GT86 Release party/Trim Index and more!

[Dave-ROR]

Originally Posted by serialk11r

Sure it's behind the axle, but remember the axles have some distance between them. They advertise a low polar moment of inertia, which suggests the mass is on average distributed close to the center of mass, aka between the axles.

If it's moved to an equal horizontal distance to the rear axle as it originally was from the front axle, then it won't affect the moment of inertia much, and if the moment is say, 0.5MR^2, (linearly distributing the mass along the axis perpendicular to both axles), then the weight distribution should actually change from 53 47 to like 51 49, if the battery is 50 pounds.

Now my eyeball figures and pulled out of thin air mass distribution may be wrong, but I would be surprised if it didn't at least move it to 52 48.

It takes 300lbs to go from 55/45 to 53/47 in this car. I really doubt the battery will change much. (i realize tgats adding weight and not moving it) I've driven cars with them relocated and have never noticed a difference from my own car (same setups otherwise).

And if it's not done properly it can be dangerous and I've seen it done properly about half the time.

Feel free to do it buts it's absolutely not worth the expense and time for me to gain... Well nothing IMO

[serialk11r]

Er where are you getting 300 pounds from? 50 pounds is about 2% of the cars mass. If you take 2% off the front and then put 2% on the rear, you are going from 53 47 to 51 49. Now of course the battery doesn't sit right over the axle, but the ratio of distance to front and rear is close enough to make the approximation. If you use a lighter AGM battery in the back of the trunk, that would offset the effect of placing it further from the center of mass (not saying this is the best idea).

[Dave-ROR]

Originally Posted by serialk11r

Er where are you getting 300 pounds from? 50 pounds is about 2% of the cars mass. If you take 2% off the front and then put 2% on the rear, you are going from 53 47 to 51 49. Now of course the battery doesn't sit right over the axle, but the ratio of distance to front and rear is close enough to make the approximation.

Toyotas spec. 55/45 with no passengers. 300lbs (two people) added to the middle of the car becomes 53/47. You are moving an item thats already behind the heaviest mass of the front (which likely weighs 30lbs as it appears to be a smaller battery) to (at best) the rear axle line, probably behind it.

As I said, do what you want. I bet if I were to record lap times of my car before and after the change the difference would be normal driver variance.

If thus were a Nissan with the battery right behind the headlight I'd be all for it though.

[serialk11r]

See the thing with adding 2 people to the middle of the car is you are adding an equal load to each side. If you take more load off one side and add it to the other, you change the distribution a lot. 30 pounds from the current spot to say where the rear seat is should at the very least move the distribution to 52/48 as I said. Levi wants to change the mass distribution of the car so that's why I mentioned it, I'm not claiming that the new weight distribution will be better in any way, as I don't have the sort of experience to say that.

But anyways, being able to move that 30 pounds lower should be a good thing too...if it's sitting say, 6 inches over the center of gravity, and we manage to move it to say 6 inches below, that would lower the center of gravity by 3.4mm, which admittedly isn't much and I'm not saying we can move the battery 1 foot down, but for people who want to do this sort of thing there is a small effect that may well be important to them.

[Dave-ROR]

Originally Posted by serialk11r

See the thing with adding 2 people to the middle of the car is you are adding an equal load to each side. If you take more load off one side and add it to the other, you change the distribution a lot. 30 pounds from the current spot to say where the rear seat is should at the very least move the distribution to 52/48 as I said. Levi wants to change the mass distribution of the car so that's why I mentioned it, I'm not claiming that the new weight distribution will be better in any way, as I don't have the sort of experience to say that.

But anyways, being able to move that 30 pounds lower should be a good thing too...if it's sitting say, 6 inches over the center of gravity, and we manage to move it to say 6 inches below, that would lower the center of gravity by 3.4mm, which admittedly isn't much and I'm not saying we can move the battery 1 foot down, but for people who want to do this sort of thing there is a small effect that may well be important to them.

I noted that adding weight was different from moving it, but the point was that shifting 30lbs isn't going to make the same difference as adding 300lbs that's closer to the rear axle than the front will (and the front passengers are closer to the rear than the front, based on the change of balance).

You are REDUCING load on the front, but not removing it, so the entire 30 lbs doesn't even shift.

Some of that load is already on the back since it's behind the axle line. If you move it in front of the rear axle, but closer to it, it shifts that weight but it's not -30 front +30 rear. The only way to get a large change in balance it to put it behind the rear axle, and that's not ideal. It's going to be hard to move it to the back and keep it in front of the axle.

while I agree with the height part, it's also going to be hard to move it all that much lower since there's no way to put it on the floor pan (while keeping the interior anyways). As best you MIGHT be able to put it at the very front of the rear seat mount/platform. However, safely mounting it there is going to be hard due to the likely shape of the sheetmetal. The most likely place the battery will be moved is to the trunk floor. Moving it 12 inches down will be very difficult, if not impossible (I have no idea what the height of the trunk pan is).

I'd rather just get a lightweight battery.

