No pistons, no fuel, no worries! Toyota Sera EV Conversion begins…

[wagonist]

First of all, top effort here - I've been subscribed and folllowing this thread for a while and I'm amazed with what you have achieved.

Now these last pics have me a little concerned about any occupants forward of that battery box in the event of any frontal collision. I presume you've got it covered but I thought I'd mention it anyway.

Do the math on the force that will be exerted by the total weight of that battery load at any given speed and then work out up to what speed those brackets will hold before letting go and crushing anything in front.
Also try and work out what force will be applied to the top centre of the largest panel in the battery box as all the batteries try and make their way out of it in an impact if the floor mounted brackets do hold.

Just looking at it, I'd be inclined to add some substantial horizontal bracing to the box across the front of it as well as adding some additional braces from the top of the box to the bodywork to prevent it twisting/tipping.

Keep up the great work and regular updates

In a bit of agreement here.
You can see in the pics how the front face of the box is already not straight. Whilst you may be bolting angle bracket to the top of the box, what's to stop that face flexing & tearing out from the bolts?
A head on crash at 60km/h I've heard can produce upto 6 or 7g's of force.
Quick rough calc:
60km/h - stop in 2seconds (not impossible in a crash)
1000kg car

Force = mass x acceleration

accleration (deceleration in this case) = 60km/h (16.66m/s) / 2s = 8.33m/s/s

Force = 1000 x 8.33 = 8333N = 8.5g's


Also what happens when an offset front impact occurs where the side of the car gets deformed as well?

IMHO, another angled bracket across the front of the box half way up would greatly increase its strength.

Keep up the good work.

[greywolf]

Some full interior shots would be good too.

[brett_celicacoupe]

In a bit of agreement here.
You can see in the pics how the front face of the box is already not straight. Whilst you may be bolting angle bracket to the top of the box, what's to stop that face flexing & tearing out from the bolts?
A head on crash at 60km/h I've heard can produce upto 6 or 7g's of force.
Quick rough calc:
60km/h - stop in 2seconds (not impossible in a crash)
1000kg car

Force = mass x acceleration

accleration (deceleration in this case) = 60km/h (16.66m/s) / 2s = 8.33m/s/s

Force = 1000 x 8.33 = 8333N = 8.5g's


Also what happens when an offset front impact occurs where the side of the car gets deformed as well?

IMHO, another angled bracket across the front of the box half way up would greatly increase its strength.

Keep up the good work.

steve,

your using the mass of the car which will give you the approximate force exerted by the object that the car is crashing into.

to work out the force acting on the fixtures of the box; use the mass of the box.

this would give about 1/8-1/10th of your initial estimation as the batt box is around 100-150kg

if the box is mounted only on the bottom then you would want to consider the moment of the battery box - primarily the rear mounting. if its mounted top and bottom then just estimate the force is equally divided through all the bolts. if they are in shear then take the shear strength as 0.58 of the tensile strength. if they are in tensile then straight up use the rating stamped on them (8.8, 10.8 etc).

cheers

[VA61DETT]

Damn thats too much maths for me!

Box is approx 30KG + 240KG of Batteries
Made out of 2.5mm mild steel, with 25 x 3mm angle brackets bolted along top front / rear.
There are literally 20 bolts (standard tensile) which attach to various available parts of the chassis.
The weakest part will be where the bolts are anchored, as the chassis material is very thin.
Hence the reason for many bolts, washers & flange nuts to spread the load & minimise the chance of tearing at the chassis level.

Once all the brackets are firmly bolted down, the box will add substantial rigidity to the interior off the car for sure!

Its the same as having 2 'large' people in the back seats, and what would they have, 1 strap with 3 M12 bolts. Eyeball engineering says its 'good enough'

More updates soon!
-A

[VA61DETT]

^^ Ripples in the box are from me overheating the metal when welding the first couple of brackets on.
It will look much better once the top brackets are bolted on

[Mr Ed]

In a bit of agreement here.
You can see in the pics how the front face of the box is already not straight. Whilst you may be bolting angle bracket to the top of the box, what's to stop that face flexing & tearing out from the bolts?
A head on crash at 60km/h I've heard can produce upto 6 or 7g's of force.
Quick rough calc:
60km/h - stop in 2seconds (not impossible in a crash)
1000kg car

Force = mass x acceleration

accleration (deceleration in this case) = 60km/h (16.66m/s) / 2s = 8.33m/s/s

Force = 1000 x 8.33 = 8333N = 8.5g's

"Gs" is a measure of deccelaration, not force. What you want to compare is the change in velocity to the change in time, wieght isnt relevant. What your figures have proved is that there is actually LESS than 1G acting on the box, however I think youll find that a car hitting another car head on, or hitting an large stationary object, will actually stop in far less than 2 seconds.

