# Three Wheeled Electric Vehicle Project - Help needed choosing batteries



## todayican (Jul 31, 2008)

Off hand I would say this is a good job for an HPGC ac-20 or ac-30 drive setup with 108v and Thundersky 100ah batteries

Guys?

BTW Robin, any pics of the project? I am building an aero trike of my own and would love to have a chat, perhaps compare notes.


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## robinfryer (Mar 31, 2010)

todayican said:


> Off hand I would say this is a good job for an HPGC ac-20 or ac-30 drive setup with 108v and Thundersky 100ah batteries
> 
> Guys?
> 
> BTW Robin, any pics of the project? I am building an aero trike of my own and would love to have a chat, perhaps compare notes.


No pics at the moment, i am building a CAD model in CATIA. I have been working on a HPV (human powered vehicle as seen in my avatar) and running it in CFD for the past few months and now moving onto this. Would be great to chat about the technical aspects of this!

I also have some graphs and suchlike on how i calulated the power consumption and required torque etc. 

Do you have a link for the specs of the setup?


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## todayican (Jul 31, 2008)

There are likely other / better? sources of info on this drive setup, including lots of posts and debate on the topic, but here is a place to get started 

http://www.thunderstruck-ev.com/AC_drive_performance.htm


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## robinfryer (Mar 31, 2010)

Thanks for the tip

I should have posted some of the specs of the vehicle;

0-60mph = 10 seconds (or just under)
Top speed = 100 mph
Max power required = 33.3 Kw (45 bhp) @ 5300 rpm (only one forward gear btw)
Max Torque = 100 Nm (probably 90 is better)

The target is not to exceed these at the cost of adding extra mass or volume. Obviously the main volume/mass will come from the battery to supply the motor so this is another reason to not have a motor which is overpowerful.


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## robinfryer (Mar 31, 2010)

From looking at the motor specs i dont think they match up to the task, my peak power requirement is at my max speed (100mph) an i need around 33kW to reach it in around 30s (from standstill). The AC-30 falls someway short of that, and for some reason they havent published the torque curve for it (which is crazy by the way).

The mass and volume of the AC24ls (the one im current using) isnt really that much more, though the controller is 10kg lighter!

If i am to use the AC-24 i have calculated i need around 12kwH of energy storage onboard for 100 miles range, which equates to around 80 Amp.Hrs for a constant 156v push of current to the motor. Does this sounds reasonable? It would mean that i only need one of the 100Ah batteries which kind of sounds wrong?


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## Duxuk (Jul 11, 2009)

I am also building a three wheeler which should be on the road within a month. I failed the MSVA test (neccessary to put it on the road in Britain) for the second time today, but next time it should all go OK. Even if your vehicle is very aerodynamic I don't think you will be going very fast if you are using only 120Wh/mile. My calculations suggest that my 330Kg trike will need at least 85Wh/mile at 40 mph. This does not include acceleration or hill climbing so I would probably expect to use >100Wh/mile cross country, at speeds mainly between 30 and 45 mph, with the odd bit of 50mph. I will post a full report as soon as I am road legal. Back to the workshop to do the fixes first though!

Andrew.


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## robinfryer (Mar 31, 2010)

Duxuk said:


> I am also building a three wheeler which should be on the road within a month. I failed the MSVA test (neccessary to put it on the road in Britain) for the second time today, but next time it should all go OK. Even if your vehicle is very aerodynamic I don't think you will be going very fast if you are using only 120Wh/mile. My calculations suggest that my 330Kg trike will need at least 85Wh/mile at 40 mph. This does not include acceleration or hill climbing so I would probably expect to use >100Wh/mile cross country, at speeds mainly between 30 and 45 mph, with the odd bit of 50mph. I will post a full report as soon as I am road legal. Back to the workshop to do the fixes first though!
> 
> Andrew.


Hi andrew i did a recalc and came out with twice the number as before, so total 24000 KwH storage needed for 100 miles. 

Ive posted the drive cycle here. Its seconds along the bottom and Kph on the y axis


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## Duxuk (Jul 11, 2009)

Don't forget that increasing the battery capacity increases weight and hence rolling resistance so doubling the batteries doesn't double the range. 

