NEW EV KIT CAR PROJECT

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stuart mills
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Joined: Wed Dec 26, 2007 2:03 pm
Location: Mansfield
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NEW EV KIT CAR PROJECT

Postby stuart mills » Wed Dec 26, 2007 2:27 pm

Hi everyone, been playing with electric vehicles for years and figure it would be a good time to develop a new micro EV as a kit.
I am a vehicle designer and you can see some of my work on www.mevltd.co.uk
I would like to develop a light weight 2 seater, 3 wheeler. A modern styled micro car. I propose to fabricate a space frame chassis with a GRP body. The motor will drive the sinlge rear wheel so no diff required and the batteries would be under the bench seat to keep COG low and central to aid stability.
I do my own fabrication and pattern making for moulds but need advise on power plants. CAN YOU HELP?
In exchange I can offer a wealth of advise on topics such as chassis engineering, suspension and steering geometry and the all important SVA, MSVA, VIC, VOSA and DVLA issues.
I need a 1425rpm 5kw, 120v motor or supplier detalis
Controller supplier that doesnt cost the earth
Battery supplier
Battery advise, i.e, Lithium, Ni met, Lead, Ni zinc, ect. Which one with out being cost prohibitive or complex to charge. 40 mph and 40 radius would be good from a vehicle weighing under 400 kgs all up, plus occupants.
Does anyone make a realistically priced multi pole motor suitable for EV's so we can keep motor speeds down without losing efficiency or friction losses through drive systems such as belts or chains?
Any assistance would be greatly appreciated.
Regards Stuart Mills

bobc
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Joined: Thu Dec 20, 2007 1:11 pm
Location: Knutsford

Postby bobc » Wed Dec 26, 2007 8:42 pm

Hi Stuart,
Sounds similar to my target spec. Because I'm a drives engineer, I'm approaching it in a slightly unusual way & going for induction motor. So I'm using a local guy to rewind a standard industrial TEFC motor with ~1/5 as many turns to get me down to a reasonable voltage, anyway that will cost me £250. I'll be doing the inverter & battery charger over the next couple of years.
The brushless DC or PM synchronous motors seem to give incredible power densities these days - & they're efficient too, but I still like the induction machine for ease of control, safety, cost & availability
Bob

MalcolmB
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Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Thu Dec 27, 2007 12:35 am

Hi Stuart

Very impressed by the machines you've built, especially the R3. Your plan for a lightweight two-seat three-wheeler sounds great - tandem or side-by-side? Probably a stupid question, but when you say 40 mile radius, is that 80 mile range or do you plan to recharge before making the return trip?

For a reasonably aerodynamic 400 kg vehicle with a top speed of 40-50 mph I'd reckon on an energy consumption of around 150 Wh/mile. Based on real-life figures that would mean a battery weight of roughly 2 kg/mile for lithium ion, and 7.5 kg/mile for lead acid, so 80 kg for a 40-mile lithium pack and 300 kg for the equivalent lead acid pack. Seems like this rules out lead acid for your target weight. The nickel chemistries are heavier than lithium and nickel prices are very high right now.
Lithium is still expensive and you do need a battery management system, but it does look as if prices will start dropping shortly and reliable battery management systems should become more widely available.

MalcolmB
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Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Thu Dec 27, 2007 2:24 pm

Just wondered – why a 120V system and such a precise rpm? 1400 rpm seems a bit low for a 120V system. Bob can obviously give you more information about the AC motors, but a permanent magnet DC Lynch-type motor such as the Perm PMG132 could give you 5 kW at 36V and 1800 rpm.