[wagonist]

Damn thats too much maths for me!

Box is approx 30KG + 240KG of Batteries
Made out of 2.5mm mild steel, with 25 x 3mm angle brackets bolted along top front / rear.
There are literally 20 bolts (standard tensile) which attach to various available parts of the chassis.
The weakest part will be where the bolts are anchored, as the chassis material is very thin.
Hence the reason for many bolts, washers & flange nuts to spread the load & minimise the chance of tearing at the chassis level.

Once all the brackets are firmly bolted down, the box will add substantial rigidity to the interior off the car for sure!

Its the same as having 2 'large' people in the back seats, and what would they have, 1 strap with 3 M12 bolts. Eyeball engineering says its 'good enough'

More updates soon!
-A

Have a good look at where the seat belts are mounted to the car. Multiple thickness of plating & generally through the "railing" system of the car.
Actually, my 2s is very conservative, it's probably more likely 1/2 a second, max. This give 4g's.
This means your box becomes the equivalent of 1000kg at 60km/h.
And if you hit something that's going the other way at 60km/h, it's like hitting something stationary at 120km/h, making your box 2000kg.

Personally, I was worried about the middle centre of the box flexing enough that it tears the edges out of the boltholes, rendering your edge reinforcement useless.

Not trying to rain on your parade, but for minimal extra effort, the box could be strengthened significantly.
And whilst your car would wrecked in an accident like above, it would be nice to walk away from it

[TERRA Operative]

Two 50mm steel tubes from B pillar to B pillar behind the front seats (one at the top of the box, one at the bottom) would keep that box in it's place.

[RAAAH23]

wow really nice champion. i built a electric scooter once this is somewhat different =P

props for the cool conversion

[Smokey228]

Two 50mm steel tubes from B pillar to B pillar behind the front seats (one at the top of the box, one at the bottom) would keep that box in it's place.

I like this idea, and then have brackets running off them into sections of the box. Would look like a drag car with the bracket from the taxi bar, to the driver seat for extra re-infocement

Cheers,
jase

[VA61DETT]

Yer, May have to investigate the 'drag bars', I honestly don't think the car would hold-up too well in a 120Km/h crash batteries or no batteries, its very light weight.

-RAAAH23

Heres my ghetto electric scooter run
http://www.youtube.com/watch?v=k24422G8084

-A

[MR22ZZ]

I don't think it's the car people are concerned about in the event of an accident, it's the ability of the batteries and battery box to become projectiles. That's some serious momentum concentrated within that box which could quite easilly crush the driver and passenger in the event of a fontal impact if the mounts aren't up to the task.

[RAAAH23]

Yer, May have to investigate the 'drag bars', I honestly don't think the car would hold-up too well in a 120Km/h crash batteries or no batteries, its very light weight.

-RAAAH23

Heres my ghetto electric scooter run
http://www.youtube.com/watch?v=k24422G8084

-A

hahaha that thing is sick wish mine had a seat now props for the sick a$$ scooter aswell

[benjamin]

And if you hit something that's going the other way at 60km/h, it's like hitting something stationary at 120km/h,

No way!!! As long as they are equal mass they would just cancel each other out and the forces exerted would be exactly the same as hitting a solid, immovable object at 60km'h.

With your above statement you are saying that instead of hitting a car head on at 60 I would be better off to avoid them, accelerate up to 120km/h and crash into a rock wall...I don't think so.

Draw two diagrams, both with two cars head long into each other but one with a brick wall between them at point of impact. Everything will be the same

[VA61DETT]

Umm, this is sounding like the age old 'if I was in a train going at the sped of light & I walked from the back to the front of the train, would I then be travelling faster then the speed of light?'

Never the less.
Ill keep in mind the following:
a. cross tube battery brace
b. avoid hitting cars head on
c. avoid hitting brick walls head on
d. Rip massif electric powered skids

Physics hurts my head, Relax ppl

-A