It's difficult with a unique vehicle to estimate the energy use but here's how I have tried to estimate. Power needed is proportional to the square of speed so P=X*V^2 We can find the factor X by comparison with a similar ICE powered vehicle where top speed and power of the engine are known. For instance my first ICE trike used a 125cc Piaggio motor with CVT from a scooter. It gave 11hp and could reach 57mph on the flat. At this point it had possibly gone over it's power peak because scooters tend to be low geared for good acceleration, so lets assume 10bhp gave 57 mph. 10hp is 7460 watts so putting this in the equation give an X of 2.296.
So 40mph requires 1600*2.296=3673.6w Divide by 40mph gives you 91.84 Wh/mile.
Of course I'm hoping that my EV, though it may be 140Kg heavier is more aerodynamic and has a smaller frontal area. The inefficiencies between battery pack and rear wheel are less than those of an ICE with the CVT transmission which could rob me of 25% of my power easily. So all in all and making comparisons with other EVs such as the vectrix I reckon I need at least 85Wh/mile at 40! Once you've worked this out Wh/mile is proportional to speed so it's easy to find your energy use at any speed!

Andrew.

You can see my trike in the garage under Kirk EV or sparky. I'm also in EV Album which is easier to navigate.


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## mszhao (Oct 17, 2009)

www.chinabatteries.net can help you


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## Duncan (Dec 8, 2008)

Hi Robin

_it would mean that i only need one of the 100Ah batteries which kind of sounds wrong?_


Don't forget each battery (cell) is only 3.3v (approx) so you will need 48 for your 156v

Also you should limit your discharge to 70 or 80% or battery life will be short


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## robinfryer (Mar 31, 2010)

> Don't forget that increasing the battery capacity increases weight and hence rolling resistance so doubling the batteries doesn't double the range.


 Yes, RR does increase but its fairly small compared to drag and inertial forces.

Doubling the battery size didnt double the range, it was a bit of a coincidence. My recalculation just showed my i neeeded *twice* the energy that i did before (more or less). I also forgot to add the mass of two drivers and luggage (increasing mass to 600kg), so again more energy required. 

But would you agree that 24kWh of energy on board would take me the 100 mile distance.


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## sunworksco (Sep 8, 2008)

todayican said:


> There are likely other / better? sources of info on this drive setup, including lots of posts and debate on the topic, but here is a place to get started
> 
> http://www.thunderstruck-ev.com/AC_drive_performance.htm


 I have had the very best service from Thunderstruck.
They support ev racing and know the ev designs that work efficiently.
You will get the best bang per dollar spent.


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## dtbaker (Jan 5, 2008)

robinfryer said:


> But would you agree that 24kWh of energy on board would take me the 100 mile distance.


at what speed? That sounds really tight unless your aerodynamics are astoundingly good.

back to batteries though. you are going to have to go Li, just choose between regular large format like Thundersky or SkyEnergy and the smaller a123 or something that would allow higher voltage in smaller space but more of an assembly challenge and be more expensive to boot. If you hvae lots of money, start looking at the kokams and other specialty units.


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## robinfryer (Mar 31, 2010)

Duncan said:


> Hi Robin
> 
> _it would mean that i only need one of the 100Ah batteries which kind of sounds wrong?_
> 
> ...



Im not sure i understand the voltage concept entirely, im a bit rubbish at knowing what to do with these things. I know i need X amount of kWh of stored power, (or X amount of Amp hours). I dont really understand the voltage bit? 

From what i saw one battery contains, say 100 Ah, how does the voltage come into this?


