Maximal Drive Chain Speed

Take a look at this. It may change your mind.

Mechanical Design Handbook: Standard roller chain drive design

So, you've got 2 chains in the design? The first is driven by a 9 tooth sprocket and it drives a 35 tooth sprocket -- this must be the one you are concerned about, right?

How many rollers does this first chain have? Let's say, for convenience, it has 80 rollers. (I figure you need 4 rollers to engage the 9 tooth sprocket, maybe 22 to engage the 35 tooth sprocket and at least 27 rollers on the sides feeding the sprockets; that gives a minimum of 80 rollers.)

If the drive sprocket with 9 teeth is spinning at 7000 rpm, then the chain is completing (9/80)*7000 = 787.5 rpm. That may still be too fast, but it's slower than 7000 rpm.

Uhm, you might want to look over that website on roller chain design, then rethink your math.

?? I guess you're saying I missed something obvious, but I looked and it didn't smack me in the face. What are you referring to?

"If the drive sprocket with 9 teeth is spinning at 7000 rpm, then the chain is completing (9/80)*7000 = 787.5 rpm."

The "chain rpm" isn't relevant to the question. Doesn't matter if the chain is 80 links or 800 links, the ratio between the drive and driven sprockets is what governs the final speed.

Of course, the chain's length and pitch is important in other factors of the design.

Tsubaki is another good source for engineering information.

I don't have a quibble with your comments, per se. But what you are complaining to me about is not what I was responding to. My response was to the OP's statement:

"...an engineer told me that probably this speed of 7000 rpm, might be far too fast for the chain!"

I simply pointed out that the chain was probably not turning at 7000 rpm. (Based on the overall phrasing of his problem, I inferred that he thought it was).

"I simply pointed out that the chain was probably not turning at 7000 rpm. (Based on the overall phrasing of his problem, I inferred that he thought it was)."

Okay.

IMHO, the engineer was likely concerned that the sprocket speed of 7000 rpm would exceed the chain's recommended linear velocity.

Maybe some tips here...

http://www.youtube.com/watch?v=bW8nAvOSntM&feature=related

7000 RPM has to be the wide open throttle (WOT) speed. You said you don't intend to run it flat out constantly? Can't you use the throttle mechanism to get desired assistance from the engine?

Here are some motorcycle rpm. The rpm you propose to use should not be a problem if you acquire the proper type chain.

1. Honda CBR250RR: 19,000 rpm
2. Yamaha FZR250: 18,500 rpm
3. Yamaha YZF-R6: 16,200 rpm
4. Honda RVF400: 14,500 rpm (With HRC ECU 15,500 rpm)
5. BMW S1000RR : 14,200 rpm
6. Honda CBR 600F-P: 14,000 rpm
7. Kawasaki ER-5 : 10,500 rpm
8. Bajaj Pulsar 220F : 10,500 rpm

The rpm's you indicated are engine, not output.These are reduced through the gearbox and do not directly drive the chain.

Most engines high gear ratio close to 1:1. The Honda CBR250RR is 1:1.035.

that ignores the primary drive ratio of just under 3:1

http://www.cbr250rr.com.au/articles/specifications-for-the-honda-cbr250rr.html

a googlification on the topic, drill down and read a few of these, ideas will come...

adding motors to bikes

Perhaps you should consider belt drive instead.With a centrifugal clutch.Previous posters are correct, that is maximum speed.Your throttle will control it to a sane speed.You will find the centrifugal clutch is very helpful.Muti-shaft gearing will still be required, but it is much safer for your application.Belt drive to a chain drive output shaft , using similar ratios.A gearbox would really be better. Have you calculated the speed of your bike with rear wheel turning 70 rpm?

A 20 inch tire has a circumference of 62.82 inches, or roughly 5 feet per revolution is about 4 mph at 70 rpm..A fast walking speed.It will have a lot of torque, if you want to pull stumps or something, or pull a trailer up a hill, but kind of slow in my opinion, but I don't know your intended use.A typical bicycle runs at a relaxed speed of about 8 --10 mph.So you could reduce your final ratio to 1/50 if you wanted to.Also, you mention assisting with pedals, so you will need an over ride clutch to allow this.

Good luck!

GA. Bubba beat me to it. Running a small radius drive wheel against the tyre gives you a huge reduction ratio.

