Reflections on the potential of human power for transportation

Saturday, January 28, 2012

Rx for a Healthy Commute

Before the bike boom in the US, during the early 1970s, the bicycle was considered by many to be a child’s plaything. After the bike boom, its popularity caused it to be considered an acceptable form of recreation for adults. But the idea of using it as a commuter vehicle has never been widely accepted.  Nevertheless, there where occasional flashes of insight into the potential of human power for commuting.
Bob Bundschuh’s marvelous Pedicar from 1973 (See “Back to the Future” below), was one of these insightful designs.

http://www.youtube.com/watch?v=zvh44wzhw9c
The Pedicar was beautifully executed and at $550 was a bargain when you consider that a custom bicycle cost about that at the time. It embodied many of the characteristics I consider necessary in a commuter vehicle. Even the industrial designers at Chrysler took notice of it if only to poke fun.  Notice the mention of rotary-action to counter the touted benefits of the Pedicar’s linear pedaling system.
Mr. Bundschuh must have had a lot of industrial resources at his disposal to produce it.
Unfortunately the Pedicar was far ahead of its time and its linear pedaling system and complex gearbox added to its cost while detracting from its performance. More on this in a subsequent post.




And there was the widespread media coverage in 1980, when the vector tricycles broke the 60mph speed barrier.
What was more captivating than the Vector single covering the flying 200m at 63mph was the Vector tandem being ridden in traffic on the freeway and covering over 50 miles in less than an hour. At last the media got the idea that pedal powered commuter vehicles were fast enough to be taken seriously. The New York Times did a piece on future bikes with the Vector as the central theme and the Reader’s Digest reprinted the article. Three years later Scientific American did an article on human-powered land vehicles and a painting of the Vector graced the cover.
One vehicle to come out of the post-Vector optimism was the Cyclodyne.  At first glance, the Cyclodyne looked like someone finally got the design of a human- powered commuter vehicle, HPCV for short, right.  It was fast. During a road test by David Kennedy for Popular Science, as he pulled into traffic he was shocked to see he was doing 30mph. With a cruise speed advertised between 20 and 45mph, front wheel drive and steering, rear suspension and reasonable cargo carrying capacity, the Cyclodyne looked to have covered all the bases. At $3800 plus $120 shipping, however, it was not cheap. (At the time, Early Winters Outfitters in Seattle was selling a Vector for the outlandish price of $10,000. No one ever bought it and it was donated to the local HPV club as a tax write-off. The Cyclodyne people claimed their vehicle was cheap by comparison but it was still much too expensive.)






So, if we build it, will they buy? After a considerable amount of thought and a considerable amount of time perusing the literature, these are my criteria for a HPCV.  Granted a lot of creative designing and building of HPCVs has taken place all over the world and it is not my intention to undervalue these contributions to the state of the art. However, IMO, a single vehicle with most of the necessary criteria does not yet exist.  The list is roughly in descending order of importance.  The focus will be on a single-rider vehicle.
It might be informative to measure the Pedicar and the Cyclodyne against these criteria, since I consider both vehicles good examples of HPCVs.
1.       Weather Protection: The HPCV needs to be usable when using a bicycle is prohibitive. By providing protection from rain and snow the driver is kept warm and dry. The body of the HPCV must also provide adequate ventilation, since three times the mechanical work required to propel the vehicle is produced as waste heat. Remember that the hour-record for streamlined recumbents was more an issue of cooling than raw power production. (See “Back to the Future” below).

With the exception of the open side windows, the Pedicar appears to provide excellent inclement weather protection. The windshield wiper is also a practical addition. The Cyclodyne is also completely enclosed with the exception of the rider’s head protruding from the faring.
  
