylinder engines in cycles, the v-twin was chosen because it fit neatly in the triangle of the frame.  Motorcycle frames no longer have that triangle, so an EV-Twin may make more sense in a bike than a v-twin does in a modern motorcycle.

You have said that Juicer is, “creating the lexicon of electromotive power.”  What do you mean by that?

Think of the language of petrol-power.  A muscle-car is replete with reminders that under the hood is a tremendously powerful engine.  The dual-exhaust, the air-scoop, wide tires all communicate this message of combustion power.  What symbols do we have to say that electrics are powerful?  Well, we have the motor, and motors like the Etek or Lynch are very attractive in an industrial way, so it is a natural choice to reveal them.  What else?  We have the battery.  Pack size is relative to power in an EV in a way that tank size is not in a combustion car.  Yes, they both correspond to range, but a longer string of cells also means your electric motor can go faster.  So rather than concealing the pack, I show off this muscle.

Why not just make motorcycles?

You know, I would love to make an electric cruiser.  I think it makes more sense than the sport-style electric motorcycles that are out now, as cool as they are.  Maybe I’ll do it one day.

Ebikes are a product of a digital age, and yet your bikes scream analog.  Why?

Partly it’s to stand out.  There are plenty of eBikes with digital readouts, and maybe that makes more sense, but I’ve always been partial to the speed-read of a needle.  Plus, I see Juicer as part of a longer tradition, and if a brand is to be timeless rather than a product of its time, classic style is required.

How do you test your bikes?

My initial rides are on the hills I live in around Dodger Stadium.  My range-test route is along the LA River.  I’ll ride at 20mph without pedaling until my BMS cuts me off.  Also, once or twice a year I’ll take a 5kW bike to Willow-Springs to race in the So-Cal Motorbicycle racing league.  I don’t have any trophies, but it’s a great way to find the limits of your machines and it’s gangs of fun.

What advice would you give to aspiring builders?

I would say don’t let your circumstances limit you.  I went to my local community college to learn welding just so I could build my first bike, and I built it with only a welder, a hand-drill, and an angle-grinder.  Many bikes later, I have a few more tools, but still no CNC.  That bike on the cover of the magazine [Electric Bike Action, February 2016] was made with that same angle-grinder.  You can do it!


Here is the Juicer Facebook page

Here is the Juicer home web page


Written by Ron/spinningmagnets, January 2016

Grew up in Los Angeles California, US Navy submarine mechanic from 1977-81/SanDiego. Hydraulic mechanic in the 1980's/Los Angeles. Heavy equipment operator in the 1990's/traveled to various locations. Dump truck driver in the 2000's/SW Utah. Currently a water plant operator since 2010/NW Kansas


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