That's the way to do it!!

GA

Why not totally change the question. RESTATED- you want to use an engine to assist you operating a bicycle.

Why don't you use the engine shaft output (through a gear-reduction drive) to drive a small diameter, smooth cylinder that rests (or is pushed onto) the top of your front tire? Your ratio would be the circumference of the cylinder to the circumference of the tire.

At a 26-inch wheel, assuming a medium width tire, the outside diameter would be about 29 inches, so the circumference would be about 91 inches. A 1/2" diameter cylinder would have a circumference of 1.6 inches. Ratio = 57. Using a 3:1 gear ratio connection, the NET would be a ratio of 171.

At 50% engine speed, the wheel would travel (7000 / 2) / 171 = 20.5 RPM. 20.5 RPM x 91 inches = 1866 inches per minute, or 21.2 MPH.

IF YOU HAD THE GUTS, AND CORRESPONDING DEPTH OF STUPIDITY, YOU COULD RUN THE ENGINE FLAT OUT AND ACHIEVE SOMEWHERE NEAR 42 MPH. Probably not enough to get yourself killed, but close.

At "near idle"- likely around 1200 RPM, you would cruise at about 7 MPH.

Just a thought, but a lot easier to install (and I think safer) than chain drive.

I can't use the friction drive, because I don't need speed, I want to use the mountain bike abilities, to bike up steep slopes that 30 years ago I could bike only with my muscles and fitness!

azi

If that is your focus- use a similar "simple" gear reduction and drive the chain connected to your rear axle and use the multi-speed, change-on-the-fly derailleur that comes with such a bike would very likely meet your needs for both "power" and speed- since you would have both engine speed and gearing.

...and now he tells us!!!!

DUUUUHHHHHH!

The friction drive is still the way to do it!!!!

bubba, robin, andy and I all agree.

"I can't use the friction drive, because I don't need speed, I want to use the mountain bike abilities, to bike up steep slopes that 30 years ago I could bike only with my muscles and fitness!"

If you're talking about actual mountain-bike dirt trails, then something like a friction drive may be best. The driving wheel is subject to considerable slip/stick action, so a direct drive is going to transmit extremely high shock loads between the engine/transmission and the sprocket/wheel. With lightweight bicycle components, this translates to broken parts!

Well,I introduced in a wrong way the situation.I want a speed range from 5 up to 30 km/h!{I may compromise the fastest to 25!

what is your maximum grade [incline]?

You can always throttle back.

Your car can can do 100MPH++ it doesn't mean you have to do it.

Buy a gas-gas or similar.

That (image of the trials bike) raises another issue -- Nearly all MTB trails are restricted to non-motorized vehicles (in California). If "az native" is planning to ride the modified bicycle on public lands, he may be in for an expensive citation.

If climbing steep slopes is the objective

A bobbin off the crank and straight onto the wheel is the easy way to do it and has been done a lot.

As recommended by others search the www, there a loads of different drive systems that have been tried.

If you drive the front wheel of the bike with an engine and pedal at the same time you will have a 2x2.

Check the Honda GX25 engine specs again. I suggest you will find that the 1HP is produced at 7,000rpm.

The engine itself will operate from an idle [I'm guessing] of about 700rpm.

Some locals around here use similar set-ups on their bicycles, by using a belt drive from a pulley of about 50mm dia [engine] driving to a larger pulley of about 150mm dia at the rear hub of the bicycle.

Sure beats worm drives etc.

Instead of augmenting the bike why not augment the rider?

Don't think that I didn't think about this!

As I became frustrated of my poor phisycal abilities due my enlarged heart, and atrial fibrilation and aging [73]!

I even came up with the idea of heart assistance pump implanting..

That's the way!

Splice a pump into an artery with some drip-less quick connects...

Scalable solution that. Could Stick on an external intercooler as well to help keep the blood cool. Vodka dosing pump there too...

About 35 years ago ,I had a nice conversation with a cardiologist about the heart and the veins, I could undestand very well what was he talking about, because the problems that he faced with the blood sistem, I faced as I worked in irrigaton in the cotton fields.

But, we had no water clotting in the pipes, instead we had sometimes fish in the pipes...

I've got clotted sewers and arteries full of marauding alligators....

phnop phan should exist crocs, not gators I think!

True.