Human/Electric hybrid velomobile?

[Jeremy Harris]

Some thoughts on regen:

As I understand it, typical BL controllers just shut off all the FETs at zero throttle. It should be possible to just fit a three phase rectifier to the motor, with it's output only switched on when the throttle is at zero.

One other snag is that the motor will most probably not generate a high enough voltage to usefully charge the battery during low speed regeneration. There may be a way around this by using a Cockroft-Walton type voltage multiplying rectifier.

The advantage of such a system would be that the regen unit could be an add-on, with no need to modify the controller, apart from taking a feed from the throttle. Even that might not be needed, if the rectifier could intelligently sense current flow to the motor.

Can any of you learned fellow see a flaw in this logic?

Jeremy

 

[Malcolm]

Some beautiful shapes and impressive craftsmanship here. I've daydreamed of creating a lightweight one or two-man fully faired or partly faired vehicle for years. I enjoy working with wood, but not enough to spend hundreds of hours at it. On the other hand, fibre and resin techniques don't appeal because of the mess and environmental impact. One material I reckon has good potential for shaping into compound curves relatively easily is polythene sheet. Has anyone here come across any DIY projects that use it?

Just to show that it can look pretty good: http://www.cree.ch/

 

[Boatmik]

I agree with not wanting to spend 100s of hours at it. But I think a plywood box could work admirably - the boats above had weights of around 30lbs with probably 2 times the surface area needed.

And be able to be put-togetherable in a weekend or two - quite possible - and the result does not need to be boxlike. Fitting the components might take a lot longer - but they can be bonded into oversize holes cut in the ply box structure, filled with epoxy/powder mix and redrilled to accurate specification. Pivots for full size commercial wind turbines used to be done this way - the wooden boat people could push sets of blades out for about $20K a set while NASA was producing them in carbon at around $220K with a tiny efficiency dividend offset by the energy used to make all the carbon, all the tooling etc.

Actually, though I can see the purpose of the form of the plywood recumbent above and really like it in terms of structure I don't necessarily think that is the best way to go for a general use 'bent that has to whip along in traffic and bring stuff back from the shops.

Something more like a Formula 1 car in terms of structure - a box at each end linked by two side boxes and a floor in the cockpit area. Keep the waistline low so the visual impact of the plywood is simply the external sidewalls that can be curved. Canopy ... if needed - carte blanch within a setting of light weight and good visibility.

The boxes don't need to be boxy as the external sidewall can be curved and tilted. This is a bit of a speciality of mine - I design plywood box boats to look rather nice - fooling the eye with some well placed curves.

My most extreme boat of this shape is a sailing canoe. Bottom is flat - sides are at 90 degrees to the bottom - sounds like an aesthetic disaster ... but ...

I like the sculptural shapes the plastic sheeting allows in your links, but it is very flexible for its weight (as I understand it?)- meaning that the structural loads have to be carried in some sort of secondary structure anyhow. Which means 2 lots of weight - one for each job - one for loadin' and one for lookin'.

Best wishes
Michael.[/img]

 

[Boatmik]

Some thoughts on regen:

One other snag is that the motor will most probably not generate a high enough voltage to usefully charge the battery during low speed regeneration. There may be a way around this by using a Cockroft-Walton type voltage multiplying rectifier.
Jeremy

Howdy Jeremy,

I have no idea about the tech details - but what sorts of efficiency under powering and under braking (imagine if even 70% could be recovered - ti would change the dynamic of city use completely).

What sort of weight penalty?

If something like this is possible and doesn't interfere with the drive efficiency of the motor ... fantastic.

Does anyone know what method the cars with "regenerative braking" use?

I am trying to frame some useful questions from a basis of complete ignorance...

Always cut the RED wire.

Michael

 

[Malcolm]

Hi Michael

Your canoe is very graceful. Like you say, hard to believe it's built using simple curves. Love the sails by the way!
We have different priorities though. I'm thinking of a road vehicle that will do 50 mph, so a stressed plywood skin won't work (unless of course I can convince the rest of UK road users to go the same way, which may take a while). I was thinking more of a shaped tubular steel frame with exterior panels that simply provide weather protection and aerodynamic efficiency.

It is one for loadin' and one for lookin', but hopefully the aerodynamic benefits of having one for lookin' will outweigh the weight penalty.

Cheers
Malcolm

 

[Boatmik]

With a direct drive hub motor, it would be much easier.

The other complication is getting a controller that can do regen at a controlled level. I don't know of any on the market that can do that. It's certainly possible to do.

Does it make it any different if conceptually it is flipped round the other way?

