Reflections on the potential of human power for transportation

Sunday, March 28, 2021

The Podbike and the Quadracycle Quandary Part 2

 From the previous post, we concluded that the Podbike, with a few refinements, was an environmentally responsible vehicle for a single individual to take short trips using pedal and battery power. The problem was that having four wheels, if did not constitute an e-bike in the US and Canada. 

 If we were to convert the design to static three wheeler and maintain the roll-over resistance, ROR, the width would have to increase by 50%, making the trike too wide to share the road with autos of share a bikeway with other cyclists. And converting the design to a leaning trike would increase the cost and complexity.

So, can we eliminate the electric assist and match the top speed of a Class 3 e-bike, 28mph? Since extremely streamlines recumbent bikes have covered a flying 200m at over 90mph and were ridden over 57 miles on a track in an hour, this should be very doable.

Let's take another look at my all-time favorite all-weather, pedal-powered commuter vehicle, the Pedicar. It was designed by two aerospace engineers, Robert Bundshuh and Lionel Martin and produced in 1973. The Pedicar is discussed in detail in "Pedicar Technology" in a previous post.

Several factors prevented the Pedicar from becoming popular. Only 20 vehicles were produced. At $550, it was expensive compared to an average bicycle and had a top speed of only about 18mph.

How would one make the Pedicar more efficient so your average cyclist could pedal comfortably at 28mph?

The main speed limiter was the drivetrain followed by the aerodynamics.

The Pedicar had a linear-motion constant-treadle pedal drive (see " Lure of the Linear Pedal Drive" in a previous post) connected to a 5-speed transmission. Bundshuh incorrectly assumed that the constant treadle would produce a 50% power increase over circular pedaling. It could produce a 50% torque increase, but the deadspots at the extremes of the pedal stroke prevented even rotary-pedaling power levels from being realized. The pedals were not coupled together and that prevented a smooth pedaling stroke. One benefit of the linear pedal stroke was the nose of the Pedicar was lower than it would have been with circular pedaling. This resulted in a very unobstructed view of the road ahead of the vehicle.

Possibly an even bigger problem was the transmission. It had five speeds and allowed a range of 1:6.8, but the step size was 60%. The size of the steps never allowed the rider to get in a comfortable gear. A derailleur system has significantly smaller steps and combined with a rotary crank was considerably lighter. The weight of the Pedicar as 125lb. So some weight reduction is in order. 

So we could replace the Pedicar transmission with a 1x12 mountain-bike drive that has a ratio of 1:5.6 and a step size of 17%. To minimize the swept pedal volume at the nose of the vehicle we could use 160 to 165mm cranks with a bottom bracket having a low "Q" factor. 

The other area for improvement is the aerodynamics.

The exposed wheels are the biggest problem. The top of the tire is entering  the airstream at twice the speed of the vehicle. So the airdrag of that tire is 4X the drag of a tire that is not rotating. The solution is to enclose each wheel in what the aviation world calls a wheel pant. 

A place to look for ideas for streamlining a single-person, four-wheel vehicle is Extreme Gravity Racing.

Many of the racers use a bod-pod + wheel-pod approach for their layouts. Even though the drag coefficient, Cd, is larger than if the driver and wheels were enclosed in a single body, the cross-sectional area is significantly lower and the product of Cd*A is low enough to  produce a noticeably more streamlined vehicle.  

The picture at the beginning of the post is a corporate entry gravity racer from General Motors. Now the picture is deceptive because the GM car is very low and the wheels are only 12" in diameter.

The height of the GM racer would need to be raised to the 1.15m minimum recommended in the previous post. The width over the wheel pants would need to be no more than 1m. For the front wheel-pods, the wheel pants would need to be enlarged to accommodate 16"dia. tires. They would also be wider to house the steering kingpins and disc brakes. The front support beams that attach the wheel-pods to the bod-pod must house brake cables and the tie-rod linking the wheel together. The rear support beam only needs to house the drive axle, since the brakes can be located inboard in the bod-pod. This would result in the rear wheel-pods being narrower than the front. The nose of the bod-pod would need to be greatly enlarged to house the swept volume of the feet on the pedals.

In the end you might wind up with something that looks like the doodle below.

Now there is an interesting consequence of having our all-weather commuter vehicle use four wheels. In a previous post, "Pedaling Along the Skyway", I talk about elevated bikeways. If these bikeways use wheel tracks to simplify construction, then a four-wheeler only requires two wheel-tracks.
Another consequence is that the tracks could supply electric power to the vehicle. The vehicle could incorporate an electric motor to drive the rear wheels but it wouldn't include a battery. Thus, when not on the bikeway, it would not be an e-bike. It would be an e-bike only when is is using the electricity from the bikeway. Getting to and from the bikeway would only be on pedal power. This approach should allow the quad to use regular bike ways and streets like conventional bikes and trikes.



