[piotrsko]

I have found that they don't go out of balance until you get crazy with battery current on discharge. In my case 600 amps. Then the most positive set go wonkers. Might have to do with cell count in modules, more cell connection, higher mismatch. The 120v module gets the worst, the 98 v modules stay balanced.

 

[Dave Koller]

Kool! Thought I would lurk here - I see my stuff is still on here for my Saturn...

 

[Duncan]

It's been cold and wet here - but we are past the shortest day so soon the weather will improve

I have fitted a tonneau cover - I can take the drivers side off and leave the passengers side on

It's a lot "bigger" than I expected but just the passengers side seems to help the aerodynamics

Also I modified and improved my "Brooklands Screens" - I took about 20mm off the top and tidied up the threaded rod

 

[poprock]

Hi Duncan. Long time no post because of frustration with my wandering IP address locking me out. Re your weight balance device ; IIRC London double- decker buses had a sliding counterbalance weight to prevent them falling over. ?? Anyone remember this?

 

[poprock]

Perhaps it was an episode of Top Gear?

 

[poprock]

Not wanting to be presumptuous but would removing the passengers Brooklands shield and head rest improve airflow?

 

[Duncan]

Yes - but the screen is not that easy to remove (my bad) - but it is easy to lay flat!

Removing the headrest is easy - I had not thought of that - could well be worth doing at any high speed events - or if I need to drive far

 

[Rdstrblk]

It goes!!!

I just highly illegally drove it down the hill and along Ruia Street

Everything worked except the pre-charge (the bulb had blown)

Now I had better bolt some bodywork on - bolting the seats down might be a good idea as well

Reading this build from start to finish and have gotten to this post. Belated congrats! I am a huge fan of the locost 7 and caterham design.

Are you fabbing all of the structure or was some of it supplied? Maybe fabbing yourself based on a design. Excuse my ignorance, it seems as I have stumbled upon some magnificent information here.

Excited to keep reading! Thanks for such a detailed thread, but ya gotta get a better camera!

 

[Duncan]

Hi
I made the structure up - it's quite simple!

but ya gotta get a better camera!

Camera was fine - it was a combination of the operator and the much smaller size of images that the site allowed back then - five years ago

 

[Rdstrblk]

Wow that is very impressive. After reading thru this so far, I am very much considering changing base platforms. My little festiva would be fun, but a rwd or even awd platform would really be ideal.

How does one even begin to consider building their own frame? Good books to read? I'm starting school in a month for mechanical engineering and a project like this is exactly what I would like to be able to accomplish concurrently. I may just buy a kit car minus motor and electronics and convert to electric, I doubt I'll ever be able to design my own frame geometry. On a more optimistic outlook, i have already done this with bicycle frames so some of the design concepts I'm sure overlap.

 

[Duncan]

Hi
The classic book is the "Locost"
Build your own sports car for as little as £250 by Ron Champion (ISBN 1-85960-636-9).

https://en.wikipedia.org/wiki/Locost

I cheated
- the rules here (NZ) mean that if you make your own wishbones then you need to do things like getting them crack tested
So I simply used the front and rear subframes off a production car - these locate most of the suspension stuff so all you need is a structure to go in between them (and sit in)

If I was doing it again I would look for the front suspension with double wishbones
The Strut suspension from the Subaru works really well - but the body I made to go around the strut mountings is ugly

As far as suspension geometry is concerned if you do go that far I recommend

https://www.amazon.com/Race-Rally-Car-Sourcebook-Competition/dp/1859608469

 

[brian_]

...
So I simply used the front and rear subframes off a production car - these locate most of the suspension stuff so all you need is a structure to go in between them (and sit in)

If I was doing it again I would look for the front suspension with double wishbones...

In the ancient history of British cars, this was the Triumph Spitfire. In this century, lightweight cars with double wishbone suspension are relatively uncommon, but the first two generations of Mazda Miata/MX-5 (the "NA" and "NB" platforms) are a popular choice. For instance, the Excocet is based on complete Miata subframes and suspensions (and complete drivetrain, but you don't need the engine). There is an interesting project in this forum which put Miata suspension under an NSU Prinz.

 

[Rdstrblk]

Heh, coincidentally I also own a boosted '94 NA. Maybe one day it will be electric too!

If you could go back in time, would you have used the miata subframes Duncan?

 

[Duncan]

If you could go back in time, would you have used the miata subframes Duncan?

