22
Jun 2012
by larry

Why I Invented an Electric Bike for Carrying Adult Passengers

Thea and JJ model the passenger bike prototype.

“On June 4, 1896 in a tiny workshop behind his home on 58 Bagley Street, [Henry] Ford put the finishing touches on his pure ethanol-powered motor car. After more than two years of experimentation, Ford, at the age of 32, had completed his first experimental automobile…The two cylinder engine could produce 4 horsepower…achieving a top speed of 20 mph (32 km/h). Ford would later go on to found the Ford Motor Company and become one of the world’s richest men.”
Wikipedia

I’m gradually reducing my car dependance. I enjoy traveling to meetings, hauling groceries, and taking my kids to their dental appointments all on my bike. But one of the few remaining compelling reasons for using my car is to carry adult passengers. For a variety of reasons my adult friends and family do not feel comfortable hopping onto my longtail cargo bike. Can bicycles ever fulfill the role of carrying adult passengers? I believe they can, and (like Henry Ford) I’ve built an experimental vehicle to test my conviction.

Here are the design goals I began with: build a bike that can safely and comfortably carry both a 200-pound driver and a 200-pound passenger at an average speed of 20mph. The bike should be able to go up and down a 20% grade. It should have a range of at least 20 miles. It should weigh less than 100 pounds, be less than 30 inches wide and less than ten feet long. And it should cost less than $2,000. I also have two significant design biases: I don’t think lightweight three-wheeled or four-wheeled vehicles are stable enough, especially on the steep descents in my town. And secondly I prefer that drivers and passengers be seated in-line rather than side-by-side, mainly because our autocentric society is none too kind to slow-moving vehicles that don’t fit on the shoulder.

What kinds of bicycles or tricycles have been built to carry adult passengers? The tandem, pedicab, and sidecar come to mind (see the photos below). Of these, the tandem comes closest to fitting my design criteria. I would argue, however, that the tandem has limited appeal for most adults. I can’t imagine my 80-year-old mom swinging her leg over the top tube and huffing up a hill pedaling in sync with me on the way to her doctor’s appointment. If not a tandem, pedicab, or sidecar, what then? What else is possible?

Well, the electric hub motor is forcing bicycle designers to reconsider what is possible. Hub motors are small, lightweight, and unobtrusive electric motors built into the hub of a bicycle wheel. They weigh between five and twenty pounds, yet have as much as thirty times the power of a human rider. Several advances have improved small electric motors recently, including better magnets and “brushless” microprocessor-driven motors. Battery technology has also improved dramatically. Electric bikes used to use heavy lead-acid batteries, the same kind used in cars. Now a six-pound lithium polymer battery (such as those found in laptop computers) can power an electric bike the same distance as a fifteen-pound lead-acid battery. These advances open bicycle design to many new possibilities.

Astute readers may object with a statement such as “If it has a motor, it’s a motorcycle, not a bicycle! Why don’t you just get a scooter instead?” This is a good question, not easily brushed off. It forces us to think about what we value in a vehicle, and to apply a name to that vehicle rather than try to fit an existing name. I seek a vehicle that is slow, narrow, and lightweight. It has to be useful–something more than an exercise machine designed to fit on a roof-rack. It has to be quiet and pleasant and pedestrian-friendly. Notwithstanding some attempts in the 1920′s to make motorcycles useful (see the gallery below) motorcycles and scooters tend to be unnecessarily fast and heavy, incredibly loud, and foul smelling. And for some reason (possibly having to do with their speed) they have pitifully small cargo space. For these reasons I say “No thanks” to scooters and motorcycles, and embrace the as-yet-unnamed class of vehicle I am building.