Friday, March 19, 2021

The Podbike and the Quadracycle Quandary Part 1

I have been reading Bill Gates' book " How to Avoid a Climate Disaster". Now one of Bill's remedies for the intolerable levels of CO2 in the atmosphere is to use electric cars. I am sure he would applaud the design of the Podbike as an environmentally responsible means of single-person short-distance travel.

As the commentator above points out, the vehicle he is testing is only a prototype. As such, we can assume that the issues he encounters will be addressed in the production version. Things like the lag between pedaling and vehicle motion, the harsh jolts from the front wheels when going over curbs and a clear canopy that will heat up like a greenhouse on a warm days. 

The Podbike has a very futuristic but functional appearance an should be very weatherproof. 

The most novel feature, however is its totally electric drive. The pedals drive a generator and there are motors in each of the rear wheels. You can drive the motors by pedaling, with the battery or both. You can brake and regenerate by backpedaling. You can also back up by pedaling backwards. You don't need any gearing and having a motor for each rear wheel eliminates the need for a differential.

The biggest drawback with this design, if you are a US or Canadian customer, it it is legally not an electric bike or trike and must be considered a small car. The three wheel regulation is archaic and is a simplistic interpretation of what constitutes a pedal-propelled vehicle.

Given the option of designing a vehicle with either three or four wheels, what would be the reasons for picking three instead of four?

There are legal reasons. If you are building an automobile, having three wheels allows it to be classified as a motorcycle if the weight is less than 1500 lb. With this comes reduced safety regulations, which in turn result in a lower-cost vehicle. And if you are designing a light-weight pedal-electric vehicle, it allows it to be classified as an e-bike.

From the technical standpoint, there are a few reasons. If you steer the single wheel, the steering can be very simple. The vehicle can be more aerodynamic if one chooses the tadpole layout. And a suspension is not required for all the wheels to touch the ground simultaneously. 

But there is a huge disadvantage selecting three wheels when you could use four wheels, roll-over resistance, ROR for short.

For a given center-of-gravity, c.g. height and an equal weight distribution on the wheels, a three-wheeled design has 2/3 the ROR of a four-wheeled design.

Consider the Aptera,  a three-wheel, two person electric car that is getting a lot of press lately.
The width of a Honda civic is about 70in. The width of the Aptera is 88in. 18 additional inches to compensate for the reduced ROR for a three-wheel layout.

The width of the Podbike is 33in. You could expect this to increase to 48" it maintain the same ROR. This brings the width to that of the Organic Transit Elf, which I consider to be too wide to share the roadways with cars and even bicyclists on bike paths.

As a tool for comparison let us look at a very well, if not the best designed velomobile available, the Leitra. Designed by Prof. Carl Georg Rasmussen in 1980, over 260 units had been produced by 2015 and it has been continually improved. The Leitra is an all-weather tadpole trike that is about 1m wide and about 51in high. The rear wheel is driven and the front wheels are steered with all wheels having suspension. The ROR is probably close to 2/3gees. 

In Washington State, where I live, a new class of e-bike has been added. Class 3 allows a top speed of 28mph with both the rider pedaling and e-motor assist. The pervious top speed, Class 2, was 20mph. For a given turn radius, a 28mph turn experiences twice the gees of a 20mph turn. So ROR is an important performance metric. 2/3gees might have been good for a 20mph top speed but it is probably inadequate for 28mph. A turning radius for a 1gee turn at 28mph is 52ft.

The ROR for the Podbike is probably about 1gee. I the design was converted to a three wheeler, the vehicle width would become too wide and like the Elf,  make the velomobile impractical.

Those of you who are not new to my blog know I have spent a lot of time designing and building leaning trikes. Theoretically, a leaning trike can have 33% more ROR than a four-wheeler and double that of a three-wheeler for a given track and c.g. height. This performance increase comes at the price of greater complexity. If the vehicle is completely weatherproof, entry and exit require the vehicle be in a statically-stable mode and then transition to a leaning mode when in motion. The mental adjustment going from static to leaning is not trivial and can be confusing. Although there are several leaning trike designs that have been produced, IMO, none are up to the task of an all-weather pedelectric commuter vehicle like the Podbike. 