Maybe -
I would have had a good look around at what I could find
So far just looking at images on the net the old triumph herald/spitfire front subframe looks best - but very very old now!

Dunno - I will have to have a good look
The Miata subframe would effectively raise my battery box - I wanted to have as low a C of G as was possible

Maybe I should have gone for a fabricated front subframe with my own wishbones and just paid to have them crack tested -

Hell I'm in a Hot Rod Club - maybe I would have gone for a light weight front beam axle!

 

[brian_]

So far just looking at images on the net the old triumph herald/spitfire front subframe looks best - but very very old now!

I don't know about the Herald, but the Spitfire doesn't have any subframes - what you're seeing is a full frame (in a bizarre backbone design) with mounting points for the suspension (and engine mounts) as welded-in parts of it; a separate body rides on that frame

The antique Spitfire also features trunnion bearings instead of lower ball joints, because back when it was designed ball joints to carry the spring load were not affordable. Although called trunnion bearings, they are actually a coarse-threaded vertical nut and bolt plus a horizontal pin and bushing... and a bunch of seals. It's quite Rube Goldbergian.

I had never heard of these things when we bought our Spitfire, so it was a interesting discovery. Following links to projects from this forum, I read about an interesting project in which the builder chose to use Spitfire parts... and by the time he replaced the parts which he found unsuitable for use, he had custom-machined spindles to use different bearings and hubs, custom-cast modified uprights to use lower ball joints different upper ball joints, aftermarket brakes... in other words, the Spitfire parts were of no value at all. To be fair, lots of people really do use actual Spitfire parts.

 

[brian_]

The Miata subframe would effectively raise my battery box - I wanted to have as low a C of G as was possible

Since front subframes are designed to fit the engine (and transmission if transverse), they can be a poor match to an entirely different powertrain; the crossmember which nicely nestles near an engine sump might really get in the way of a rectangular battery box.

Swapping larger engines into Miatas is somewhat popular, so more than one company offers a tubular steel bolt-in subframe, to use stock suspension bits with no fabrication, but allow more space for a different engine. One of them is available with no motor mounts, leaving a big clear space for a battery box. Yeah, it's a lot of parts to buy (Miata subframe with parts, aftermarket subframe) and you're still building your own frame (but a simple one without suspension mounting points).

One of the "interesting" features of vehicles using Miata subframes is that the shocks and springs - both front and rear - do not mount to the subframe, but to the body (in the stock vehicle). That means that the frame of a custom vehicle needs structural points for not just the subframes, but also for four spring/shock mounts. They're lower and further inboard than typical struts, but this is still no formula car setup.

I'm not trying to sell or discourage the idea of Miata bits - the commonly used but now old NA/NB or the more recent generations which are entirely different - but they are an option and provide some examples of the issues that car builders face.

 

[brian_]

So I simply used the front and rear subframes off a production car - these locate most of the suspension stuff so all you need is a structure to go in between them (and sit in)

If I was doing it again I would look for the front suspension with double wishbones
The Strut suspension from the Subaru works really well - but the body I made to go around the strut mountings is ugly...

The Subaru BRZ / Toyota 86 / Scion FR-S came too late for Duncan's Dubious Device, but if repeating the project now, the BRZ could provide a set of running gear which are derived from the Impreza, but altered for a lower car and suited to a rear-drive (only) drivetrain. The front struts are lower and lean in more, there are no front axle shafts (no hacksawing required), and the final drive unit is the one from RWD Toyota products such as the Lexus IS, rather than the rear unit from an AWD Subaru.

 

[knoef]

Hi Duncan,
I have just scored a hitachi 10kw 48v motor which I intend to mount in a Nissan Sunny, I am Chch based and am looking for a suitable controller. Do you have any advice for a newbie? what sort of voltage should I be working towards for runs around town and the occasional short stretch at 110 k/h?

 

[Duncan]

Hi Knoef

Are you using the gearbox? - you may not need to with a light car like that

With 130v I topped out at 100kph - with 500 amps I was quite acceptably rapid in what is effectively top gear!

I like the Paul & Sabrina controller - it's 144v and 500 amps

What are you using for a battery?

 

[knoef]

The Sunny has a transverse engine/gearbox going to two front wheels so it just seems easier to connect to the bell housing of the gearbox directly (with or without the clutch). I haven't sorted any batteries yet but want to go lithium iron phosphate with either 60 or 100Ah. I think these can be ordered through Ali express from China directly. Where did you source your Volt batteries?