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Building a Better Motorized Bicycle
toyotaboy writes "Saw this in 'design news' magazine. It's a bicycle using an engine that looks like something pulled off of an R/C airplane. He uses a gear reduction system as well as a overrunning clutch to keep the engine running while stopped. Claims to get 20 mile range from its 1/4 gallon gas tank (80mpg). If you figure most engines like that are 30k rpm with 1:100 gear reduction, and an average bike rim is 26", you should get potentially 1,458,000 inches per hour, or 23mph! He goes on to say that similar devices in electric form (segway) fail because of their heavy 80lb weight and limited 10-15 mile range (and where do you recharge?) This thing can be filled back up at any gas station."
I fly rc planes... I know about this stuff... The engines that turn 30k rpm are tiny glow fuel powered engines, NOT weedeater gas engines (max of around 10k) Glow fuel runs from $15 to $20 per gallon, not very cost effective! Also, the picture isn't clear enough to really show anything of the engine!
Modern two smokes run fairly clean. Oil is injected instead of mixed with the fuel in the gas tank. A well designed naturally carburated engine will expell most of the exhaust gasses. Larger 2strokes will use a supercharger to get the same effect. A 4 stroke will still be cleaner then a 2 stroke though. 2 strokes also tend to be louder as you need an unrestricted exhaust.
While two strokes are inefficient, pound for pound a 2stroke engine will be more powerfull then a 4 stroke engine (the common type). A 2 stroke cylinder has a power stroke every revolution of the crankshaft. A 4 stroke only has a power stroke every second revolution.
Grand Prix motorcycle racing until last year was all 2 stroke engines. What used to be the class of 500cc motorcycles is now the MotoGP class which allows 1000cc 4 strokes to compete with 500cc 2 strokes. Dirt bike racing is still dominated by the 2strokes, but that is changeing as manufacturers introduce new 4 strokes. From a racing technology point of few it has only been very recently that a 4 stroke engine has been able to compete with a 2 stroke engine that is half the size.
There are active groups dedicated to such vehicles. One such is the power-assist elist on yahoogroups (formerly egroups.com).
/. editors thought this particularly newsworthy.
http://www.power-assist.org/
The list has both ICE and EV partisans.
Most of the commerical and homebrew systems strike me as more clearly thought out than the "headline" design. I don't see why the
Motor Assisted Bicycles are a Good Thing[tm] ...
( unless one's Gov't has decided to destroy one's possible choices, for the benefit of their authority, OR for the benefit of their preferred lobby-groups )
... compared with many alternatives...
BUT:
MX5 Super Bike Engine seems to be the one that works best ( though I gather it requires a bit of break-in/tuning ), and unfortunately, it's a 2-stroke, and
( halfway down the page ) Honda 4-stroke 31cc Bicycle Engine, while it is a 4-stroke, it boshes one's ability to stack stuff on the rear rack...
Also, I'm told that Small Engine Care & Repair is the best book to get with 'em.
/dev/motor-assisted-bicycle(random||forum) can be found here
Messages to/for me ( in me journal )
Exactly and all for what? 23mph, 80mpg! I had a little motorbike that did 80mpg and 45mph. Why not put the effort into improving a conventional motorbike, it has room for a larger fuel tank and big silencer. Much easier route to tackle the problem. I bet if you developed this model engine mountain bike into something people would buy in volume it would end up looking like a conventional motorbike. Alternatively pedal the damn thing and get fit as well.