Friday, September 19, 2008
Tuesday, September 16, 2008
- the 2 -wheels forward design, the delta (v.s. tadpole) is more stable.
- a full width trike generally does not play well with traffic
- a narrower leaning trike addresses this.
D: I bike to work on Waterloo Westmount-Northfield.
For c. 500 feet past University, it is as narrow as 1' before becoming a bike lane.
By placing a white line on the road edge, despite a clear curb and whatnot, it implies to traffic that
- that is where bikes go
- maybe it is wide enough for bikes
- just staying on the other side of the white lines will avoid me.
Nope. This road would be much better off with NO white line until it reaches a full bike lane width.
Why such a wide bike lane?
No surprise at all.
With a car, the mirrors stick out. Allowing another 6" of wander on both sides, that amounts to an additional 2' lane width v.s. the actual car width.
Bikes are much the same.
If I ride the curb,
- I risk the tire catching on the curb lip.
- I risk the pedal hitting the curb.
I ride a decadent (sarcasm) 1' away from the curb itself.
Deal with it.
Monday, September 15, 2008
Between classical front-wheel steering, and strictly rear-wheel steering, is a class of bikes with a pivot point somewhere between these two extremes and referred to as 'center-steering'. These design allow for simple front-wheel drive and appear to be quite stable, even ridable no-hands, as many photographs attest.
These designs usually have very lax head angles (40° to 65°) and positive or even negative trail. The builder of a bike with negative trail states that steering the bike from straight ahead forces the seat (and thus the rider) to rise slightly and this offsets the destabilizing effect of the negative trail.
D: compare to the disastrous handling of the original Flevobike.
No one who was present that day would consent to demonstrating the machine, but several people volunteered that they had seen a rider earlier in the day who displayed extended no-hands riding! I couldn’t believe it. I didn’t think it was possible to ride a recumbent without hands. At least my experience to that point hadn’t convinced me that it was possible.
So I spent half the day trying to learn to ride it, and it certainly exhibited some strange behaviors. To begin with, it just wouldn’t stay upright. The front half wants to fall over, and fall over fast. It isn’t the kind of bike that you can push along gracefully while holding the back of the seat. In fact, holding the back of the seat is a sure way to let the front half fall over and of course, that happens rather quickly. And to make matters worse, just like more conventional underseat-steering recumbents, the handlebars are a little low to be comfortably used to direct the bike when standing to the side. But in the case of the Chinkara, the handlebars don’t even provide enough leverage to counteract the front half of the bike, which seems to have a mind of its own. Such behavior made it hard to handle the bike. It wouldn’t stand up on its own. It seemed impossible to control, and this was before even trying to get on...
I thought something like the Triton Trike for steering would be desirable.
I'd be curious about a steering system with some gears to amplify the effect near the far range of motion. By that I mean:
- handles normally for minor movements
- when turned, say 45 degrees, amplifies the turn on front wheel by 1.5x
- at much more, by 2x.
I hear under-seat-steering has problems turning the wheel severely.
In a bike very sensitive to steering, maybe even reducing the wheel-turning below 1:1 in the middle would be desirable.
Steering which is speed-sensitive would be nice, but the mechanical details would be a nightmare.
D: latest Cruzbike thought.
I think an even more severe oval that exists commercially *might* be desirable.
I do wish the company website had warned against the combo of short wheelbase AND high seat height.
Like I said, I wouldn't trust the stability of mine at faster than 30kph.
I suppose that is fine for a commuter.
I finally figured out the aluminum sleeve included is to serve as a gap-filler on a stem adapter.
The spare parts for use in other kits were confusing.
Aside: I found a 135 degree angle for seat/pedal combo. It looks ideal for future models, with the pedals below seat height and a modest seat back angle.
I am also intrigued by laying in all electric lo/hi power wiring and shifter/brake cables internally on the internal-chain version.
Wednesday, September 10, 2008
D: I hope this will address an issue with my Cruzbike.
Biopace is a patented non-round chainwheel design made and licensed by Shimano. To a casual glance they resemble elliptical chainwheels, but on closer examination they turn out to be the exact opposite of the classical elliptical design. The product of extensive research and computer-aided design, Biopace chainwheels have the small radius engaged when the cranks are horizontal, the large when they are vertical. This is because the Biopace design is based on a dynamic analysis of the motion and momentum of moving cranks and legs, unlike the static, geometric analysis that produced classical ellipticals.
The theory is that during the power stroke, when the cranks are more or less horizontal, you are using the power of your legs to accelerate your feet, which get going quite fast in the lower gear provided for that part of the stroke. The momentum of your feet then carries the pedals through the "dead spot" when the cranks are near vertical. Since the rider doesn't push as hard during the power phase of the stroke, and motion is slower when the leg is changing direction, the Biopace design is gentler on the knees than even round chainwheels."
I am only used to normal bikes. I once rode a SWB recumbent.
I am totally unfamiliar with anything that feels like a mid-steering bike.
So I push too hard on the pedals, and this pulls around the steering.
With practice, I can keep my pedals smoother, or countertug on the handlebars.
But there must be an easier way!
I think there is.
An asymmetrical chain-ring should manage to smooth out this 'power crank' I do, thereby minimizing the steering demands on me.
I am not yet precisely sure what sort I should be looking for, though.
Aside: see KneeSavers for a nifty add-on to
1) prevent knee pain on a normal bike
2) minimize 'heel clip' on a SWB 'bent.
Wednesday, September 3, 2008
I measured my wheelbase. It's 43"'
That is less than Bacchetta's 47 but more than the Cruzbike Sylvio.
