I confess to being overly fascinated by the Pedicar. Maybe
because it became available when I was discovering recumbents and realizing
there were more utilitarian human-powered vehicles than the safety bicycle. It
made a significant public relations splash because it was aimed at replacing
the automobile for short trips. And at least one auto maker, Chrysler, took
enough notice to lampoon the vehicle.
Now if available today, the Pedicar would make a worthy
commuter vehicle. Placing the rider’s head at the same height as an auto
driver, it had good visibility on the road, a feature I feel is a must if you
are going to ride next to 35mph traffic in a 36” wide bike lane. Add wheel
pants and a more aerodynamic body along with rotary pedals and a derailleur
shifting system and you would have a faster, lighter and less expensive
vehicle. (It probably would not climb hills as well.)
Drive the wheel (wheels) with an electric motor and you
would have a very functional all-weather E-bike. (I use the word bike in this
sense to refer to a pedal-powered vehicle that can have more than two wheels.)
But not so fast! In the US and other countries, and E-bike
can have no more than three wheels. Add a fourth wheel and you become a moped,
losing the legal status that lets you use bike lanes and bikeways.
And removing that fourth wheel causes problems with the
vehicles ability to corner without overturning. The Pedicar, with a 36” track
had a rollover resistance of in excess on one gee. If you went to a three-wheel
layout and located the center of gravity (c.g.) such that each wheel was
equally loaded, (1/3 of the wheelbase from the paired wheels,) the rollover
resistance would be reduced to 66% that of a four-wheel vehicle.
Let’s look at some contemporary all-weather E-bikes.
The ELF is manufactured by Organic Transit and uses the
tadpole wheel configuration (two front steered wheels and one rear driven
wheel). I would consider it a laudable effort at producing an all-weather
E-bike, (AWEB) but it has some issues that would prevent me from using in in my
commute to work, namely it has a 48” width.
The width is necessary to prevent rollovers when cornering.
I will assume the track is 44” and there is 2/3rds of the weight on the front
wheels. Even with the added width, compared to the Pedicar the ELF’s roll over
resistance is only 80%.
In addition to the 48” with causing the ELF to hang out into
the auto traffic lane on some bike lanes, it results in poor aerodynamics. This
may not be an issue because E-bikes in the US are limited to 20mph, in some
cases with pedal assist and in others without.
The ELF uses a 750W
electric motor to achieve its 20mph, which is the maximum power for the E-bike
regulations the Organic Transit people are citing. With respect to the power a
human can generate, 750W is a lot of power. World-class cyclists can sustain
half that amount for about an hour. A racing cyclist requires about 155W to go
20mph (Bicycling Science 3ed-D.G.Wilson). This source states that a
commuter-human-powered vehicle should require on the order of 75W to go 20mph.
(The Organic Transit site states that the ELF has the same drag coefficient, Cd
as a bike rider. We know that air drag is proportional to the product of Cd and
cross-sectional area, so we can extrapolate that the ELF has about four times
the frontal area of a bike rider.)
Vehicle weight is between 170 and 190lb
.
So as a pedal-powered-only vehicle, the ELF is not very
efficient. As long as the battery is at full charge, this is probably not an
issue. Run the battery down, however, and you will be working very hard to hit
15mph and with a topped off battery it will require a lot of effort to reach
25mph.
The prototype Velocar from VeloMetro has a layout similar to
the ELF and, as a result will be subject to the same issues.
Now the 33% loss of rollover resistance when going from a
quad to a trike is based on locating the c.g. so all the wheels are equally
loaded. There is no requirement to do this. If the c.g. were located near the
paired wheels the rollover resistance of a trike would be minimally
compromised. With a typical tadpole layout, this would result in a lightly loaded
drive wheel and potential tire slippage. Unless, of course you are driving and
steering the front wheels (which, while technically interesting is more complex
an approach than driven the rear wheel only).
The alternative trike layout is the delta, with one wheel
forward and two wheels back. Biasing the weight toward the rear wheels aids
traction but results in the front tire being lightly loaded and more prone to
lateral slippage in slippery conditions. A delta trike, with an enclosing body,
is inherently more streamlined than the tadpole trike, because the
steered-front wheel is easily enclosed within the body.
The Sinclair C5 was a delta trike. A sectioned view is shown
below.