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## Duncan (Dec 8, 2008)

Hi Robin

The voltage is the "pressure" (volts) the amperage is the "flow" (amps)

a Watt is a measure of "Power" (energy flow) (1 amp X 1 volt = 1 watt)

These give you the "Power" to drive your car

The next thing is how long can it drive - this is where Amphours comes in

1 AH (ampere-hour) is the ability to give 1 amp for one hour

A batteries consists of a number of cells (separate or all in one box) 

Each cell has a voltage and an AH 

a 100Ah lithium cell has about 3.3 volts so it can produce 100 amps for one hour at 3.3 volts

3.3 volts X 100 amps is 330 watts - less than half a horsepower -not a lot for a car!

so we put 48 cells together and get 48 X 3.3v = 158 volts

158 volts X 100 amps = 15855 watts or 15.8 Kilo-Watts about 21 horsepower for one hour

That is a more useful "battery"

158 volts X 100 amps X 1 hour = 15.8 Kilo-Watt-Hours

How much you need depends on 

Size of vehicle
Speed it will be driven at - less obvious it takes a lot more energy to go fast
Range

kilo-watt-hours needed per mile can be from
0.15 Kwhrs/mile very efficient car (EV1)
0.3 Kwhrs/mile normal car

If you are making something like an electric recumbent bike these number can get *a lot* less


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## robinfryer (Mar 31, 2010)

Duncan said:


> kilo-watt-hours needed per mile can be from
> 0.15 Kwhrs/mile very efficient car (EV1)
> 0.3 Kwhrs/mile normal car


Thanks for that useful info Duncan. At the moment my calculations are coming out as 0.14 kWhrs/mile, albeit i havent taken into account efficiencys yet. That is also based on a 3 part drive cycle urban/rural/motorway at 10 minutes each, repeated until the distance reaches 100 miles. It is 'supposed' to be very efficient (Cd=0.15, very light, low rr tyres). 

With constant motorway driving i need around 19500 Kwhrs to make 100 miles.

I also found that if doing performance tests 0-100mph, i can do only 5 cycles of 0-100mph before needing a recharge!

Can anyone quote me some efficiency numbers for transmission? I have a planned 1 gear transmission (just the diff) 1:5. The motor im currently looking at has 0.85 peak efficiency. Does battery efficiency matter as well??


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## todayican (Jul 31, 2008)

Its worth saying this.

When I said "There are likely other / better? sources of info on this drive setup," I in no way meant to disparage Thunderstruck, I have purchased from them as well and did get a first class experience.

Tom


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## robinfryer (Mar 31, 2010)

Can anyone quote me some efficiency numbers for transmission? I have a planned 1 gear transmission (just the diff) 1:5. The motor im currently looking at has 0.85 peak efficiency. Does battery efficiency matter as well??


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## sunworksco (Sep 8, 2008)

You may want to use aluminum pulleys and toothed belts with around a 7-1 gear ratio.This creates less friction and lessens the weight.You can also use the internal limited slip differential from a Honda.


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## robinfryer (Mar 31, 2010)

sunworksco said:


> You may want to use aluminum pulleys and toothed belts with around a 7-1 gear ratio.This creates less friction and lessens the weight.You can also use the internal limited slip differential from a Honda.


I see youve done trikes before? Mine has 1 wheel on the rear axle, did you use front wheel or rear wheel drive? I will probably go with front wheel simply because more grip is available in traction and it would move the centre of gravity towards the front.

Dynamics calculations show that the mass should be in the front 2/3rds of the vehicle to avoid roll over and lateral instability, so i guess the increased mass of mechanisms at the front would improve it.

However its also true that a rear wheel driven config would be simpler and lighter like a motorbike setup. Im also not sure i like the idea of a caster wheel at the back doing not much!


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## sunworksco (Sep 8, 2008)

Front-wheel-drive works best because you have better control in a turn,skid or any other task.If you talk to Morgan trike club members,they will tell you that the front wheels are better to drive than the rear wheel.The weight distribution and cg are where they need to be,too.
You could build a twin wheel setup on the rear like the Proxima,but use Ducati 1098 hub design.The Silver Trike is the design that I am building.The Yvhers is a nice old design.


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## robinfryer (Mar 31, 2010)

sunworksco said:


> Front-wheel-drive works best because you have better control in a turn,skid or any other task.If you talk to Morgan trike club members,they will tell you that the front wheels are better to drive than the rear wheel.The weight distribution and cg are where they need to be,too.
> You could build a twin wheel setup on the rear like the Proxima,but use Ducati 1098 hub design.The Silver Trike is the design that I am building.The Yvhers is a nice old design.