Oh and once Levi builds his "race car" and no longer has a passenger seat he can mount it there.

[Godzpeed]

just get a lightweight lithium battery and you dont need to worry about relocating anything

[serialk11r]

Actually that's not correct. If you draw an imaginary line connecting the 2 axles looking at the car from the side, the only thing that matters for front/rear distribution is the spot on the imaginary line over which you're placing the weight. The distribution of that weight between the front and rear will be the ratio between the distance to the front and the distance to the rear. If you add weight dead in the center, the effect is MUCH smaller because you're adding that 300 pounds very close to the center of mass (somewhere around the driver's hip). If the 30 pound mass is say 6 inches from the center of mass in a 90inch wheelbase, then 28 pounds goes to the front, 2 goes to the rear.

If you move 30 pounds which sits much further from the center of mass to an equal distance on the opposite side, it is the same as adding "negative mass" to the front, then positive mass to the rear. You can think of moving 30 pounds across the center of mass as having about 2 times the effect of adding 30 pounds, and the further you move it, the greater the effect. A driver sitting only inches away from the center of mass vs. a 30 pound weight sitting a few inches from the axle on a wheelbase of almost 100 inches, the 30 pound weight can easily cause a greater change in weight distribution depending on how close the driver sits to the center of mass.

EDIT: oh and I apologize for flipping between distance from wheel and distance to center of mass, that might be confusing.

[tripjammer]

Originally Posted by Godzpeed

just get a lightweight lithium battery and you dont need to worry about relocating anything

+1

I found a 3 pound one for like $300....I am getting it...

[Carwhisperer]

Originally Posted by Tainen

except you'd never be able to get it, since you don't live in Japan.

I live in the states and getting it imported is simple. Therefore you can get it in the US, If you wanted the gt86 badly.

[Dave-ROR]

Originally Posted by serialk11r

Actually that's not correct. If you draw an imaginary line connecting the 2 axles looking at the car from the side, the only thing that matters for front/rear distribution is the spot on the imaginary line over which you're placing the weight. The distribution of that weight between the front and rear will be the ratio between the distance to the front and the distance to the rear. If you add weight dead in the center, the effect is MUCH smaller because you're adding that 300 pounds very close to the center of mass (somewhere around the driver's hip).

If you move 30 pounds which sits much further from the center of mass to an equal distance on the opposite side, it is the same as adding "negative mass" to the front, then positive mass to the rear. You can think of moving 30 pounds across the center of mass as having about 2 times the effect of adding 30 pounds, and the further you move it, the greater the effect. A driver sitting only inches away from the center of mass vs. a 30 pound weight sitting a few inches from the axle on a wheelbase of almost 100 inches, the 30 pound weight can easily cause a greater change in weight distribution depending on how close the driver sits to the center of mass.

I don't disagree with this. Your original statement was that move 50lbs would move the entire 50lbs (or 2%) off the front axle to the rear. That's what I don't agree with. Obviously the farther from the center of mass, the effect is greater. We don't even know where the actual center of mass is though so you can't even say if it'll be closer or farther to/from the center in the new location. I don't disagree that it'll CHANGE the distribution, but whether it changes it enough to be WORTH the hassle..... IMO it won't be. I won't try to claim I know what the shift will be, but in my experience it simply won't be noticable to the driver (except maybe in their own head) and it's a far easier solution to simply put a lightweight battery in the car than it is to buy a proper box, mount it properly, run new cables, etc.

[serialk11r]

Meh, I'm not going to run calculations again, but I assure you moving it from a few inches ahead of the axle is essentially moving the entire weight from on top of one axle to the other. 50 pounds would be very close to transferring 2% of the weight from one axle to the other in fact.

Sure buying a lightweight battery helps and is easier, but if it's a lead acid you lose capacity (unless you go for a relatively big AGM) which may or may not be acceptable, and lithium ion batteries are tons of money to replace after they lose capacity from sitting at near full charge for a long time, which is what happens in a car. Moving the battery has a much larger effect on the vehicle dynamics, albeit still not very big.

[Dave-ROR]

Originally Posted by serialk11r

Meh, I'm not going to run calculations again, but I assure you moving it from a few inches ahead of the axle is essentially moving the entire weight from on top of one axle to the other. 50 pounds would be very close to transferring 2% of the weight from one axle to the other in fact.

Since when did the battery move in front of the axle? As far as I know it's been behind the axle this whole time...

And I'd still rather have it there than behind the rear axle (the likely only available place to mount it realistically) plus the extra box weight, wire weight, bolts, etc.

Plenty of people will move it and plenty of people will leave it where it is and go with a light weight battery.. and the majority of people will just leave it alone.

I bet equal drivers in otherwise equal cars wouldn't be able to pick out which is which without prior knowledge

Anyways, it doesn't really matter anyways.

[serialk11r]

Sorry that was a typo, I meant behind. Yea I know, but I'm just getting nitpicky about the physics. Haven't slept all night.

[russv]

Originally Posted by DIG1992

More RC spec

I'm not getting the black parts. Is it a Japanese thing?