So what is the answer? I think that four-wheelers (quads) should be legal e-bikes. In addition to regulating power, (mopeds can have up to 1500 kW motors) regulate the vehicle dimensions. If the e-quad is ridden along the edge of a roadway or on bikeway adjacent to said roadway, limit the the width to 1m and require the height to be at least 1.15m. If the e-quad is lower than 1.15m, require the use of a bike flag at least 1.5m high. Don't try to regulate speed. Let the speed limits of the infrastructure be the controllers. 15mph for bikeways and the posted speed limits of the roadways. Just like regular bicycles.

It is counterproductive to let antiquated regulations eliminate environmentally-responsible transportation solutions. 



Sunday, May 10, 2020

Velomobiles, E-trikes and the Transportation Infrastructure

It has been forty years since the Reader's Digest Magazine published this digest of a New York Times article from August of 1980. That summer, at the International Human Powered Speed Championships, a streamlined tandem tricycle, the Vector, was the first human-powered vehicle to break the 60mph barrier for a flying 200m speed run. But what captured the media's attention was that same tandem trike was pedaled from Stockton to Sacramento California on Highway 5 covering 41.8 miles at an average speed of 50.5 mph. Finally, it seemed that streamlined human-powered vehicles could provide a  viable, healthy alternatives to the automobile. 

In this vein, the magazine article described a hypothetical future commute to work by "Joe Wheeler", pedaling a single-person, Vector-like velomobile, the Shooting Star. Joe, riding along dedicated human-powered-vehicle lanes, covers 25 miles at an average speed of 60mph.

The article goes on to show a schematic of the single-person Vector.

And I have added a close-up photo of the Vector's interior. Note that the width of the Vector is 25in. and the height is 32in.

So 40 years has passed and why aren't people zipping to work in bullet shaped tricycles? One answer is transportation infrastructure. There are no limited-access high-speed bike paths for vehicles like the Vector. I do occasionally see a bright-yellow Quest velomobile on the local bike way, but I have never seen it 1n the bike lanes adjacent to local roads.

Now the progression in HPV speeds has continued in the ensuing 40 years. The longest distance covered in an hour is 58 miles and the flying 200m record is almost 90mph. The current trend has been to use a two-wheel layout since the aerodynamics are significantly better than three and four wheel design.

The Vector trikes, like the dragsters of the automotive world, were limited-use vehicles. The same small cross-section that made them so aerodynamic also made them very difficult to see from the perspective of an automotive driver. During its record setting 42 mile highway run, the Vector tandem was bracketed, front and back, by guard vehicles to protect it from autos merging into the space it occupied. The limited wheel lock for the steered front wheels made only large radius turns possible. The lightweight high-pressure tires required a clean road surface to prevent punctures. And the rider in the Vector had a limited field of view. Not to mention that a light 51 lb. vehicle provides woefully inadequate crash protection for a vehicle traveling at 60mph. Finally, these low-narrow layouts require the assistance of at least another person for the rider to get in and out of the vehicle 

Now, after the Vector speed records, Alan Carpenter, a designer from Colorado, build a production vehicle that he felt would be a practical human-powered vehicle. The Cyclodyne was a very well thought out and well-engineered vehicle.

The Cyclodyne was a tadpole trike, like the Vector. It was, however higher at 40in. for better visibility and wider at 38in. to provide the necessary roll-over resistance. It even incorporated driven front wheels to double the drive traction over the typical tadpole trike. A fit cyclist could pedal the Cyclodyne at over 30mph.

One owner related a critical problem with the Cyclodyne. Even being pedaled at 35mph, it was not fast enough to prevent traffic backups behind it  when ridden in automobile lanes. The motorists didn't know what to make of the vehicle. In frustration, he finally removed the faring so the drivers could see he was operating only on pedal power. His speed fell drastically, but the cars lost their reluctance to  pass him and the backups were eliminated.

Since the Cyclodyne was only 38in. wide, it would comfortably fit within most bike lanes located adjacent to many roadways but it was not fast enough to be interleaved with automobiles. The appropriate traffic infrastructure wasn't available for the above owner.

The Cyclodyne demonstrates that, with a bit more attention paid to aerodynamics, an enclosed all-weather trike could reasonably be expected to have a top speed of over 40mph.

So back to transportation infrastructure. Where could such a vehicle be ridden? Do legal vehicle speeds preclude the use of such vehicles? 

A catalog of the places and speed limits for use in the Seattle, Washington reads something like this:

Sidewalks, no speed limits
Residential streets, 25mph
Local roads, 35 to 40mph. Most of these roads have adjacent bike lanes.
Interstate highways. 60mph in the city and 70mph outside the city. Many of the highways outside the city have wide shoulders that allow cyclists to safely use them.

So residential streets and any other roads with adjacent bike lanes would be acceptable. For safety reasons there are the two requirements that the vehicle should be clearly visible to motorists and narrow enough to not obstruct traffic. A Cyclodyne-like vehicle satisfies these requirements.

