Introduction:
So how did we get here? The goal was to produce an
all-weather pedal-powered commuter vehicle that would be as high as an
automobile, as narrow as a bicycle and be stable on slippery road surfaces. The
solution that was chosen was a leaning tricycle, the EcoVia.
To date, the high-water mark in pedal-powered commuter
vehicles is the Pedicar from 1973. The Pedicar was completely enclosed and
obtained its stability from four wheels. The Pedicar only had a top speed of
about 18mph because of the exposed wheels and the blocky body. Having a width
of about 38”, it was somewhat limited as to where it could be ridden.
Non-motorized vehicle barriers in my area can be as narrow as 36”.
Riding without the faring:
The EcoVia balances just like a recumbent bicycle. In fact,
when the delta-trike layout was first assembled, the rider could not tell if
they were riding a bicycle or a tricycle, unless they looked behind them. Subsequent
modifications that required re-brazing on the areas holding that Igus bushings
that allow the leaning have warped the bushing seats and increased the friction
associated with leaning. Nevertheless, it still rides essentially like a
bicycle.
Starting and stopping was done by lifting the support leg
from the ground after thrusting the pedal forward with the other leg. Stopping
was simply the reverse, putting down the support leg just prior to stopping.
This process is typical of a recumbent having a mid-height (20”) bottom bracket
and a seat height slightly higher.
Starting & stopping with the faring:
Problems with starting and stopping began when the faring
was added. Once up to speed (several mph) it continued to ride like a recumbent
bicycle. The problem arose because, since the faring pivots are part of
structure that surrounds the front wheel, this structure got in the way of
lifting the support leg when starting and putting the support leg down when
stopping. It also restricted how far the foot could be placed away from the trike,
severely limiting the ability to stop tipping.
The picture below shows the framework that supports the
faring pivot at the bottom right.
As a result I sustained five low-speed crashes. Three were
making tight turns where there was not enough speed to keep the trike upright
and two were in attempting to start from a stop.
Lean locks:
Now the EcoVia has a lean lock that clamps a disk-brake
rotor attached to the link that connects the pivoting wheel beams. It is activated
by a lever next to the seat. The lever is an extension of a frame-mount gear-shift
lever.
The logical approach when starting and stopping with
the faring would be to engage the lean-lock lever for stopping and release it
when the trike is moving. Unfortunately, with the faring in place, it was
difficult to reach the lean-lock lever. As an alternative, I tried using a
twist-grip shifter to pull on the caliper cable. It would not produce enough
force to clamp the brake rotor hard enough to prevent tipping. Nothing is worse
for stability than a partially engaged lean lock. It doesn’t prevent you from
tipping but it does prevent you from balancing.
After three of the crashes, I went back to the seat-mounted
lever. The faring did not sit straight on the frame and one side had more room
next to the seat than the other. It was on this side that I reinstalled the
lever. I also dropped the seat and faring height by about 4” to improve the
static stability when the lean lock was engaged.
That didn’t solve the problem however. Since I had to
release the steering to reach the lever, the trike would no longer being going
straight by the time the lean lock was engaged and the trike ended up being
tilted. To change the tilt one had to release the lean lock again, balance to
get the trike upright and then reengage it before falling over. This was a
problem.
I read that the Piaggio MP3 tilting-trike scooter had
similar problems. It had a lean-lock that can only be engaged when the trike is
going below several mph.
If the rider is not sufficiently upright when the lean-lock
in engaged, there was a risk of falling over when the rider tried to stop.
It occurred to me that, if the trike was moved to an upright
position when the lean lock was engaged, there would be no concern for falling
over, within the limits of the static stability of the vehicle. I added two
semi-vertical posts to the wheel beams. The pivoting of these beams allow the
trike to lean. I also added a crosslink that would pivot and press against the
wheel-beam posts. The crosslink was moved by a lever connected through a toggle
that allowed a large force to be produced. The crosslink would prevent the
wheel-beams from rotating and keep them parallel so the trike was held upright.
I call this device the no-lean lock, NLL.
The NLL was never intended to center the trike from a fully
leaned over position. At max lean of 27deg., the tipping moment is approx. 3000
in-lb. One would have to exert over 200 lb. on the 14” NLL lever to pick the
trike up. Neither is it feasible to pull on the lever with this force or if it
was the lever would bend before the trike moved. The intended range of
operation is probably closer to 5deg. from being upright.
Below there are two pictures with the NLL on. Notice the
toggle link is just slightly past horizontal.
Below is a picture of the NLL lever which is located
outboard of the rider’s left thigh.
Below are two pictures of the NLL off. The tike is tilted
away from the viewer with the near wheel-beam down and the far wheel-beam up.
The crossbeam is in contact with the far wheel-beam post. The trike is tilted
to its limit and the lever is all the way forward.
The NLL reduced the tendency for falls and the problem with
starting and stopping while the faring was installed was resolved.
Starting dynamically-stable vehicles:
So after building and riding a number of dynamically-stable
vehicles, bicycles and recumbents, I can offer some observations on those
factors that influence ease of starting. The two factors appear to be seat
height and bottom bracket height. (This discussion assumes that the geometry
of the vehicle produces a stable configuration when moving as opposed to vehicle
like a rear-steering bicycle.)
