New Drive Design - Ceramicspeed Driven 1

I have been watching it for past couple months. Great idea!
It will be interesting to see how it evolves. I think it will eventually make it's way internally in the frame.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

That would be pretty awesome as long as it doesn't make maintenance/access to the drive impossible for anyone other than exclusive workshops.

Andrew H.

I used to work in the industry, it can be easily done. It's the market that drives it.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

Their pinions appear to comprise a ring of ordinary Conrad bearings, with no housings to support the outer races. Stressing a bearing race in that way usually shortens its life.

Mike Halloran
Pembroke Pines, FL, USA

Did you hear the comment about 8hrs to machine the rear sprockets? So the back cluster will only cost what, $1,000?

Keith Cress
kcress -

Oh yeah, it seems like there is loads more to do before this thing is ready. I don't think any of it is limiting feasibility yet though. I like that they don't appear to be rushing into it. I mean, I haven't found any indication that they've integrated a shifting mechanism yet, so there's a long road ahead still before this could enter the market.

I think its great they are trying something:
[ul]
[li]out of the ordinary[/li]
[li]visually appealing[/li]
[li]efficiency/performance driven[/li]
[li]just plain cool technologically if they can make it all work[/li]
[/ul]


Andrew H.

Why not dump the mechanical stuff altogether and use pedal-electric. You could have zero gears and no mechanical linkage and a whole lot more. Pedal a generator and feed the traction motor directly. It would even remove all the bike frame linkage geometry constraints from variable geometry bikes with suspension.


Keith Cress
kcress -

itsmoked, the average rider can only produce about 1/4 hp for any length of time. This means efficiency is vital, and a generator/motor combination can't match the efficiency of a chain drive.



My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

itsmoked,

Unless you have an electric motor that is powerful and efficient throughout its speed range, you need gears.

--
JHG

I'm a cyclist. I do it for fun and exercise. For me personally, I would never ride a electric bike unless I went on vacation somewhere and rented one and all they had were electric bikes.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

ctopher, wouldn't it be a lot more exercise to use the generator to run an electric motor than it would by a direct mechanical linkage?

And wouldn't it be more fun to use a high tech solution as a means to a simple end for the pure joy of getting to explain it to people who don't understand it at every opportunity?



Andrew H.

ACtrafficengr said:

generator/motor combination can't match the efficiency of a chain drive.

Click to expand...

Not sure that's true anymore. Motors and modern drives run in the upper 90% ranges. What's a bunch of chain and gears efficiency?

drawoh said:

Unless you have an electric motor that is powerful and efficient throughout its speed range, you need gears.

Click to expand...

Definitely not true anymore. I'm talking about a system that's like a diesel-electric locomotive. They store nothing and they start standing-still trains weighing 20,000 tons and bring them up to 90MPH while not shifting a single gear.

Now if you add a single scuddy little battery (18650) you could store braking energy and get it back when pulling away from that $%^@&* stop sign.

Keith Cress
kcress -

So, if your generator is similar, 90% system efficiency should be possible. Interesting.

I found this:

On the efficiency of bicycle chain drives said:

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf[/URL]]
Experimental results indicated that the efficiency of the chain drive varied as a function of chain tension. It was found that the efficiency varied linearly with the reciprocal of the average chain tension with the highest efficiencies occurring at high chain tensions and lowest at low chain tensions. For example, the highest efficiency measured in the study, 98.6%, was measured at a chain tension of 305 N and the lowest, 80.9%, at 76.2 N.

Click to expand...

I'd always heard the 98.6% efficiency result, and never heard the 80.9% figure. It's also interesting to hear that chainline tension has such a big effect. I would have thought chainring/sprocket offset, sprocket size and lubrication would have been bigger.

So your idea could be competitive. For someone that just wants a reliable bike without fiddly shifters and greasy chains, it might be tempting. If you used a variable speed drive so the rider could maintain a cadence of 80-100 rpm, how would that affect the efficiency?

My glass has a v/c ratio of 0.5

Maybe the tyranny of Murphy is the penalty for hubris. -

MotoLuber,
I prefer the old style crank/chain method. I get more exercise using my own muscles powering the bike. I average 40 miles per ride, average 20 mph.

Chris, CSWP
SolidWorks '17
ctophers home
SolidWorks Legion

AC; That's an interesting bit about chain drive eff. I wouldn't have thought it was that high, though I've never really sensed much heat off of a chain drive like I do off of belt drives or especially out of gear boxes. I still wonder at a bike chain drive with its diddly-squat derailleur and couple of N of tension.

Pedal rate; That would be the advantage of a wee bit of storage, you could conceivably start from a stop and immediately be pedaling at 80 rpm while the bike accelerates up using an unrelated or rather loosely related, to pedaling rate, curve. Ultimately the bike comes to whatever steady state speed the pedaling force is providing. You could have a thumb rate control that 'suggests' the speed you're after and the result is more pedaling force at the same exact pedaling speed - pedal speed kept constant. Interesting in that you could thumb up a mountain climb that on level ground ultimately results in hauling ass, whereas that's pretty hard to do with the usual setup as more force would result, on level ground, in out-of-range pedaling rpm.

