Reflections on the potential of human power for transportation

Friday, September 4, 2015

Make My Velomobile a Quad!

I was talking to my son Kyle the other night. I told him I had finished the testing of my leaning-trike proof-of-concept commuter vehicle and that I had met the cruise-speed goals I had in mind for the project. I also told him about the latest lean-lock mechanism I had incorporated to ease stopping and starting with its faring in place. He listened patiently and after I have finished explaining, he pointed out that this was to be a commuter vehicle and the requirement to lock and unlock the leaning for stopping and starting was too complicated to expect riders to have to cope with. And I couldn’t argue with him. 

Now Kyle says he doesn’t read my blog, too much information, even though he is a road cyclist and an accomplished mountain biker. He has had the misfortune of riding and crashing one of my ill-fated rear-steering leaning-trike prototypes. With misplaced fatherly devotion, I was more concerned with the bent-up trike than his welfare. So he has a right to mistrust his old man’s hair-brained contraptions
Sometime after that I was reading Miles Kingsbury’s account of his riding his Quattro on the Roll Across America velomobile tour and how his four-wheel vehicle handled road imperfections better than the trikes with whom he was riding. Below is another picture of the Quattro in its convertible guise.

And another with the top in place.

So I had to ask myself, am I avoiding a four-wheel layout for my human-powered commuter vehicle because it is too simple to satisfy the gizmologist in me? Since I have no plans to use powered assist, the vehicle-classification reasons for not using four wheels is not an issue. So rethinking my assumptions is in order.

The historically significant velomobile, the Pedicar had four wheels. However its 38” width made it difficult to fit thru some barriers and its exposed wheels gave it poor aerodynamics. And of course it had the linear-pedal drive that had some efficiency issues.

It probably is not a good starting point to speculate on an efficient quad velomobile design.

The Quattro, on the other hand, IMO is too close to the ground for commuting in traffic. I do like the fact that the steering wheels are enclosed. Driving and steering the front wheels does make things complicated. There are the velocity fluctuations associated with single-universal joints. There does not appear to be any differential to account for the different wheel speeds during cornering.

Another candidate the design of a commuter quad is the Quest velomobile. It also has enclosed steering wheels and I have always been impressed by the level of refinement in its implementation. And its overall width of 30” is narrow enough to fit through bike-trail barriers.

Now my assumption is that the Quest’s current rollerover resistance is adequate for most situations. That being the case, the addition of a fourth wheel should increase that resistance by about 1.5X. Since rollover resistance is a function of vehicle track (spacing between the paired wheels) divided by the c.g. height, one could use that 1.5X to increase the c.g. height and maintain the three-wheel rollover resistance.

Referring to the dimensioned drawings, 

the faring behind the rider’s head is about 34” off the ground. That puts the riders head about 36” off the ground. If this could be raised to 48”, I would feel a lot more confident riding the vehicle in traffic. If the c.g. is raised 48/36 of 1.33 times, this is within the 1.5X rollover margin that the fourth wheel contributes.

Raising the rider and making the rear faring wider to accommodate the fourth wheel will make the vehicle less aerodynamic, but this should be acceptable considering that the original vehicle had a racing heritage and a commuter does not need to be as fast. One benefit to raising the rider's position is that ease of entry and exit can be greatly improved.

Since the rider is up higher, the steering can be located beneath or alongside the seat. This will allow the faring to be lower between the rider’s knees and his head and provide better forward visibility,
So the front end construction of the Quest quad can remain the same.

Behind the seat, the drive chain has to drive two wheels instead of one. The easiest way to do this is attach the cassette to an intermediary jack shaft. At the ends of the jackshaft, at the same width as the rear wheels, attach single-speed freewheels. Then connect the wheels to the jackshaft freewheels with two additional chains. The two-freewheel drive approach produces a posi-traction-like drive. That in combination with at least 50% of the vehicle weight being on the drive wheels (as opposed to 33% with a tadpole trike) provides exceptional traction for slippery-road conditions.

Depending on which side the rear wheels are being driven from and how the freewheels are threaded, one of the freewheel ratchets, its threading and the cog threaded on one of the rear wheels may need to be left handed. Left handed freewheels are available as BMX components.  The rear-wheel suspension can be based on the wheels pivoting around the jackshaft, so chain tension is not affected by suspension movement.

Yea, the quad conversion may not be that simple as I just proposed, but the Quest Quad would make a very attractive commuter vehicle.


Tuesday, September 1, 2015

Trikes & Leaning Trikes: A Second Look

Why designers select three wheels for vehicles:

Compared to their four-wheel cousins, you see very few three wheel automobiles. I think that the basic reason for this is that, for layouts where all three wheels are equally loaded, and the vehicle tracks (width over the paired wheels) are the same, quad wheelers can corner at a 50% higher accelerations than trikes. Thus trikes need to be about 50% wider than quad wheelers for comparable tipping resistance.

So why is there continued interest in trikes by progressive vehicle designers? One reason it that tricycles are less regulated that quads. If light enough (less than 1500 lb. in the US?) the vehicles are considered motorcycles. And if the power is low enough, they can be considered mopeds. And if slow enough (less than 20mph in the US) they can be considered electric bicycles and have access to bicycle paths.

Another reason trikes are popular platform for new vehicle concepts is that they can be simpler than quads. For tadpole layouts (two wheels front, one behind) they can use motorcycle or bicycle transmissions to drive the rear wheel. For delta layouts (one wheel front, two behind) they can use motorcycle or bicycle fork steering. And delta trikes can be more aerodynamic than quads.