Optimise the system for electric power but add a regular bicycle drive train as well to add power when needed.

It seems to me that the pedal power system is much more flexible in terms of implementation - so to design around the less flexible electric set up???

Then add the human powered on the side - probably literally as well as figuratively?

 

[Boatmik]

Hi Michael

I'm thinking of a road vehicle that will do 50 mph, so a stressed plywood skin won't work (unless of course I can convince the rest of UK road users to go the same way, which may take a while)

It is one for loadin' and one for lookin', but hopefully the aerodynamic benefits of having one for lookin' will outweigh the weight penalty.

Cheers
Malcolm

Howdy Malcolm,

thanks for the kind words on the appearance of the canoe.

Do you really have to convert all of British road users? If you build something for your own use and it has pedals I can't see the problem - what is your concern?

The plywood box would allow substantially more protection that someone (probably me) gets screaming down a hill on a touring bike and hitting something more or less immovable - even at 40 on the flat it hurts.

Also there is probably no land vehicle equivalent to either the point loads for the rigging or the impact loads from dropping off waves repeatedly at speed.... maybe

I know from the type of structures that you are considering that if you clad a steel frame in thin plywood you can probably get a very large part (if not more) strength and almost certainly more stiffness from the shell structure - so long as the corners are joined adequately!

Boats went through this in the early 80's - everyone went space frame mad until they realised that the spaceframes could be eliminated with small amounts of internal structure bonded to the hull skin for the same purposes at a huge weight saving.

 

[lawsonuw]

I'll interject two bits here from my Battlebot experience. I've found that wood is *VERY* good at absorbing energy. A wooden box frame should make an excellent crush zone in a crash. (add some honeycomb or light foam inside the box sections to make it even better) That said, It'd still be nice to have a proper roll cage if a car suddenly decides you make a good speed bump.

Marty

P.S. prime example http://www.buildersdb.com/search_ro...or+french+fries&ClassID=&City=&State=&Weapon= the 'bots Bob, Al, and Ty use wooden frames and are some of the most durable 'bots I've ever seen.

 

[Malcolm]

Mmm. Plenty of food for thought here. Thanks!

I live in a congested city where people seem to think a bloody big SUV is essential to drop off the kids at school and pick up the shopping. I'd love to build something long and low and light to get around in, but while these monsters are on the road it wouldn't be a pleasant experience. The best compromise I can imagine is something along the lines of the Cree three-wheeler that I posted the link to – tall but narrow. Just trying to figure out a fairly simple way of building an aerodynamic shell that would also be strong.

Sorry, I don't mean to hijack the thread.

 

[BiGH]

Mmm. Plenty of food for thought here. Thanks!

I live in a congested city where people seem to think a bloody big SUV is essential to drop off the kids at school and pick up the shopping.

Sorry, I don't mean to hijack the thread.

i like what top gear said about those 4x4 drivers... something like they think they need a 4x4 because there are leaves on the road, when a vw beetle will cross africa!

 

[Jeremy Harris]

Malcolm,

I'm thinking along similar lines. I'd feel too vulnerable riding around in something as low a conventional recumbent trike, so would prefer something that's around the height of my SWB recumbent bike, which has a seat height that's around the same as that of a small car.

Having a high seat makes for slightly poorer stability, unless the front wheels are spaced out further. This makes them less suited to cycle-only tracks, but that wouldn't bother me for a commuting vehicle.

One major advantage of a relatively high seat is that the chain run gets easier - it can be pretty much dead straight from the crank back to the hub, with just guide tubes or a chain case, rather than any idler rollers.

I'm looking at keeping the front wheels outside the body, which will mean slightly more drag from the wheels but will allow the body to be narrower and lighter.

Jeremy

 

[lawsonuw]

Hm if you're planning a tall narrow trike it'd be worthwhile to look into the various ways to make a tilting trike.

Marty

 

[Geebee]

Malcolm,

I'm thinking along similar lines. I'd feel too vulnerable riding around in something as low a conventional recumbent trike, so would prefer something that's around the height of my SWB recumbent bike, which has a seat height that's around the same as that of a small car.

Having a high seat makes for slightly poorer stability, unless the front wheels are spaced out further. This makes them less suited to cycle-only tracks, but that wouldn't bother me for a commuting vehicle.

One major advantage of a relatively high seat is that the chain run gets easier - it can be pretty much dead straight from the crank back to the hub, with just guide tubes or a chain case, rather than any idler rollers.

I'm looking at keeping the front wheels outside the body, which will mean slightly more drag from the wheels but will allow the body to be narrower and lighter.