Carpenter made one bad decision that limited the sales of the Cyclodyne. Its price tag of $4000 in 1980's dollars. He justification was that Early Winters, an outdoor outfitter in Seattle, was selling a used Vector trike for $10,000. Now the the Vector cost was not representative of a production vehicle. There was only one of them and it never sold. It ultimately was donated to a Seattle human-powered vehicle club.

Let us assume that a Cyclodyne-like tadpole trike, with some aerodynamic improvements would allow a reasonably fit rider to reach 40mph without sprinting. So the technology predicted in the Reader's Digest article exists, albeit at a 40mph level instead of a 60mph level.

(In fact, since the Cyclodyne already had front-wheel drive, one big improvement would be to allow the rear wheel to do the steering. The front wheels would present less frontal area. The main faring could just enclose the rider and the rear-steered wheel. The front wheels could be mounted outside the faring with individual wheel pants to streamline them. Joy-stick steering could be substituted for the under-seat steering to further reduce the faring width. While the drag coefficient for this layout might be greater that the original design, the cross-sectional area would be significantly reduced and the product of drag coefficient and cross-sectional area would make the vehicle more aerodynamic.This would be at the expense of some cargo capacity. In addition, having two front wheels that do not steer is much more stable when going over obstacles when compared to two steered wheels which can be deflected causing unwanted steering inputs.)

The continued development or an all-weather commuter vehicle that could be safely integrated with traffic has also been largely curtailed by pedal-electric technology.

But is the electrification of bicycles and tricycles a bad thing for the development of human-powered commuter vehicles?

Let's look at the electric bicycle regulations for Washington state to get more specific on answering that question. Keeping in mind that tricycles and velomobiles fall under these requirements. 

The above regulation lost part of a sentence, one that is as important as the categories. The second sentence should read "The electric bike must have two or three wheels and fully functioning pedals" .
The eliminates vehicles like the Pod Bike (strange name for a four-wheel vehicle) and the Quattro Velo if it includes electrification. Now this is a bad requirement if one is designing an all-weather commuter vehicle, since for a given track and weight distribution, a quad had 50% more rollover resistance than a trike. On the other hand, a four-wheel motorized vehicle falls into the category of a micro car with all of its extra regulations.

Another electric bike regulation says that the vehicle must have a bicycle seat and for trikes, one of the wheels must be at least 20" in diameter. Now requiring a bike seat would eliminate all recumbents. And I, like the Cyclodyne designer, prefer three 16" wheels because they allow a smaller vehicle volume.

Class 3 is a recent and welcome addition to what is considered an pedal-electric vehicle.

Now a fit cyclist can generate 200+ Watts of mechanical power. So with more than three times the available power, aerodynamic and weight considerations can essentially be ignored. One problem that this surplus power can't solve is vehicle width.

For visibility in traffic, it is desirable that the rider's head height is no lower that that of a driver in a sports car. For static tricycles, roll-over-resistance is developed by making the vehicle width approximately on the order of twice the height of the vehicles center-of-gravity, c.g. If the designer is not diligent in keeping the c.g. low, the vehicle width can get excessive.  It is my opinion that electric velomobiles like the Elf, with a 48" width, are too wide to share dedicated bike lanes with other vehicles.
I think that electric velomobiles should have a width restriction of 1m (39") for access to dedicated and roadway adjacent bike lanes.

An electrified version of the Cyclodyne, at a 38" width, could easily manage the 28mph speed limit for a Class 3 electric tricycle and be a very beneficial all-weather pedal-electric commuter vehicle.


Friday, October 25, 2019

David Gordon Wilson: The Father of the Modern Human-powered-vehicle Movement

Prof. David Gordon Wilson died on May 2nd 2019 at the age of 91. He began the modern human-powered-vehicle movement when he sponsored a design competition for an improved version of human-powered land transport in 1967.

Wilson received his PhD in mechanical engineering from the University of Nottingham in 1953. Between that time and 1966 when he joined the faculty of MIT in 1966, he engaged in multiple pursuits.

 He received a Commonwealth Fund Fellowship to conduct research in the USA with MIT an Harvard concluding with work for the Boeing Commercial Airplane Company as a gas turbine engineer.

Wilson did a two-year stint in Africa, teaching at he University of Ibadan in Ziria. Nigeria.

After doing two years of Voluntary Service in Cameroon, Wilson contracted malaria and was forced to more back to England.

In 1960, he was invited to be the technical director of the Northern Research and Engineering Corp to form a London branch specializing in turbo-power machinery and heat transfer.