2.       Statically Stable:  I am assuming the HPCV will be used in snow and icy-road conditions. When the wheels of a bicycle slip laterally, the cyclist falls over. The value of static stability was made very clear to me on an icy bike trail with a tight curve. I watched a cyclist fall over into the grass when he hit the ice. I was on three-wheeled roller skis for Nordic training. I didn’t fall when I hit the ice but only slid laterally. So the HPCV must have three or four wheels.
A bit here about three-wheel layouts and I will exclude rear steerers. (See “Bucky and the Urbee” below).  The symmetric layouts are one-wheel forward, OWF and two-wheels forward, or TWF. Each has advantages and disadvantages when it comes to occupant packaging. If all three tires on the vehicle are the same, there are advantages to having each tire equally loaded.  For a triangle this occurs when the center-of-gravity is located one-third of the wheelbase distance from the twin wheels or two-thirds of the wheel base distance from the single wheel. Consider the riders c.g. to be located at approximately his belt buckle and assume the major mass component of the system is the rider.
For the OWF layout, this locates the rider within the wheels resulting in a very compact package. In addition, all three wheels fit within the body without requiring any openings for the steered wheel. The downside of this layout is there is no volume left over for cargo carrying and the rider’s legs are located in the same volume as the steered wheel.
For the TWF layout, the rider’s legs protrude in front of the two front wheels causing the overall vehicle length to be significantly longer than the OWF layout.  Openings in the body are also required to allow for the steering of the front wheels.  On the upside, the rider’s legs do not interfere with the steered front wheels and the volume around the rear wheel and be used for cargo carrying.
The Pedicar’s four wheels would make it very stable in slippery conditions as do the Cyclodyne’s three.
3.       Reasonable Cruise Speed: The body that provides the weather protection should also be aerodynamic and therefore increase cruising speed. An average cyclist can cruise between 12 and 15mph. If the rider in the HPCV can cruise between 20 and 25mph this would allow for short to moderate (up to 10mi?) commutes to be conducted in acceptable times. This speed target is very arbitrary.
The exposed wheels of the Pedicar gave it excessive aero drag and this detracted from any gains provided by the body. Cruise speed estimates were between 13 and 18mph which is little better than the bicycle. The Cyclodyne, on the other hand, boasted a very impressive cruise speed.
4.       Cargo Carrying Capacity: The traditional measure for minimal cargo capacity has been two bags of groceries. An alternative could be a briefcase and a lunchbox.  (The 17”-wheeled Moulton bicycles were designed for increased cargo-carrying capacity. I met a math Prof. in Milwaukee who broke his Moulton’s frame trying to carry a 65lb. filing cabinet.)
It looks like you could fit a filing cabinet into the back of the Pedicar and the cargo capacity of the Cyclodyne appeared to be more than adequate.
5.       No Wider than a Bicycle: The HPCV may be significantly faster than a bicycle but in many situations it won’t be as fast a car. As a result, it should be able to fit within bike lanes and bike paths and should protrude minimally into traffic.  
The Cyclodyne fell down on this point.  The problem with this was brought to light by someone who bought a used version. While pedaling down a two lane road, he noticed there was a long line of cars backed up behind him. He wasn’t going at the posted speed, but the cars nevertheless were unwilling to pass him. Apparently, the drivers didn’t know what to make of the vehicle. This occurrence was nerve-racking for the rider and happened frequently enough that he removed the faring so the car drivers could see he was only riding a pedaled tricycle.  Thus, the Cyclodyne’s impressive cruise speed was reduced to that of a bicycle.
The Pedicar, while not as wide as the Cyclodyne, was significantly wider than a bicycle.
6.       Same Height as an Auto: I am fortunate that in over 45 years of riding derailleur bicycles I have never been hurt by being hit by a car. I have been hit three times however, and each time the driver claimed that he/she didn’t see me. I believe that HPCVs should be more visible than bicycles, not less, and to me, that means keeping the rider’s head height at least equal to that of a driver sitting in a sports car.

The Pedicar has good rider height and the Cyclodyne has adequate rider height.               
Now, a statically stable vehicle (three of four wheels) prevents rollovers by maintaining a certain ratio (determined by the Gees the vehicle is designed to resist) of vehicle width to vehicle height. Narrow vehicles must be kept low while higher vehicles must get wider. So the prudent observer will see the apparent conflict between point 5 and point 6.
The solution is to allow the vehicle to lean into corners like a bicycle at regular speeds, but to lock out the leaning at low speeds and when riding during slippery road conditions. This can be accomplished by articulating the paired wheels. One goes up, the other goes down and the vehicle leans. The lean-lock can be manually engaged or automatically engaged during braking. I will spend more time discussing leaning tricycles in my next post.
7.       Comfortable posture and ease of entry:  Someone said that getting on an upright bicycle was like performing a stunt. Your leg must be lifted high over the top tube during mounting. This requirement resulted in the concave curved top tube of older women’s bikes and some modern bikes. At best, I believe that a HPCV should require a low step-over height for entry and that the pedal bottom bracket (I have assumed rotary crank drive here, more about alternatives in a future post) should be at least 10” below the seat. Seat height should be about 24”
   