Jeremy

The wheels outside of the shell will add significant drag unless you allow for spacing to prevent interference drag and fully fair the wheels and crossbar, disregard if you are not after speed.

 

[Malcolm]

Jeremy

Must be convergent evolution.

I agree about keeping the wheels outside the body, it makes construction a lot simpler. The shape I keep coming back to is a stretched egg with the rear raised 20-30 degrees above horizontal. Actually the front end of a glider fuselage would be a great starting point. You don't happen to know of any glider scrapyards do you?

The composite spring axles you mentioned sound interesting, do you have any pictures?

Regarding registration, I guess it all depends on your local police. You're bound to get noticed, but as long as you're not being daft or going over 30 mph they'll probably leave you alone. Just one thought though, if they see a motor and a generator and a couple of controllers and a load of wiring and relays they might take a different attitude. I'd make it as "stealth" as possible.

Hm if you're planning a tall narrow trike it'd be worthwhile to look into the various ways to make a tilting trike.

Funny you should say that Marty. I'm a real fan of tilting three wheelers. Here's a little sample: http://www.maxmatic.com/ttw_index.htm.
I've an idea I want to try out that would use foot pedals to control tilt and handlebars to control steering, so you keep the control axes separate and let your brain do the clever stuff. No idea if it will work yet, but I'm collecting materials for the proof of concept. The obvious drawback is that it will have to be fully motorised.

 

[Jeremy Harris]

I've done some quick drag calculations and it looks like the penalty for having exposed wheels(albeit fitted with discs) is pretty small, less than 5% drag increase over enclosed wheels with open wheel arches. Having a flat composite beam spring will help. I've already made a semi-elliptic carbon composite spring for a home made paramotor trike (see picture) which is very light and works well.

I plan on just making a flatter version and enclosing it inside a streamlined fairing. I've played around with a short Teleflex cable and it seems ideal as a replacement for track rods to control the steering. A couple of short cables could be fed up inside the beam fairing and would make the steering connections very simple.


A glider fuselage section might be both too heavy and a bit small, as you need a lot of room to pedal. One way to reduce the amount of room needed right in the nose might be to use a couple of bottom hinged pedals, connecting to cables and short lengths of chain running over a couple of sprockets running on free wheels to an intermediate drive shaft. If these short chains were interconnected by either a swinging lever or another cable running over a pulley, then drive would be near continuous. In fact it might be smoother than conventional pedals, as a quick sum seems to show that the torque delivery would be more even than with a crank. Such a system might even be lighter than a conventional front mounted crank, chain wheel and long chain, as well as being more compact. I've drawn up a scheme to see how much space it would take up and it certainly looks like it would make for a slimmer "pod".

Raising the rear as you suggest gives a couple of advantages. Aerodynamically, it should reduce drag slightly, by allowing smoother, more laminar, flow over the rear underbody. Much of the drag comes from the rear of any vehicle, as this is where flow has usually fully separated and is pretty turbulent (which is why tailbox fairings are so effective at reducing drag). A higher rear would also enhance visibility and allow high level rear lights/reflectors.

I agree about the "stealth" aspect. I'm sure that, provided you could easily demonstrate that it was just a "pedal car" the local police wouldn't be bothered.

Jeremy

 

[Geebee]

Jeremy, does that figure include the interference drag betwen body and wheel as speed rises? I have been involved in some HPV racing and the external wheels do seem to hurt performance noticably.
One negative of going taller is that as you get higher off the road the wind speed will increase and will be less blocked by your surrounds, at speed a lot of lower velos have issues at higher wind speeds especially gusty side wind conditions so a taller one....
Have you seen the Aurora velo? it's a higher delta velomobile.

 

[Malcolm]

The paramotor trike looks very light. I guess I need to start looking at composite construction.

That's a lot of novel ideas you plan to combine in one project! Look forward to seeing how they take shape

 

[Jeremy Harris]

Geebee,

If I space the wheels far enough away from a narrow body, then interference drag shouldn't start to be a problem until the thing gets to fairly high speeds, where boundary layer interference would start to have an impact. With 20" front wheels, fitted with discs inside and out, I reckon that things should be OK up to maybe 35mph, which is OK for the mission I have in mind.

Thanks for the tip about the Aurora, I shall do some more Googling!

Malcolm,

The paramotor trike is heavier than I wished, as I used commercially available pultruded sections, which are way too heavy for the job. The total weight, excluding the paramotor, but including the wheels etc is 8kg. This could easily have been reduced to around 5kg if I'd been a bit smarter with the material choices. The rear semi-elliptic spring weighs about 1.4kg, but has a design load factor of 6g, to allow for hard landings. For a road going trike front beam I am sure I could build something more than strong enough that would weigh a bit less.

