[ExI] towed evs again

spike at rainier66.com spike at rainier66.com
Mon Oct 23 19:48:03 UTC 2023


...> On Behalf Of BillK via extropy-chat
Cc: BillK <pharos at gmail.com>
Subject: Re: [ExI] towed evs again


On Mon, 23 Oct 2023 at 18:43, < <mailto:spike at rainier66.com> spike at rainier66.com> wrote:


>>... My design exercise led to exactly that conclusion Mike.  I had to give up the notion of axles close together if it is to be self-propelled.  Those two requirements are just incompatible:

oscillating instability in all configurations with close axles...  So… pay the price in cost and weight, carry more capacity.


> spike




>...Hang on a minute!  You now have a very heavy, long camper with two widely separated axles...


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.   


>…I recommend waiting a year or two for much improved, lighter weight, quick recharge batteries.  :)  BillK



BillK, there may be a few evolutionary improvements on the horizon in power storage, but do keep in mind that none of the currently-plausible developments improve on energy to weight ratio.  Mr. Musk started with the best we are likely to do in energy to weight ratio because he wanted sports cars, at the expense of battery life, battery cost and other considerations.  He understood why the EV-1 failed and didn’t want to repeat that expensive mistake.


With that in mind, we can wait for future lithium sulfur and lithium solid state and lithium iron chemistries if we wish, but for the well to do (we started with a Palo Alto resident as an assumption) glamper wanting to be free of dinosaurs in order to pretend she isn’t operating her naturemobile on coal and natural gas, the current state of the art Lion tech with its energy to weight ratio is compelling.


Future chemistries will likely beat the current state of the art Lions in lifespan as measured by number of charge cycles, but that is nearly irrelevant for camper use because the camper batteries aren’t cycled much.  The Palo Alto resident is lucky to get out to the Sierras 6 or 8 times a year, which is likely more use than a similarly-price yacht or personal aircraft, both of which burn dinosaurs, lots of em.


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.



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