Utilizing the derailleur gear system?

[heathyoung]

And to keep people from reinventing the wheel, so to speak.

I think its a great idea, but no 4 stroke support - yet.

 

[duivendyk]

I think it would make sense to figure out the complete gearing on this arrangement, including any internal reduction in the engine itself,before jumping off the deep end and first come up with a paper design to achieve an overall reduction from crank to rear wheel (wheel size?),including of course the derailleur.

 

[86BG]

How would you suggest finding out the internal gearing? I suspect if there's any gear reduction its in the wet bath clutch housing, or at least that's what it looks like. I don't even know what type of oil to put into it once I drain it. Gear oil? makes sense.

I doubt there was any gearing adustments made internally, because the wheels on the scooter were so small that it wasn't needed. I still have the original tires and sprocket if that's of any importance.

 

[86BG]

Ok, so here's the math I used to get where I'm at now. Hopefully someone can take the uncertainty out of this so I can stop stressing it.



At the lowest gear setting the front and rear gears on the bike are 1:1 so those aren't included in the diagram or the math, and a 30t 35 pitch sprocket is nearly the size of those gears, so it's not worth complicating the math with them, so let's just assume it is 1:1 from the end of the diagram out.

I use:
http://www.diygokarts.com/speed-calculator.html

31t / 11t is 2.72 ratio, and this ratio drop happens twice, so you add the 2 ratios together and you get 5.42. Since the shaft on the bicycle crank will be spinning 5.42 times slower you take the expected shift RPM and divided it by this number.

6000RPM / 5.42 = 1107RPM

Enter the tire size of 24 into the calculator, the RPM of 1107 , the axle sprocket size of 5.42 and the clutch sprocket size of 1.42. The calculator basically makes a ratio of these two numbers, so it makes it easier to just give it the ratio here.

Hit convert and you get 13 MPH top speed in first gear.

I don't trust my math though.

I believe that a 1 way drive sprocket like this would allow me to attach pedals and turn it back into a pedal bike.

http://surpluscenter.com/item.asp?UID=2008092306301436&item=1-1594-A&catname=

or am I visualizing it wrong?

 

[86BG]

forgot to attach

 

[ibdennyak]

Thanks for the link to the one way sprocket....been looking for something like that.

One thing, you multiply reduction ratios when they are in series instead of adding. Other than that fine.

 

[Pablo]

I wasn't referring to your private message kerf, but others who mention the same product and website after it's been posted in the thread 4 times already.

The jackshaft and derailleur kit is probably 10 bucks in parts or less and sells for $200. They are selling tiny sprockets on their site for 20 bucks when they sell for 1.50-3.00 everywhere else..

My turn! SurplusCenter.com

$10 bucks in parts? Hardly. Or - we wish!

The sprockets are custom made, you can't buy them elsewhere for $3 and they aren't $20 on our site.

We aren't stopping anyone from making their own system. That's for sure.

 

[86BG]

Sorry about that. It was only later that I realized the kit included cranks. The website information layout is a bit unorganized and confusing but its still my fault.

After some looking over I am a little more impressed with you guys' system. It's not half bad. I'm not anal when it comes to having as few moving parts as possible so I can't justfiy spending 200 bucks, especially when the point of the bike is to save as much money as possible. That I AM anal about.

One thing, you multiply reduction ratios when they are in series instead of adding. Other than that fine.

So is my gear ratio wrong? What do you mean you multiply it?

 

[duivendyk]

Your calculations are wrong, to begin with, if you have two reductions in cascade you multiply the two to get the overall reduction,so the reduction is 2.72*2.72= 7.4,.The crank will be running at 6000/7.4=811 rpm.I can't make any sense out of the rest at all,what is 1.42 and 5.42 ??,sprocket sizes?.Please explain.The way to find out if there is internal gearing is to take out the plug,rotate the crankshaft somehow and look at the output sprocket (mark a tooth).if it takes let's say 3 revolutions of the crank (check top position of piston), for one of the output,the reduction is 3 to1,is that clear?

 

[86BG]

As I mentioned earlier there's a type of wet clutch housing attached to the engine and spinning it slowly will not induce enough centrifugal forces to engage the clutch and spin the only output shaft visible.

I guess I'll just run with it. If it hits 6000 rpm at the expected speed I'm set, if not, I'll buy a new sprocket and keep the one for my go kart and buggy projects.

Thanks for the multiplication tip.