A three-wheel pedal-electric vehicle:

 So let’s look at a hypothetical pedal-powered commuter vehicle with electric assist. We make it a three-wheeler to take advantage of the reduced vehicle regulations. We want car-type seating with pedals about 10” below the seat, so we choose the tadpole layout. The pedals easily fit between the two front wheels.

We want a rollover resistance of at least one gee. The rollover gee limit for static vehicles is approx.


Where w is the track width (distance between paired wheels) and hcg is the height of the center-of-gravity off the ground. For tricycles, where the weight is equally distributed over the three wheels, w is approx. 2/3 the spacing between the wheels.

Automobiles regularly have rollover resistances in excess of one gee. And some sports cars can approach two gees or more.

For the one gee roll over resistance and a hcg of 16", we will need a track of about 48".
Both the Elf from Organic Transit and the Velocar from VeloMetro are actual examples of our hypothetical tricycle layout vehicle. Not surprisingly, they both have tracks of 48"

The Elf is shown below.

The proof-of-concept for the Velocar is shown below.

Does the rollover resistance need to be as large as one gee? Judge for yourself. The vehicle below is a Mango velomobile,  one of the better designed tadpole trikes. The vehicle width is 30” and I estimate the track to be about 28”. If hcg is 13”, Gees= approx. 0.7. Clearly in the case below it is not high enough for the turn that is attempted. And the turkey isn’t even wearing a helmet…

If a track of 48” is too wide for the paths the vehicle is to use, there is an unconventional trike layout that can be employed. I call it the Coventry-trike layout in honor of James Starley’s Coventry Rotary tricycle of the 1880s.

A modern version of the design would probably use equal sized wheels, all cantilevered for ease of removal and tire replacement.  One advantage of this approach is that, if the drive wheel is located along the c.g. in the side-to-side direction, 50% of the vehicle weight in on the drive wheel as opposed to the conventional tadpole layout which only has about 33%. 

One downside of this layout is that the trike would tip forward during hard braking. Tipping could be prevented, however, by having a caster near the ground opposite the front steering wheel and in front of the driving wheel. This caster could be frictionally loaded so when the trike tipped forward and the castor contacted the ground it contributed to braking.

The most complicated method of reducing the width of the trike, but maintaining its rollover resistance is to allow it to lean. The designers at VeloMetro considered making their Velocar a leaning trike, but since their business model was to rent their trikes to people for short trips, the associated learning curve would have been impractical. Leaning trikes have all the issues of recumbent bicycles, plus more if the vehicle is in and enclosed body. See below,

For bicycles and free-leaning trikes, 

                Gees=tan (alpha)

Where alpha is the lean angle from vertical. For one gee of rollover resistance the lean angle is 45deg, which is quite a bit of leaning, and is to the state when the tire contact with the ground could be on the sidewalls, not the best for adhesion.

If properly implemented, however, leaning trikes can develop more rollover resistance than just the bicycle-lean effect.

Since I have spent a good deal of time working with the delta trike layout, let us examine another hypothetical vehicle. It has a width of 30” and a track of 26”, a wheelbase of 48” and a c.g. height of 24”. It can lean 30deg. from vertical.

Below are diagrams of this trike seen from the top and the back. The trike is fully leaned over.

There are four rollover accelerations associated with this design. Two are common and the other two are associated with leaning trikes.

(Lean locks are discussed in more depth in the post above.)

The first acceleration is when the trike is locked (lean-locked) in its upright position. This upright–locked acceleration is 8.5” (dim a. in figure 1. from the upright c.g. to the tipping line A-B) divided by 24” (the c.g. height) or .35gees.

The second acceleration is due to leaning (like a bicycle). This free-leaning acceleration is tan(30deg) or .58 gees.

A leaning trike can corner harder than a bicycle for a given lean angle because the wheel opposite the lean direction increases the distance from the c.g. to the line of tipping This acceleration is when the trike is fully leaned over and the lean-lock is engaged. This lean-plus acceleration is 20” (dim b in fig.1 the distance from the c.g. to the tipping line A-B) divided by 20.78 (dim d in figure 2). The lean-plus acceleration is .96 gees, almost .4 gees greater than the free-leaning acceleration.

The last acceleration is associated with the tendency of the trike in the leaned-over but lean-locked state to tip in the opposite direction. This counter-tipping acceleration is 3.5” (dim c in fig 1, the distance the c.g. overhangs the tipping line A-C) divided by 20.78 (dim d in figure 2) or .17 gees.
Sounds confusing, doesn’t it.

To try and make things clearer, let’s have our rider, from the Mango tipping video above, ride our trike through a progressively tightening turn. The rider gets into the delta trike with leaning locked upright. The rider begins to make a turn. When the acceleration of the turn reaches .35 gees, the lean lock must be released to prevent tipping. The turn gets tighter and the rider leans into the turn. As the turn gets to .58 gees the rider is at the lean limit. If the turn gets tighter the rider will not be able to maintain the lean and will be pulled upright. However, if the lean lock is again engaged at maximum lean, the rider can corner with an extra .38 gees without tipping.

Now even though the trike is locked up with the c.g. outboard of the left tip line (A-C) the trike won’t tip over as long as the turn is at least .17 gees, the counter-tipping acceleration. The acceleration of the turn must drop from the .96 gee max to .17 gees before the lean-lock needs to be released and free leaning can resume. This is plenty of time to do this.

The requirement to continually engage and disengage the lean lock may be too much of a complication for a human-powered commuter vehicle. But for powered vehicles that can employ automatic lean actuators based on vehicle accelerations, this would all be transparent to the user. The driver would just steer and the onboard computer would determine the appropriate amount of lean.


Saturday, August 29, 2015

Transcending the Pedicar; The EcoVia, Epilog


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.