I formed this opinion after riding an Avatar 2000 for almost 22 years. (That’s the great Prof. David Gordon Wilson in the picture, the co-developer of the Avatar, lifelong cycle commuter and HPV guru par excel lance). I have ridden a number of other recumbent layouts (most my own creations) but none were as easy to mount and as comfortable to ride as the Avatar. People who test rode Avatars were unanimous in how easy it was for them to master.  With a seat height of 24” and a bottom bracket height of 13” it had good visibility on the road and, as I told an inquisitive bystander, if someone would steer it, I could pedal and sleep at the same time. The under-seat steering also contributed to ease of mounting and provided a very comfortable hand position.  
8.       Two-wheel drive:  If a tricycle layout is used that equally loads all the tires, then a two-wheel drive vehicle will have twice the tractive force of a one-wheel drive vehicle. Maybe it’s because I live in an area where almost everyone has a least one four-wheel-drive car that makes me think this would be a nice feature. That being said, if you are designing a OWF vehicle, than all you need is the addition of some type of differential between the back wheels. A TWF configuration is more complicated. It needs two constant-velocity couplings to drive and steer in addition to a differential.
       
The Pedicar drove both rear wheels through separate gear sets, each of which incorporated a one-way clutch. The result was the pair of clutches acted like a posi-traction type differential. This, coupled with a significant rear-tire weight bias, resulted in the Pedicar's ability to climb 20% grades on snow-covered roads with regular tires. 

The Cyclodyne drove both front wheels. This also resulted in excellent traction on slippery surfaces.  The Cyclodyne people did make an Ecodyne tricycle with rear-wheel drive for $2500, so we can deduce that the front-wheel drive and differential added $1300 to the cost of the vehicle.

9.   Car-type Wheels:  Since the thought process here is to give a HPCV some of the conveniences of a car, why not be able to change a wheel when a tire goes flat instead of having to fix the tire. Make all the wheels interchangeable, mount them on only one side (cantilevered) so they are easy to remove and attach them with only a few bolts. Even if not easy to remove, cantilevered wheels allow one to remove the tire without removing the wheel. 
During the 1960’s the Italian  bicycle company Cinelli produced some bivalent hubs that allowed the front and rear wheels of a derailleur bike to be interchanged. Quite ingenious. (By the way, Cinelli also had clipless pedals in the 60’s as well!)
So instead of carrying a patch kit or a spare tube, just carry a spare wheel.  Extra weight, but added convenience.
It appears that since the Pedicar’s wheels are cantilevered that they may be interchangeable.  The Cyclodyne’s front wheels appear cantilevered but the rear is supported on both sides. I suspect they are not interchangeable nor are the front wheels, being driven, easy to remove.
10.   Electric Assist for Hills: Adding electric drive assist to all types of commuter vehicles is the current trend. Should a HPCV also have an electric assist for hills? Reasonable streamlining should insure that pedaling alone can produce adequate cruise speeds. However, since the vehicles are much heavier than a bicycle, the Pedicar being 125lb. and the Cyclodyne being over 70lb., electric assist could make hill climbing more acceptable.

Another issue for electric assist is a legal. In Seattle, a vehicle classified as an electric-bicycle cannot exceed 20mph with both pedaling and the electric assist. So, exceeding 20mph with electric assist would make the HPVC a motorized vehicle and thereby deny the rider access to bike paths and trails. If the electric assist is only used for hill climbing and the motor is geared so 20mph cannot be exceeded, the HPVC is still legally be an electric bicycle.
Whew! That was one long windy rant! So what’s the bottom line here? Both the Pedicar and Cyclodyne were well thought out HPCVs,  but they didn’t meet all my criteria. The vehicle width issue is a serious one, but to address it and keep the rider sitting high requires the added complexity of leaning the vehicle.  In my next post I will discuss two current HPCV products that lean. And we haven’t discussed cost. What is an acceptable cost when a Tata Nano is selling for $3000 in Asia?
Hephaestus






Sunday, January 15, 2012

Bucky Fuller and the Urbee


The Urbee hybrid two-seater car has had a lot of media hype lately, largely because its body is manufactured using 3D printing (rapid prototyping). But its claims of high efficiency are due to the compactness and low aerodynamic drag of its body and its light weight. What is of interest here is the car uses a three-wheel chassis. The two front wheels are driven and the single-rear wheel does the steering.