Looks awesome, what are your views on open wheel/closed wheel trikes? Are you bothered about the aero implications? Do you find the packaging becomes too tight and the roll over becomes too likely?


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## sunworksco (Sep 8, 2008)

Better to go open wheel.The frontal area is less.Look at the Indy cars.Easier to build as well.I would use DP wish-bone front suspension system or build your own.


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## Duxuk (Jul 11, 2009)

My EV trike is my fifth build so this advice may even carry some authority! I believe that a trike always needs some anti roll control in the front suspension (assuming you have two wheels at the front). I built an anti roll bar for my 600cc Honda Silverwing powered vehicle. It transformed the drive by reducing the swaying when changing direction and helped to keep the inside wheel in contact with the ground on hard cornering. OK so I can still get some wheel lift on tight corners but usually only under hard acceleration. With my EV (single rear wheel drive) the C of G is very much lower so the problems associated with body roll will be lessened, but I have still included a cross linked anti roll suspension system and it drives like a go kart! My weights are 104Kg for each front wheel and 121Kg for the rear. The driver sits centrally so I will add about 25Kg to each wheel.


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## robinfryer (Mar 31, 2010)

Duxuk said:


> My EV trike is my fifth build so this advice may even carry some authority! I believe that a trike always needs some anti roll control in the front suspension (assuming you have two wheels at the front). I built an anti roll bar for my 600cc Honda Silverwing powered vehicle. It transformed the drive by reducing the swaying when changing direction and helped to keep the inside wheel in contact with the ground on hard cornering. OK so I can still get some wheel lift on tight corners but usually only under hard acceleration. With my EV (single rear wheel drive) the C of G is very much lower so the problems associated with body roll will be lessened, but I have still included a cross linked anti roll suspension system and it drives like a go kart! My weights are 104Kg for each front wheel and 121Kg for the rear. The driver sits centrally so I will add about 25Kg to each wheel.


Sounds nice! How do you find the balance on oversteer and understeer, i read vehicle with the CoM towards the rear 2F/1R config move towards oversteer?


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## TomA (Mar 26, 2009)

Duxuk said:


> ...I believe that a trike always needs some anti roll control in the front suspension (assuming you have two wheels at the front)...


Agreed. Roll control is important on a reverse trike.

In the lightest weight class, there are great units built for late-model snowmobiles that are cheap used and would nearly bolt right on. I found a custom setup from a racing quad that is also appropriate up to maybe 300Kg. For a little bigger chassis, there are great custom racing bits just the right size that are easily adapted. See Speedway Motors or almost any racing suspension website.

-----But that isn't why I've jumped into this thread...-----

More generally, robinfryer, I think your baseline specifications are kind of extreme, and need validating sooner rather than later:

0-60mph in under 10 seconds, 100mph top speed and 100 mile range is pretty astounding performance for any EV. Certainly, those marks will be extremely difficult to achieve in the same charge cycle.

I'm not being critical, I'm just asking a basic question: are these performance targets you actually need in order to make the vehicle viable for you to build and use? If they are, you are facing a very costly project. Do you really want a $20,000-$25,000 two-seat electric trike? My WAG is that's what it would take to achieve these goals, unless you could do almost all the design and fabrication yourself, saving maybe 1/3 of that. 

If you don't actually need these performance metrics, then it would be prudent to decide what you absolutely do need in the way of performance, range and payload. From there you can work up the costs. You can also go the other way: figure out the maximum you want to spend on the vehicle, and see how much speed, range and payload that will buy. I think most projects wind up going at the problem at least little of both directions as the compromises become clearer and the hard facts of what you are trying to do start to become immovable. 

Don't get me wrong, its absolutely worthwhile to set high targets and see what it would take to get there, but the exercise isn't grounded anywhere until you decide how fast, how far, and with how much you want to go, (and of course at what cost.) 

TomA


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## robinfryer (Mar 31, 2010)

Hi TomA, 

I understand what you are saying about cost and ambition, unfortunately i forgot to mention some important details about this project.

The project is my disertation for my degree, and is really a hypothetical design so i am not going to actually construct this. 
The project is primarily based on the low drag aerodynamics of such a vehicle which is my area of expertise.

