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Packable Electric Kick Scooter

A folding electric scooter that takes up only half the space in your backpack

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If a powerful electric scooter could pack tightly enough to fill only half of the space of a backpack, would it address previously unmet or poorly-met transportation needs?

I'm here to document the design and production process for a folding electric scooter and glean insights and feedback from fellow hackers.

Guiding Design Principles

These priorities dictate the design direction that I'd like to pursue with this project.

Ultra-portable

  • Compact enough to fit two in a medium-sized backpack
  • No protruding elements that could scratch or break your laptop
  • As light-weight as safely possible

Powerful

  • 15mph at 15% grade

Safe

  • Brakes quickly and effectively
  • Extra durability where it counts

Robust

  • Road-ready, rain or shine
  • Tough enough for bumps and curbs

High Longevity

All wear components should be swappable or repairable without special tools. This is a scooter that you can keep around for the long haul.

What I'm NOT optimizing

There are a few items that do not appear as guiding design principles, which I think deserve an explanation. Their omission will also define the direction of this project.

Cost

Not competing on cost lets me use durable components, serviceable designs, and deliver more fully the Guiding Design Principles.  It is a core value of mine to encourage repairs over replacements (more on that in a future post). However, I also want this scooter to be affordable by those who have less cash on-hand.  To that end, if you good people convince me to produce this thing, then I plan to offer the scooter both fully assembled and tested, and also as a parts kit. The parts kit will be much less expensive, but requires embarking on an assembly quest aided by documentation and your own wiles.

This is also my invitation to you to let your imagination run wild and contribute to the community. Kits would be bundled and a-la-carte, so you can source different-from-stock third-party components, and mod your scooter to your heart's content.

Comfort

As I stated up top, I am testing the premise that a tight-packing e-scooter could meet unmet needs.  To stay focused on this question, I am giving myself latitude to design aggressively towards the guiding principles.  To achieve a small size, this scooter will feature solid urethane wheels, no shocks, and will not provide a full-width support for your foot.  In other words, it will be a harsh ride, and the rider will need to stay engaged while they're riding to avoid hazards (e.g. rail road tracks, potholes).

Aesthetic

This scooter will be no-frills, emphasizing function over form.  

View all 8 components

  • Need Bigger Wheels

    Mike Thielvoldt07/30/2019 at 04:16 0 comments

    In continuing tests, I managed to tag the flange on the rear pulley and completely crack it off.  Oops!  What did I hit?  The little bump at the beginning of the driveway ramp through a sidewalk.  

    This thing. 

    So no, the wheels are not big enough, for this and several other reasons.  

    However, in the interest of continued learning, I will keep moving forward with the current design, building out the steering column next so we can all see an e-scooter actually fit in half the space of a normal backpack.

  • First Rides

    Mike Thielvoldt07/19/2019 at 12:50 4 comments

    I could not wait any longer for a ride, so I chopped the steering off of a Razor scooter and welded it to my neck assembly.  The resulting frankenscooter feels very undersized, but it does go! 

    The new to-do items are as follows:

    Increase available thrust

    On a steep hill, the scooter does not quite perform as well as I would hope.  I did not find a hill that stopped it, but on a ramp to a train platform, I experienced the scooter just barely maintaining speed at the rated motor current of 35A.  I know the motor can handle 65A for short durations without de-magnetizing, but I'd prefer 50% more headroom. 

    Configure ESC for smoother control of braking and acceleration

    The available torque, despite being inadequate for steep hills, can still produce a scary amount of acceleration given the present wheelbase.  Wheelies are easy to produce.  Ultimately, a slower turn-on of the current and a mapping to decrease sensitivity at the low end of the control would be easy improvements. 

    Either decrease the top speed target, or increase wheel diameter and wheelbase

    I have only run with 6S (6 3.7V Li-Ion cells in series) configuration so far, which is half the voltage I was originally planning on.  This produces roughly (not accounting for increased drag) half the speed on the flat as the planned 12S configuration would.  The max speed is presently 11mph. 

    22mph would be too fast for this chassis, given how 11mph feels.   I can either make it safer at speed or design for a lower speed.  For now, I'm goitn to target 15mph, defer on increasing the size of wheels or the base and focus on maintaining 15mph on steep terrain. 

    Prioritize mounting the electronics

    It is very cramped inside the frames with the batteries.  I can't actually close the case as presently designed with both batteries and all the cables and connectors.  I hope I can get away with just shortening leads up and re-arranging. 

    Here is what the front end adaptation looked like.   My finest for sure. 

  • Deck Frames Milled

    Mike Thielvoldt07/06/2019 at 09:10 0 comments

    Progress Report: 

    The machining is underway and the decks are beginning to take shape.  