This layout has some significant advantages that allow for a car with a narrow cross-section. Since the two front wheels do not turn, the width of the vehicle can be minimized.  It is only made up of the width of the two passengers and the two narrow wheels. The extra volume required for steering the rear wheel easily fits within the frontal width and allows the vehicle to be tapered for better aerodynamics. Contrast this layout with the wheels-on-pontoons approach of the Very Light Car (see “Back to the Future” below). If the steering allows the rear wheel to turn perpendicular to the front wheels, the vehicle can make extremely tight turns, having a turning radius little more than the vehicle’s wheelbase.
Of course the most famous use of this wheel configuration was Richard Buckminster (Bucky) Fuller’s Dymaxion car of 1933.
  
Fuller didn’t arrive at this layout arbitrarily. He was trying to design an omnidirectional transport that could be used on land, in the water and in the air. As a result the wheel layout was identical to the tail-dragger approach common in aircraft of the day. Fuller envisioned that at high speed the rear wheel would lift off the ground and steering would be controlled by means other than the rear wheel. The body was intended to be essentially horizontal in this state and, as a result, the body has an upward-forward slant in its layout.

The Dymaxion car was much more aerodynamic and had much more internal space than contemporary cars. The Dymaxion car was quite revolutionary for its time but suffered from several traffic accidents that undermined the design. The accidents were blamed on driver error, but I suspect the rear-wheel-steering system.



You see, rear-steering tricycles are inherently unstable. If the rear wheel is given positive castor (see “The New Balance” below) then during turns, the radial acceleration forces will cause the turn to tighten. This positive-feedback effect will cause a “ground loop” which will eventually cause the vehicle to overturn. This is the reason that there are no longer any pivoting tailwheel aircraft. Contrast this with a front steerer where taking ones hands off the wheel causes the turn to be reduced. If the wheel is given negative castor, the ground loop problem is eliminated but the vehicle won’t run straight will hands off the steering.
The typical design approach to remedy these problems is to make the steering kinematically neutral and provide a secondary means to cause the steered wheel to straighten when hands are off the steering.
The Urbee’s rear wheel is located in the center of a horizontal bearing with the rolling elements located outboard of the wheel. This approach is kinematically neutral but the mechanism to cause the wheel to self-center is unclear. The Urbee engineers feel that they have eliminated any stability issues with this design. Their approach appears to allow for 90 degrees of steering angle.
The Dymaxion car used a near-vertical single-bladed steering fork whose axis intersected the ground within the contact patch of the tire, essentially resulting in near-zero castor.  Notice between the two versions shown, the side the fork was on has been reversed and notice the fork is raked from side-to-side in addition to front-to-back.
Of course this three-wheel configuration has been used numerous times. I have used it twice. The first time was for the University of Wisconsin’s entry to the 1979 SCORE (Student Competition on Relevant Engineering) Energy Efficient Vehicle Competition. The entry of a pedal-assist small-gas engine three-wheeler into a field of automobile-type vehicles was the brain-child of the late-great Prof. Ali A. Seireg. Prof. Seireg was a bit of a showman and he realized that to get the media to notice our entry, we needed to present an unconventional approach. Prof. Seireg did make the right call. Time Magazine’s coverage of the event had pictures of only two vehicles, and the UW runabout was one of them.
Despite how technically tantalizing this vehicle layout is, I have to question the wisdom of using it for mass-produced consumer vehicles, thought it may be acceptable for experimental vehicles, record-setting vehicles and military vehicles. Even though the stability problem may be addressed, any litigation involving a crash of the vehicle is bound to raise the issue of its unconventional steering. How do you counter the prosecution’s expert-witness’s first utterance that “Everyone knows a rear-wheel-steered vehicle is unstable”?


