# "from scratch" build



## Duncan (Dec 8, 2008)

Hi Jordan

This is my scratch built
http://www.diyelectriccar.com/forum...ns-dubious-device-44370.html?highlight=duncan

Mine weighs 710Kg - but could be made a lot lighter

As it is fairly light it does not have a gearbox - direct drive to the diff


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## vmrod (Jul 2, 2010)

While we are at it, here's my construction blog.

http://xr3.proboards.com/index.cgi?board=diary&action=display&thread=19

...and a quick youtube video is here;

http://m.youtube.com/watch?v=Ctl3FjS9-BI

I have placed this project on hold until my electric Opel GT is completed. (which should be very soon)


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## Yabert (Feb 7, 2010)

JWB37 said:


> What kind of gearbox or transmission would you recommend for a ground up build?


Depending of your build, you can use a regular FWD transmission in rear position. Example
Also, there are few transmission originally coming with integrated limited slip differential... a big gain! (Honda type R/Si, Nissan spec-V, Focus RS, etc.)


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## vmrod (Jul 2, 2010)

An old volkswagon tranny works good for me.

They can be professionally rebuilt to be very strong and utilize different gearing. Some models have LSD.

You can also use them with the motor mounted to the rear (originally), or flip the internal ring-gear and have the motor mounted in the front (what I did).

You could buy a specific one from Rancho vw transaxles.


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## JWB37 (Mar 14, 2013)

Wow! thank you guys! I will be studying all of those builds for quite a while.

What are some rough average dimensions for a motor with direct drive, and what are the size of the batteries that are normally used? I'm trying to play around with some single seat designs, but without knowing those dimensions, its really hard for me to design a car. I want to to be as close to a 50/50 weight ratio F/R as possible. possibly with a slight rear bias. We will see. It's beginning to sound like direct drive would be better for a light weight car like this? I plan to distribute power via a rear differential(ford 9in?). If I choose the right gearing in the diff, would direct drive be the best deal? would that limit my top speed? I want to be able to hit a cruisable 65-70 mph. But I don't want to stall at low speeds or not be able to start on an incline

I have to say though, vmrod, that little trike roadster you got has really got me questioning my design. I have some thoughts for a 3 wheel RWD chain driven roadster that might be worth using for my project. I'll have to play around with solid works and see what weighs less and is more practical.


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## vmrod (Jul 2, 2010)

Mine is FWD. It is safer than RWD as far as fishtailing goes.
With RWD, you would have a lot of roon in the front for batteries.
However for a trike, it is best/safest to have about 2/3 of the weight at the front axles. This really helps protect against rollover.

I flew through some curves with mine during testing. Far faster than in the video. It stays glued to the road.


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## JWB37 (Mar 14, 2013)

vmrod said:


> Mine is FWD. It is safer than RWD as far as fishtailing goes.
> With RWD, you would have a lot of roon in the front for batteries.
> However for a trike, it is best/safest to have about 2/3 of the weight at the front axles. This really helps protect against rollover.
> 
> I flew through some curves with mine during testing. Far faster than in the video. It stays glued to the road.


that is true. FWD would be safer, but I'm not too worried about that(although safety of the vehicle is very important to me). I'll most likely be doing a RWD tube chassis roadster. From what more I've read, I plan on going direct drive with a short driveshaft to a ford 9in differential(or comparable). I'll use independent suspension all around, and I'll probably make it a two seater, cause what fun is a fast electric car if you can't share the ride?

That said, what batteries would you all recommend? I really like the LiFePo batteries but they are expensive! what else is powerful and affordable? and if you know the dimensions, that would be much appreciated!

Thanks!


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## Yabert (Feb 7, 2010)

JWB37 said:


> That said, what batteries would you all recommend? I really like the LiFePo batteries but they are expensive! what else is powerful and affordable? and if you know the dimensions, that would be much appreciated!


If you do a serious build, Lifepo4 is the better choice at the moment.
The best advice I can give to you.... build your car first and by the time you will finish it (6 month? One year? Two years?) the battery technology will grow up and the price will probably reduce.
Simply plan enough space for the cells. Maybe start with currently available battery shape (example). Or more complex build with cylindrical cell (example).


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## JWB37 (Mar 14, 2013)

Yabert said:


> If you do a serious build, Lifepo4 is the better choice at the moment.
> The best advice I can give to you.... build your car first and by the time you will finish it (6 month? One year? Two years?) the battery technology will grow up and the price will probably reduce.
> Simply plan enough space for the cells. Maybe start with currently available battery shape (example). Or more complex build with cylindrical cell (example).


Thank you so much! Is there a way to figure out how many batteries I need given its voltage and Ah rating? I want a car that will drive for at least 4 hours before needing to be charged. Is there a formula for this roughly? 

for example, if I use this battery,
http://stores.headway-headquarters....tteries,-40160s/Detail.bok?category=BATTERIES

How can I determine how many I need? Also, what determines the voltage in the system? I figure(from what I've looked at) I'll end up with 2-4 battery packs in parallel of equal voltage, all made up of the cells that I buy.


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## Yabert (Feb 7, 2010)

JWB37 said:


> How can I determine how many I need? Also, what determines the voltage in the system?.


Generally speaking, we describe range as miles per charge instead of time per charge.
Anyway, 4 hours seem unlikely (except at low speed 15-20 mph) and let me start an example based on your battery example (headway 40152S).

Each cells are rated 3.2v and 15Ah, that give 48 wh of energy storage.
Let say your car is small and light, it can use as low than 200 wh/mile at 40 mph (8000 w to sustain 40 mph). If you need to drive 1 hour at this speed, you will need 8000 wh in energy storage to do this (200 wh per mile X 40 miles).
8000 wh (or 8 Kwh) divide by 48 wh (one cell) = 167 cells (let say 168 cells)
Those 168 cells can be distribute as: 42 *S*eries and 4 *P*arallele (134v and 60Ah) or 21S 8P (67v 120Ah) or 28S 6P (90v 90Ah) or any thing else (84S 2P for 269v 30Ah) based on the system voltage (motor and controler).

So, what kind of range, top and continous speed do you expect?


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## JWB37 (Mar 14, 2013)

Yabert said:


> Generally speaking, we describe range as miles per charge instead of time per charge.
> Anyway, 4 hours seem unlikely (except at low speed 15-20 mph) and let me start an example based on your battery example (headway 40152S).
> 
> Each cells are rated 3.2v and 15Ah, that give 48 wh of energy storage.
> ...


Hmm, that is quite humbling. More realistically I am hoping to be able to hit freeway speeds(70-75mph max) but have the ability to make a 30-50 mile commute daily.(60-100 miles round trip) Or about 2-2.5 hours of driving. I'm not expecting all of that to be freeway driving though.

Would it make sense to have more batteries in parallel, and have a system with less voltage? Does voltage have a direct relationship to the amount of power the car makes?


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## Ziggythewiz (May 16, 2010)

JWB37 said:


> Would it make sense to have more batteries in parallel, and have a system with less voltage? Does voltage have a direct relationship to the amount of power the car makes?


P = volts * amps, so yeah, that's a direct relationship.

You can compensate for lower voltage with higher amps (amp-hours for range) but the voltage ultimately limits your top speed.


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## JWB37 (Mar 14, 2013)

Ziggythewiz said:


> P = volts * amps, so yeah, that's a direct relationship.
> 
> You can compensate for lower voltage with higher amps (amp-hours for range) but the voltage ultimately limits your top speed.


Sounds like I'm gonna need a lot of batteries.


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