Over the past three years I’ve put many kinds of electric cargo bikes to the test (as have my blogging colleageages). My first bike has high torque. My second bike is capable of faster speeds. Lastly I’ve started building a third bike that has the best of both worlds. Allow me to indulge in some details. The first bike is a Surly Big Dummy with a Stokemonkey mid-frame motor. This bike has incredible torque. It’s like a winch on wheels. This is because the motor is geared down first with a chain to the crank and then through a second chain to the rear wheel. It can easily carry 400 pounds of people up steep hills. However, it suffers from what I call the “intimacy problem”: passengers must snuggle up behind the driver in a way that is just not socially acceptable to all but the most intimate of acquaintances. The Stoked BD is also somewhat slow. For me this is a safety issue–I dreaded making a left turn in busy traffic while going uphill with a load. I tried making the system more powerful but then ran into troubles such as broken chains and broken freewheels. The mid-frame motor is just not as elegant and trouble-free a solution as a hub motor.

So I built a second bike that is capable of carrying an adult and that uses a hub motor instead of the Stokemonkey mid-frame motor. I began by putting an Xtracycle extension on a mountain bike. The mountain bike has good quality shock absorbers and hydraulic disc brakes; I recommend both for any bicycle intended to carry adult passengers. I outfitted this bike with the largest hub motor I could find. This bike is fast–it’s capable of going over 40mph–but surprisingly it cannot carry a lot of weight up a steep hill. It is designed to have maximum power at a high speed.

I concluded that my ideal bike needs two hub motors: one fast and one high-torque. It’s kind of like a two-speed transmission for an electric bike. The fast motor will be most efficient on the flats, and the high-torque motor will shine on the hills. The fast motor should be a high voltage direct-drive hub motor in a 26″ wheel. The high-torque motor should be a “geared” hub motor in a 20″ wheel.

Another issue is pedals–does this vehicle even need them? They add very little power. The average human only produces about 100 watts of power, whereas a hub motor can produce 3,000 watts of power. Pedals seem superfluous. (In fact some Chinese electric scooters have removable vestigial pedals.) However, ideologically pedals add a lot. They make it possible for this vehicle to mix with other bicycles. They make it legally a bike. That’s worth a lot. Eventually our legal system will judge a vehicle by it’s weight and speed rather than its power source, and pedals won’t be necessary for larger ebikes. But for now I plan to keep the pedals.

Another design issue: how can I avoid carrying the extra weight of a seat if I’m not carrying an adult passenger? A tentative solution: the whole back end of my passenger bike is detachable. I can potentially replace it with back ends designed for other purposes: carrying cargo, carrying kids, farming implements, whatever. This design direction has been tried in the past–in the late 20s Dunelt motorcycles had detachable sidecars for various trades during the week which could be swapped out for carrying friends and families on the weekend.

So last month, inspired by Atomic Zombies’ Brad Graham, I set out to build a passenger bike in time for the Ithaca Festival Parade. It was surprisingly easy. I started with a bike that my kids outgrew. To this I added parts from a discarded “Mobo Triton” crummy adult trike. I welded together my own Xtracycle-like extension out of a length of two-inch square tubing. I bolted the extension to the bike at the bottom bracket and the dropouts. Then I added a 20-inch hub motor and the Triton seat to the backend. Lastly I replaced the bike’s front wheel with a 26-inch hub motor and presto, I was ready to go. The parade was a great success (see photos).

Did I meet my design goals? I haven’t quite finished the bike, so that remains to be seen. But so far so good: it weighs 84 pounds, it cost about $1,400 so far, and it has fair hill-climbing ability. I’ll keep you posted. It’s amazing what an amateur bike builder such as myself can accomplish. I think if cool bike companies like Yuba and Surly and Xtracycle embraced electric hub motors, they could create a new industry. Henry Ford had a similar humble start.

Related Posts

If you thought that was interesting, you might also enjoy these related posts:

  • ElectricBIke

    Have you seen the big dummy when they put an extra set of handlebars behind the rear seat and adult passengers sits on the back rack….pretty effective for 2 adults. I really like your site and find it to be a good resource. I am the webmaster for electricbike.com.