Invited to MIT for a permanent position in 1966, Wilson taught thermodynamics and mechanical engineer. Students he advised conducted research in turbo-machinery, fluid mechanics and other design topics.

Wilson retired from MIT in 1994 after 28 years. He acted as professor emeritus until his death.

Outside of the university he pursued issues as an environmental activist particularly in regard to transportation. Wilson was appointed to a commission of the Massachusetts Bay Transportation Authority.   He served on the Center for Transportation Studies.  He joined the Massachusetts chapter of Common Cause and was the co-founder of the Massachusetts Action on Smoking and Health which advocated for the rights of non-smokers.

In later years Wilson invented a heat-exchanger and a micro-turbine which are fundamental to non-photo voltaic solar power production. The company, Wilson Turbo-power was formed to commercialize the inventions.

And in 1974, Wilson came up with the idea of the Carbon Tax.

Of course, when it comes to the environment and responsible transportation, Wilson will be most remembered as a life-long commuter cyclist who used a bicycle instead of an automobile. Wilson was not deterred from using bicycle by the most severe weather.

Up until the mid 70's, Wilson rode a Moulton. Now at the time the Moulton design was quite sophisticated. It used 17" narrow high-pressure tires and had front and rear suspension. The small wheels made room for carrying quite a bit of cargo over the front and rear wheels. (I knew a college physics professor, an all season cycle commuter like Wilson, who carried a 55 lb. filing cabinet on the back of his Moulton.) The Moulton could also be folded in half for storage and transport.

So, even though he was riding the best engineered commuter bicycle, he still felt there was a lot of room for improvement.

As Wilson was about to leave the UK for the USA and his job at MIT, he found out he would not be able to take his savings with him.So in 1967 he took his savings and organized an international competition for man-powered land transport. There were 73 entrants before the judging in 1969.

A summary of the results can be found in the magazine:

Engineering (London) vol. 2071, no 5372, 11 April 1969, pp. 567-573

The winning design was from W. D. Lydiard, a British aerospace engineer. Not only did he submit a paper design he build an actual prototype of his Mk.3 version. He called this version the Bicar.

Shown below is a  schematic of the Mk. 3 version top and the Mk. 4 bottom.

The Bicar was an enclosed recumbent bicycle that used 16" wheels. Lydiard invariably encountered what I call "the recumbent bicycle problem", that being, for a front steered recumbent bicycle, the pedals want to be in the same location as the front wheel for an ideal weight distribution. He solution was to use an non-circular, elongated pedal path located above the front wheel. the pedals moved in near linear tracks and  were attached to connecting rods that pulled on a conventional crank. This mechanism is what I refer to as a "oscillating treadle".

The post listed below discusses linear pedal motion in some depth.;postID=5532337496842064005;onPublishedMenu=template;onClosedMenu=template;postNum=9;src=postname

Lydiard encountered interference with the pull rods when he put his feet on the ground through the flaps in the body, so he also presented a Mk. 4 version that used what I refer to as a constant-torque treadle.

Wilson was quite taken with the use of an elongated pedal path to minimize foot-front-wheel interference and came up with over a dozen sketches of different concepts, eventually detailing the design show below.

In 1973 Wilson was approached by Frank Rowland Whitt, a chemical engineer and a writer of technical articles for cycling publications. Whitt had gathered material for a book about Bicycling Science and he approached Wilson in hopes that he could help him get it published. Wilson in turn approached MIT Press and they agreed to publish it if Wilson would be a co-author.

The first edition was published in 1974. It was the first technical treatment of bicycle technology since Archibald Sharp's Bicycles and Tricycles published in 1896 and republished by MIT press in 1977. At last, human-power vehicle enthusiasts had a technical reference to aid in their research and designing. The technical bible had arrived and has only gotten more comprehensive with each edition.

Soon to be in it's forth edition, it is MIT Press's best selling publication.

In the mid 70's Wilson was contacted by a California bicycle mechanic named Frederick Willkie regarding the design of a recumbent bicycle and Wilson sent him several sketches. What resulted in what Willkie call the Green Planet Special 1 shown below.

The GPS1 was very similar to the Ravat recumbent of the 1930's.

Willkie found the GPS1 uncomfortable to ride and asked for some modification suggestions. Wilson told him to lower the pedals in front of the front wheel, locate the handlebars below the legs directly on top of the fork and lean the seat back. The GPS2 was born.

For reasons not revealed, Wilson purchased the GPS2 form Willkie. He made subsequent modifications and the Wilson-Willkie recumbent bicycle was created. Wilson added a number of creative features to the WW. Loops attached to the pedals that allowed one to ride with dress shoes, a large luggage box behind the seat and a hammock style seat.

