[ExI] towed evs again

spike at rainier66.com spike at rainier66.com
Mon Oct 23 21:50:47 UTC 2023

-----Original Message-----
From: extropy-chat <extropy-chat-bounces at lists.extropy.org> On Behalf Of BillK via extropy-chat
Sent: Monday, 23 October, 2023 1:44 PM
To: Extropy Chat <extropy-chat at lists.extropy.org>
Cc: BillK <pharos at gmail.com>
Subject: Re: [ExI] towed evs again

On Mon, 23 Oct 2023 at 20:48, <spike at rainier66.com> wrote:
> True this is a weight penalty for needing a heavier frame.  However with this notion the camper is not necessarily long and the aft axle is not very far aft.  Consider the position of the rear axle in this view:
> Imagine your heaviest stuff (the batteries) located forward of the front axle in a bulbous front end (for better air drag characteristics) and above the rear axle.  Now imagine your lighter weight stuff in the longest span and out on the cantilevered aft end.
> Now imagine two scenarios.  One has a driven straight across axle, rear wheel drive only.  But if we don’t care about rough rides (because no one rides in the camper while it is underway) then you can go with four hub mounted motors and the associated weight savings and space savings.
> Now imagine away all the IC engine stuff underneath there, the exhaust system and such.  Now the entire rig can ride lower, and since we don’t care if it is a noisy rough ride (nobody back there while underway) then short rigid springs suffice and we can even tolerate underdamping (since side to side sway doesn’t matter (no one to get seasick back there.)  Lower profile, less wind resistance.
> BillK, to your point, with the heavy batteries mounted above the rear axles and forward of the front axle, the frame weight is manageable and the oscillation problem goes away because of the excellent damping characteristics of good old rubber tires.  The bigger problem is the cost of all that storage, rather than primarily a controls problem.  We could guide such a beast with a Tesla, assuming we don’t get carried away with trying to make the camper push the little Musk-ito to the Sierras.
> spike

>...Sorry, but you seem to be redesigning the towing camper industry.  :) Surely they haven't been doing it wrong all this time?

Ja of course, for we are now looking to tow with an existing electric passenger car, which the camper industry has never done.  So... I am not so much redesigning as designing for the first time.

The tow vehicle isn't actually towing in this case, but rather just guiding.  For an electric vehicle to fulfill this role, the towed vehicle must be mostly or completely self propelled.

>...That photo is misleading as it is an RV, not a towable camper van...

BillK I understand that, but I am using it to demonstrate that if we have a self-propelled towed vehicle, all the rules change.  The axles close together as in a traditional towed vehicle leads to oscillating instability if the wheels on the towed vehicle are powered.

>...You said you didn't want a single axle van, as that would be too small.
Single axle vans also have legal max weight restrictions which your large collection of batteries might exceed...

Ja the weight of this rig is likely to be a big challenge, even if we assume two axles.  But since you mention legalities, this is likely to be another big challenge, in that (as far as I know) it has never been done.  The legal system doesn't take well to innovation on the highway.

You have to take into account the towing characteristics as well.
>...The reason twin-axle camper vans are placed in the center of the van is for better stability and balance....

Of course, but a self-propelled towed vehicle rewrites all the stability rules.  Using a Tesla as a "tow" vehicle rewrites all the rules as well.  

>... By placing both axles in the center of the van, the weight is more evenly distributed, which reduces the risk of the van tipping or swaying while driving...

Ja, again not necessarily applicable to a self-propelled "towed" vehicle, which is really a guided vehicle.  The Tesla doesn't have a lot of extra energy to pull anything.  I had a notion we could push the Tesla with the towed vehicle, but that too gets scary.  The current theoretical design looks a little like a traditional motorhome but has no driver interfaces other than a hitch up front which is used to guide the beast.  It would be simple enough with battery placement to match the wheelbase, the weight, the moments of inertia etc of the tried-and-true motorhome.

>...This is especially important when towing a camper van, as the added weight of the trailer can make the van more prone to swaying...

This is why I suggested short-travel sturdy springs: if the self-propelled towed vehicle has a rough ride, it doesn't matter because no one is back there.  The passengers are in the Tesla.

>...Additionally, placing the twin axles in the center of the van allows for a more even distribution of weight, which can help to improve the van's handling and braking performance. This is because the weight of the van is more evenly distributed between the two axles, which can improve the van's overall stability and traction...

Agreed, but not applicable to a self-propelled "towed" vehicle.


>...This is critical as your batteries will be heavy, so swaying could be a problem...

Not really, if we go with heavy suspension, short suspension travel, the kind you have on a traditional towed trailer but not suitable for motorhomes.  With a self-propelled guided-from-in-front vehicle, we can go with spread axles with heavy-duty suspension.

>...I am not even sure that a Tesla could safely tow a thing like this.  :)



Ja, well it is entirely possible you are right on this one.  If one engineered something like this, you know some crazy goofball is going to find a way to hurt herself with it.


More information about the extropy-chat mailing list