Chain efficiency: losses in runs?

I haven't seen anything about losses on efficiency over long runs, such as are typical on rear-wheel
drive recumbents. However, the IHPVA Web site and the journal Cycling Science might be good
resources.

I've also wondered if the bouncing mass of a long chain causes losses. That long chain is to me the
worst mechanical aspect of the recumbent design, and most of the "solutions" seem to me to be
kludgy. For example, the encasing of the chain in long guide tubes, to the various intermediate
"jockey wheel" designs, and also the two stage designs with an intermediate jack shaft.

Here's a couple of alternatives, although I have no idea how they ride. The second one, designed by
Izzy Urieli, has been through at least 5 iterations.

traylorfwd.home.mindspring.comfwd.htmlOpen ↗

ent.ohiou.edu~urieliOpen ↗ (click on "Human Powered Vehicles"😉

and the most entertaining of this ilk:

users.bigpond.comrecum.htmOpen ↗

Simon Brooke may have said:

Following on from the excellent discussion of chain efficiency, consider three recumbent bicycle
designs (and please, I'm asking about chain efficiency, not the relative merits of recumbents wrt
diamond frames).

Firstly, consider the two sets of photographs at the bottom of this page <URL:
kingcycle.co.ukHachi.htmlOpen ↗ >

The upper photographs show a bicycle (call it 'A'😉 with relatively short chain runs driving the
front wheel. The lower photographs show a bicycle (call it 'B'😉 with extremely long chain runs
driving the rear wheel by way of a jockey wheel. A third design ('C'😉, of which I can't immediately
find a good illustration, has an extremely long chain run driving the rear wheel with the chain
running through plastic tubes.

All things otherwise being comparable:

C is likely to be least efficient. Chainguides introduce substantial drag in my experience. (This is
from experience with material handling conveyor systems, where sometimes the chain must be enclosed
for dust reasons.)

B is likely to be most efficient, though in the illustrated instance, the fact that the jockey wheel
is on the transmission section of the chain will reduce that effectiveness relative to what would be
obtained with a more direct path.

A is likely to be at best equal to, and more likely worse than B.

Quoted message said:

The previous discussion considered losses only at the chainwheel and sprocket, ignoring losses
in between.

Absent a chain guide, there should be no measurable losses in between.

Quoted message said:

If these are all the losses there are, there should be no appreciable cost of design 'B' wrt
design 'A' - the transmission efficiency should be the same. (actually 'B' should be better, since
it only has one chain whereas 'A' has two).

There is reason to believe that B should be better; the total change of direction for the two
chains exceeds the total change of direction for the single chain, and the single chain's crank
sprocket is larger.

Quoted message said:

My instinct - and I've no figures to back this up - is that this probably isn't true, that waves
will tend to propagate in the relatively long unsupported spans which will interfere with the
smooth transmission of power, so that longer unsupported chains will tend to be less efficient than
shorter chains. Does anyone know of any work on this?

I have only experience with chains on conveyors to use as a guide here; on those, slack can cause
whipping that will shorten the life of the chain, but it appears to have no effect on the drag. The
length of the run is pretty much irrelevant until the sagging weight starts to become an issue.

Quoted message said:

And, as a supplementary question, in the total engineering of the bicycle, how severe are
these losses?

IMO, not severe for A and B. C is unquantifiable without testing.

Quoted message said:

If, as the previous discussion suggested, we're using of the order of 3% of the total energy input
in driving the chain, what proportion of the energy (at, say, 250w input at peak speed on a smooth
level road with no wind) what proportion of the energy is being used in overcoming rolling
resistence of the tyres, what proportion is being used in overcoming air resistance, what
proportion is being used in overcoming friction in the bearings, what proportion in things I
haven't thought of?

Can't authoritatively help you there. I can say that the distribution will depend on multiple
variables, of which speed is one. What's dominant at any given velocity would have to be determined
by testing.

I can't say that I'd want to ride either of the bikes shown in A or B, though. They strike me as
being likely to be rather unpleasant for a variety of reasons.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
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Simon Brooke said:

With design 'C' the span is supported so is relatively protected from harmonic effects, but the
chain is being dragged through the guide tube and presumably incurs frictional losses. My instinct
is that this is the least good of the three designs. Does anyone have any figures/experience on
this point?

The frictional power loss in the chain as it slides through the plastic tube can be estimated by

(1) Ploss = mu*f*N*l*rho

where

mu = coefficient of friction, steel and plastic ~= 0.15 f = pedaling frequency ~= 90*rpm N =
number of teeth in chainwheel = 53 l = length of tube ~= 3 feet [guess] rho = weight per link
~= (2.7 gmf)

This gives

Ploss = 0.3 W

which is small compared to the total chain loss for a reasonable output power.

Joe Riel

My guess is most of the friction in a chain is due to the pins rotating under link tension as they
roll onto the sprocket.

Long flopping chains isn't as big a factor as two chains.

Bret Cahill

Joe Riel said:

The frictional power loss in the chain as it slides through the plastic tube can be estimated by

(1) Ploss = mu*f*N*l*rho

Forgot to mention that this assumes that the chain is essentially sliding on the bottom of the tube,
a [seemingly] reasonable estimate for the return path. If the tube is curved so that the chain is
forced against a wall, then the friction losses will be higher.

The inefficiency for a forced bend in the driving (top) section of the chain is

Ploss/Ptotal = exp(mu*theta) - 1

where

mu = coefficient of friction, steel to plastic ~= 0.15
theta = total curvature of the bend (in radians, of course)

The following table gives the inefficiency for several curvatures

theta (degrees) 5 10 15 20 25 30
inefficiency (%) 1.3 2.6 4.0 5.4 6.8 8.2

Clearly, any bend must be kept to a minimum.

