decisions on motor bike configuration

[Fabian]

I'm sure gobsmacking torque is lots of torque.

Lots and lots and lots of torque. When doing heavy haul in low range first gear, i can feel the frame flexing; trying to fold itself in half. I have been surprised to see just how much stress can be put through an aluminium frame; would have thought that it should have visible stress cracks all through it, but no, it just keeps on trucking along.

HOW MUCH? A number, not a description. Count gear teeth, count sprocket teeth, look up prime mover peak torque - it's easy.......

My setup has the following numbers being driven by a 66cc Chinese 2-stroke bicycle engine, that has been optioned with aftermarket accessories to give it more low rpm torque. Peak power is about the same as a standard engine.

With regard to the maximum pulling power in low range first gear, my SickBikeParts optional jackshaft gearing is as follows: 9 tooth jackshaft sprocket transmitting power to a 48 tooth bottom bracket chainwheel sprocket.

Bottom bracket (low range) sprocket size to jail broken rear cassette: 24 tooth bottom bracket sprocket driving a 36 tooth cassette sprocket.

4,500 rpm works out to around 6 mph, maybe a bit less.


Top gear uses a 38 tooth large sprocket (unavailable from SickBikeParts) driving an 11 tooth rear cassette sprocket.

 

[KCvale]

preventec47 hasn't been back in 2 weeks.

 

[bigoilbob]

Fabian, big thanks for the info, and my apologies for my jerky demanding tone. I reread my last post and it came out bad.

I'm interested because the numbers behind your achievement can help us all learn from you on how to build tougher. One detail please - putting together 4500 r/m, 9 tooth jackshaft sprocket, 48 tooth chainwheel sprocket, 24 tooth bottom bracket sprocket, 36 tooth cassette sprocket, 6 m/h, and assuming a 26" powered wheel, I'm missing a ~9.4/1 gearbox reduction. Would you please provide your actual ratio, or correct my incorrect arithmetic and/or assumption of such a gearbox?

Looking forward to doing the 7th grade arithmetic to estimate your chain pulls and rear hub input torque. My guess is that your pull and torque is much more than I could provide with only my legs....

 

[Fabian]

I reread my last post and it came out bad.

It did not sound bad to me.

Would you please provide your actual ratio, or correct my incorrect arithmetic and/or assumption of such a gearbox?

It's all in this thread, but please remember that i have deleted the midrange gearing and changed the high range bottom bracket sprocket size from 36 to 38 teeth; knocking off around 300 rpm for the same max speed (that i limit myself to) in high range top gear. The drop from 5,000 rpm to 4,700 rpm yields a noticeable reduction in engine vibration:

http://www.motoredbikes.com/showthread.php?40780-Gear-Ratio-Calculations-for-the-SickBikeParts-Shift-Kit&highlight=ratio

 

[bigoilbob]

Yes, it is all there, except for your 66cc torque. I looked around unsuccessfully, so let's just guess 3.5 lb*ft. Ratio up or down if you know better. That means 3.5*4*1.7*48/9= ~127 ft*lb of twist at your 24 tooth sprocket, almost 800 lb of chain pull to your cassette, over 190 ft*lb of input hub torque, and maybe 175 lb of forward thrust, assuming a 2.065 m rolling circumference. A true trailer hauler/hill climber. I did this to show that;

1. You do indeed pull very hard. Is your chain spec'd for it? I can see why you can feel the flex. My Bikee E2/GX35 recumbent chain pulls less than 300 lb, and I have had to gird up my engine/gearbox mounting twice to accommodate it.
2. Folks should not gut out the picking of drive components based on the assumption that you will never twist harder than your legs. You are pulling harder than your legs with your build now. And per an earlier post, even if a builder found that his pull/torque was LESS motorized than non motorized, those "Goodman stresses" - the tens of thousands of repeated loads that he/she would place on his/her drive components throughout their lives - are much, much, greater than those available from human power.

Missed your old thread, and must commend you for doing your home engineering the right way. Did not see torque and pull calculations, but I probably missed them. I see lots of failure reports from builders much more talented than I, with 1 thing in common. They did not appear to have done the basic pull/torque estimates and compare them against their component specs. As an example, I'm pretty sure that you could use my treatment of your numbers to wave you off even the manliest of expensive, off road, IGH's.

Thx again.

 

[Fabian]

Is your chain spec'd for it?

I use the cheapest 9 speed chain that i can find, because wear between the most expensive (stainless steel) Wipperman chain (at around $50 on eBay) and the cheapest chain (at around $10 on eBay) measures in at only 15% extended wear life, and, has proven to give the same reliability as the top of the line product.
I have never broken a chain from tensile induced stress.