The C5, the brainchild of the British industrialist Sir Clive
Sinclair, had been called one of the world’s worst inventions. Even so, until
the sale of the Nissan Leaf, It held the record for number of electric vehicles
sold at over 7500 units. The separation between genius and madness is often
small.
The C5 used a 250W motor to reach 15mph, the legal limit for
vehicles of the type in Great Britain. IMO the vehicle was quite attractive and
relatively aerodynamic. Bicycling Science gives a racing cyclist’s power to
travel at 15mph as approx. 80W, but unlike the ELF the C5’s inefficiencies were
a result of rolling resistance and mechanical losses.
The front tire was 12” in diameter, the rear tires were 16”
in diameter. There was only one pedal speed and no provision to adjust the
distance between the seat and pedals. The crank length was about 130mm (normal
is closer to 170mm) and the gear was about 44”.
Wheelbase was 51” (not too long for a recumbent bicycle),
width was 29” and the seat height appeared to be on the order of 12 to 14”.
Vehicle weight with a battery was about 99lb.
A custom geared motor drove the left-rear wheel through a
belt drive and the pedals drove the right-rear wheel through a freewheel on the
axle.
An attempt was made to allow the wheel-support outriggers on
the rear chassis to flex and result in some suspension. (Photos of used vehicles
show that the chassis developed cracks between the outriggers, suggesting that
the chassis designer, Lotus Sports Cars, underestimated the stresses the
flexing would cause.)
The video below is quite lengthy. If nothing else, skip to
the end to the C5 on the road. It doesn’t seem to roll very smoothly. I don’t
know if it is due to wheel size or lack of rear suspension. The original front
wheel rims were plastic with caliper brakes acting on them. The brakes resulted
in the rims melting so restorers often used pram wheels in the front. These
could be as small as 8” in diameter.
From a human-powered assist perspective, the biggest design
flaw was that the pedals seemed to be added after fact as opposed to being
integrated into the design. Restorers often insert a 3-speed hub ahead of the
rear axle to get the extra speeds. Making the seat to pedal distance adjustable
is not something that could be easily retrofit-able because of one-piece
chassis and one-piece lower body pan.
Besides the pedal-ergonomic issues, other concerns were that
the rider sat too low for good visibility in traffic and inadequate weather protection.
The former concern was addressed by adding a framework behind and above the
rider that held reflectors. The latter was addressed by optional side curtains
and a rain suit for the rider.
Three factors probably resulted in adequate rollover
resistance. The seat height was relatively low compared to the track of the
trike. The c.g. was biased strongly over the rear wheels and the maximum
vehicle speed was only 15mph.
In 2010 Sinclair was working on resurrecting the concept of an
all-weather E-bike in the form of the X1, which is a true bicycle, having only
two wheels.
The latter part of the video below deals with the X1.
As the comparison illustration states, the X1 had better
weather protection and a higher rider height Than the C5. The top of the
vehicle is 55”, which in the photo next to an auto, looks like it should be
even higher for good visibility. On the other hand, the roof of my Honda Civic
is about that height. The width at 27” is 2” narrower than the C5. Both wheels
are now 16” in diameter. Although it is not stated, the fact that, at 83”, the
X1 is approx. 12” longer than the C5 may indicate that the seat to pedal
distance may be adjustable by sliding the seat. There is no indication that the
vehicle had more than one pedal speed. The electric motor drives the rear wheel
and produces 190W and the overall vehicle weight with battery is a light 66lb.
Like the C5, the design of the body is quite attractive. The vehicle seems to
roll with less vibration than the C5. Partly because of the longer wheelbase, (about
73” vs the 51” for the C5) but mostly because both wheels appear to be
suspended.
The fact that five years have passed and there is still no
commercial X1 may indicate that the design had issues that prevented it from
being commercially viable. I can speculate about what one major issue might
have been.
Going from a tricycle to a bicycle, one loses the static
stability necessary to get into a semi-enclosed vehicle. The body can interfere
with lifting the support foot up when starting and putting a foot down when
stopping. Even though there are cutouts in the lower body so the feet can touch
the ground, the cutouts prevent the feet being paced laterally very far from
the vehicle. So one must put their foot down before the vehicle has tipped very
far. In the video above, we see the rider stopping but not restarting, the more
difficult of the operations. See below.
So the Sinclair team apparently went from three to two
wheels as a weight saving and lost the static stability in the process.