Monday, January 2, 2012

The New Balance: Life after Leonardo da Vinci's Bicycle


It was too much to expect.  That the world’s most creative mind would have conceived of the world’s most efficient means of transportation. That Leonardo da Vinci would conceive of a machine with the three essential sub-systems of the modern bicycle almost 300 years before Karl von Drais. Those sub-systems being a pivoting-fork front-wheel steering layout, rotary pedal propulsion and a chain and sprocket transmission.
I don’t know who was more disappointed, those of us that are Leonardophiles of the Italians. It was just too good to be true.



Now all of the hoopla over the Leonardo’s Bicycle Hoax should not be allowed to detract from the quantum leap Karl von Drais took when he invented his laufmaschine (running machine) or what history calls the Draisienne.  
The fascinating thing is that there were no precursors to the Draisienne. Earlier bicycle historians postulated that things began with a child’s stick horse. A wheel is added to the bottom of the stick, and then another wheel is added inline with the first. This is then scaled up to adult size and the antecedent of the Draisienne is created. Not only is there no solid historical evidence for this scenario, but more importantly, the two wheel version of the stick horse could not be balanced.
 Here is a key point. The ability to steer is necessary to balance an inline-two-wheeled vehicle.
Why are steering and balancing linked in the function of a dynamically-stable two-wheeled inline vehicle?
Let me propose a simple model of the bicycle-rider system, possibly a bit too simplistic for the academic dynamicists out there and it does leave out things like the precessional effects of the wheels. But it did aid me in understanding what was going on during ten years of experimenting with rear-steering recumbent bicycles.
The two mechanisms that allow a bicycle-type device to balance are castor and lean-steer. Consider the bicycle as a system with two masses and three-degrees-freedom for motion. The front mass consists of the wheel, fork and handlebars. The back mass consists of the rider and the rest of the vehicle. The front mass is attached to the back mass by a pivoting connection. From a disturbance standpoint, we will ignore one motion DOF, that being the bicycle moving forward. The disturbance motions are the fork mass pivoting with respect to the frame mass and the frame mass leaning from side to side. The two disturbance motions are not independent and the nature of their coupling is determined by the steering geometry of the vehicle.
Now for castor to occur, the contact point of the front wheel with the ground must be located behind where the steering axis intersects the ground, where behind is defined as opposite the direction of motion. For any angular disturbance of the fork mass, castor results in a moment being generated that tends to reduce the disturbance until the contact patch is inline with and behind the steering axis.
Lean-steer occurs along with castor, as long as the steered wheel is at the front of the bicycle. As you lean a bicycle to the side you will observe that the fork mass rotates toward the direction of lean. A disturbance that causes the frame mass to lean results in the fork mass steering the vehicle in the direction of the lean. The vehicle is now going in a circle and the radial acceleration associated with the change in direction picks up the frame mass and corrects for the lean disturbance.
So the amazing thing is that von Drais could not evolve his design based on non-steered precursors but has to create it in one quantum-leap of imagination.
Notice for the Draisienne restoration above the steering axis appears to be located near the front of the triangle supporting the front wheel and the axis is near vertical. The contact point “trails” the steering axis by almost half a wheel diameter. Compared to a modern bicycle with several inches of castor the Draisienne has a many times that. However the friction associated with the largely wood on wood steering pivot is much greater than that associated with a ball-bearing steering headset. The torque of the castor moment must overcome this friction to return the fork mass to being aligned with the direction of motion.  So a significantly greater amount of trail would make sense.
The weight of the Draisienne was about 44lb. With the forward vehicle speed equaling the rearward speed of the foot, any speed advantage was gained by gliding, similar to a classic-style Nordic skier or a person using a scooter. With no cushioning from pneumatic tires or frame compliance, let alone suspension, the ride must have been bumpy on all but the smoothest of roads. Prior to inventing the Draisine, von Drais was a forester. The mountain biker in me would like to imagine him gliding along smooth single-track trails, but there is no documentation of this. Since horse’s hooves and rain make for very bumpy roads, the opportunities for extended gliding might have been less than frequent.
And Leonardo? His notebooks show sketches for chain-sprocket drives, ratchets and ball bearings. But the invention of a dynamically-stable two-wheeled-inline vehicle was 300 years in his future.










Hephaestus