Joe Riel

Tim McNamara said:

I haven't seen anything about losses on efficiency over long runs, such as are typical on
rear-wheel drive recumbents. However, the IHPVA Web site and the journal Cycling Science might be
good resources.

I've also wondered if the bouncing mass of a long chain causes losses. That long chain is to me
the worst mechanical aspect of the recumbent design, and most of the "solutions" seem to me to be
kludgy. For example, the encasing of the chain in long guide tubes, to the various intermediate
"jockey wheel" designs, and also the two stage designs with an intermediate jack shaft.

Here's a couple of alternatives, although I have no idea how they ride. The second one, designed
by Izzy Urieli, has been through at least 5 iterations.

traylorfwd.home.mindspring.comfwd.htmlOpen ↗

ent.ohiou.edu~urieliOpen ↗ (click on "Human Powered Vehicles"😉

and the most entertaining of this ilk:

users.bigpond.comrecum.htmOpen ↗

H'mmmm....

Has anyone here actually tried to ride one of these 'steer with the feet designs? You certainly get
a short chain run, but....

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; of 90+ years of protection, but a cure for cancer, only 14? -- user 'Tackhead', in /.
discussion of copyright law, 22/05/02

Joe Riel said:

Joe Riel said:

The frictional power loss in the chain as it slides through the plastic tube can be estimated by

(1) Ploss = mu*f*N*l*rho

Forgot to mention that this assumes that the chain is essentially sliding on the bottom of the
tube, a [seemingly] reasonable estimate for the return path. If the tube is curved so that the
chain is forced against a wall, then the friction losses will be higher.

The inefficiency for a forced bend in the driving (top) section of the chain is

Ploss/Ptotal = exp(mu*theta) - 1

where

mu = coefficient of friction, steel to plastic ~= 0.15
theta = total curvature of the bend (in radians, of course)

The following table gives the inefficiency for several curvatures

theta (degrees) 5 10 15 20 25 30
inefficiency (%) 1.3 2.6 4.0 5.4 6.8 8.2

Clearly, any bend must be kept to a minimum.

Thanks, that's helpful.

--
[email hidden] (Simon Brooke) jasmine.org.uk~simonOpen ↗

;; of 90+ years of protection, but a cure for cancer, only 14? -- user 'Tackhead', in /.
discussion of copyright law, 22/05/02

Werehatrack said:

C is likely to be least efficient. Chainguides introduce substantial drag in my experience. (This
is from experience with material handling conveyor systems, where sometimes the chain must be
enclosed for dust reasons.)

Hey, I just got an idea: if the majority of the energy loss in a chain is where it has to bend
around a gear, then...

...how about idlers to keep the chain from bouncing, rather than a tube/chainguide? These should
introduce relatively little energy loss, according to the threads that we've had about chains on
here lately.

--
Rick Onanian

Rick Onanian may have said:

Werehatrack said:

C is likely to be least efficient. Chainguides introduce substantial drag in my experience. (This
is from experience with material handling conveyor systems, where sometimes the chain must be
enclosed for dust reasons.)

Hey, I just got an idea: if the majority of the energy loss in a chain is where it has to bend
around a gear, then...

...how about idlers to keep the chain from bouncing, rather than a tube/chainguide? These should
introduce relatively little energy loss, according to the threads that we've had about chains on
here lately.

If the system didn't need a fully enclosed chain, that's usually what I saw done on conveyors.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy.

Quoted post said:

Originally posted by Tim McNamara
I haven't seen anything about losses on efficiency over long runs, such as are typical on rear-wheel
drive recumbents. However, the IHPVA Web site and the journal Cycling Science might be good
resources.

I've also wondered if the bouncing mass of a long chain causes losses. That long chain is to me the
worst mechanical aspect of the recumbent design, and most of the "solutions" seem to me to be
kludgy. For example, the encasing of the chain in long guide tubes, to the various intermediate
"jockey wheel" designs, and also the two stage designs with an intermediate jack shaft.

Here's a couple of alternatives, although I have no idea how they ride. The second one, designed by
Izzy Urieli, has been through at least 5 iterations.

traylorfwd.home.mindspring.comfwd.htmlOpen ↗

ent.ohiou.edu~urieliOpen ↗ (click on "Human Powered Vehicles"😉

and the most entertaining of this ilk:

users.bigpond.comrecum.htmOpen ↗

Those are ridable fwd bents.

Big weight savings with the fwd bents and you avoid the losses with the extra chain bends. Eliminating bends helps efficiencies as well.

Traynor’s fwd device works well and he attributes a big portion of it to getting the trail and rake correct. See Tom’s main page for awd back to back tandems, fwd aluminum and carbon fiber monocoque competition bikes, sailbikes, bike inspired boats.

Another site is Frankenbike: http://home.comcast.net/~r.desmarais

The feet can assist in the steering with Traynor’s and Desmarais’ designs, but not steer alone. Steering is slower but adjustable.

One swinging pedal boom fwd builder I communicated with had trouble swinging the mass associated with that subframe for balancing the bike, but he modified an existing 2 wheeler.
Other’s have tried keeping the pedals and crank proximate to in-line with the steerer tube so you don’t have a big polar moment of inertia: http://web.uct.ac.za/depts/psychology/bok/fwd.html
I notice the grasshopper 5F has turned the fork around apparently for this reason.

Another homebuilder can actually steer hands with his feet with one of these designs that keeps the pedals proximate the steerer/head tube.

I’ve been gathering parts for recumbent conversions of a folder and an electric scooter with smaller 16” and 12” tires. Izzy’s two grasshopper 5 models are the two closest bikes to my conversions I have seen.

I didn't want the losses associated with routing the chain like the Scooby bike (my electric scooter uses that same frame).

http://www.homestead.com/feetfirst/BikeStuff.html