Considering an R-Pod

Looks like California is giving higher incentives to hydrogen cars than to electric vehicles these days, so the experiments are still being encouraged. I think for most people battery will make more sense though, because you mostly just plug in over night in your garage and with solar panels on the roof of the house you don't have to worry about your consumption not being offset by clean energy. Always full in the morning and never having to stop to fill up is hard to beat, for those 90% of driving we do for our daily things. And supercharging works rather well when we go the distance, which is not that often but when we do we don't mind, i.e. 900 mile round trip to family in southern california, or into the sierra mountains for camping etc. 

I started skimming through that forum discussion and saw this:


johnse | May 26, 2015

Just thinking about the actual work imparted on the trailer to bring it to Siskiyou pass elevation 1314m (assuming from sea level)...
mass = 2721 kg
g = 9.8 m/s^2
d = 1314 m

Work = m * g * d = 35.04MJ = 9733 Wh or 9.733 kWh

So, ignoring the aerodynamic drag, this would imply that about 11% of an 85kWh battery's charge would be spent hauling the extra mass up the mountain.

This suggests that towing isn't actually as detrimental range as one might have thought. Drag might be, but you can mitigate that by driving more slowly or having more streamlined trailers.

Please point out if my 40-years dormant physics has flaws in it :)
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jjs | May 26, 2015

@johnse Although the 85kWH battery has at least the capacity to store 85kWH of power when new, not all of it is usable. Some is saved as a buffer to protect the battery from damage. It has been estimated at about 10%. So assume usable battery power of 76.5 kWH. So if your calculations regarding the work required is correct it would be more like 13%. Still not too bad. If you consider a round trip then you get to recover some of that on the trip back down.
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georgehawley.fl.us | May 26, 2015

@johnse: let's see. There is also the work getting the MX up the mountain, another 2.3 kg. there is also the rolling friction to overcome, about 300 wh/mile for the trailer plus the MX and then there's the drag depending on speed. 150 miles gobbles up more than 45 kWh on top of the 20 kWh of work elevating the car plus load. That's 65 kWh not counting drag and things like climate control. That's why 150 miles is a stretch.

But it is still pretty good.

[Farther down someone else mentioned it would be good for short-haul towing but not for long-haul for the reasons that we've already mentioned on this thread. And note that the 1314 m (4311 ft) pass mentioned above is just one mountain, depending on where you are going you can go over multiple passes - techntrek]

StephenH, good post, sums it up well. When I was driving through many parts of the US west of the Mississippi if I got down to 2-3 gallons of gas I was starting to seriously worry about filling up because that only left me 20-30 miles before I was sitting on the side of the road. Starting out with 2-3 gallons equivalent of energy is a problem.

cmt489 - I came back to this thread to try to sum it up this way: towing is a very energy-intensive activity, and while electric motors are perfect for towing (thus their use by railroads for high torque to get thousands of tons moving from a dead stop) the current energy storage and recharging options are not - except in limited use-cases.

Or to put it another way, if it was a good option for highway use the trucking industry would already be using it. The only reason railroads do is they can either get unlimited supply from catenaries, third rail, or they can carry a very large load of diesel (with the downside of high conversion losses chemical-kinetic-electric).

Congrats!!

Fred - actually I've wanted to build a pusher for years.  Read about it years ago in an issue of Home Power magazine.  Often built on the rear half of a pickup frame since you can load it up with lead-acid weight and just need to add the electric motor on the existing drive shaft since the rest of what you need to put the power on the pavement is already there.  I figured I would add a second accelerator on the left side of the brake pedal and let the gas engine idle as much as possible to power the various accessories like the brakes, power steering, etc.  I'd be happy with a 50% mpg increase.