Overview
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 flats | testing |
| Sustain 10MPH on 4% inclines | testing |
| Under 20lbs total weight | Final weight: 22lbs |
| Travel 2+ miles per charge | testing |
Ride Highlights
I've used the scooter as purely a kick-scooter…works alright so-far.
Parts List
| Item | Model | Price | Notes |
|---|---|---|---|
| Motor | Scorpion 4025-16 | $99.95 | While 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 Pulley | 6A25M013DF0906 | $9.61 | This is an aluminum pulley, I'd recommend procuring a hardened steel one. If you can find them, please let me know too  |
| FreeWheel/Clutch Bearing | It's a standard screw-on freewheel, I'll add info once I dig it up | ||
| Wheel Sprocket | Currie branded 65-tooth #25 chain sprocket | ||
| Belt | 5mm HTD, 9mm wide | ||
| Speed Controller (ESC) | Castle Phoenix HV85 | $169.95 | This 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 Regulator | KoolSystems Ultimate BEC | $49 | A 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 | $13.95 | This 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 Connectors | Deans UltraPlugs | $5/pair | These 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  |
| Motor Connectors | 4mm female bullet connector | $1/each | El-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 Housing | Matt's eDrive | $230 | beautiful piece of work…and fits VERY well! |
| Motor Mount | angle-bar…cut & drilled to fit | ||
| ESC Housing | Still testing a few ideas. | ||
| 10 gauge wire | Deans Wet Noodle | $5 | A 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:
- The RC modeling market has been flooded with this highly efficient motor design over the past couple of years.
- These motors efficiently pack a tremendous amount of power inside a very small package.
- It's brushless, which means less wear & tear and a minimal amount of maintenance.
- I wanted to use an AC tri-phase motor simply because I sought to incorpoate Nikola Tesla's technologies.
Motor Mount
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?
http://www.york-ind.com/cgi-bin/png_dp.cgi?ttype=DP&size=4&hhtype=P&btype=UB&pmaterial=A&pprofile=F&diam=100&pwidth=&pwidthI=.42&bearingt=B&mclear=.23&mclearM=&threadst=E&amov=AC&springs=S&part=DP4UB-F100A42-B23PE-ACS http://www.york-ind.com/tensioners/instock_DP.htm
Links
VXB's one way bearings list http://www.vxb.com/page/bearings/PROD/kit949 https://sdp-si.com/eStore/Direct.asp?Exp1=41799&GroupID=227 http://store.todayshightech.com/e7070197.html http://gbgearworks.com/ http://www.torquetrans.com/pulleys/timing/index.htm http://www.gears-reducers.com/timing-belt-pulleys.html http://www.onviollc.com/dotnetnuke/Pulleys/tabid/73/Default.aspx
Kill Switches
- For the main battery, I'm thinking a deans-plug style kill switch.
- A coworker suggested a watersports equipment killswitch lanyard.
