Monday, July 5, 2010

modified mark I 'stretch model' SWB. gear hubs.

D - am on a Mac so don't have access to simple Paint program.
I miss my PC.

Will post pic later.
Was doodling at work with my idea for a short wheel base recumbent.
See 'Mark I'.
Basically a simplified DIY cheap Flevobike GreenMachine knockoff.
With chain to rear tire inside the bike frame itself.
That means gear hubs.

I was looking at the Nuvinci and Imotion 9.
The latest Nuvinci N360 has an impressive 360% range versus the IM9's 340%.
But Nuvinci has always been evasive about efficiency.
And even at 30% lighter, it is still POUNDS heavier than the IM9.
Not sure if the gee-whiz factor could be worth it.

But while looking, I found reference to a new mid-level gear hub, the Alfine 11-gear!
D - I fear we are dealing with 'vapourware' right now.
The gear range doesn't add up, for example.

The numbers don’t add up! The original article says the 11-speed hub has a range of 409% with two 17% jumps and eight 13% jumps. Doing the math, 11 gears and those jumps is only 363.9%.

I played around with the numbers in a spreadsheet, and I had to increase the jumps quite a bit to get to 409%. I ended up with two 20% jumps and eight 14% jumps resulting in 410.7%.

The challenge with gearing for my bent bike layout is
1) must be gear hubs
2) should be cheap and light
3) must have good granny gear for going uphill with the extra weight but
4) can use a very high 'gear inch' at the other end to use the low drag to go fast downhill!
On top of that, ideally the gear hub most efficient 'direct drive' would be in the typical all-day cruising speed for a touring bike.
The Rohloff hub does as much as one hub can do, but is very expensive. It will be lighter than trying to pair a mid-range hub to a Schlumph bottom bracket drive, and likely more efficient.

I have sent an e-mail query to Schlumph about whether their highspeed and hyperspeed x1.65 and x2.5 models have different efficiency.
After all, at x2.5 for their Hyperspeed model, if that is the same efficiency, then I might as well just get the cheaper IM9 hub to go with it.

I thought about it and think the NuVinci only makes sense if silent cycling is a priority.
if so, then I would also pair it with a chainless belted drive.
I talked to the maintenance guys at work and they directed me to Canada Bearings in Kitchener for good industrial belts.
Since a belt would not be the correct length, I would need to use my adjustable frame geometry proposal (see earlier blog).

E.g IM9 340% range x 2.5 SHD. With 18" granny gear base, good range.
E.g. Alfine 11 408% range x 1.65 SH. With " ", good range.
The price ranges from 8-900 bux, circa.
The bike can get by without the Schlumph until I can afford it.
I can tweak the chainring/cog arrangement a bit to make up for it.
STRETCH SWB 'bent bike.

I am not sure why nobody has proposed this. It is not much of a stretch from current designs.
I suggest
1) begin with a standard SWB layout, much like a Bachetta/Greenmachine.
2) extend the rear portion behind the rider's seat.
This is much like an upright cargo bike.
If we begin with a typical 48" wheelbase, adding 12" results in a 60" wheelbase.
This is much like a typical long wheelbase recumbent.
So why bother, you ask?
Drag profile. Fairing design.
I'd like to point out I'm designing the Mark I for crossing canada on.
That means steady mid-speed all-day biking.
It must be a practical road design. It can be plenty stable and not too nimble- like a long wheelbase is good at.
It needs to be resistant to crosswind and 'truck suck'.
It needs some limited offroad capability, primarily the ability to handle some gravel on a road shoulder and some dirt trails.
It needs to carry quite a lot of cargo.

Most recumbents just try to tack cargo on wherever it will fit as an afterthought.
I imagine a dedicated trailer could also make sense. One with a teardrop fairing shape.
I am thinking of what is basically a highracer design. I'll never use a lowracer since the lack of see-and-be-seen with traffic scares the living heck out of me!
So all the cross-section for air resistance is basically above the tires.
So the fairing needs to be above the tires.
The only cross-wind fairing part will be very near the ground - the tires and the lower bike frame. That is it. There is little wind near the ground, plus this will not leverage the bike sideways to make it tilt.
There is NO fairing whatsoever above tire level on the sides.
There IS a fairing top and bottom along the whole length.
Lyrcra can be used to variably improve drag profile on the sides, where there is no fairing.
I am thinking of a coupla spandex bits to simulate a nose cone and tail box, with the option for more in the middle.
Cooling issues require a vent of some variety or tilting fairing that can send more air flow onto the cyclist.

I had initially considered a mesh-seat-back only and solid bottom seat.
But a dedicated touring bike is not a commuting bike.
Mostly I'll be reclined and pedalling, not traffic stop-and-go.
Plus I don't like having a sweaty ASS. Eww.
So now I'm thinking of a one-piece mesh bucket seat.
The suspension - a thudbuster of sorts- I'm proposing isolates the rider from the frame.
Combined with front fork suspension, this mimics a full suspension bike.
Though on bumpy ground, the frame weight will make it catch more air than a full suspension bike would get.
Plus road vibrations disrupting laminar air flow on the fairing is a very real consideration.
Using elastomer shock mounts where the fairing attaches should address this and more cheaply than Pantour wheel hubs.

(I have some space shuttle shock absorbing material lying around from a custom ballistic vest I designed. It was used in orthopedic shoe pads. Not cheap!)

The bottom fairing does have some lycra where the legs must come down.

OK, imagine a SWB bent bike from the top.
You have c. 2/3 width at the pedals.
The shoulders are the widest part. This also means the steering hands are widest.
With a USS steering arrangement, this means that lower down, the fairing must still be wide forward of the torso.
Behind the cyclist we have cargo storage. In my case I will likely use Alice pack or thereabouts as the seat back.
I just take it with me when I get off the bike.
The pack is somewhat narrower than shoulders, as wide as the legs.
Behind that, we continue the gradual taper of width with whatever we wanna attach to a bike rack.
I was thinking I'd like to weld a .50cal ammo box the the bike rack for some sort of secure weather-resistant storage.
This leaves the sides open in theory for either folding baskets or panniers.
With the fabric removed from the alice pack (which needs mesh now to support the back), the seat back can recline as far as the
ammo pack, which it then rests upon at a severe tilt.
If we allow a pivoting fairing arrangement, the fairing can be lowered along with the cyclist.
This has no practical use on a road tour.
It would be strictly be of use to show just how damn fast this thing can go on a track or downhill.
Taken to the logical extreme, this feature in the Mark II III IV and V designs, along with a fold-down seat and steering, allows the fairing to be fully closed like a clamshell. This renders the bike theft-resistant and weather-proof.

OK, so now you should see the benefit of a SWB 'stretch' layout.
Even without a partial fairing, it allows for a lot of cargo storage with a surprisingly good drag profile.
Combined with a partial fairing, the drag profile should be brilliant. For a partial fairing.
I have no interest in a full fairing, other than the adjustable clamshell design I just described above.

I suspect I could tweak the steering properties for around-town commuting by adjusting the front fork angle.
Or incorporating some sort of variable steering I am still trying to figure out.

Presently, I am concerned that the whole bike frame is off centre and weighted to the right.
Using a thicker strut on the left with all the cabling in it would offset this.

I have some ideas about embedding a 12V light electric motor assist/ generator (dynamo ish) in the frame to power consumer electronics on road tours.


No comments: