KC8QVO

I figured I would start a new thread here as I am deviating more from my original thread (here). The theme in the thread here is technical information related to the theories and feasibility of ideas in custom building a velomobile.

First off - 3 wheels vs. 4.
There are several schools of thought I've seen/heard now. The pluses for 3 wheels generally come down to less parts and less resistance. On the subject of less parts - a single rear wheel is the overwhelming majority of designs due to being standard with all bicycles - same hub and drivetrain can be used. Less rolling material (rims, tires, spokes) means less energy soaked up in that movement of mass. Less tires contacting the ground = less resistance from the ground resistance. Less wheels protruding from the under-side of the body/fairing means less wind resistance/more aerodynamic.

Two down sides appear to be stability/traction and tire track related. On the subject of stability - 3 wheels doesn't handle lateral force/motion nearly as well (hard side wind, g-force in a turn). As to track - with 3 wheels in a triangle pattern all 3 create their own track (snow, dirt) where all 3 wheels will lose efficiency pushing down what ever soft material they are rolling over.

The pluses for 4 wheels really come down to stability, traction, and track. Stability-wise - they handle lateral forces a lot better. Traction - much the same - 4 wheels is an extra tire's worth of traction, but due to the ability to have a tire in each "corner" the stability and traction increase really do go hand-in-hand there. As to tracking - with both the front and rear pair on the same track width only the front tires would have the resistance of packing down material (again - snow, dirt) - when going in a straight line anyway. So that makes 2 tracks and not 3.

Aerodynamics:
One of my ultimate irritants on rides is the wind. I am giving a lot of credit to those that I've heard/seen explain head winds and tail winds not affecting their performance in velomobiles to the extent it does with any other non-aerodynamic option. So for this reason I am effectively tossing wind in-line with the direction of travel (with or against) out the window. However, lateral wind (from the side) is a whole other beast. For that reason I am wanting to focus on that for performance, not head winds and tail winds (I know there are ways to increase efficiency in those directions, but I suspect that is going to be very easy with a small cross-sectional area whereas lateral winds are going to be harder to work with as the body will have magnitudes larger cross sectional area).

Goal of aerodynamics and wheels = stable design that will be efficient to pedal and won't get blown off the road or in to an adjacent lane on the road = safe to control on open roads with traffic.

Having the above design goal - 4 wheels is the obvious choice.

Wheel size
It looks like a lot of recumbents and velomobiles use multiple wheel sizes, and smaller wheel sizes, than upright bikes. I would imagine that has to do with profile. The bigger the wheel size the higher and larger the profile gets, and the longer the wheel base gets. Profile gets in to the aerodynamic question, which in turn gets in to the stability question. The larger the wheel diameter the larger the cross sectional area the side of the design becomes = more of a problem for lateral wind.

I will use my 20" folding bike as an example here. It has under 400 miles on it and I can see a good amount of tire wear on it. In fact, I swapped the front and rear tires to balance the wear more. My 700c tires have a couple thousand miles on them (not sure on the mileage, I lost my ride data spanning about 3 years) and have similar wear - at magnitudes more mileage. Then again, the smaller wheels are spinning a lot faster for the same speed so the outside of the tires contact more road surface for the same distance as the larger ones.

Having said that - I think the benefits of larger tires are certainly something to consider. Take a 26" wheel for example. That is a very common size. The extra diameter (and in turn - circumference) would, in the same theory as the 20" folder above having quicker tire wear, have slower wear.

Are there any big reasons I am missing, other than profile, that you can think of? Are there any profile points that you think should be highlighted?

Drivetrain
It appears there are a few ways to drive "an axle and two wheels" (I quote that because that is a poor statement). There are two common methods. One with a single wheel drive (one side drive) using a conventional freewheel on one side and a plain hub on the other. The second is a "ratcheting drive" using, essentially, two freewheels - one on each wheel - where only the slowest wheel is driven, the faster wheel coasts as it speeds up on the outside of a turn.

From a mechanical power transfer perspective, I really don't like either of the above methods. One can argue the ratcheting drive method may be superior from the standpoint of always getting power to a wheel with traction, however it falls short in tight maneuvering - especially at slow speed or from a stand still with no momentum.

A differential is a solution to getting power to 2 wheels across an axle, while having the wheels able to turn at different speeds (not only the same speed as with a fixed axle). The obvious drawback is the fact that in a standard differential if one wheel looses traction there is no way to power the wheel with traction. However, when both have traction the wheels share the power, not one (one at a time or the same one all the time).

Here is one manufacturer that appears to make differentials for trikes etc:Samagaga

Gearing and Chain Routing
Going with a rear drive there is a lot of space between the bottom bracket and the axle being driven. There are a few schools of thought for chain routing that come down to chain tubes or idler sprockets. As for gearing - the long distance makes it possible to get pretty creative with gearing options and mid-drives. For example - a triple chain ring at the crank and 11 speed cassette at the axle could run through a mid drive with two more gear range selections for the possibility of a "high range" normal road range favoring the top end speed and what slow speed maneuvering may need to be done on flat ground and shallow hills on one gear and a "low range" for grinding real slow when needed to lug up a steeper or longer incline. Yeah, every bearing, every sprocket, and every chain link adds resistance to the drivetrain, however the ability to expand the gear ratio, to me, seems like a real bonus. The top end speed of velomobiles in the 40-50mph range make the opposite end of the spectrum pretty hard to see getting in the conventional chain ring/cassette combination. With one more level of range selection it seems more probable.

Suspension
I am getting the vibe that suspension isn't needed for comfort, rather it helps a lot for traction and stability. I suppose the faster you go the ability to keep the tires on the ground becomes harder and harder unless the wheels can move up and down independently of the bulk of the mass of the vehicle so they can follow the ground contour. Is there anything I am missing here? With suspension the other associated idea is that of dampening to hold back bouncing (like shock absorbers do on cars/trucks, just smaller scale). However, too much dampening (too much resistance) may cause the same concern of stability with wheels not staying on the ground well at speed as a non-suspension design. Maybe adjustable resistance dampeners would be good to experiment with.

Ground clearance
This goes right along with suspension I think. Ground clearance is another animal to consider. Some velomobile body designs use a channel/tunnel that protrudes from the bottom of the body where the chain passes through. It seems anything lower than the body is just another obstacle and risk of snagging or scraping things below. It would seem multiple ride heights would be nice to have - similar to the cut adjustments to lawn mower decks (not necessarily designed the same way, but the theory of the adjustable height). If each corner of the suspension had 3 positions, for example, that could be set by moving a pin it would be easy to drop down to a lower profile/high speed level for down-hills and go up a level or two to clear speed bumps or curbed driveway entrances/path to road transitions.

Brakes
Nothing but disks I believe. I have heard drum brakes exist in the cycling world, however I don't know what the feasibility of them would be. I would think a disk brake per wheel would be pretty good - the larger the disk diameter the stronger the stopping power, all other factors being equal (I know there are differences in pads and calipers, mechanical vs hydraulic, etc also).

Steering
Tiller steering seems popular. From a mechanical perspective I am not too crazy about it. It seems speed handling and maneuverability are a bit opposite each other. For running really fast a very shallow steering response would be desirable. That wouldn't lend itself to a very small turning radius. Having a small turning radius, on the other side of the coin, would mean the steering response at speed would be hairy. Adding a damper to the steering system would be smart, however getting the input increment vs output response balanced to cover both ends of the speed range and maneuverability is tricky.

Fairing design and construction
Foam insulation as a frame then fiberglass seems to be a logical option. Carbon fiber is lighter, but I think that might not pay off vs the investment cost of it. I will have to put some numbers to the weight percentage difference then give that a more scientific analysis.

Ideas so far? I will toss out some more thoughts as I have them.

Leisesturm

I'm not sure there is any way to put this kindly. It is clear from your writings in this and the other thread that you simply do not have the background, or experience in these very specialized vehicles to design and build one. It's not going to happen. There is only one, one, four wheel velomobile in production in the world and its designer was hugely experienced and had years and years of commercial success with three wheeled velomobiles. Nevertheless, it took him YEARS to get the Quattrovelo to reality. A four wheel velomobile is not just a three wheeled one with an extra wheel. There are incredible engineering problems that need to be solved. If it was easy we would all be doing it.

You cannot put an e-assist in a velomobile. It is illegal in just about every country in the world. Comes too close to being a car. Can't have that. You will want an e-assist. You come to some interesting conclusions about things in vehicle design. Like 26" wheels. There aren't any in current designs. Maybe someone somewhere used a single 26" wheel in the rear. Once maybe. Tire wear was not the reason. Another time maybe I can go through your ideas one by one but some essential reading for you is the treatise on trike design by Ricky Horwitz. He designed a commercial Trike and then made plans and the design treatise free to the public.

You should buy an inexpensive trike and build a fairing for it. There are two ways to home build a fairing: composite (wood counts as a composite) and coroplast. Of these two, coroplast is more accessible and cheaper. Sadly, most coroplast fairings are ugly. Look up a fairing called "The Facet". It is not ugly. It doesn't try to mimic compound curves and look like a composite fairing that it cannot. You can have much of the performance of a velomobile by equipping a suitable trike with e-assist. With the money you just saved you can buy top of the line rain-gear and maybe a windscreen. I am right in this. You cannot build a velomobile that is safe, will track straight, and won't make people laugh. That way lies madness. Learn about them, Buy one if you can. Leave the design and fabrication to the trained professionals.

BlazingPedals

Drum brakes. Not Discs and especially not rim brakes.

KC8QVO

Interesting comments.

To some: doubt and criticism = motivation.

KC8QVO

The 20" folding bike as an example again - I am already seeing rim wear on that bike. I knew that was going to happen, but I didn't expect to see it as quick as I have. That is a bit of a learning experience, however I am not concerned with it now. As it progresses I will keep tabs on it and build a new wheel set when the time comes, unless the frame shows signs of fatigue etc then it might be more of a retirement/replacement of the whole bike. I hope not. My point, though - for loaded touring (on any bike) I wouldn't consider any kind of rim brake. My upright touring bike is a Disk Trucker. I weighed the pros/cons of both rim and disk and decided to go with disks. I'm glad I did - they handle hard stops with loads and still work well in the rain. Adding weight with anything (vehicle weight or gear weight, it all rolls on the same wheels) only exacerbates what the brakes do.

Between drums and disks - what is the downfall of disks that drums help with? I suppose I should clarify my perspective here - I am speaking solely in respect to bikes (pedal powered transportation), not motor cycles, cars, and trucks = traditional lever on a handlebar actuation that you find on normal bikes. For the most part that implies mechanical/cable actuation, as opposed to hydraulic, however I know there are bike-style hydraulic systems also.

Steamer

Drums require almost no maintenance, and if you needed to work on them, it can be done outboard of the wheel. Access inside a velo shell isn't the greatest. In many (all?) velos I have seen, the wheel well structure would prevent access to a disc brake.

Drums have fading issues though. But if you get large diameter drums (90mm) that have air cooled heat sinks, this can be managed.

Leisesturm

"unless [until] the frame shows signs of fatigue". That will not happen. Frames don't show signs of fatigue. Not any you can determine anyway. They fail, or they don't. Folding bikes frequently fail before their time. Full size steel frames often outlive their owners. Aluminum frames as well. Rim brakes are not the devil. Rim brakes are still OEM on most models of 'road bike'. My most recent road bike purchase has rim brakes. So does our recent tandem. The rear brake was out on that tandem for awhile and the single front brake could easily stop 550lbs+ of Captain, Stoker, tandem, trailer, and trailer payload, on a downhill run. But a rim brake would be hard to use in a velomobile build, even if you wanted to. Drums vs disks is really up to preference. Just remember you are in a small, confined space with those brakes for company. Would you rather breathe the byproducts of the braking process directly, or have them contained by the structure of the hub?

Steamer

I find I disagree with Leisesturm a lot, but I agree with most of what he wrote here. I could quibble about a few things, but it's mostly correct, and the quibbling would dilute the point being made.

You need to keep doing some research. Another hint is to break down your original email. You can't tackle every aspect of this all at once. Even my eyes glazed over a bit. One thing at a time, man.

I realize you posted here looking for information, but I'll tell you straight - this is not the right place. The BF recumbent forum is an internet backwater. I also know its bad form to write something like that, but it's true, and I am actually trying to help you.

The BentRideronLine velo forum is pretty active. There is a homebuilder section there too. In fact, there is one long thread about a homebuilt velo. It might give you an appreciation for what it takes to build one. Answer: metric sh_te-ton.

The recumbents dot com forum is another place, but it's a bit of a ghost town. But the few who do hang out are mostly homebuilders too.

KC8QVO

Whos to say the wheels and brakes can't be enclosed behind panels or fairings? Like on non-retractable landing gear on some airplanes there are fairings hiding the wheels. That is just one idea. However, that would only work with a wide track width where there is still room for the body inside the track width so as not to be too narrow for the operator.

Steamer

The wheel well is structural. You can't just casually blow holes in it.

There are streamliner designs that have used retractile landing gear, but those are hardly touring machines, which what I thought you were after. Streamliners are crosswind sensitive, and require great skill to pilot. A practical streamliner is a velo.

You need to study the state of the art and come to understand why things are the way they are before you try to innovate. People who skip that part and jump straight to innovation end up reinventing the wheel, and doing it more poorly at that.

Edited to Add: I'm out.

BlazingPedals

I'll just add that trying to build a velomobile with no prior hands-on isn't necessarily a recipe for failure; but you can expect to build 3 or 4 of them before you have a practical machine that fits *most* of your design criteria. Or you can buy one that's already been through all those design steps. The guys who have successfully built them on BROL are those who have owned several and copied those designs into their homebuilts. Or they are someone who has build a coroplast velo body around an existing trike.

