Probably ridiculous question about shaft drives & alternatives
 

I know I'm missing something, but after participating in this thread:

http://www.bikeforums.net/showthread.php?t=487629

I was left with the impression that the problem with shaft drives is that they lose efficiency by having to transfer energy at right angles at each end of the shaft. (Simply put.)

The advantages seem to have mostly to do with ease of maintenance, coping with difficult environmental/weather conditions, reduced failure rate, easier to deal with on commuting bikes, etc. Possibly also less vibration and a quieter bike.

Yet, the consensus seems to be that there just can't be any shaft drive that will approach the same efficiency as a chain or belt drive for bicycle drive-trains, due to the 'angle' problem.

Yesterday while channel surfing I came across an old western, a crowd scene at a rail yard. Something about it caught my eye, but I wasn't sure what.

I realized what it was this morning. To wit:

Train Wheels Rigged

Looking at this animation, why not a transmission in which the front wheel shown here is the crankarm-wheel and the back wheel is flywheel (or whatever the correct term is) driving an IGH?

Is there something inherently even less efficient about this motion, or something about it that makes it unsuitable for a two-wheeled vehicle?

I know it's probably a silly question, but I'd like to know why.

The "trainwheel" animation you show is pretty much the same motion that your leg and the crank use. The pivot mounted on the rear wheel is your ankle on the pedal and the pivot at the rear of the picture is your knee. The linkage changes nearly linear motion to circular motion in both cases.

The bar connecting the two wheels is just there to allow both wheels to share the drive load and traction. Connecting the two wheels on a bike this way is impractical since one (the front) has to be able to turn.

No, that's not what he means. I get it.

You want to have a wheel like:

(a)_(b), (-)-(b), (a)^(b), (a)-(-)

where a is the chain wheel and b is the sprocket.

In other words, you want to use the linkage shown in the animation to connect your pedals to the rear wheel.

I need to think about that, but the first off problem is that the chainstay is going to get in the way.

If I understand your idea, you'd have to attach the drive shaft to the pedals, then have another crank attached at the axle of the rear wheel to attach. Ratios could be changed by sliding the connection up and down the arms.

However, that's a really complex mechanism sticking way out the sides of the bike.

Also, never, ever read the comments on YouTube. I gotta remember that.

The chain stay is a big problem, but could be solved by a one-sided wheel mount such as currently exist in production and (more commonly) prototypes.

The locomotive drive only works if the shaft is mounted at the same radius from the axle on both the driver and driven wheels (otherwise, it would need to stretch and contract over each revolution), and it's strictly a one-for-one revolution gearing. (Moving the mount point in or out doesn't change the gearing, though it does change the loads the shaft needs to tolerate.) So you're looking at the same problem the penny-farthings had: to get the speeds cyclists want, you'll need wheels from 30 to 100 inches in diameter.

You could probably use such a shaft on a tandem to connect the two chainwheels. Reducing play in the mounting bearings would be a big engineering challenge.

Chip C
Toronto

I thought it might have something to do with the dimensions neccessary vs. the frame in terms of the rod moving up and down at each end as it's attachment points revolve. Although I hadn't pictured the connection sliding, I had pictured a fixed rod from what is normally the chainwheel connecting to a similar wheel on the rear axle (say, where the cassette is normally) and driving an IGH in the hub to determine gearing. A fixed shaft that doesn't spin but rather moves back and forth as shown in the animation above. Possibly the rod could have a pivot if neccessary (if it needs to be slightly variable in length to handle the range of motion within a certain dimension? Or even to accommodate being driven by pedals w/o interfering with the crank arms?) Again, not sure about the physics implications in terms of the directions of the forces being applied and the relative efficiency.

I hadn't thought about the mounting bearings and other practical considerations.

EDIT: Having determined that this seems to be a "reciprocating rod" arrangement (or something similar) I googled up a number of patents:
http://www.patentstorm.us/images/patents/6382043.png

So one assumes that this has been tried (at least once) and discarded.

You're right. I'm wrong about changing the ratio.

It could use an internally geared hub.

Curiously, a chain, with its many moving parts, doesn't have the issue of reducing play because it's only ever in tension.

The one-to-one issue isn't a problem -- you just use an internal gear hub. If they'd been around at the time a penny farthing could have used one too.

Ok. Now I've got my next bike project: a rolhoff on a penny farthing.

My big, ridiculous and hypothetical project is a recumbent penny farthing.

http://www.sccs.swarthmore.edu/users...mages/bike.gif

If you add an idler I don't think you need to modify the frame from the traditional diamond that supports the wheel on both sides.

You'd also need to enclose the whole thing, but I don't think that's too problematic.

I've ridden a recumbent penny farthing trike, so it's not too hard to imagine.

Yes, this exactly.
Maybe with more than one joint, if it needs to be more compact? (Again, I'm no mechanical engineer.)