Chain life (to 100% stretch) consistently comes in at 1,000 kilometers, but it can be much less if traveling on sandy/dusty surfaces.
It's the smaller cassette sprockets (particularly the 11 tooth sprocket) that wears out way to quickly; having the chain skip over the tooth profile by 80% stretch when the engine operates through max torque.

 

[Fabian]

Most importantly i use 9 speed chain on an 8 speed cassette (using original 8 speed sprocket spacing) because it allows for greater derailleur misalignment, thereby preventing ghost shifting, when compared to a 9 speed cassette and 9 speed chain arrangement.

If you look at 9 speed chain on a 9 speed cassette, you will see that the chain rubs against the next larger adjacent gear. Even the most slight misalignment in 2nd gear will have the chain ghost shifting into top gear; bending the 1st gear sprocket in the process. The reverse happens when in top gear, especially when the derailleur has had a bit of use and the odd knock, bump and grind, having it be somewhat resistant to jumping up to 8th gear. You can overcome this by adjustment of the barrel adjuster, but then problems surface when in 2nd gear and the resultant ghost shifts to 1st gear when under power.

The width of 8 speed sprockets is identical to 9 speed sprockets; enabling 9 speed chain to be used, and thus being able to take advantage of advantageous mechanical dimensions; giving a slight gap between the outer chain face and the next larger adjacent gear.
Ghost shifts are completely eliminated when using the above mentioned combination. A side benefit of 8 speed cassettes is that they are around 50% cheaper than 9 speed cassettes, yet retain the major benefit of an 11 tooth smallest sprocket, as well as being able to substitute the 34 tooth sprocket for a 29'er 36 tooth 9 speed sprocket.

It's a "win, win, win" situation

 

[KCvale]

your legs produce way more torque than any kit available

Holly crap, I just spit my beverage up laughing out loud at that statement!

I know there was more to your post ezDave I'm not dissing you, my point is simple...

This isn't a topic about a high performance build, it's a topic for simple options of a starting point for things that work and all this foot pound torque and minimal concerns to divert attention from the point is all.

Most any decent bicycle parts will take the ~3HP most any <66c engine can do, it is all about how you operate the thing after that.

 

[bigoilbob]

KC, the first post or 2 was about choosing and using durable MB components. EZ Dave was wrong in his quoted statement, but both that statement and all this "foot pound torque" discussion is highly relevant. Your statement about "most any decent bicycle parts" might be true for middle of the road MB's, but look at Fabian's. His duty is much, greater than those "decent bicycle parts", such as cassettes are designed for. If your experience is that those components are so over designed that we don't have to check torques and such, I have to consider it, given your greater experience. But how do we explain all of the component fails reported on both fora, for MB's that pull much less hard than Fabian's? I would still like for you to back calc the torques you imposed on the NV171 hubs that shelled on you, against the then available constant duty torque spec of 48 ft*lb, 96 ft*lb max. I think it might be an eye opener.

All in the spirit of continued respect for your craftsmanship and design skills.

 

[keatonx]

Yes, it is all there, except for your 66cc torque. I looked around unsuccessfully, so let's just guess 3.5 lb*ft. Ratio up or down if you know better. That means 3.5*4*1.7*48/9= ~127 ft*lb of twist at your 24 tooth sprocket, almost 800 lb of chain pull to your cassette, over 190 ft*lb of input hub torque, and maybe 175 lb of forward thrust, assuming a 2.065 m rolling circumference. A true trailer hauler/hill climber. I did this to show that;

1. You do indeed pull very hard. Is your chain spec'd for it? I can see why you can feel the flex. My Bikee E2/GX35 recumbent chain pulls less than 300 lb, and I have had to gird up my engine/gearbox mounting twice to accommodate it.
2. Folks should not gut out the picking of drive components based on the assumption that you will never twist harder than your legs. You are pulling harder than your legs with your build now. And per an earlier post, even if a builder found that his pull/torque was LESS motorized than non motorized, those "Goodman stresses" - the tens of thousands of repeated loads that he/she would place on his/her drive components throughout their lives - are much, much, greater than those available from human power.

Missed your old thread, and must commend you for doing your home engineering the right way. Did not see torque and pull calculations, but I probably missed them. I see lots of failure reports from builders much more talented than I, with 1 thing in common. They did not appear to have done the basic pull/torque estimates and compare them against their component specs. As an example, I'm pretty sure that you could use my treatment of your numbers to wave you off even the manliest of expensive, off road, IGH's.

Thx again.

There was a post from a while back where a stock 66cc was dynoed at 2.5hp or so.
Hp=torque*rpm/5252
Stock HT maxxes out at around 5500rpm, so assuming the engine makes max power at 5000rpm or so the engine will have 2.626ft lbs of torque