By 1976, Wilson riding the Wilson-Willkie recumbent became the poster child for a better bicycle, at least in the USA. He was featured in newspapers, magazines and a commercial for creativity by the Mobile Oil Company

I sure the irony of a man riding an alternative to the automobile being showcased by an oil company was not lost on Wilson.

Wilson teamed up with Harold Maciejewski and Richard Forrestal to investigate making commercial recumbents.

The Avatar 1000 thus followed the WW.

And the Avatar 2000 followed that.

The Avatar 2000 went on sale in 1980 and was the first commercial recumbent since the Second World War. ( The Hypercycle, being a knock-off of the Wilson-Willkie quickly followed.)

I have ridden s.n.85 Avatar 2000 for 35 years and I must say it is the most comfortable bicycle and recumbent that has ever been manufactured. The only negatives I have encountered are the difficulty in transporting a bicycle with a 63" wheelbase and a lightly loaded front wheel which can wash out on slippery surfaces.

Wilson generated a chart comparing the weight distributions of various upright and recumbent designs.

The ideal appears to be having between 36 & 40% of the vehicle and rider weight on the front wheel.

It is interesting to note that if one used a 16" and was to allowed an intermediary bottom bracket with sprockets on both sides, ( as the GPS1 and GPS2 had) then the wheelbase could be made 8" shorter than the Avatar 2000 and the front-wheel weight distribution could be increased the 35.5%, getting very close to the idea.

In later years Wilson did not commute on an Avatar 2000. When he rode to the campus  at MIT he had to carry his bike up quite few flights of stairs to his office. The Avatar 2000 was much too cumbersome for that task so he rode more compact recumbents of his own design.

The second picture was probably Dave's last recumbent and is of interest because it uses a timing belt to connect the pedals to the intermediary bottom bracket.

I was first introduced to Wilson in 1972 reading his 1968 article "Where Are We Going In Bicycle Design?" reprinted in Harley M. Leete's "Best of Bicycling" book.

I bought the first edition of "Bicycling Science Ergonomics and Mechanics" in 1974.(I subsequently bought the second and third editions and will buy the fourth edition when it is published next year).

  I started communicating with him in 1976 while in grad school requesting more information about his recumbent designs.

 In 1989 he edited my article on rear-steering recumbent bicycles published in "Human Power", the magazine of the International Human-powered Vehicle Association (IHPVA).

He sent me over a dozen of his designs for linear pedaling recumbents.

I met Prof. Wilson at the 1990 IHPVA speed championships held in Portland Oregon. I believe he was the president of the IHPVA at that time.

 And he endorsed the Lefthandedcyclist blog and his friend and publisher Richard Ballantine expressed interest in publishing a collection of my posts.

Prof. Wilson, the bicyclist and human-powered vehicle builders of the world are greatly in you debt.

Dr. Recumbent, we solute you!


Thursday, November 29, 2018

Aerion: An Optimized All-weather Ped-electric Trycicle

Those of you that have followed my blog at all know my opinion on what constitutes an optimal ped-electric commuter vehicle.

1. The vehicle should have three wheels for stability on slippery surfaces.
2. It should place the rider's head at the height of a typical automobile.
3. It should be narrow enough to comfortably fit in a bike lane. I can be more specific on this. It should fit between barriers spaced 36" apart, so assume a maximal width of 34".
4. It should not overturn when cornering. Assume a tipping resistance of 1 gee.
4. It should be enclosed to protect the rider from the elements.
5. And for traction on slippery surfaces, it should drive two wheels.

Now if the vehicle is a static tricycle point 2 and 3 are at odds with each other. High enough rider and wide enough to not tip over in turns results in a vehicle that has a width of about 48".

The solution to this contradiction is a leaning tricycle.

When correctly designed, leaning trikes can be balanced just like bicycles. Like bicycles, the most difficult task is getting started from a stop. One has to develop balancing speed often with one pedal thrust to avoid tipping over or having to put a foot down and start again.

Problems appear when the leaning trike is enclose in a body that interferes with the action of starting.
To remedy this potential problem the vehicle need a mechanism to lock-up the leaning for starting, and stopping. The locked-up mode could also be used in slippery conditions when balancing is not practical. You now have two modes of operation, balancing and being stable. The rider has to switch modes and decide when to do so.
Refer to the Velotilt design where the leaning needs to be locked up when the rider gets into the vehicle and starts moving or when the vehicle is stopping.

I discussed the problems I had starting and stopping my EcoVia trike in the post below.

When a fellow HPV-er tried to ride the EcoVia he pointed out the average rider would have trouble mentally switching from one mode to the other. I could not disagree, having once forgotten that I was in the balancing mode and thinking I was in the static mode. This resulted in a swerve that may have ended my HPV career had there been any other cars near me at the time.