Keith Cress
kcress -

itsmoked,

Perhaps the diesel electric trains are efficient while running at some planned constant speed. Do they need to be efficient while they are accelerating?

I am familiar with permanent magnet DC motors. At constant voltage, the torque curve is a straight line from the stall torque to the no-load speed. The power curve is a parabola with zero power at stall and no-load speed, and maximum power at half no-load speed. The maximum efficiency occurs at two thirds no-load speed. Motors like this perform well on drag strips because their maximum torque is at stall. They are great for accelerating.

I have not worked with AC motors.

--
JHG

drawoh; I don't believe the efficiency is greatly different in accelerating trains verses steady state trains since the engines tend to run about the same speed and that's in their power-band as compared to, say, an automobile. Trains on average including stops and starts move a ton 480 miles on a single gallon of fuel though that's mostly about steel it's still includes dishing up thousands of horsepower.

I'm not clear on specifically the motor speed verses efficiency. I suspect it stays pretty high because a motor doesn't really realize it's being run away from its design speed because the magnetic saturation is kept constant. From a 'load' perspective they do well keeping up around high %80 eff down to 25% load while rising quickly back to the 90s by 50% loading.

Keith Cress
kcress -

The Ceramicspeed drive is a nice engineering adventure and a beautifully machined system of parts. But it does not have all the goods their Youtube videos indicate or intimate. Their representative is a smooth talker and has the script well memorized and he is proud of the product and the potential. The issues I see:
1. Shifting between gears is going to be difficult or impossible at high rotation speeds - hence, why none of their videos show gear shifting. They do explain a potential method of shifting using pre-machined shift channels and software/sensor control but as complication is added so is potential failure. The slightest bend/deformation of any of the driven cogs' teeth will send this system into total chaos/failure . . . (If there is a video showing actual at-speed shifting being done - I missed it and I will eat crow on this observation )
2. The claim of their system not being limited for gear ratios is misleading. True, additional cogged teeth could be added radially (out to the limit of the wheel radius) since the thickness of the cog cluster does not increase, but the driven cog wheel is a disk and as mass is added radially, the rotational inertia of the system increases. This will have to be a stiff, wear resistant material. Aluminium won't last and with grit and contact pressure, even steel or titanium, etc. will wear. Hmmm, mass applied at increasing radii - efficiency will be affected . . .
3. The final drive bearing "sprocket" will only stay engaged to the driven cog wheel if sufficient side load is applied to prevent the drive from skipping out of engagement. The stiffness of the driven cog wheel decreases as its radius increases. Thus, the drive will be very prone to skipping as the drive is moved to the larger radius locations (lower gear). Oh, and the drive bearing sprocket has rotating bearing drivers that geometrically do not want to stay engaged in their drive "pockets" because they are intrinsically trying to roll out/off the surface of the driven tooth. Only cross load/clamp pressure of the axle bearing set can hold these faces together. As clamp pressure increases so does the mechanical loss of the system. I suspect the gear position Ceramicspeed chose to use in their videos is the best working position on the whole prototype.

I'm a gearhead so I love beautiful machines and mechanisms, so my enthusiasm was raised when I saw the original post. But I got pulled back to earth after checking it out. I ride about 160 miles per week by bicycle, year-around, rain or shine and I will harp needlessly about the simplicity, ruggedness and efficiency of the chain derailleur system used on bicycles. Generally, the chain and sprocket system on bikes can be neglected completely and it will still get you where you want to go. An abused chain and sprocket system will make noise and efficiency will be reduced but can it transmit human power to forward motion of the bicycle? Yes. Reliably? Yes. Inexpensively? Yes.

I'll keep checking on the development of this drive to see where they can take it. I am a realist and I believe a wall of technical/material capability will doom the drive - some of the comments on the Youtube videos are expecting just throwing more money at the problems will solve them - the drive can be made from Unobtainium and it will be infinitely light, infinitely stiff/wear resistant and inexpensive. If only I could get a hold of some of that great material!

Shifting looks like the death of this fascinating idea. I agree with Brian Malone that shifting is the crucial point, but for a different reason. Although I agree with what he says about it.

This rig is a brilliant idea on paper. I admire the people who thought it up. It might work flawlessly in a clean lab and achieve everything they claim, including the shifting.

But get that bike on the road and get some dirt in the drive train, especially the rear cog. That will be the real test. I predict that it will fail completely. The dirt will prevent the mechanism from shifting reliably.

Even if it doesn't, the dirt will degrade the efficiency so much that the old chain drive with derailleur would be better. I also suspect that they would have trouble keeping the dirt out of the bearings.

The only way to avoid this disaster is to enclose the entire drive drain. If they can figure out how to do that at an acceptable cost and weight, then they might have something. But I predict that they won't be able to do that either.