[ExI] towed evs again

spike at rainier66.com spike at rainier66.com
Mon Oct 23 16:14:15 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 5:20 AM
To: ExI chat list <extropy-chat at lists.extropy.org>
Cc: BillK <pharos at gmail.com>
Subject: Re: [ExI] towed evs again

On Mon, 23 Oct 2023 at 02:45, spike jones via extropy-chat <extropy-chat at lists.extropy.org> wrote:
> But a trailer doesn't need to be up there, thanks to smaller tires and no differential so the wind resistance is lower.  If it is hauling its own weight plus gently pushing the Tesla, the towed jeep is unnecessary.  Then if you are an affluent Gaian with such a rig, you can pretend to be green.  You aren't really, but you are not required to admit that to yourself.
> spike
> _______________________________________________

This new trailer may help.  :)
It doesn't solve your driveway crowding or 'push' the electric tow car.
But it does lighten the towing load to extend the range and gives you a week's luxury camping power, with solar panels.

The tech-packed vehicle comes with an optional dual-motor power train and, if that wasn’t enough, can even set up camp for you.



Thx BillK.  Most people don't want the inherent limitations that go with a single axle camper.

I went thru some design iterations last night.  An abbreviated version of what happened in that exercise: the goal is to avoid forcing the Gaian to own a pickup truck, for she is far too embarrassed to be seen in it, analogous to the Baptist deacon who occasionally visits the stripper bar, so she must wear a covid mask, dark aviator shades and a 49ers cap turned backwards, hoping her Gaian friends will not recognize her in that rude old dinosaur burning truck.

To go camping dinosaur-free, the assumption is that the camper is to pull its own weight, with the desired outcome that it has a little thrust left over to gently push the Tesla while out on the freeway, making it plausible to drive from Palo Alto to the Sierras and back without an external charge.  The requisite charge very quickly rules out any single-axle configuration, and is quite the challenge even for a heavy duty double axle, even assuming D rated tires.

As my intuition suggested, if the trailer axles are driven with the CG of the camper in the usual place, you have oscillating instability.  The root locus plot, even with just single-digit estimates on weights and moments of inertia, shows the poles in the right half plane.  Oy.  From just estimates, it wasn't at all clear that there is enough damping available from even a big pickup truck aft tires, never mind a little Tesla.

So... how to get some oscillation damping, perhaps with active counterbalance?  (Note: we never suggested this would be cheap, only cool.)  Long story short: it is probably possible to do the task with active vibration counteraction, but it is scary.  If the thing stops working, or some mechanical actuator gets misbehaving, the likely outcome is a crash, as the rocking oscillation about the vertical axis of the camper makes the system unstable and uncontrollable.

So... the most attractive engineering solution is to separate the axles on the camper, so that the camper tires dial in some oscillation stabilization.  But... that makes the camper too hard to turn.  This is solved by making one of the axles (probably the forward one) fitted with steerable wheels, such as on the forward axle of a Tesla.  (Note as above: we never suggested this scheme would be cheap, only cool.)  

Once you have a steerable axle, it makes engineering sense to separate the axles (giving us weight savings as a bonus.)  Once you separate the axles, that oscillating instability problem just goes right away as the axles get separated farther, until the thing looks a little like a UPS delivery truck except with no front windows.

Having the axles at either end rather than close together allows the batteries to be located fore and aft, which dials in moment of inertia about the vertical axis, which helps stability even more.  From what I can tell, if all that, then we don't even need active controls anymore, no high-performance oscillation cancellation, just dump the instability into the camper tires, where it really belongs.  That also solves the problem of weight on the back of the Tesla, which really isn't designed to haul loads.  The active suspension goes away: regular cheap passive shock absorbers, like the ones the other proles have on their humble conveyances, will do.

With the axles located fore and aft, as in a delivery truck, it looks to me like we have a configuration which can be guided by a Tesla (rather than "towed" in the conventional sense) and maaaaybe can be controlled well enough to gently push the Muskmobile to the Sierras and back on a single charge.  I wouldn't rule out the simpler speed-matching, where there is very little longitudinal force on the hitch.  So that way the Tesla is guiding the camper rather than towing it, and the charge runs down at the normal rate.  Then perhaps the camper can charge the Tesla up at the lake.  This of course requires a looootta lotta of batteries, but as I have already said at least twice, this scheme is not cheap, only cool.


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