Its really an "investigation" into the design of such a vehicle , rather than a design project itself. I want to produce a general design practice, present issues and potential solutions for future EV trikes. As i already said, most of this is aimed at aerodynamics and low mass to keep the "fuel economy" high. 

The part i am doing at the moment is the powertrain etc. The idea is not to spend too much time on actually choosing the batterys/motors etc but outline the calculations about how to go about it. Cost of course is an important factor in this.

During all this of course i am designing a sort of mock vehicle in order to design for aerodynamics and produce some sort of end product, whether it meets the targets or not is not tooooo important but its obviously better that it does!

Basically at the end of it all I want a handbook to how to produce something like this (again main focus is aero, which hasnt been done before) with a hypothetical design as an example.

The end user of the report would probably more likely be companies like Aptera who build expensive production trikes aimed at "being green" rather than the single production "kitcar" ones people like to build, though it should offer guidence for those as well really!

Sorry for the long post!


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## TomA (Mar 26, 2009)

OK, all very good to know.

Two critical references for your studies:

1. Walter Korff, who invented the Duo-Delta and was the aerodynamicist for the Summers Brother's Goldenrod and many other projects. His work is a must-read in the unlikely event you aren't familiar with it.

2. Dave Malewicki, who designed and built the California Commuter, among many other things, and set fuel economy records with it.

Just a comment- you might want to lock in a mechanical and size configuration, and it almost doesn't matter much what that is, Make that the assumption, and then see how top-shelf aero will impact on the performance of such a machine. At least you won't be wasting time juggling drive configurations and specs, when what you really are interested in is aerodynamic efficiency.

Have you seen the BYU Electric Streamliner? Very interesting envelope shape and surface development on that one...

Lastly, and I'm sure you will find this out if you haven't already, but hypothetical designs are notorious for missing facts that are obvious only in the flesh. This isn't a criticism, just a hard fact. Data models of vehicles, unless you are NASA, have a _very_ high rate of inaccuracy.

I personally would not be comfortable defending a thesis that had zero experimental data, but that's maybe why my doctorate is in law and not in engineering...

TomA


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## robinfryer (Mar 31, 2010)

Cheers, yes like you say the hypothetical designs are usually missing alot of details.

The problem is i simply dont have enough time to design properly. For the mechanical envelope the idea is to spec some basic motors, batteries and passengers seats etc which take up the bulk of internal volume and then that is the outline.

However being keen, i keep getting carried away and worrying how much power the car stereo is using and do i need more batteries!!! The electric nature of the vehicle seems to make it more complicated as i feel a need to talk about the design process.

I will look up those papers, hopefully they are free of charge, at least on the university network. 

I didnt hear about the BYU streamliner, i couldnt see any images on google, i found one CAD model on youtube showing how parametric it was or something but that was all?


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## TomA (Mar 26, 2009)

The deformation model on YouTube is very cool:

http://www.youtube.com/watch?v=dWpYoLs4n2w

Here's the home page:

http://www.byustreamliner.com/homepage/tiki-index.php

Actually, EV design is considerably simpler than the same vehicle with an ICE. You are being pixillated by possibility because you don't have a customer with needs and a budget in front of you, nor do you yourself have needs, a budget and an intent to build to them. Without those two fences on the landscape, everything is possible, and actually terribly interesting.

Also a waste of your precious time. Try this: survey 5 or 10 people you think are a representative sample of possible enlightened early adopting EV owners. Ask them what they would want: How far, how fast, how many people and how much stuff, and how much money they would pay for such an EV? Average the answers and move on to your project.

You might just find that meeting the current perceived needs is impossible at the desired price. I would bet heavily on that outcome... Anyway, doing this validates assumptions, and the spec will reign in your current groundless bench-spec'ing exercises. 

