Scooter/bike hybrid

[Dockspa1]

I don't mean to be stubborn here and I really don't mean to step on this thread but the direct relationship of two different sprockets or cogs make a big difference in torgue and speed. Can you imagins how fast you would be going if you had a 56" wheel? It would become a tractor correct? I mean what is the difference between a driven sprocket and a drive sprocket on a bicycle? Everyone knows the bigger the rear sprocket the slower and more torque the bicycle will have. I just can't fathom the difference between a chain drive and a direct drive. The more revolutions it takes to turn your wheel one time around the slower the vehicle. Look at an old cogged bench press, it goes a lot slower than the handle but it definatly has more torque.
I guess, I'm just stuck on stupid if I'm wrong.
Doc

 

[capturedbyrobots]

Just think of the drive roller rolling on the ground.
That's how fast you're moving. Period.

When you're messing with chains and sprockets
you have 3 factors, and you need the 3 to vary torque and speed.
You need:
1. tire size
2. front sprocket
3. back sprocket

With just spindle and tire, you don't have those 3 variables

 

[Dockspa1]

What if your sprocket was as big as your tire and there were no chain, just direct gearing? Same thing. You have a tractor. If you go back to the site pointed out earlier you can see that the little wheel touching the larger wheel makes the little wheel spin 2.5 times faster thus, loosing the speed on the larger. I guess what you are saying is even if it was a 20' wheel and a 1" driver it would still be going the same speed. Is this correct? Ok, what if you had a 14" driver and a 7" wheel does that mean that the wheel will be going twice as fast as the driver? Yes, it would.
Maybe I should start a different thread. Sorry. http://www.howstuffworks.com/gears.htm
Doc

 

[Caithness]

Capturedbyrobots has it right. I have a hard tire Goped scooter with a 6" hard rubber wheel. Before I blew up my old engine I ran a .750 spindle and the thing would do a little over 30 MPH. If you plug those numbers into this calculator you see the engine was running around 15000 rpm. Notice that wheel diameter doesn't factor into the equation, just spindle size and RPM. Using this other calculator if you plug in the speed (30 MPH) and the wheel and tire diameter (4" + 2" to make up 6") you see the wheel RPM is around 630 rpm. If you try a 26" wheel plus 2" of tire, the wheel RPM goes all the way down to 44 RPM but you're still doing the same speed and the spindle is still "scrubbing" over the same distance on the tire. The smaller wheel simply spun a lot faster and the spindle spun fully around it many more times than it would on the 26" wheel, which is why the little 6" rubber tires heated up and got squirrelly and I had to buy a beadlock rim to stabilize it.

Neat build, by the way. I followed this build over from the Gopednation DIY forum and it's inspired me to build a similar conversion. I'm going to weld up a mount out of some scrap steel and bolt an old 1.2 HP 22.5cc engine to an old Mongoose MTB with a direct spindle drive using a standard .625 knurled spindle. I hope to commute to university and back, about 4 miles each way, and I'm shooting for only 17-19 MPH top speed. I used to pedal myself back and forth at an 18 MPH average and because of traffic and parking I got there faster than I can drive there. Unfortunately I had to give it up because I got tired of arriving at class drenched in sweat. Now I'm inspired to go out and have some fun with this little project, and save some serious cash on parking permits and gas. I'm hoping for 75-100 MPG, a heck of a lot better than my car's 15 MPG average when we're looking at $4 a gallon gas this summer.

This is a neat forum you guys have going here. When I get around to building the bike I'll take some pictures and post a build thread. Capturedbyrobots- Remember that imitation is flattery; I'm going to copy several of your ideas, especially the hardware store tensioning system. Mine will just be a whole lot uglier version since I'm a real function over form kinda guy.

 

[azbill]

nice post caithness
could you go and introduce yourself, so we can say HI !

 

[capturedbyrobots]

Super!
Feel free, as I don't have any patents on anything...

Can't wait to see it.

Are you going to lock it up outside at school?
I would be careful, as locked up motorized bicycles can attract
unwanted attention by thieves...

 

[Caithness]

USF (the university I attend) has a real problem with bike theft, but it's the people who keep their bikes on campus on a permanent basis who are usually victimized. Locking a bike outside a class in a high traffic area, in the middle of the day, I would be very surprised if it was gone when I came out an hour later. Leaving it overnight would be a bad idea. I had a $20 pawn shop bike I used to shuttle from commuter parking to classes a few years back. I left it locked to a pole for a few days over holiday, and when I came back it was gone. The lock they destroyed to steal it was worth more than the bike.

More than anything I'm worried about acts of casual vandalism by bored passers-by poking and prodding at fuel lines, controls, etc. and I'm considering making a cover for the engine to protect it from both people and the elements. However, the amount of money into this bike is going to be very small, since I'm getting the engine from a friend for free, my father (the master of finding and salvaging neat stuff) actually found the bicycle in a mangrove swamp several years ago, and I already have the scrap steel and spare Goped parts sitting around. Plus, it should be ugly enough to deter most would-be thieves in the first place if it follows the pattern set by other projects in my past.

 

[Alaskavan]

Caithness, you might want to look at this thread:
http://www.motoredbikes.com/showthread.php?t=5568&highlight=Milk+crate

 

[capturedbyrobots]

Ha!
Do you mean USF in San Francisco?
I live like 4 blocks from there...

If I was leaving my bike out chained up,
I would build a cage around the motor with lock nuts
or special unusual fittings.

I use a brute lock that is super thick, and it rules.

 

[azbill]

look at his info...he's in florida