A practical electric bicyckle
After finishing the working prototype, Fredrik, Simon and I went
window-shopping to figure out
the next step towards the Eco-mobile. Eco as in Ecological or
economical transport vehicle.
Use Cases
- Commuting to work within the same city, instead of car, bus or taxi.
Means 20-30 km/h, 2h runtime, easy to use (e.g. as an ordinary bike with a pushbutton for power).
- Easy to build and maintain
Means standard components and simple design
- Usable even with dead batterypack
Means pedals must work, no space stolen from legs,
not to heavy, low enough gears, enginesystem are not allowed
to increase rolling resistance much, might demand "fre-wheeling" engine or clutch.
- Pedals will not have to move when the engine is engaged
Means separate powertrain to the engine.
- Some form of Engine control, e.g. relay with pushbutton
like a "dead mans grip".
To do
- Run battery load test, run fully charged untill discharged,
meassure at least time, amps / voltage would be nice to.
- Meassure the weights of all components.
- Check the wheight of the too heavyily loaded bike from last year.
A guess is 60 kg inc. bike.
Done:
- Check rolling resistance on prototype with no power to
engine.
low enough = no clutch or frewheeling.
Result: feels ok in praktical test, slow acceleration since it is a little heavy.
Much more resistance if engine is pushed hard against the wheel.
- Check if the prototype bike runs faster with lower
gearing, smaller "engine drive wheel" (bought 2 sizes).
Yes, it is geared for 72, 68 km/h under some load, but only manages 25+-5km/h
We can easily get twice the current acceleration if a 5cm transmission-wheel
would work.
- Meassure rpm under ordinary load of the small engine (VW-90), or use the big one.
Result70km/h /3.6 = 19.4 m/s. 19.4/(0.1m*Pi) = 62 rps = 3713 rpm!
Findings:
- It is not possible to let the power from the motor
work through the ordinary power transmission if the
pedals should not have to move with the engine.
If we don't build in an clutch / freewheeling thing
in the crankset. Which is hard.
- It is not easy to fit an extra Chainring to the backwheel
for the engine on the bikes we have looked at.
But if we replace any hub on any bike with a hub made for
disc-brakes, we can add an extra chainring instead of
disc-brakes!
- The project bike "Distance" has 36 spokes, and so does
the next project bike (20" remade to recumbent).
We need 1-2 "Rear Disc hubs" 36 spokes, 6 bolt is standard.
- Meassure torque Nm of the engines (needed for gears), calculated 0.76 Nm.
~500 SEK Rear Disc hub 36 spokes
250 SEK big Chainring 52T,5 holes (56T is 44$)
50 SEK small Chainwheel 8T (11 is 5,5$, 12 ok to)
sheet metal to buld Chainring-Disc hub adapter
2:1 to 4:1 downgearing
Engine speed 2500 rpm = 42 rps
Target speed: 30km/h = 8.33m/s / 2.24m (circumference for 28")
= 3.72 rps
which means 11.3:1 (339/11.3 = 30 km/h. 339/20km/h gives 17:1)
56:8 = 7 :1 42rps@28" --> 48 km/h @20" --> 34 km/h
52:8 = 6.5 :1 --> 52 km/h --> 37 km/h
56:11 = 5.1 :1
52:11 = 4.73:1
56:12 = 4.7 :1
52:12 = 4.3 :1
Later 20" vehicles will not need any more stages (downgearing).
Om man får fel utväxling, så vore det praktiskt att kunna byta
drev, dvs bäst att inte ta extremaste sakerna överallt.
Får två uppsättningar nedväxlingar för motorn plats?
Vad är bäst, kedje/kedje, växellåda/kedje?
vilket maxvridmoment har motorn/vad ska kugghjulen klara?
Har jag kugghjul som duger hemma? /kolla webben.
Two choises:
#1 Gearbox + chain
Fördelar:
Tar lite plats
#2 chain + chain
Fördelar:
Håller för vridmomentet
0.2 kW @ 2500 rpm equals 0.76 Nm torque
Which means module 3, 30mm coggwidth, at least 14 teeth,
in acetal.
sdp-si.com:
Spur Gears, Module (pitch) 3.0, plastic, Face Width 30, no of
plastic Steel
teeth 14 29$ ea 34$
teeth 40 84$ ea 120$
qtcgears.com
teeth 14 29$ea
Mekanex.se Module 3. Do not mix plastic and steel,
steel + brass is perfect.
Teeth plastic steel
12 220 SEK 215
14 not avaiable
18 240
40 580 605
A Gearbox is expensive !
---------------------------
3.3:1 (40:12) Gearbox Module 3
220 SEK Gear 12 teeth
580 SEK Gear 40 teeth
400 bearings and gearbox material
-------
1200 + moms !
Chain and chainwheels: jensonusa.com
3.7:1 14:52
250 SEK big Chainring 52T,5 holes (56T is 44$)
9.75$ Shimano Ultegra 9-speed cogs 11,12,13,14.
small Chainwheel 12T
200 homebuilt hub or casette?
----------------
550 SEK
8 gear casette 11,13,15,, 190 KR (EC)
Latest calculation:
Powertrain:
2 Big Chainring 52T, disc-like, for monogear chain 35kr!,
EC guess 150-300
2 Small cogwheel Shimano Ultegra 9-speed cogs 11,12,13,14 (9,75$)
2 Chains 30 SEK (BT)
2 Chain tensioners about 21? 37$ ea. (jensonusa.com)
1 Rear Disc Hub 36 spokes Shimano FHN975 354 SEK (EC)
36 spokes (5-10 SEK ea depening on quality, 28" and 20" same
price (EC)) 180 SEK
1 Disc mount to Big Chainring adapter (homemade) guess: 100 SEK
1 Extra cogwheel "hub" mounted on the bike,
might freewheel. guess : 200 SEK
-------------------------------
1164 SEK + 2 chain tensioners (guess 250 SEK ea.) = 1664 SEK
Engine package:
1 Battery 150 SEK
1 Engine 200W 3700 rpm during moderate load 300 SEK
1 Dead mans grip 30 SEK
4m Thick cupper whire guess: 80 SEK
2 Battery pole screws guess: 60 SEK
-------------------------
620 SEK
engine: 3700 rpm = 62 rps
target: 3.72 rps for 30km/h with 28"
62/3.72 = 16.6:1
12:52 teeths = 4.33:1
4.33^2 = 18.8 which is:
26 km/h with the small engine@3700 rpm
18 km/h with the big engine @ 2500 rpm
14:52 = 3.7:1, 3.7^2=13.8 which corresponds to 36 km/h
Shops:
Cykelringen in Uppsala
Cykel-viktor --""--
EC = Eriksbergs cykel --""--
www.jensonusa.com good stuff.
racerdepan.se shimano deore baknav skivbroms 366kr
cykelcity.se
cykelogen.se
cykelkraft.se
BT = biltema.se
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