So as is my want, l would like to speculate about the
changes required to the C5 to make is a viable all-weather E-bike for the US
market where the top speed could be 20mph.
I would use larger
wheels, 16” in front for better rolling resistance and 20” in the rear for the
ability to obtain higher gears.
I would make the seat to pedal distance adjustable by making
the structural frame in two parts. The rear part would hold the rear wheels,
the seat, batteries and any cargo. The front part would hold the front wheel
and the pedals. The front part could be slid into the rear part to adjust seat
to pedal distance. A similar approach is used in the Kettwiesel tricycle below.
I would have the seat height about 18”, placing the riders
head about 48” off the ground wearing a helmet. I would keep the bottom bracket
at about 15”, as low as I could get it without having the rider’s heals scrape
the ground.
I would use a single chainring in front and attach a
cassette to the rear axle. I would connect both rear wheels to that axle
through freewheels, thus insuring a posi-traction-type drive.
I would use a hub-motor in the front wheel for the electric
drive.
I would suspend the rear wheels and load the front wheel
lightly enough so it didn’t need suspension, say 25% of the vehicle weight.
I would divide the body into two parts. The front cowl would
completely enclose the front wheel and cover the rider up over the legs. This cowl
would move with the crank and front wheel when adjusting the
seat-to-bottom-bracket distance. The rear portion of the body would cover the
riders head and the rest of the body. The rear portion would rotate upward
about a pivot in the back of the vehicle to allow the rider to enter and exit.
I call the vehicle below the Avacar because it has a similar
rider layout to the Avatar recumbent. The rider’s head height with helmet is 48”.
The wheelbase is 53” and the vehicle track is 26”.
To this point I haven’t discussed turn-induced rollover
issues with my redesigned C5. One advantage of making the Sinclair X1 a bicycle
is that it has dynamic stability and can lean into the turns.
Let us assume that the original C5 had no rollover issues. I
have made two changes that will reduce its rollover resistance, (ROR). I have
raised the c.g. of the vehicle and I have increased its top speed. The 4”
increase in seat height reduces the ROR by about 10%, assuming a c.g. height of
about 17” for the original C5. The 5mph increase in speed reduces the ROR by
about 44%. Together I have reduced the ROR by about 50%
.
The track of the old C5 was about 27”. To maintain the ROR
of the original, the track would have to increase to 40.5” and the width to
almost 43”. The width of the redesign is no better than the ELF or the Velocar.
That brings me to the question,” Should the AWEB be a
leaning tricycle?” There is an all-weather E-bike on the market, the Drymer. It
utilizes the tadpole layout.
Now I have discussed the design of leaning trikes ad nauseam.
However, I have two new observations about the design of leaners when they have
bodies that prevent riders from easily putting their feet on the ground to
support the vehicle.
The first observation is related to the lean-lock mechanism
that prevents leaning at very low speeds and when entering and exiting the
vehicle. The default state for the lean-lock should be engaged and the rider
should actively disengage it. For electric vehicles, engagement could occur
when power is shut off or when vehicle speed falls below a predetermined low
level. Engagement must be quick and positive, where the engagement force is not
provided by the rider but inherent in the mechanism. The rider merely overcomes
the engagement. This approach insures that there is always enough engagement
force for complete prevention of leaning. Engagement mechanisms that are
position dependent as opposed to force dependent are preferred.
The second observation is that, under no circumstances,
should the vehicle be allowed to lean far enough to tip over statically. Now,
an observant reader might point out that under these circumstances, the dynamic
ROR is only slightly better than the static ROR. But that is not true if the
lean-lock is engaged when the vehicle is completely leaned over. (The vehicle
is leaned into the turn and locked in that position.) With the leaning locked
in that position, the acceleration is acting against the full track of the
vehicle instead of just one-half the track as in the static case.
Now I decided I wanted my design to be able to resist one
gee acceleration when locked fully leaned over at the same time it was at its
static tipping limit. It turns out the lean angle for this condition is
24.5deg. For a given c.g. height the vehicle track at the c.g. location is .829
times the c.g. height. The actual track is the c.g. track divided by the % of
the weight on the rear wheels.
For example, if my CG height is 20.5”, the c.g. track is 17”.
If 71% of the weight is on the rear wheels, the actual track would be 24”.
The Avacar drawing above is based on these numbers with 2”
added to the track for a little safety margin. The vehicle width is 4” wider
than this or 30”.
Hephaestus
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.
