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Old 05-20-2021, 03:53 PM   #1 (permalink)
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Non static main battery location

I posted this "futuristic" topic on another forum, but it got little traction, pun intended:

So not exactly in the vein of structural battery utilization, maybe heading the alternative direction?

My thinking, here out loud, batteries are a large part of vehicle mass with electrics, beyond the motor itself. It seems it needs to be always considered the battery has a useful limited lifespan, and replacement at least once will be required. Because of its mass and density, its placement on the vehicle is always a consideration, lower, and more centered being normal goals. It also is likely somewhat conformable in final shape, ie, doesn't need to need to be a single unit/mass.

So with new electric PU's on the horizon, which will need greater battery capacity (meaning size/weight) than many current typical auto offerings, and the fact most PU's have higher ground clearance, and my observations most PU operate at effectively zero load carry at 50% of the time ( this number is just my guess), leads me to the following questions/idea;

Would an underslung, relatively flat, single unit battery pack, be a significant advantage in ride, handling, aero, replacement, safety, etc, if it was was dynamically moveable to optimise the COG for varying load and/or driving conditions? My thinking in beginning development, the battery movement would be very slow, but if found later to be real world effective, speed of movement of the battery could be increased, almost like a side rider on motorcycle racing sidecar. As electrical technology is improved in capacity/density, using another electrical motor for main battery movement would be an easy adaption. It seems active suspension could address many of the above concerns, with greater complexity, but not as well in the end, as an optimized COG is hard to mimic?"

Another commented COG could also be altered by moving axles locations, and manufacturers don't consider it worthwhile, my reply:

"Yes it would have an effect, but my thinking much less effect, be much more complicated, and would directly effect the drivers perception of turning, overhang clearances, aero balance etc, and I suspect for the average driver, be a potential driving hazard. Regarding no manufacturers not feeling its a worthwhile goal currently, at one time, nobody felt streamlining an outside mirror was worthwhile.

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Old 05-20-2021, 05:14 PM   #2 (permalink)
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I like the unconventional thinking.

My thought is they would have implemented such a system with fuel tanks if the benefits outweighed the costs.

Packaging is extremely important in vehicle design, so no volume is wasted. That means no dead spaces where weight can actively shift.

The main issue is that it's not needed. By my observation, 90% of drivers are afraid to take a corner fast enough to even feel lateral G forces (the bane of my existence). If people are already too uncomfortable to drive their vehicles anywhere approaching the limits, why would they value a higher performing vehicle?

Active suspension has more versatility because it can deal with shifting CG as well as uneven terrain.

A moving battery introduces safety and reliability challenges. If it can move, then how will it survive in a collision vs being rigidly contained. How about the stress of the wires and coolant hoses that must articulate to accommodate the battery position.

Finally, it would be tricky to implement as the shifts need to occur prior to cornering. If the shift occurs during cornering it simply places more force on the tires.
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Old 05-20-2021, 06:19 PM   #3 (permalink)
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This sounds like an application for one of my new favorite things the planetary screw. duckduckgo.com/?q=planetary+screw

Load balancing would not require fast reaction. Countering corner forces would.

I'm reminded of Bucky Fuller's Omnidirectional Transporter. It had a two-piece (later three-) frame so that when the two front wheels were hammered the Ford V-8 bounced up and down, but the passenger cabin rode in the rocking chair.
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Old 05-21-2021, 09:58 AM   #4 (permalink)
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Even with the biggest massive battery I can conceive, you're looking at most 1,000 lbs including the holding structure. My volt battery is 88 lbs of battery and 300 ish pounds of holder.

I see a lot of yahoos in my 'hood putting 2000 pounds of construction materials into their Toyota pickups. You can tell they are that heavy because the tires in the back partially disappear, and I know what a pallet of concrete block weighs. Moving the battery around is going to solve that?
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Old 05-21-2021, 11:39 AM   #5 (permalink)
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Interesting concept indeed.
However the additional weight and space requirements of such a system would cancel out any potential benefits and let's not ignore the cost and reliability issues associetad with such a system.
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Old 05-21-2021, 12:45 PM   #6 (permalink)
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Quote:
Originally Posted by freebeard View Post
This sounds like an application for one of my new favorite things the planetary screw. duckduckgo.com/?q=planetary+screw

Load balancing would not require fast reaction. Countering corner forces would.
Maybe I wasn't clear enough, my idea was to initially improve load balancing, with a 50/50 weight bias being the ultimate goal. I was thinking if the idea took hold, then the battery might become more of a solution to improve handling/cornering by more active movement, but regardless, a 50/50 weight bias loaded to unloaded, is nearly always ideal in every situation, and I thought worthy, but mainly thinking PU and thier loads. I personally don't see it a complex effort for requiring flexible wiring/coolant lines, ie we have had 4 wheel hydraulic brakes for many decades reliably.

Thanks for the reasoned replies.
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Old 05-21-2021, 01:32 PM   #7 (permalink)
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Quote:
Originally Posted by Piotrsko View Post
Even with the biggest massive battery I can conceive, you're looking at most 1,000 lbs including the holding structure. My volt battery is 88 lbs of battery and 300 ish pounds of holder.

My ignorance makes it hard to understand the reasoning behind the above numbers. Is the battery encased in a 2" thick Ti tub or something, or is this just unique to a Volt for some reason?
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Old 05-22-2021, 11:09 AM   #8 (permalink)
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Factory says the assembly weighs 480 lbs. Huge and heavy metal back bone and nosecone with 88 metal retaining clips and attaching nuts, bolts washers and spacers, 2 gallons coolant, 30 estimated pounds of plastic battery case, 20lbs control electronics, 10lbs wiring and 40lbs plastic waterproofing cover and way over engineered assembly with even more attaching hardware. The 88 lbs is reported by "Yabert" over on DIYELECTRICCAR when he disassembled his volt pack back 6 years ago.

I don't speculate what a tesla skateboard weighs.
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Old 05-22-2021, 03:38 PM   #9 (permalink)
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I like this idea! I don't know how practical it would be, but I like the idea.

One area where it would help is in 2WD winter traction. Ideally you want a huge weight difference at slow speeds. Cars that I've driven with nearly a 70:30 weight ratio (more weight over drive wheels, whether RWD or FWD) can pull out of sticky situations nearly as well as an AWD vehicle. But once going down the road that weight bias becomes a problem since it contributes to oversteer and understeer. So being able to change that weight on the fly would be nice. Right now the only way to do that is manually moving around heavy objects like sand bags. It's kind of hard to put them over the hood though when you need the weight up front.
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Old 05-23-2021, 01:27 PM   #10 (permalink)
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