So how to address this problem?

I believe you must have the static mode for starting, stopping and slippery conditions. The balancing mode is the most problematic so eliminate that. Since you still need to lean the trike to prevent tipping over in corners, make it controlled by the rider by means other than balancing. 

Now since accelerometers, controllers and stepper motors are inexpensive, the logical approach for controlling lean for an electric vehicle is computer control, with it being transparent to the rider. Since lean angle is a function of radial acceleration, which in turn is a function of steering angle and vehicle speed, the necessary calculations are relatively simple.

Lean control for non-electric vehicles is more problematic.

GM's Lean Machine from the 1980's used foot pedals, since the vehicle as gas-powered.

A human-powered vehicle more likely than not uses foot pedals for propulsion, so that is not an option.

One could combine lean control and steering into one action. I tried that with the first version of the EcoVia, but the approach introduced bump-steer with disastrous consequences.

Or one could use dual-control that used two hand motions, one for steering and one for leaning. The Tripendo uses this approach with apparent success. It employs two long levers. One does the steering and one does the leaning. The rider continually adjusts both to keep the trike stable.

Dual control could be used without requiring continuous lean adjustment. For example, the MK3 version of my EcoVia has a c.g. height of approx. 23 in. an a track of 30". This allows for a .43 gee turn without needing to lean.


One can calculate the required geometry for a fixed lean that can resist one gee just at the limit of tipping over.

For a vehicle that leans by having its wheels move essentially vertically, staying parallel to the vehicle, like the Toyota iRoad above, the relations below apply:

The first equation calculates the relation between width, height and lean angle at the limit of tipping. The second equation calculates the relation between the width, height and lean angle that will resist one gee laterally without tipping.

Interestingly, the lean angle for this condition is not a function of w (track) or h (cg height). It ends up being 26.6deg. Not surprisingly,  The lean angle of the iRoad is about 26deg. And the iRoad width is about 34"

The cg. height for the above conditions is a function of the lean angle and the effective track, w. If the actual track is 30", the effective track is approx 2/3 of that for an equal-wheel-load configuration or 20". For a 20 track the required c.g. height is 25".

 Let us compare the gee limits for several configurations with this geometry.

1. Statically, without any lean, it would take .4 gees to tip over.
2. For balanced leaning, it could withstand .5 gees. The vehicle would have to lean 45deg to resist 1 gee.
3. If the vehicle had four wheels where the front and back track was equal, it could withstand .6 gees. The track would have to be 50" to resist 1 gee statically.
4. And with the lean locked at its 26.6 deg limit, it could withstand 1 gee.

Clearly, for a given track width, a tricycle with controlled leaning gives the greatest resistance to tipping.

So our optimal all-weather ped-electric trike will have controlled leaning where the leaning is determined by computer.

What about the wheel layout? Should it be a delta trike or a tadpole trike. Due to drive-train complexity I will eliminate the tadpole configuration where the front wheels drive and steer. That means that if the two front wheels drive, the single rear-wheel steers. (Like the iRoad).

Below is the EcoVia Mk3. The long lever controls the leaning while steering is located below the seat.

The biggest advantage of the delta configuration is the pedals can overlapped with the front wheel to produce a very short vehicle. The vehicle can be lighter weight because the structure supporting the front wheel can also support the pedals. Along with these advantages comes three disadvantages. The steering lock is limited. Not enough to be a problem for normal turns but enough to prevent tight turns. Only one wheel is available up front for braking where the load is transferred to during hard braking. Lastly, the steered wheel is the first wheel to encounter obstacles like railroad tracks. The obstacles can perturb the steering and unexpectedly change vehicle direction.

Below is the EcoVia Mk1

The biggest advantage of the tadpole configuration is it doesn't suffer from the three issues plaguing the delta configuration. On the other hand, the package is longer that the delta configuration because the pedals are on one end and the steered wheel is on the other. The space between the seat and the rear wheel could be used as a trunk. And there is the issue with rear-wheel steering. Since the controlled leaning approach does not involve balancing, this should not be a show-stopper. After several communications with Jim Kor of Urbee fame, he described his approach to make his rear steering stable. The Urbee without body is shown below.

I believe despite its problems, the tadpole configuration wins out.

Below is a drawing and photo of the Cyclodyne, a tadpole trike from the early 1980s that was capable of cruising at over 30mph. The Cyclodyne, of all the commercial human powered vehicles, came the closest to harnessing the potential of human power as a transportation alternative.