Over & out,

TomA


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## Duxuk (Jul 11, 2009)

I've just looked in "Three Wheelers" by Chris Rees. (ISBN 1-901860-01-9) The California Commuter looks cool but I prefer the Feora by Chuck Ophorst, built in LA in 1982. 92mph from 22bhp. If you could match the aerodynamics you could use 2 19bhp Mars PM 48V motors, one driving each front wheel. This reduces weight because you don't need a diff. I'm sure 100mph would be easily possible. Make it a tandem 2 seater then you can fit the batteries down each side of the cockpit. You may, in fact, need the higher torque 72V motors to give you decent performance from 0-100mph with only a single gear. My trike, which is pictured in the garage section, is also in EVAlbum under Kirk EV or Sparky. It uses a single 72v Mars driving the rear wheel and should reach 60mph, only limited by gearing, voltage sag etc. I'm sure I could have geared higher but wanted to keep the ampage draw down. What do you think of the aerodynamics? I styled it on a Le Mans prototype! It's mainly single curvature panels but I did try to panel beat 2 pieces near the front. All I can say is they fill the holes in. It tapers nicely at the rear and the only sticky outy bit is the driver. I haven't done much testing 'til it's on the road but it did not slow from 43mph up a 10% gradient.


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## sunworksco (Sep 8, 2008)

There is no need for torsion bars or sway bars if the suspension is lightweight.A 700lb. RT would have a very uncomfortable ride.I can see where a balls to the walls snowmobile would need suspension control.
Here is an RT with photo-shopped Ducati 1098 wheels.


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## TomA (Mar 26, 2009)

sunworksco said:


> There is no need for torsion bars or sway bars if the suspension is lightweight.


I disagree. You either need stiffness in roll (anti-roll bar) or you need a very stiff suspension that doesn't roll, (or absorb much of anything) or any RT is likely to lean over unacceptably in turns. This is because, compared to a 4-wheeler, much more of the vehicle weight is shifting onto the outside wheel as lateral forces build. The spring on that wheel needs help with all that shifted weight. I don't think gross vehicle weight or suspension mass has much to do with it- its just a dynamic consequence of the configuration.



> _A 700lb. RT would have a very uncomfortable ride._


What is the basis of that conclusion? Is it the unsprung to sprung weight ratio? Damping or springs? Something else?

I'm just not buying either of these statements...

TomA


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## TomA (Mar 26, 2009)

Duxuk, I love your trike. It reminds me of the aluminum body Grumman Aviation built for Briggs Cunningham's 1950 or so Cadillac to run at LeMans- "Le Monstre" as it was called by the locals. It was actually a thing of beauty, sort of, and a very careful work of aerodynamics. But for a collision, it would have stunned the racing world with a top 5 finish in that race- on an almost stock Cadillac chassis. Some car; one of my all-time favorites.

I like the Cal Commuter because it is a proven record-setting design that is completely sorted and well-documented. (Plans can still be purchased, even.) 

Cool as it looks, the Feora does not strike me as equal or close to the aero efficiency of the Cal Commuter, or the Summers Brothers' Polliwog. Its fuel efficiency was listed as 85mpg in Popular Mechanics, about half the Cal Commuter's mileage- but it was bigger and maybe even a 2-seater. Plans and kits were to be available, but who knows if there is any more to the Feora than a grainy old photograph, or even if the reported information on speed and mileage was accurate? I really do like the door and greenhouse shapes, though. Are there more pictures of this design available than the one at 3wheelers.com?

TomA


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## sunworksco (Sep 8, 2008)

Because an anti-roll bar connects wheels on the opposite sides of the vehicle together, the bar will transmit the force of one-wheel bumps to the opposite wheel. On rough or broken pavement, anti-roll bars can produce jarring, side-to-side body motions (a "waddling" sensation), which increase in severity with the diameter and stiffness of the sway bars. Excessive roll stiffness, typically achieved by configuring an anti-roll bar too aggressively, will cause the inside wheels to lift off the ground during very hard cornering. This, of course, is only possible if the regular spring rate actually allows the outside wheels to handle the much increased load. 
An RT with a low cg,wide track double wish-bone suspension and low overall weight does not need an anti-roll bar.High weight + high CG = anti-roll bar.


