Overview

img_0143.jpgimg_4744.jpg eWalker: Electric Sidewalker Scooter

I took a Sidewalker Micro, added airless tires, and a brushless outrunner motor…and in doing so, turned this adult-sized kick-scooter into a viable primary vehicle for quickly zipping around short distances.

Power Assist Highlights

  • 20lbs - all equipment, including battery
  • Assembled with roughly $800 in parts and materials (including scooter)

Original Design

GOAL STATUS
Sustain 20MPH on flatstesting
Sustain 10MPH on 4% inclinestesting
Under 20lbs total weightFinal weight: 22lbs
Travel 2+ miles per chargetesting

Ride Highlights

I've used the scooter as purely a kick-scooter…works alright so-far.

Parts List

ItemModelPriceNotes
MotorScorpion 4025-16$99.95While its fairly over-rated for my intended uses, Scorpion motors are apparently the ONLY brand which uses N50 NdFeB magnets (200C/392F temperature rating)…meaning they have a far higher heat tolerance than most other outrunner motors on the market.
Motor Pulley6A25M013DF0906$9.61This is an aluminum pulley, I'd recommend procuring a hardened steel one. If you can find them, please let me know too :-)
FreeWheel/Clutch BearingIt's a standard screw-on freewheel, I'll add info once I dig it up
Wheel SprocketCurrie branded 65-tooth #25 chain sprocket
Belt5mm HTD, 9mm wide
Speed Controller (ESC)Castle Phoenix HV85$169.95This ESC is larger than I need, but my use/load-patterns dont exactly match a model aircraft…so I'm shooting high. Model comparison.
Voltage RegulatorKoolSystems Ultimate BEC$49A different model pushed me about 20 feel before going up in a little ball of smoke…despite working fine through at least a dozen zero-load tests. On the other hand, the KoolSystems model has worked for at least 20 miles, without issue. Model comparisons.
Servo Tester E-Sky EK2-0907 1-2ms$13.95This device sends the necessary PWM signals to the ESC…it effectively acts as your throttle. Since the Castle Phoenix ESC only responds to 1.5ms-2ms signals, this particular test unit has more than sufficiency capacity as a throttle.
Battery ConnectorsDeans UltraPlugs$5/pairThese can handle upwards of 200A at 50V, with ZERO resistive losses. They're also relatively cheap, and idiot-proof to connect - what could go wrong 8-)
Motor Connectors4mm female bullet connector$1/eachEl-cheapo 4mm bullet connectors. The motor came with male connectors already soldered on, and I was simply too lazy (and cheap) to change anything out. They're working…we'll see for how long.
Motor HousingMatt's eDrive $230beautiful piece of work…and fits VERY well!
Motor Mount angle-bar…cut & drilled to fit
ESC HousingStill testing a few ideas.
10 gauge wireDeans Wet Noodle$5A single foot of this wire cost $5…though it's 10-gauge wire that's as flexible as a wet noodle. I'm using it between various connections.

Battery Options

Battery packs utilizes a LiFePO4 battery chemistry; one of the newest mass-produced battery chemistry, and also an ideal type for EV use.

DeWalt Battery Pack

These battery packs retail for around $150, but eBay often has these for as low as $50…I picked mine up for $70 (including shipping).

The packs utilize A123 brand LiFePO4 batteries; arguably the best brand available.

Construction Details

Rear Wheel

Motor Selection

I selected a Brushless Outrunner simply because:

  1. The RC modeling market has been flooded with this highly efficient motor design over the past couple of years.
  2. These motors efficiently pack a tremendous amount of power inside a very small package.
  3. It's brushless, which means less wear & tear and a minimal amount of maintenance.
  4. I wanted to use an AC tri-phase motor simply because I sought to incorpoate Nikola Tesla's technologies.

Motor Mount

img_0142.jpg

Pulley Discussion

Stage Ratio Details
Motor/belt reduction 5.45:1 11-tooth HTD –> 60-tooth HTD
Chain/wheel reduction 2.6:1 25-tooth #25 chain sprocket –> 65-tooth
Chain/wheel reduction 3.25:1 20-tooth #25 chain sprocket –> 65-tooth
Chain/wheel reduction 4.33:1 15-tooth #25 chain sprocket –> 65-tooth

At 8,000 RPM, the following top-speeds are possible (12.5“ tire = 34.5” rollout):

Belt Ratio Chain Ratio Final Ratio Output RPM Top Ground Speed
5.45:1 2.6:1 14.7:1 564.57 RPM 18.45 MPH
5.45:1 3.25:1 17.7125:1 451.66 RPM 14.756 MPH
5.45:1 4.33:1 23.599:1 338.997 RPM 11.08 MPH

Engineering Discussions

As for me, I just need to move around town (friends, clients, office, social) within “reasonable” timeframes.

Design Improvements

Not “flaws”…areas for improvement :-)

These folks supplied my metal:

Throttle

The basic idea is to mount a fully sealed cermet potentiometer to the handlebars…then run the wires into the PWM signaling device (aka: servo tester). This allows for on-handlebar throttle control.

Allied Electronics carries what I was looking for; 4.7K ohm, 3W, sealed cermet “PE30”. Mfg part # PE30L0FL472MAB (click for detailed specs).

Belt Tensioner?

Kill Switches

Other Photos

Lessons Learned

Speed Controller

Links & Inspirations

ewalker.txt · Last modified: 2014/05/16 12:35 (external edit)
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