Malcolm

stuart mills
Posts: 80
Joined: Wed Dec 26, 2007 2:03 pm
Location: Mansfield
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Postby stuart mills » Sun Dec 30, 2007 11:49 pm

Having looked further into the Lithium option I consider them too expensive if the kit is going to sell. I would prefer to find a multi pole motor of 96v at 800rpm of around 6kw. Does anyone know of a controller or motor manufacturer that could produce a prototype for me? My 400kgs all up weight allows for 150 kgs of batteries which I hope will give me a 40 mile range not radius. Maybe optomistic but having experimented with Nickel Zinc cells I feel it maybe possible but my supplier is no longer and one packed up after 26 cycles. Are they now out of the running? Regards Stuart

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MB
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Location: Coventry, England
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Postby MB » Wed Jan 02, 2008 10:02 pm

I would recommend you talk to Martin Rees of BBIG - www.bbig.co.uk. This is exactly the sort of project Martin would relish and as the current holder of the UK electric car land speed record - and with ambitions to break the world land speed record this year - he knows a thing or two about a thing or two when it comes to electric vehicles.

stuart mills
Posts: 80
Joined: Wed Dec 26, 2007 2:03 pm
Location: Mansfield
Contact:

Postby stuart mills » Thu Jan 03, 2008 10:03 pm

Thankyou for your help chaps. I have now sourced a suitable motor but at 3000rpm design speed I would need a ratio reduction of 3-1. A chain drive or belt drive would be traveling at a demanding speed and the chain would no doubt be noisy. Has anyone got any suggestions for an economical geared reduction. Regards Stuart

MalcolmB
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Joined: Sat Jun 23, 2007 8:07 pm

Postby MalcolmB » Thu Jan 03, 2008 10:50 pm

Good to hear you found a motor! What did you decide on in the end?

A well-aligned and lubricated chain drive shouldn't be too noisy with a 3:1 reduction. I use a 5.5:1 chain reduction on my motorbike, with motor rpm up to 4500 and that's not bad at all. I'd like to switch to a belt drive at some point as I reckon it would be even quieter. The rear sprocket from a Harley belt drive or Kawasaki Scorpion would be suitable for a 3:1 reduction, but they're a little pricey.

On the battery front the Evercel batteries are no longer in production and I've heard a few stories of reliability problems like you've experienced. For what it's worth I get 15 miles range from 47.5 kg of Enersys SBS 26Ah lead acid batteries (60V system) and my motorbike weighs 130 kg.

stuart mills
Posts: 80
Joined: Wed Dec 26, 2007 2:03 pm
Location: Mansfield
Contact:

Postby stuart mills » Fri Jan 04, 2008 4:46 pm

I found a 3 phase brushless DC motor, 15hp peak@3000rpm, I will let all you good people know if its any good. Regards Stuart

Deker
Posts: 104
Joined: Fri Jul 21, 2006 2:40 am
Location: Borehamwood

Drive trains

Postby Deker » Thu Feb 21, 2008 4:30 am

Hi All.

Stuart needs drive reduction for his anticipated project.
I can supply a MS Office spreadsheet for calculation of motor/s RPM to roadspeed in English via whatever powertrain device/s one prefers.
NO calculation is given for frictional, aerodynamic or hillclimbing losses.

Stuart, if your'e concerned about chain noise, then HTD toothed belt should be considered, frictional losses are very minimal with HTD.
I have found a way to cheat for finalising the ratio.
This is to save purchasing an expensive large diameter toothed pulley, only to find it's the wrong size !

Method - Use calculated toothed pulley or chain sprocket on motor. On the final drive, make an oversized temporary wooden pulley with a flat bottomed V groove into which the toothed belt is a snug fit.
Test drive, then adjust pully size until you are satisfied with the result.
Use the nearest stock size sprocket/pulley etc. UP, do NOT use the next stock size down, you'd be surprised how much overloading that can put on the motor and batteries.

Of course the wooden pulley would need metal boss/es to clamp it to driveshaft.

I have succesfully used this method for permanent drive on my electric scooter using a Sinclair motor, fitted with toothed pulley AND flat pulley on final drive, the ratio was a massive 9:1 in a single step.

One thing I did find to my cost, was to have a 50% wider belt than the manufactures horsepower rating.

Any questions, please ask.

Finally, V belts really do sap power, and are to be avoided in battery powered applications.

Deker.


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