Hands on building a mid drive e-trike

February 20, 2018

Guest post by Brian Lynch

Ok, so you want to build an e-trike.
Yeah, me too. Above is the result.
Goal achieved, bye, thanks for reading!
OK, lets rewind back for a moment:

It is Thanksgiving 2017 when, in the normal course of holiday communications and well wishing, an email arrives with a “what do you think of this” subject line. Knowing the sender often has something of interest I clicked immediately. A picture of an adult trike with a fat’ish front hub, and skinny tires, appeared. Ok, I thought, “what do you think of this?” may have been too broad a question. At first glance, “I don’t think” came to mind. Upon reading I became aware the picture was of an electrically driven adult trike. Cool enough I thought, but, as I looked further, the “I gotta get one of these” moment failed to happen.

The sender is an aging guy (81years) who we’ll call Stan, because that is his name. By any standard, Stan goes full speed. He and his wife of 61+ years will outpace most younger folks in mental energy and stamina. Various health issues have dulled the physical abilities, however, in a cruel irony, have sharpened the drive. A strong appreciation for technology and world affairs keep them, and me by association, busy enough.

The challenge

Would an electric adult trike work to enable an oxygen toting guy to cover several miles of golf course community trails in a dependable, powerful, and stylish manner? Sure, lets go!, I’m totally in, but…, just not that thing in the picture, I thought.

A few taps on google will lead one to the LunaCycle site. Once there the idea of a preassembled, toy style, novelty grade, hub-drive, trike, will dissipate quickly. The idea of a programmable mid drive unit, custom battery configuration, and the safety of a well thought out “system”, quickly tarnished the original idea. The ride away cost of a “Luna”, if done right, would be comparable. The performance, the safety, and the cool factor, would blow away any ready made option, regardless of cost.

Choosing the trike was the first challenge. There are many, and the choice is largely personal, however, in my single experience, the following are some concerns worth heeding to for a good build:

  1. Not all adult trikes are adult size. Look at the dimensions and size of the trike to the rider,
    and riding style. Recumbent trikes are often more tech oriented, however, for more leisurely
    riding comfort and ease of mounting/dismounting may not be optimum.
  2. Since the “mid drive” units need a three piece crank set up any one piece cast type crank
    will need adapting.
  3. The model selected should have braking abilities to accommodate the additional weight
    and speed of a driven trike. I recommend a model with disc brakes. As most bike/trike disc
    brakes may still be lighter duty by design I recommend readjusting, resetting the caliper,
    checking trueness of the disc, etc. to assure safe operation.
  4. The average operating speed of an “adult” trike is well below the capabilities of an e-bike
    conversion. Things as small as a tire that is not properly “seated” on the rim will be
    exaggerated when run at four or five times the design speed. After spending dollars and
    time the failure of even a simple part to perform, or keep up, can make you sad, or dead (or
    alive and in pain while you spend more money and time rebuilding) (because we ALWAYS
  5. Last, and perhaps to most important, make it a cool looking model as the attention it will
    attract can’t be understated.


As for the build, if you are reading this I assume you have the basic skills and tools. I can wholeheartedly say that as you compose your own system, and it is a “system”, consult the staff at Luna as they know what they are doing. They helped confirm my purchase choices and made slight changes that assured a straight forward approach to my project. Big props to Joel, and the folks that I didn’t speak to directly, but, I know they rocked their function in all of this!

The items selected from Luna for the build were the BBSHD kit, added the DPC-18 display, gear shift sensor, a “flat fish” battery, and a 36 tooth sprocket. This seemed to be the coolest and easy to service, set up. It proved to be essential to have a programming cable and, if you want, the special spanner wrench for the drive unit.
The sprocket, however non-essential, was kinda cosmetic (fill you in later).



The model Trike selected was the “Baja” from Sun bicycles. This is because it looks cool.


The main challenges would be the adaptation of the drive unit, the wiring and control mounting, and the configuration of the battery system. Some minor mods were needed to the trike, however, mostly for comfort and cosmetics.

The first item of attention is the crankset. When I ordered it I thought (incorrectly) the bike came with a three piece crankset. Well, time to learn about adapters. An adapter is a simple part designed to take up the space when a smaller diameter crankset is installed in a bigger hole.

There are many bottom bracket adapter questions, and the answer to almost all of them is 40. The adapter shown here is the American Style Eccentric BB to BSA Adapter, from Luna. It is about 40 bucks and would have saved me hours, and resulted in a slightly cleaner build. Why then you ask did I not cough up the dough for this miracle item? Well, the way I figure, they must have heard my crying as I took the hard road as the primary reason for developing such an item. Yep, thats it, or…they introduced this after I had finished this build.


For me, back in the dark ages, most adapters I found were either to change for a three piece crank so riders can get more choices in crank length etc. for motocross, trick riding, etc. Others were for taking up slack (adjusting) the chain on single speed bikes without adjustable axle position. The latter, like the LunaCycle piece, have the holes offset so, when rotated, they slightly move the crankshaft fore, or aft, in the housing, while many just have the shaft opening in the center. This matters to the builder as moving the shaft location forward, up, or down, may be needed to provide the clearance required for the drive unit (typically forward of the crankset under the main frame tube). Other mounting options work, however, you may have a drive unit that is “upside down” in appearance. The adapter I used is detailed below.



As seen here, at first, the centering appears to be good in the crank opening.
It is, upon closer inspection, slightly off. The LunaCycle adapter would have instantly cured this issue.