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## TomA (Mar 26, 2009)

sunworksco said:


> Because an anti-roll bar connects wheels on the opposite sides of the vehicle together, the bar will transmit the force of one-wheel bumps to the opposite wheel. On rough or broken pavement, anti-roll bars can produce jarring, side-to-side body motions (a "waddling" sensation), which increase in severity with the diameter and stiffness of the sway bars. Excessive roll stiffness, typically achieved by configuring an anti-roll bar too aggressively, will cause the inside wheels to lift off the ground during very hard cornering. This, of course, is only possible if the regular spring rate actually allows the outside wheels to handle the much increased load.


This is a basic explanation of the pitfalls of anti-roll bars that doesn't support the next statement:


> _An RT with a low cg, wide track double wish-bone suspension and low overall weight does not need an anti-roll bar. High weight + high CG = anti-roll bar._


We still disagree. I'm not building my trike without roll control.

No worries, everyone should build what they want.

TomA


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## robinfryer (Mar 31, 2010)

> . What do you think of the aerodynamics? I styled it on a Le Mans prototype! It's mainly single curvature panels but I did try to panel beat 2 pieces near the front. All I can say is they fill the holes in. It tapers nicely at the rear and the only sticky outy bit is the driver. I haven't done much testing 'til it's on the road but it did not slow from 43mph up a 10% gradient.


Looks like the basics are right, tough to do any aerodynamics optimisation with small budgets, basics are just cutting out steep gradients, making everything curvature continuous and seemless. With mine its more about reducing the skin friction drag since pressure drag/wake are almost non existent, and thats a whole different and difficult challenge. I think the biggest issue with this type of vehicle would be the centre of pressure location (where all the resulant aeroforces act). Lots of surface area ahead of the centre of mass sometimes means the CoP is ahead of the CoM and therefore produces an unfavourable behaviour in crosswinds (to cut a long story short). 
*
Im looking at regen braking for this as well*, does anyone know a typical efficiency for energy recovery?
Also does anyone know how much current a typical liion battery will accept under charge, i couldnt thunderstrucks battery specs in detail? I dont really want to go down the supercapacitor route to be honest, it just adds more weight and i cant be bothered to figure out the discharge characteristics and look up all the specs etc...


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## Duxuk (Jul 11, 2009)

TomA, I agree with you about anti roll control. When I fitted my anti roll torsion bar I did no other modifications and did not notice a deterioration in ride quality, just a much better driving experience. My scooter died yesterday! So it's ICE trike to work every day until the EV trike is on the road. The scooter problem is an interesting one. The regulator seems to have developed an intermitant fault. When I measure the charging current to the battery sometimes it is, say, 12.8v, rising to 13.9 when you rev it on the stand. At other times the whole thing stinks of what I can only presume is hydrogen sulphide. When I measure the charging voltage then a foul smelling mist is streaming out of the vent hole and the charging voltage is over 16V. I think this would destroy the new £50 battery in short order. I also don't want a sulphuric acid mist that close to my backside!


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## TomA (Mar 26, 2009)

robinfryer said:


> Lots of surface area ahead of the centre of mass sometimes means the CoP is ahead of the CoM and therefore produces an unfavourable behaviour in crosswinds (to cut a long story short).


Actually, there is a more basic problem. It is most acute with "dustbin" aero motorcycles, but applies generally. From the side, there must not be too much body area ahead of the center of gravity. The lateral Center of Area (CoA) needs to be well rearward of the vehicle Cg for stability. This was discovered at Bonneville in the early 1960s, after some incidents with the then-new, and initially pretty unstable jet cars. The big tail fins you see on them now address this issue more than they provide direct aerodynamic stability, or shift the Center of Pressure rearward.

This phenomenon acts similarly to moving the CoP around in relation to the Cg or CoA, but it is not the same thing, and in a cross-wind, it is actually much more significant. I call it the "Weathervane Principal" because the lateral CoA's location behind the pivot point of a weathervane is precisely what points it into the wind. Center of Pressure has nothing to do with it.

A crosswind is already going to blow you off course. You really want gusts to at least blow your nose into the crosswind, not away from it. This has a corrective action, and it makes the vehicle much easier to control. Painfully simple, but not very obvious to anybody until there were injuries. 

On the other hand, sailing vessels have been made that way for _centuries,_ so I guess it all comes down to whose knowledge base you are working from...