Jeremy

 

[Malcolm]

Still thinking about alternative lightweight materials and construction methods. I built a few balsa airplanes when I was a kid. They used balsa formers and stringers, covered with tissue that shrank when it was wetted or painted with dope. I remember being impressed with how rigid the structure was when it dried. Is there a modern equivalent that can be scaled up. What construction methods do enclosed microlights use?

 

[Boatmik]

Still thinking about alternative lightweight materials and construction methods. I built a few balsa airplanes when I was a kid. They used balsa formers and stringers, covered with tissue that shrank when it was wetted or painted with dope. I remember being impressed with how rigid the structure was when it dried. Is there a modern equivalent that can be scaled up. What construction methods do enclosed microlights use?

The place where that construction is most evolved in terms of loads sustained is in small wooden boats. Monocoque - whether rounded using strips of wood or make up out of flat surfaces. There are a couple of examples on previous pages.

Exactly the same feeling of surprise when comparing stiffness to weight.
MIK

 

[Malcolm]

I'm sure you're right Mik. I guess it's the image problem that's difficult to get over for me. I've had a similar discussion with Xyster over using wood components on a bike. Wood is something that looks great on boats and planes, but at some point it became unfashionable to use it on road vehicles, and it's stayed that way ever since. The only exception I can think of is the Morgan roadster, which is usually bought by strict traditionalists. I'm not a slave of fashion by any means, but I feel that EVs have enough of a battle to gain acceptance as it is, without the added burden of overcoming people's prejudices over choice of materials.

I guess I could build it from wood and then give it a mock carbon fibre paint job :lol:

 

[Jeremy Harris]

I've been experimenting a bit with materials and found that thin foam with thin epoxy glass on one side, is a reasonable substitute for thin plywood. I found some 6mm thick EPS foam in my local B&Q (pretty much like Home Depot for our US participants) that is intended as rigid underfloor insulation for use with laminate flooring. Epoxy bonds very well to it - it's pretty much the same type of foam as used by Bert Rutan in his mouldless composite aircraft.

Cut into planks and glassed on one side, this stuff takes a fair curve well and is very light. Once edge bonded together, the thing could be glassed inside and out to make a light yet rigid shell fairly easily.

Using light aircraft type construction, with a light frame covered in heat-shrunk Dacron would be another option. The result might look a bit like an airship, but it would be very light. Aircraft covering fabric is pretty cheap and really easy to use. Anyone can learn the skills needed to cover even complex shapes in a few hours. You essentially just glue the edges of the fabric in place, pulling the stuff so that it lays smoothly without wrinkles. You then just iron it to get it to shrink tight, then fill the weave and apply paint. You can get a surprisingly good finish without a great deal of effort.

Jeremy

 

[Boatmik]

I guess I could build it from wood and then give it a mock carbon fibre paint job :lol:

I think you can probably buy wide PVC "contact" already with the Carbon pattern printed on it.

One of my friends a while ago entered a fibreglass Laser Dinghy in a Wooden boat festival race a few years ago - he covered it in the same product but with a wood grain print.

Contrasting colours for the deck and hull. The judges saw the joke but were so impressed they gave him one of the minor prizes!

So why not go the other way!!

MIK

 

[Boatmik]

I've been experimenting a bit with materials and found that thin foam with thin epoxy glass on one side, is a reasonable substitute for thin plywood.

SNIP

Cut into planks and glassed on one side, this stuff takes a fair curve well and is very light. Once edge bonded together, the thing could be glassed inside and out to make a light yet rigid shell fairly easily.

Using light aircraft type construction, with a light frame covered in heat-shrunk Dacron would be another option.

SNIP

Jeremy

I hope I am being useful here... I know I am pushing my own angle... but I'm trying to keep it as informative as possible.

Howdy Jeremy,

Foam/glass has almost completely overwhelmed plywood as a material for boats.

You can build boats of much the same weight - though in true lightweight construction with Moth class dinghies - when they tried foam/glass they needed pretty sophisticated building methods to get down to the hullweights of wood.

The Moth class has no minimum weight. On that evidence I think that the foam might end up heavier than plywood built backyard style as you suggest. I am not using "backyard" as a pejorative - the wooden Moths were all backyard too!

With other boats with a higher minimum weight the story is different...

With boats The ply is much less labour, but the glass provides a better panel stiffness which is important for sailing boat performance as the hull distorts less under water pressure.

So the extra weight is used up by making the panels in the foam/glass boat somewhat stiffer than plywood for that reason.