    Here the rear axle supports are being milled.  These parts clamp either side of the rear axle and distribute the load while also allowing the belt tension to be adjusted then locked in.  

    Why start with Milling? 

    I chose to emphasize milling in the prototype stage for the following reasons: 

    1. Milling itself works as both a low-volume and mid-volume process.
    2. I can use strong materials.
    3. Milling generally produces good results on the first parts.
    4. Milling lends itself to threaded fasteners, which is like giving myself an "undo" button as I navigate assembly!   
    5. Milling has many relatives in NC-controlled cutting family.  By starting with milling, I can more readily bring part designs to contract manufacturers with other cutting capabilities.  For example, I would really like to see the deck frames become laser-cut tubes.  Maybe someday! 

  • Battery Selection

    Cristina07/06/2019 at 05:00 0 comments

    In selecting the battery, I was looking for something that was compact enough to fit in the narrow deck frame, but high-powered enough to make it up hills and last for miles. Lithium ion batteries are somewhat expensive, but have a high enough energy density to satisfy my target specs for speed and power. Here are the ones that I opted for:

    https://hobbyking.com/en_us/turnigy-high-capacity-10000mah-6s-12c-multi-rotor-lipo-pack-w-xt90.html

    There are two of these batteries included in the deck assembly for a single scooter.

    If this scooter were to be produced on a larger scale, I would purchase Lithium Ion 18650 cells and attempt to produce a custom pack. This form factor is cheaper than the rectangular batteries, and because of its popularity, provides more options for customization and replacement.

  • Target Specs

    Cristina07/05/2019 at 19:46 0 comments

    While I'm still developing the first prototype, here are some target specs that I'm aiming for:

    weight< 30 lbs 
    packed dimensions12" x 3" x 16"
    power15 mph at 15% grade
    capacity220 lbs
    speed24 mph on a flat surface
    max grade20%

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Discussions

de∫hipu wrote 08/18/2019 at 12:35 point

  Are you sure? yes | no

Mike Thielvoldt wrote 08/20/2019 at 04:05 point

Thanks again for keeping us apprised!  This scooter looks pretty darn tiny, which I love, and with a car company building it, perhaps it will be available soon!  After watching the video and searching for information, I still wish I could see: 

A) Performance specs: Range, Speed, and Maximum Incline.  

B) Whether the added width and rubber on their 4" wheels are enough to mitigate the road roughness.  These are even smaller than the wheels on my prototype now, which I also think are too small.  

C) How the latch on the bottom of the frame is designed given it must handle the bending loads from the rider's weight and be subject to various impacts. 

D) Is it short enough to get into a normal backpack? 

http://www.koreaherald.com/view.php?ud=20180827000493

If you run across any specs, please share! 

  Are you sure? yes | no

de∫hipu wrote 08/20/2019 at 07:53 point

I think that was just a designer fantasy, but there is an actual scooter available from China: https://www.aliexpress.com/item/32994693447.html — looks a bit bigger though, and pretty shady.

There is another model too: https://www.aliexpress.com/item/32994786067.html

  Are you sure? yes | no

Mike Thielvoldt wrote 07/03/2019 at 16:41 point

Right!  I understand the capacity of the Li-Ion battery is the problem.  The limit for flying without prior approval is a battery with 100W-h.  This scooter has two batteries, so I wonder if dividing it up into separate 100 W-h batteries, potentially stored separately, would actually permit you to fly with it. 

Right now, I'm planning on using a total of 444 W-h in capacity, which I estimate delivers at least 15 miles.  

Question for you, @de∫hipu : Let's assume we design in a reduced-range configuration; call it "Airplane Mode".  What range do you think it would need to retain in Airplane Mode to still be usefui?  

  Are you sure? yes | no

de∫hipu wrote 07/03/2019 at 17:07 point

The use case I have in mind is flying to various conferences, and then getting from the airport/train station/metro to your hotel, the venue, etc. If the airport is outside the city, that is not feasible (just take a train), but I assume your hotel wouldn't be farther away than, say, 2-3km from the venue/train station.

Then again, I'm afraid that the airport security might get foam on their mouths from just seeing a scooter, no matter what the battery capacity is.

  Are you sure? yes | no

Mike Thielvoldt wrote 07/03/2019 at 17:22 point

Great use case!  I think 5-6km (2-3km round-trip) is a very interesting technical target.  I'm sure that with a little effort, we can find some airport security personnel to advise on the second issue.   

Thanks! 

  Are you sure? yes | no

de∫hipu wrote 07/03/2019 at 07:43 point

That would work so well if only you were allowed to take it on an airplane...

  Are you sure? yes | no

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