The tricky part is that although with my “centered” adapter the drive can be “bolted up”, the contact area on the case (see arrow) prevented the drive from seating well against the crank housing. Tightening the nut would have angle stressed the crankshaft resulting in a binding, or death of the unit.

After relieving (grinding) the adapter (see below) the unit could seat totally flat against the crank housing, but…













In the both photos you can see that the adapter I used had a depressed center section. This meant that by the time I had adjusted (shimmed) the crank shaft to ensure the BBSHD triangle plate would sit flat against the crank housing, I had lost the direct “grip” of the unit to the housing. This contact is critical for the gripping of the triangle plate to prevent rotation of the drive unit through vibration or torque as one rides. Again, a problem that is eliminated by the LunaCycle adapter.

Even with the unit torqued down, I still fabricated the “power strap” seen here, just in case.












The “gearsensor” was a straight forward install (per instructions) as there was enough room on the way to the derailleur. As a side note, on this install, the need for shifting with the derailleur is not needed. The speed is so adjustable with the program set up, along with the “level” settings and pedal assist, that there is no straining when encountering hills, etc.

Without the traditional strain, the need to relieve the strain is gone. The top, low, and any mid range speed can be achieved, set, and even restricted if desired, with the BBSHD program.

In hindsight, even a single speed bike will work, however, one should not depend solely on the attributes of an ancient “coaster” brake model. The power cutoff feature of the Luna levers, as well as the effectiveness of the disc brakes, will reward those who evolve.






The next issue was the mounting of the battery. When reading the various warnings on the handling and use of these monster batteries one starts to realize that, like most newer technologies, any failure will cost some money and parts. Most fabrication failures from the last century would cost a social standing, a day or two delay, maybe a body part, we knew scars made good stories, and was the end of it. Apparently failures with these voltage villains can result in project destruction, the government visiting you, and the loss of all the things you own that can burn. Plus all the other stuff from the last century…just say’n.

With caution in mind (really) I decided to mount the battery where it looked the coolest. Since “adult trike” conjures a image of the cat lady venturing out once a week for feline food, most, will have a fancy basket over the rear axle. I thought this would allow the space to make a nice protected cubby for the Flat Fish pack. Below you can see the fabrication of the battery mount. The included “slide mount” for the battery was the basis for the whole thing. Once attached to the frame I just had to extend the mounting points for the basket. Once complete the battery can be removed easily by pulling the handle rearward (once unplugged and unlocked)


The handlebars presented a less yielding challenge as the wiring harness for the bar controls, and display, would be very time consuming to splice and lengthen. Fortunately the stock bars were such that replacement was an upgrade, both cosmetically and functionally. The allowable distance between the brake levers, the throttle (thumb), the switch array, and the display can’t vary by more than a few
inches. I found some medium profile MX bars, with about a five inch rise that worked out well. The cross bar came in handy to mount the switch array and the bundled wire/plug package. Although the
display appears to be a bit “undercover’ it can be seen well from the seated position. The brightness and the color make it very easy to read even in sunlight. Polarized glasses will still make it appear blank, but you will look so cool you won’t care about data.







The speed sensor was another story, this story in fact. With its wheels far out to either side, any chance of mounting the pick up, or the trigger, as I have seen in pictures, would not work. First thought was to
install it on the front wheel, however, with so much cable needed, and the run traveling along the steering forks, I bailed on that. The trikes typically have only drive/stop related parts towards
the middle axle area. After much thought I fabricated a bracket to mount to the only inboard item that rotated as does the wheel. The brake disc. You can see in the pictures it is a fiddley little bit, but, it does the job.

The trigger, piggybacked with couple of the disc mounting screws, should not allow for any wobble or other undesirable movement. The pick up had to be fixed solid and close (3mm? come on guys). I fabricated a
bracket to attach to the “axle” nut where the rear axle would be on a conventional bike. You
can see the brackets for the trigger and pick up in the picture.






The desire to bring along a few small animals was strong so a trailer from a pet trailer
company (yes they do exist) was modified to mount to the center of the frame. It actually tows
straight and true and the doggies seem to like it. You can also see it in the first picture along
with Stan.

Onto the finishing touches.











The last item was kinda a thing from the start with me. I like a build to look factory. Whether a
car, boat, or one off e-trike, I like good engineering and finish. I don’t know what kind of sick factory would make a trike like this, but, I would work there. To that end, the final Fab
project was to get out the new 36 tooth, precision cut, Luna One sprocket.

Simple was the mod to the chain guard and the look is very stock, perfect!

So, that about speaks to all of the difficult issues. The rest of the build was normal fab/fit
issues with a project like this. I upgraded the pedals, the grips, etc.








So, that about speaks to all of the difficult issues. The rest of the build was normal fab/fit issues with a project like this. I upgraded the pedals, the grips, etc.

I can say without reservation the Luna Cycle crew has done their work well. Everything works better than promised and their acceptance of an odd project was very helpful. As I stated
earlier, speed, range, and power, although common priorities for most builds, took second place to the quality of experience for this build.

As it is programed, Stan can use this trike to “walk” alongside his wife and pets (level 1 = 2-4MPH), climb any hills (level 3&4 = 4-12MPH), or rip by the amazed neighbors (level 5 = 16-18MPH).
Stan (the old guy) has plenty of inspiration, but, not an abundance of health so this is a great way to be cool and get out in the coastal California days.

Thanks to everybody at Luna Cycles. You have done more than you know.

Brian Lynch


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