They are more prone to denting and have to be kept on a cradle on land, but on the water - they are stiffer and faster.

Stick and fabric In larger scale structures it becomes quite hard to engineer and loses its apparent simplicity.

The big problem is the torsional resistance (actually it is a huge problem with traditionally built boats too). Problem is that anything made of a grid of sticks can be distorted in shear very easily. It relies on the efficiency of the joints to resist this. If the efficiency of the joins is low the boat (or bicycle) will twist along the longitudinal axis.

If you make a gate for your garden out of horizontal and vertical pieces - you need to add one diagonal to take care of these sheet loads.

There is a boat designer "Platt Montford" that specialises in boats of this type - Geodesic Airolights. At one stage they were promoted on their lightness - they seemed to fade away a little as their most popular design is the based on the same design as my balsa canoe - so the boats were the same in terms of volume and shape.

Geodesic Airolight Wee Lassie - 18lbs
Balsa/Glass Wee Lassie - 12lbs

Recently they have produced a lighter version - but I do wonder how durable it is - whereas the balsa canoe was highly durable - rock solid - if a little prone to puncturing the outside glass - it happened around 5 times over 5 years of use - with my careful use.

Going to the Moth dinghies again ... the plywood boats were lighter than the balsa ones, but the balsa ones could be built with a rounded hullshape.

Now I'm mentioning Montford because he does have a REALLY good idea in his boats. To take the torsional loads he simply uses a Kevlar (high stiffness fibre - aramid) tow (unidirectional fibres loosely bundled into a flat tape.

He builds the stick part. Then runs strands of the kevlar at 45deg angles to the sticks around the circumference of the boat - gluing them down at each place they cross the sticks and fastening at the edge of the boat. Then the fabric is put over the top.

A neat way of increasing the torsional stiffness with a minimum weight penalty! Cool, eh!

As far as structural efficiency goes - with a stick and fabric construction you are back to the same problem of having two separate structures. One for carrying the loads - the other for reducing the wind resistance.

There is a weight penalty in separating these functions.

MIK

It does give a slightly lumpy appearance as water (or air) pressure is applied, but it is quite stiff.

 

[loftyendeavors]

Would it be possible to use a set up similar to this to continually recharge a e-bike battery system? (To use as a range extender):
---------------------------------------------------------------------------------------
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H-100 PEM Fuel Cell System
Includes control electronics, connectors, and electronic valves.

TECHNICAL SPECIFICATIONS

Number of cells 20
Rated power 100W
Maximum power 150W
Performance 12V @ 8.5A
Reactants Hydrogen and air
External temperature 5-40ºC
Maximum stack temperature 65ºC
Hydrogen pressure 2.9-4.35 PSI
Humidification Self humidified
Cooling Air (integrated cooling fan)
Weight (with fan and casing) 835g
Dimensions 10.5cm x 8.6cm x 13.4cm
Type of fuel cell PEM
Hydrogen flow rate 1.6 l/min of hydrogen at maximum power
Start up time Immediate
Stack efficiency 45% at 12V

In Combination With This For Storage:
---------------------------------------------------------------------------------------
http://www.fuelcellstore.com/cgi-bin/tornado/view=Item/cat=5/product=1183

Ovonic Solid Hydrogen Storage canisters utilize proprietary metal hydride technology to safely store hydrogen in a compact manner at a low pressure. The metal alloy powder contained in the canister is formulated to absorb and release hydrogen similar to a sponge absorbing water. Canisters are designed to operate at ambient temperatures with no requirement for added heat and can store several times more hydrogen than similarly sized high-pressure compressed hydrogen cylinders.

TECHNICAL SPECIFICATIONS

Diameter: 2.5in.
Length: 10.4in.
Weight: 4.8lbs.
Nominal Capacity: 225 std. liters
Nominal Discharge Rate: 300W
Standard Fitting: Female 1/8 NPT interface
Optional Quick Connect Couplings available
---------------------------------------------------------------------------------------

Assuming you also had a method of producing hydrogen, would it be possible to rig up such a system to extend the usable range of an e-bike?

The system I imagine would consist of two alternating batteries, one being used and one being constantly recharged.

I'm a bit of a laymen when it comes to determining the increased range or feasibility of such a system,
but I would learn to know what you guys think!

Also, might it be possible to further increase the range of such a design by adding 100w worth of solar panels?

I am envisioning a powered trailer that incorporate two high capacity lithium batteries and a 100w PEM fuel cell and 100w solar array to assist in recharging. The goal of the project would be to extract as much range as possible.

What do you think?