Hubs in other applications

[capner2112]

At my school, Kalamazoo Valley Community College, they have a wind sail they made and have been debating the best way to transfer the power from the sail to the generator. It is a low RPM application at under 100 RPM. Currently they use a 10sp cassette and derailleur but there are problems. Mainly is it in a smaller space and shorter chain allowing only three gears to be used. They also want to use a belt over a chain for better efficiency, but common industrial pulley's don't work for this.

I suggested using an internal geared hub with three or more speeds. I also looked into the belt-drive system by Gates (are there other bike belt manufacturers?) but it's very costly.

Any other ideas are welcome for this. It's a long-term project so I can't say when or if it will be implemented.

[DaveM]

There's a few real engineers on this list so hopefully they'll have some good input. But I can tell you this:
- internal geared hubs are a little less efficient than external gear systems (5%-10% ?) So, good idea, but it would set you back a little right away.
- Again, I'm not an engineer, but I'm not so sure belts are inherently more efficient than chains. I think it depends on the belt/pulley interface design.

What might help is if you could tell us what kind of gear ratio range you need. There are internal gear hubs with pretty wide ranges. If the range is critical, it might be worth the small efficiency loss. Also, what is it about the small space that limits how many gears you can use on the current set up? Are the two chainrings so close that you get an unacceptable chain angle? Note that a steep angle on the chain is also going to introduce some drag which might point you back to going IGH anyway.

[capner2112]

Thanks Dave for the reply. Yes, according to industrial standards belts have higher efficiency (98% minimum) compared to chains (around 95%). The spacing issue is exactly as you describe with a poor chain angle because of distance between centers. I'm not sure about going hybrid with an IGH considering the spacing for more moving parts (i.e. multiple shifters).

The generator itself can be cranked by hand and at higher RPM's around 60 it produces a lot of drag hence where gearing comes in handy. I'll dig for some more specifics on the ratios from sail to generator.

The Gates belt system we found wouldn't work because it is a unique pulley/belt combination and belts are only produced in cycling lengths.

[DaveM]

Interesting. From what I can find, it looks like IGHs are about 2-5% less efficient than derailleur systems. But the most recent data I can find (http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf) is over 10 years old. My understanding is that the newer IGH hubs are better on efficiency, though I can't find any data on that. I'd be surprised if they would give you any hard data, but I wonder if you contacted Shimano, Sturmey Archer, and SRAM if they might give you some better guidance.

That all said, if you're running a derailleur system with steep chain angles, I bet you're losing a couple % right there. So a system with a straight chain line might be better regardless.

Seems like it would be fairly straight forward to weld a belt pulley onto the toothed cog on an IGH. I assume there's an industrial belt system that will be cheap, efficient, and could be retrofitted.

What kind of loads will be on the system when it shifts? IGH's are pretty tough, but no bike system is made to handle high torque loads, especially during shifts.

[capner2112]

Thanks for that document. This will be very valuable information, though slightly outdated.

I never thought of welding a timing cog to an IGH or something along those lines (we have a machine shop and plenty of skilled students/faculty). Here's an article with the schematic of the turbine: http://photos.mlive.com/kalamazoogazette/2010/09/kvcc_wind_turbine_project_1.html

Most of the torque is smooth considering the sail design. All parts are stationary (besides the sail) so loads are axial. The most torque in theory is at the beginning of motion and when the generator hits that "sweet" spot. Some fine calculations can probably maintain an adequate gear ratio from sail to generator reducing the drag on high spindle output. What the actual torque measurements come out to I do not know.

The sails are dismantled right now for work so it's a prime time to discuss all of this stuff.

[DaveM]

Even built your own generator! Aren't you industrious! Looks like a very cool project.
I've nothing to base this on, but just looking at the size of your sails, I'm guessing this thing puts out a lot more power than bike parts are really designed for. It's rare a human can put out more than a few hundred watts of power for any sustained period. I suspect you'll burn up a bicycle transmission fairly quick. (That said, you have been running the chain so maybe I'm off base)

Maybe what you should be looking at is a motorcycle or scooter transmission. Probably not as efficient, but a lot more durable.

[DaveM]

Even built your own generator! Aren't you industrious! Looks like a very cool project.
I've nothing to base this on, but just looking at the size of your sails, I'm guessing this thing puts out a lot more power than bike parts are really designed for. It's rare a human can put out more than a few hundred watts of power for any sustained period. I suspect you'll burn up a bicycle transmission fairly quick. (That said, you have been running the chain so maybe I'm off base)

Maybe what you should be looking at is a motorcycle or scooter transmission. Probably not as efficient, but a lot more durable.

[nfmisso]

(11-09-2011, 02:17 PM)capner2112 Wrote:  At my school, Kalamazoo Valley Community College, they have a wind sail they made and have been debating the best way to transfer the power from the sail to the generator. It is a low RPM application at under 100 RPM. Currently they use a 10sp cassette and derailleur but there are problems. Mainly is it in a smaller space and shorter chain allowing only three gears to be used. They also want to use a belt over a chain for better efficiency, but common industrial pulley's don't work for this.

I suggested using an internal geared hub with three or more speeds. I also looked into the belt-drive system by Gates (are there other bike belt manufacturers?) but it's very costly.

Any other ideas are welcome for this. It's a long-term project so I can't say when or if it will be implemented.

As a Mechanical Design Engineer specializing in Product Design, with a great deal of HDD spindle motor experience; I have to ask the question: why not direct drive?

If you are designing and building the generator; attach the rotor directly to the spindle of the turbine. This would save the cost and efficiency lose of the transmission.

[capner2112]

Nigel- The primary reason not going with direct drive is because of radial loads on the shaft from wind gusts. Also, using a variable gear drive allows for more efficient options of power transfer considering the sail is low RPM.