I think that is why the latter has only 8 gears.
If it had more, it would destabilize at high speed.
I used a kid's (?) 15"? v.s. suggested 17" frame as the basis.
I am unsure if I should try to expand my gear range.
I think it might destabilize at high speeds anyway.
In time, I'm sure I will think of the bike as 'nimble'.
Right now, it just feels unstable.
A coupla thoughts:
1) one part requires matching allen key sizes. Having 2 different ones might mean less tools are needed.
2) a modified handlebar holder can also mount the front boom. Easier, cheaper?
3) I would like to find an aftermarket seat that can be adjusted more.
We tapped out and threaded extra anchor points for the seat.
I wouldn't feel comfortable with just a coupla straps.
A tap kit would be a welome addition, or suggested supplement.
I'm having a hard time finding place on the frame to mount all my accessories.
D: I had the worst time figuring out how to put the battery in!
Push the tabs on both sides simultaneously. It's tricky.
Once the battery was in, I could not find any way to test it.
A spare cable, in case the first is cut, or a spare shorter one would be welcome.
Where I want to mount it, the extra-wide rear spring housing wants to hit it.
THIS concept, I'd like to incorporate inside a bike frame.
I'd like the bike to be structurally compromised if the alarm is bashed.
Honestly, the plastic U on the mount doesn't look so tough.
A bike has all these widgets that require power of some variety.
A horn. A light(s). Power assist. Signal? A cellphone would be nice. A siren alarm.
Point is, wiring the whole bike for power of various levels, with internal cables too, would make for a neater looking bike. A central power supply for all these would be nice.
The off-the-shelf 12V battery pack for Tetz's power assist would do nicely.
Aside: once my 'closing clamshell' fairing is a reality, then throwing a solar thinfilm recharger inside could be practical.
D: terrific primer.
D: to get yer ergonomics, just use cardboard to replicate your hip/knee/ankle joints. Pin it all together. Make sure your bike suits your ergonomics.
Seat back (ergo hip tilt) will also affect performance.
A look at nice finished bikes.
D: I wish to create a variant Greenmachine.
My bud Fern in London is an accomplished welder.
I plan to use the Python's choice of material - 16gg square tubing. Stainless for me.
The cuts for square tubing are simpler, with only a slight weight penalty.
By the time paint coats and gloss finish are considered, the weight savings of a carbon steel frame are partly gone. Plus I can just satin the stainless - no paint chips.
D: it won't be monotube though.
I want to parallel pipes. I plan to run the whole rear-wheel-drive chain through them.
With gear hubs, this will mean the chain is totally sealed away from the outside world.
I don't imagine that is really true- I'd need hermetic seals v.s. moisture.
Still, it should keep rain off, and dirt out.
I'm intrigued by placing all valuable hub drives in the bike frame.
The wheels, if stolen, are cheap and easy to replace.
Alternatively, they can house fancy stuff like a hub motor or a SON dynamo hub.
What would be very nice for a rear-drive is if those kevlar belt products were made in a more useful length.
Monday, September 1, 2008
D: I dislike fairing design as it exists.
Keep in mind that a fairing is a design compromise.
It is not only to minimize drag.
It is also to keep the rain off sometimes.
This means it often has a larger front cross-section than is needed.
I imagine production methods (the blown bubble) has something to do with that.
D: there are 2 concepts to be understood.
1) laminar flow (or else turbulence) and
2) air pressure
D: the first step and what 'bents do is to minimize front cross-sectional area.
For the standard bike in the upright position, we have this:
At 250 Watts, the upright bike goes 29 Km/Hr or 8.0556 m/s. To go 40 Km/Hr or 11.111 m/s, the upright bike needs 622 Watts.
For the recumbent bike with the full foam fairing, we have this:
At 250 Watts, the bike goes 51 Km/Hr or 14.167 m/s. To go 40 Km/Hr or 11.111 m/s, the bike needs 135 Watts.
For the recumbent bike with the full hard shell fairing, we have this:
At 250 Watts, the bike goes 69 Km/Hr or 19.167 m/s. To go 40 Km/Hr or 11.111 m/s, the bike needs 75 Watts.
D: practical, my ass. Recumbents get enough cross-wind, are top-heavy and are plain heavy enough already.
The typical 'bent partial fairing is a nose cone and tail box.
Sadly, one is better off with
1) maintain laminar flow over >1/2 the length
2) suddenly truncate to induce turbulence once body taper has reduced the rear to < 1/2 the surface area.
To avoid pressure spikes on the front and delaminated flow (turbulence) on the rear half, the surface angles should all be gradual. The surface texture needs to be fairly smooth.
Road vibrations will also disrupt it.
1) Pantour hub elastomer on a stiff frame
2) ? special padded fairing mounts or
3) full suspension
After all, a poorly designed fairing is just so much dead-weight.
I prefer a total-body-length cover for the TOP and bottom.
With open sides.
Ergo, no crosswind.
There is risk of being top-heavy, though.
Aggressive design to place all mass as low as possible is wise.
The chopper handle hands-out is the lowest drag.
The Bachetta bikes are a good example.
Under-seat-steering increases front cross-section.
Of course, a fairing that is one blown bubble will occupy far more front area than is needed.
For this reason, some fairly complex shapes are justified.
The additional perk of over-the-top fairings (and window) is sun/rain use.
A simple non-moving version would be the transparent middle fairing on the mid-down pic.
Then chop out the sides on a diagonal, narrow at the bottom.
A body sock lends itself to use with a top/bottom fairing. It has plenty of anchor points.