    • http://knowledgetown.com/newsandevents/ News & Events

       EB,

      My first two bikes were as you describe, Xtracycles with an extra set of handlebars clamped onto the seat post for a rider on the back. This works fine for many situations. The main problem is what I call the “intimacy” issue: a passenger who is only a mere acquaintance of the driver is unlikely to want to snuggle up just behind the driver. Another major problem in Ithaca is that even with the most powerful possible ebike motor (a 3kw Crystalyte 3540) an Xtracycle is unable to make it up the 20% grades here with two adults.

      -Larry

      • ElectricBIke

        Way cool! So it has the big wheel up front and the small wheel with the small hub motor in the back…different! So awd, and the ability to increase or decrease distance based on intimacy wanted. I like it! Can i post a pic of this bike in our cargo bike story on electricbike.com and link back to this blog?

  • ElectricBIke

    Larry,

    So what motor are you going to use to deal with climbing those hills?
    Are you going with some kind of mid drive? Right now it looks like you
    just got a front hub motor on that bike…wont you have the same problem
    you had with xtracycle?

    And regarding intimacy…imo it looks like in this new design there is too much distance between rider and passenger….those 2 passengers are so far apart it looks like they hate each other ;)

    ERIC

    • http://knowledgetown.com/newsandevents/ News & Events

      The passenger bike has a 20″ geared drive rear hub motor in addition to the 26″ direct drive front hub motor. The geared motor has a small diameter so you might have missed it.

      The bike frame length is adjustable, so if the passengers want to get closer they can unscrew a knob and make the frame shorter.

    • http://knowledgetown.com/newsandevents/ News & Events

      Please do! By the way I wanted to tell you that I appreciate all your hard work on the ElectricBike.com website. It does a good job of distilling Endless Sphere knowledge and personality for a broad audience.

      • ElectricBIke

        Thanks for the compliment Larry. Yes we have a lot of “ES” on our site. I posted the pic and reference to your site on two different articles…cargo bike big mommas, and ten ways a cargo bike can save you money

  • Pingback: 10 ways a Cargo Electric Bike Saves Money | ELECTRICBIKE.COM

  • Pingback: Cargo Electric Bikes: Big Mommas | ELECTRICBIKE.COM

  • Colin

    The Excelsior sidecarrier is indeed carrying cycle parts. When you take photos from my websites it’s a common courtesy to include a link or at least a mention of where you got them from! I’ve spent years scouring & buying old magazines to share these images with fellow enthusiasts (without any commercial gain). Thanks, Colin http://oldbike.eu

    • markstos

      Colin, my apologies. I see that the photos have been updated now to reference your site. Thanks for finding and sharing those photos!

  • Colin

    Use.

    Paragraphs.

    • markstos

      Colin, thanks for bringing the formatting problem to our attention. Paragraph breaks were intended, but not visible. That isuse has now been addressed.

  • http://twitter.com/YubaBicycles Yuba Bicycles

    Larry – are you aware of the Electric Boda Boda? Other than price, it meets your requirements for speed, capacity and weight.

  • Althenuker

    Larry, very interesting projects. I have been doing much the same over the last 3 years with a goal to mount enough Ryobi Li-Ion batteries to supplement my Bionx 37V with 350W hub motor mounted on a 700c rear wheel, -see poor quality attached photo with eight 18V Li-ion batteries. I can now go 150 km/day on one charge (about 800 Wh stored charge). Next year, I hope to add more batteries while keeping a low centre of mass for stability and increase my daily distance to about 200+km/charge. The question I have is: have you ever considered adding two separate battery packs with different voltages (say 36 and 54V) to resolve the high torque/ high cruising speed issue that you mentioned above? It would be like having two gears: 1st gear with 36V for startup and hill ascent and 2nd gear with 54V for cruising on the flat stretches? I think the Bionx motor can take the higher voltage. What do you think?
    Al
    (manzeral@aol.com)

  • http://knowledgetown.com/newsandevents/ News & Events

    Al,

    Sounds like you have quite the setup. I recently converted an old touring bike to an ebike and took it around the lake here (about 100 miles) in five hours. I was packing 2,160 watt-hours but only used 1,839. Average speed 20.7mph, 18.1 wh/mile.

    Higher voltage batteries can give you more acceleration and speed, so you’re right that if one of the motors in a dual drive bike can handle a higher voltage you might consider two battery packs. What might be simpler though is using a single battery pack and choosing two motors that are similar in size or limiting the power of the smaller motor.

    • Althenuker

      Hi Larry

      A 100 miles in 5 hours is an amazing achievement. At that speed, I suspect that there was not much assistance by human power. In my case, my 90 mile trip (150 km) was done at about half your speed (8 hours) with an estimated electrical consumption rate of about 8.4 wh/mile (800 wh charge) which is less than half your rate. However, I forgot to mention that I probably added another 500 wh of pedal power and cheated by adding another 150 wh of charge during a lunch break where I could plug in for an hour and half. If I factor this into the equation, I get a total consumption rate similar to yours, about 16 wh/mile. Of course, there are other factors in the comparison not considered like: wind friction, total mass of bike and rider, and terrain. In my case, more than half the trip was done on old British railway lines built in the 1800s, converted to very flat bike paths which really help reduce the consumption rate..

      Back to the dual battery pack versus dual motor options, I prefer not to add a second motor to the front wheel because: a) it adds more weight without adding more energy, and b) my front forks might get bent with the extra torque unless I go with a smaller wheel size. It’s easier for me to just add battery packs and switches which I will do over the winter.

      Another idea for adding a second motor would be to start with a recumbent bike that has 3 sprockets (pedal, intermediate and rear wheel sprockets). You could replace the intermediate sprocket with a second motor by fixing the hub and allowing the motor to spin the sprocket in the same direction as the pedal sprocket, The second motor could then assist the rear wheel motor at the appropriate selected gears, In this way, you still would have your pedal sprocket and the recumbent still qualifies as a bike.

      Any thoughts on this?

      Al

      • http://knowledgetown.com/newsandevents/ News & Events

        Thank you for the sentence “100 miles in 5 hours is an amazing achievement.” I felt this was a breakthrough towards making electric bikes competitive with trains and buses for practical long-distance travel. But my friends just yawned. And I suspect many ebike hobbyists are too wrapped up in bikes that look and perform like motorcycles to be impressed by a bike that looks like a touring bike. So I appreciate that you are also chasing the long-distance dream.

        Sorry I assumed you were planning the dual voltage setup for a dual motor bike. It’s a good question if dual motors would benefit a long-distance bike. However there are plenty of discussions about dual motor vs. single motor bikes on the Endless Sphere forum so I won’t go into that. As for dual voltage, it’s not true in my experience that a low voltage setup has higher torque. A higher voltage setup has both higher torque and higher speed, but is less efficient. Also with a high voltage setup one tends to go faster because one can, and so uses more wh per mile and also incurs more wind resistance.

        So if you were to make a dual voltage system it wouldn’t be low voltage for hills, high voltage for flats. It would be low voltage for long-distance trips and high voltage for carrying groceries back from the grocery store down the hill.

        A switch for changing voltages on the fly would be fun to make, but it might be easier to just re-wire your battery pack before each trip after deciding if you’re going on a long low wh/mile trip or a short high wh/mile trip. I use two 36v batteries that connect either in series or parallel depending on my needs. I use special Anderson harnesses I created as described in this post:http://bikes-as-transportation.com/my-diy-sla-trip-batteries/. When you change the voltage of your dual-voltage system it is also a good idea to change the low voltage cutoff using a Cycle Analyst. If you forget this step and leave the LVC at 32v when using 72v batteries you risk draining the batteries too far and damaging them. Some batteries have a battery management system that might prevent such damage.

        Let me know how it works out!

        -Laurence

  • DiDi Wu

    The Chinese market are full of electric powered bike. The motorize wheel and controllers can be mail ordered easily.

  • schoolbuslover1945

    I love school buses so for Halloween I decided to make a school bike lol I carried my little brother around town lol it was funny

  • schoolbuslover1945

    so it was funny