Notso_fastLane

I'm an engineer. An aerospace engineer to be exact, with over 20 years of experience...in the aircraft industry. I own a recumbent bike that I've had since 2011, and a Strada (CF) that I have had since June 2018.

I have test rode a few velos, done a lot of reading, research, and even some aerodynamic simulations. I wouldn't even attempt to build a velo from scratch without doing a lot of preliminary work first.

For me, I'm more of an analyst than a hands on guy. I plan on setting up a shop in my garage (I'm buying a house this May) and learning to build CF parts, starting with small, fairly uncomplicated structures. I will purchase parts, like the race hood, that's already had years of development and professional experience. I will likely use that as a baseline to make my own, but that's a small part of the overall design.

I would recommend you do the following if you are serious about this.

1) Evaluate what you want out of this project. Do you want weather protection, primarily, so you can ride all year even in inclement weather? Are you primarily interested in speed/aerodynamics?

2) Buy an appropriate trike based on the above (I would avoid even trying 4 wheels as a first project, that's a whole other level of complexity). This alone can involve months of research, depending on your answers to 1. You want speed? Get a Cattrike 700C, ICE VTX, or something similar. You want practical and rugged? A Catrike trail, adventure, Velotechnik, all kinds of choices.
2a) Ride the trike for a while to get a feel for the handling. Work on it. Learn the things that are unique to having multiple track steering (wheel alignment, toe-in, camber, etc).

3) Build a shell for the trike. I highly recommend learning with cloroplast and experimenting. There are many great threads on bentrideronline.com (BROL) that you could research for ideas. The folks over there are also very happy to answer questions...even dumb questions.

4) Buy an actual velomobile, or at least see if you can find someone close to you that will let you ride or look at theirs. If you can get your own, ride it. Figure out what you would change/improve, even if it's just for yourself. There's a great thread on BROL by a guy building his own. It's been an ongoing project for a while already, so be prepared for a real investment in time.

Learn. Read. Research. There are some good instructional videos on youtube, there are lots of people that have done or tried to do, what you want to do. Don't re-invent the wheel, just try to make it yours.

KC8QVO

Thanks for all the constructive comments. Good stuff.

It certainly won't be anything any time soon, but the idea really intrigues me.

I haven't been riding my mountain bike in years. It is a 26" wheel bike. I am half way thinking about building a recumbent and harvesting the components from the mountain bike, at least for the project. That would give me something to play with on testing fabrication processes, seating position/posture, steering ideas, etc. We'll see where it goes. Off the bat it wouldn't be an "efficient design" on a lot of fronts, but having a platform to try things with would be a lot of fun.

As to a velo body being structural - that may be true in commercial velos. The idea of building a fairing around an existing trike, however, is totally different. The velo fairing in that case could not be structural - the trike is a stand-alone vehicle already. So with that in mind - if a chassis was made in the same sense of a stand-alone trike, why would there be any reason to rely on the fairing for structural purposes? The combination of a partial frame and the velo fairing being akin to a unibody constructed car is a different idea entirely - the body is the chassis. Lots to consider, though.

One thing that bothers me about composite construction (the unibody idea specifically, but composite structural components of any kind) is just that - relying on composites for structural integrity, as opposed to just being a skin on top of a sound structure. It would seem to me a sound metal structure would be easier to make strong - and would be field-repairable if something did go wrong. That is a benefit for chromoly steel on top of the frame idea, even though it is heavier than aluminum - steel is more readily weldable. A 6061 frame, or other type of light weight aluminum, is another idea - though, for repairs on-the-go it would probably be really good to have some spare filler metal so any shop with a tig machine could get things repaired in a worst-case scenario.

seibaatgung

One upside to a 4 wheeler is that you can change a tube or tire without taking the wheel off the axle, which is excellent for touring or commuting.

Notso_fastLane

The front tires on my velo change easily without removing the wheel. It has a single sided swing arm (as do most modern design velos) so the rear is a little more difficult, but still doesn't require removing the wheel.

BlazingPedals

Rotovelo is an example of a shell over a trike chassis. Even with a shell-over-chassis, the shell still needs to be stiff enough to hold its shape rather than flattening out like a water balloon, especially if you'll need to climb on it to get in.

BlazingPedals

From what I've both heard and read, putting a velo body on an existing trike is a sub-optimal solution for the most part. The reason is that most trikes are not suspended, at least the most popular trikes to add bodies to are not. Having suspension on the rear is an important safety feature, because it's easy to lose traction in the rear, say from hitting a rumble strip or a buzz strip. When that happens, without sufficient damping, the velo will quickly lose control, either flipping or swerving uncontrollably. There was a video out there somewhere of somebody losing control that way, fishtailing a few times, going on his side, and actually grazing an oncoming car's tires before coming to a rest in the middle of the road. Scary stuff!