To resist tipping rider's head height was about 39" and the vehicle width was about 48". Roll-over resistance as at least 1gee. While the rider's head height was acceptable, being comparable to a sports car, the width was too wide to fit comfortably on a road shoulder.

Had it been made a quad by adding a fourth wheel, the width could have been reduced to the target 34" and speed would have been increased as well, making it a very practical commuter vehicle. But the fourth wheel would prevent it from being considered an electric bike if a motor was added.
Adding controlled leaning could have reduced the vehicle width, increased visibility by raising the rider's head height and allowed it to be electrified. An optimal all-weather tricycle configuration.

Even though it only exists as a few equations and a few crude sketches, I have a need to give a name to this all-weather, ped-electric, fixed-leaning, front-driving, rear-steering tricycle. I will call it the Aerion. (Aerion is also the name of an aviation company developing a supersonic business jet).

I have a bias for the Toyota iRoad. My first configuration in 1990 for the EcoVia was a front-driven, rear-steered leaning configuration. I was not using controlled leaning but was balancing the vehicle and I could not make the rear-steering stable. More than two decades later, electronic controls allow the iRoad to do what I couldn't and reap the benefits of an optimal configuration.


Wednesday, December 23, 2015

The Velotilt: a Pedal-Powered Commuter Trike for a Bike-Friendly World

In 1980, after the Vector trikes shattered the Human Powered Vehicle Championship speed records, people began to believe that human-powered vehicles could travel fast enough to be viable transportation vehicles. The ultimate nod to HPV recognition was an illustration of a Vector trike on the cover of Scientific American magazine. The age of pedal-power had arrived.

Well, not really. Vehicles like the Vector were low to the ground, and, as a result, not very visible in traffic. Their extreme streamlining kept the wheel-track narrow so high-gee turns were not possible.
One vehicle, the Cyclodyne did come close to being a practical commuter vehicle. A tadpole-layout trike with front-wheel drive and steering, the Cyclodyne could be pedaled over 30mph by a fit rider. Its practicality was compromised, however, by its width. It was too wide to fit in a 36” bike lane next to a car lane, but not fast enough to keep up with 35mph traffic in the car lane. A noble effort, but a dead-end.

Now to some extent, the lack of a fast commuter vehicle may be as much a problem with a lack of suitable places to ride them as the vehicles themselves. The really fast vehicles (>30mph) are low to the ground for minimal aerodynamic drag. Such vehicles are difficult to see in traffic. On the other hand, dedicated bike paths, where vehicle visibility may not be an issue, have 15mph speed limits that prohibit high-speed vehicles. (Riders on the Burke-Gillman trail in Seattle have received tickets for exceeding 15mph.)

If there was a bike-commuter infrastructure that separated bicycles from car traffic and allowed for very-fast pedaled vehicles, Wim Schermer’s Velotilt would be the vehicle to ride.


The Velotilt is a delta trike where the front wheel is driven and the rear wheels are attached to beams that can pivot. The act of pivoting allows the Velotilt to lean into corners like a bicycle.


 The degree of leaning is limited so the vehicle cannot tip over statically. The beams are interconnected by a mechanism that causes one beam to move down while the other moves up. The middle link in the mechanism is composed of a sector of an arc. As the mechanism moves the sector rotates. This sector can be clamped in any portion of its extremes of travel and thereby lock the leaning.


In addition the entire mechanism can translate, allowing both beams to pivot together. This motion is resisted by a mountain-bike shock and provides suspension for the rear wheels.
The rider’s legs wrap around the front-steered wheel. The cranks are located in front of that wheel and the wheel is driven through a very pricey Rolloff 14 speed internal-geared hub.

All three wheels have disc brakes but in all the photos, the rear disc are lacking calipers and actuation cables.

Commercial vehicle weight is expected to be 55lb. The vehicle height is approx. 40”.

The Velotilt body and the rear-wheel pants make the vehicle extremely aerodynamic. Schermer calculates that it will take 150W to do 40mph. Bicycling Science 3rd Ed (D.W. Wilson) estimates that an ultimate HPV would require 200W to do 40mph, so the efficiency of the Velotilt is indeed impressive.
An optional 750W motor could help propel the Velotilt to 60mph for a duration of over 2.5 hours, but where would you ride it? Too low to mingle with car traffic and too fast to mingle with regular bicycles.

Possibly, one could transform the high efficiency into something other than raw speed.
For example, the Velotilt might be able to sustain a constant 15mph on solar power alone. Or the vehicle could be made higher than its current 40"to be more visible in traffic. As it stands, I believe some evolution remains in the Velotilt’s future.


Some of the pictures in this post came from Adam Ruggiero’s article, “The Future of Human-Powered Transport is a Trike” in the March 18 issue of GearJunkie.