The rider begins by sitting on the seat with one foot on the
ground and the other foot on the pedal. The rider pushes down on the pedal. If
the rider can obtain the minimum speed for balancing by the time the second
foot lifts from the ground and presses on the pedal for the second stroke,
balance is achieved. If the vehicle has not reached that speed when the rider
lefts the ground foot, the foot must be quickly placed back on the ground and
the procedure started again.
How quickly the vehicle tips is a strong function of how
high the seat is off the ground. The higher the rider, the greater the inertia
that must be rotated and the slower the tipping. This is why it is easier to
start off on an upright bicycle than a recumbent. (It is easier to balance a
meter ruler on your finger than a pencil.) People who are very experienced riding upright
bicycles still require a learning curve when learning to ride recumbents.
The time it takes for the rider to lift the foot from the
ground to the second pedal is a function of how far the pedal is from the
ground. The higher the bottom bracket, the longer it takes to lift the foot and
the farther the vehicle will have tipped before the second pedal thrust.
Recumbents with low seats and high bottom-brackets are hard to get started.
Current examples of leaning trikes:
My no-lean lock mechanism fixed my starting/stopping
problems with the EcoVia, but how do other leaning trikes deal with the
problem?
We will look at three other vehicles, the Drymer, the Varna
Trike and the Velotilt.
Below is a picture of the Drymer
Below is a picture of the Varna Trike
And finally two pictures of the Velotilt.
The Drymer has a high seat height relative to the bottom
bracket. As a result, it appears to start similar to a well-mannered recumbent
like the Avatar 2000. Feet have clear access the ground with minimal
obstructions. It does not appear that the Drymer has a lean lock nor does it
probably need one for starting.
The Varna Trike should be considered a semi-leaning trike
since only the rider and the front wheel lean. It uses a torsion bar type
spring through the central frame tube to assist with balance.
I added strings to the wheel-beam posts on the EcoVia.
The springs were strong enough to develop about 50% of the
tipping moment produced by the weight of the rider and the trike. Despite this
high spring rate the friction associated with the leaning mechanism was great
enough to prevent the springs from forcing the trike to become upright without
a rider. While riding the trike with the springs, their presence was not
apparent during low-g turns but appeared to resist proper leaning during
higher-g turns. At this point I will assume that the torsion bar on the Varna
trike merely serves to keep the trike upright without a rider. When the EcoVia
was new and the leaning mechanism had lower friction, it would fall over
without the lean-lock being engaged.
The Velotilt has a lean lock. Since its cover prevents any
foot or hand contact with the ground while starting, the lean lock is required
for operation. The lean lock is activated by a twist-grip shifter pulling on a
cable for a disk brake caliper. Instead of a brake disk, a plate attached to
the leaning mechanism is gripped by the caliper.
Faring performance with weather sealing:
In my previous post, I expressed disappointment that the
faring did not increase the speed of the trike more than about 2-3mph, about
17mph without the faring and 20mph with the faring. It occurred to me later
that, since the Spandura fabric had no moisture proof coating, much of the air
was passing through the fabric instead of around. After adding several coats of
moisture proofing, the cruse speed was raised to about 24mph. This speed was
close to the original 40kph goal and is probably obtainable by reducing some of
the mechanical frictions associated with the drive mechanism.
The road forward:
I believe the EcoVia needs to function in both statically
stable and dynamically stable modes. Statically stable for low speeds, starting
and stopping. Leaning would be employed for higher speeds. Better, quicker access
to the lean-lock, for example a twist grip acting on a large radius plate to
produce the necessary torque may eliminate the need for the no-lean lock. The
left handlebar would have the lean-lock twist-grip and the right handlebar
would have the gear-shift twist-grip.
The crashes painfully pointed out that I had designed no
provisions for those possibilities. The nosecone can absorb frontal impacts,
but the semi-rigid faring provides little protection when tipping over. The
fabric gets shredded and the aluminum stringers get bent. The rider’s arm and
ribs take the brunt of the impact with the ground. The next design will include
three large diameter tubes spanning the width of the trike. One will be behind
the rider’ shoulders, one will be beneath the seat and the third will be
beneath the thighs. In the event of the vehicle tipping over, the three tubes
will support the trike on the ground and take the impact. A provision will be
provided to keep the rider constrained laterally in the seat.
One can trade off cruise speed for static stability. The
EcoVia has a maximum faring width of 27.5” with a 20” wheel track. I plan to
increase the track to 24” but keep the faring width at about 28-30” If I make
the track wider the upper speed at which static stability is maintained
increases, but the faring becomes wider and cruise speed is reduced.
As an asymptote for this approach, consider the Kettwiesel
trike below.
The Kettwiesel has about the same seat height and bottom
bracket height as the EcoVia, but has a track about 32”. It does have the seat
closer to the rear wheels than does the EcoVia, which can reduce tipping at the
expense of a very-lightly loaded steering wheel. One can imagine that is the
EcoVia’s dimensions were made similar to the Kettwiesel that leaning might
become unnecessary. The EcoVia would be slower, less visible, but lower cost and
lighter weight.
As a proof-of-concept the EcoVia has demonstrated that a
leaning trike with lean locking can be high enough to be very visible in
traffic (53” to the top of the helmet) and narrow enough (27.5”) to easily fit
within roadside bike lanes. Using a semi-rigid faring with a nosecone, cruse
speeds on the order of 25mph can be sustained by a reasonably fit rider. In
addition, with drive to both rear wheels through what is essentially a
positraction-type mechanism, the EcoVia offers outstanding performance for slippery
road conditions.
Hephaestus