TomA


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## robinfryer (Mar 31, 2010)

TomA said:


> Actually, there is a more basic problem. It is most acute with "dustbin" aero motorcycles, but applies generally. From the side, there must not be too much body area ahead of the center of gravity. The lateral Center of Area (CoA) needs to be well rearward of the vehicle Cg for stability. This was discovered at Bonneville in the early 1960s, after some incidents with the then-new, and initially pretty unstable jet cars. The big tail fins you see on them now address this issue more than they provide direct aerodynamic stability, or shift the Center of Pressure rearward.
> 
> This phenomenon acts similarly to moving the CoP around in relation to the Cg or CoA, but it is not the same thing, and in a cross-wind, it is actually much more significant. I call it the "Weathervane Principal" because the lateral CoA's location behind the pivot point of a weathervane is precisely what points it into the wind. Center of Pressure has nothing to do with it.
> 
> ...


Hmm this is what i was trying to say, big fin on the rear moves the CoP rearwards. Like you said this is favourable becuase from a crosswind, or gust it steers the vehicle into the crosswind thereby reducing the oscilation period of getting the vehicle back in the intended direction....

Centre of pressure is where the net aerodynamic forces act, and it will probably act at the CoA. I have several literature using the exact terminology stating if the CoP is aft of the centre of mass "bla bla etc" .


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## TomA (Mar 26, 2009)

robinfryer said:


> Hmm this is what i was trying to say, big fin on the rear moves the CoP rearwards.


Well, you missed my point. We are both sort-of correct, but neither answer is precisely correct. What you are talking about is longitudinal static stability, and increasing the marginal stability by moving the CoP away from the CoM. You could also just move the CoM forward, but that wouldn't make a dustbin motorcycle more stable in a crosswind, so there is something else going on. My point wasn't about bodies in fluid (aircraft,) its about the leverage a crosswind has on the handling behavior of a land vehicle. Pure fluid aerodynamics from aviation doesn't give you the right answer. 

The part I forgot to mention is the importance of the location of the wheelbase and tire contact patches relative to the point at which a crosswind loads the body. This is more critical than the vehicle's Cg, because the contact patches are most of how a land vehicle resists the crosswind. (with a boat in would be keel and rudder.) The CoP for this side loading must be biased toward the rear contact patches (rear axle) in order to point the nose into the wind. Sorry I wasn't clearer before. 



> Centre of pressure is where the net aerodynamic forces act, and it will probably act at the CoA.


This is only true with relatively symmetrical bodies (like a fuselage with protruding airfoils) in a fluid, and it is certainly not the case with a dirty, asymmetrical shape in ground effect. These forces are much trickier to predict, which is why cars spend more time in wind tunnels than airplanes do. 

The CoP I am referring to is this purely lateral one, not the actual or 3-dimensional CoP- That might be at the CoA of the side of the car, but I wouldn't bet on it. Considering them equivalent is unnecessary. (I also don't like to make assumptions I know aren't really the case...) 

The big issue is how the lateral area is balanced relative to the tire contact patches; Ideally, the CoA should be slightly rearward of the center of the wheelbase.



> I have several literature using the exact terminology stating if the CoP is aft of the centre of mass "bla bla etc" .


I'm sure. I'm also sure there isn't much in them based on experimental data specific to the high speed stability of land craft... 

Anyway, I hope we understand each other. Its like two adventurers using different techniques and assumptions to arrive at the same spot.

No worries, and enough from me about it.

TomA


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## robinfryer (Mar 31, 2010)

> The big issue is how the lateral area is balanced relative to the tire contact patches; Ideally, the CoA should be slightly rearward of the center of the wheelbase.


Yes i think i know what you mean, i.e. the centre of rotation in yaw is not at the centre of mass because of the contact patch, so moving the CoM relative doesnt necceserily yield the expected result. 

I think usually in the case where people bother about the lateral stability in crosswinds they tend to stick a massive fin on the rear just to make sure, the streamliner and some human powered vehicles are good examples. Even the Aptera 2E (3W EV) has some sort of large surface area fairing over the rear single wheel, presumebly to improve the lateral stability. 

I agree that this is purely the Lateral CoP that produces this.


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