Interestingly, the one in the auction lot above had it on both sides--that would seem to have something to do reducing with play from slackening/extension of the linkage by opposing the action on either side?

There must be something undesirable about this arrangement, yes?

No. I'm an idiot. My drawing can't work. With a conventional hub, if the axle is supported on both sides, then the linkage between the rear wheel and pedals or idler has to go through the axle once every rotation.

To get around this you would need to change the way rear hubs work. The shaft needs to be at the end of the axle, hence outside the chainstay. Then you use a *rotating axle* along with bearings at the dropouts. Pretty weird.

yes, you'd use the rod to drive essentially a large sprocket on a gearhub. But you'd have to find a gearhub that gave you decent ratios with 1:1 drive ratio; most of the current ones expect something like 38:13 or so.

And you wouldn't technically need to mount the wheel on one side only; the drive-side seat stay could come out far enough to clear the drive shaft; or you could engineer the drive axle to come out through the dropout, and have the whole drive system outboard.

Plus now I'm thinking that the play would be no different than what pedals need to handle, and that doesn't seem to be a big problem. So maybe this would be an effective alternative for the link between driver and stoker on a tandem. Really you could just replace both their pedals, on each side, with kind of a long running board that spanned the length of the bike; you could have as many people "pedaling" as could fit along its length, either standing or sitting on a long narrow bench.

Chip C

Just about any type of drive mechanism you can conceive has been tried, at least once, and probably prior to the year 1900.
By the turn of the 20th century, it is said, half of all patents on file in the USA were bicycle related.
I've seen pictures and drawings of everything from treadle drives, to intermediate cogs, and yes, reciprocating linkages.
There is a guy on another cycling group that keeps finding and posting all these old oddities. I find them fascinating, but I always come away thinking the best solution won out in the end. That is of course, the good old roller chain.

The notion of a multi-seat tandem with driving boards is an interesting notion. Sounds almost like a hybrid of more familiar tandem riding and crew.

I sort of figured that this would be the bottom line. But, if one is willing to make the compromises involved w/a shaft drive for the reasons mentioned above (or in the commuting thread I linked) might this kind of linkage be able to attain greater efficiency?

Oh no, maybe I'm the "guy", and I've infiltrated your forum. How about a lever driven tadpole from 1880?

http://patentpending.blogs.com/paten...0884436_pm.jpg




How about a drive shaft drive with multiple gears from 1897?




http://patentpending.blogs.com/paten...shift_bike.JPG

Ohh, nice. Do you have anything that fits the pattern mentioned above? I suppose the lever-action seem to have something kind of similar.

I also found the Alenax Transbar, but that seems to be the worst of both worlds and requires some kind of bizzare pedaling technique from hell.

That Alenax Transbar does indeed look like the bike from hell. There were a large number of lever powered bikes in the early years, because chains were notoriously weak, and a strong rider could rip a chain in two almost at will. It was not until the bush roller chain was invented by Hans Reynold that chains became bombproof. McMillans bike in the EARLY 1800s had a lever and rod drive, a la locomotive wheels.

http://patentpending.blogs.com/paten...5100925_am.jpg


My secret stash of bicycle patents is in the bicycle technology section of the Patent Pending blog, at http://patentpending.blogs.com.

That's pretty close to what I had in mind, I think. I whipped this up, but cbr was faster.

http://dev.innatech.net/locodrive.png
[Rough diagram. The red power arms are attached to drive wheels on either end of the rear axle which would be engaged by a system of gears in the IGH (in blue.) ]

Don't dare me to dig up more lever drive bikes!


http://patentpending.blogs.com/paten...machine_co.jpg

Per one bike history I have read there was one quite efficient shaft drive done in the late 1890s, the Waltham Orient as I recall. Rather than standard bevel gears it used some form of rollers for the gear teeth.

Several track speed records were set with this bike while being ridden by Major Taylor per what I read. That would indicate high efficiency it appears.

I believe the major problem with current shaft drive bikes is poor design on the shaft drive itself per posts in a recent thread here on Dynamic Bicycles shaft drive bike problems. They just do not stand up to agressive riding, even without the question of efficiency. Hub gear failures were also mentioned so they may have too low an input ratio to the gear hub.

Any member have a link to info and drawings of the roller drive bvel gear arrangement used in the Waltham Orient?

Some interesting stuff here (including mention of the Orient: )
http://books.google.com/books?id=0JJ...sult#PPA334,M1

Might anyone who owns this book please provide a scan of the diagram on p 332 blanked out by google (for all of our educational fair use, of course?)

Let's see, chain drives are;

1) Cheap
2) Easy to maintain
3) Reliable
4) Flexible re gear ratios and changes thereto
5) Easy to replace when warranted by wear
6) Lightweight
7) Easy to understand and adjust
8) Reasonably priced upgrades improve precision

Who could ask for more? Or; Don't fix what ain't broke. bk