Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
What About the Gas?
#41
(09-14-2017, 04:46 PM)pogson Wrote:
(09-14-2017, 02:43 PM)Rickb Wrote: You obviously haven't seen the specs on the SRK's twin front wheel drive motor and are making assumptions.

This SRK platform photo looks like a simple, solid, and efficiently engineered drive train package with 70% of the vehicle's weight over the twin motor front drive wheels for enhanced performance and agility in a little over a 1000# vehicle with motors centered between the front wheels.

I'm not making assumptions. "Scale" is about mathematical/physical principles. For instance, if you examine a cube of one unit of length, it has a surface area of six square units and a volume of one cubic unit. If I cut it up into smaller cubes, say, eight cubes, the total volume/weight remains the same but the surface area is now larger, 12 square units.. Similarly, if one has a design for an electric motor, one can increase its power by lengthening it or increasing its diameter or both. Invariably the scaling causes the larger motor to be more efficient than two or more motors of similar design and total combined output equal.

An obvious example: Take a big motor and cut it into two halves. You might think the losses due to the resistance of the windings would be the same but we now miss two cross-pieces to make a circuit so more conductor has to be added to make the thing work.We need the same current as before to get the same power so our resistive losses are higher. Worst case is replacing one big motor with two identical motors. If you actually use twice the power, losses and efficiency would remain the same but you drain the battery twice as fast. So, you have to use only a fraction of the capacity of the motor and efficiency plunges. You have twice the weight, double the number of bearings and fans and internal air-resistance for no gain at all except acceleration perhaps which is rarely useful and dangerous.

Not only are you making assumptions, you are making incorrect ones.  For a simple example, see Tesla.  Their dual motor cars have better performance and economy than their single motor vehicles with the same battery packs.
I'm done.
Reply
#42
(09-15-2017, 12:06 AM)flying_solo Wrote: For a simple example, see Tesla.  Their dual motor cars have better performance and economy than their single motor vehicles with the same battery packs.

"Where gasoline-powered all wheel drive cars sacrifice efficiency in return for all weather traction, Tesla’s Dual Motor propulsion system actually increases efficiency while delivering exceptional traction and control in slippery conditions. By precisely splitting the delivery of current from the battery to each motor, the Model S 85D actually gains an additional 10 miles of highway driving range compared to its rear motor Model S counterpart."

see Dual Motor Model S and Autopilot

They get that increase by reducing slippage, not anything to do with the motors. Further, that's Tesla's claim. A real world test (<-link) shows 85 uses less kW/mile than 85D, 0.329 versus 0.350 kWh/mile. So, the real-world saving on energy is twice the size and negative to the claim. If you don't have slippage, there certainly is no increase in efficiency. They also have a slight increase in weight so efficiency on hills will be a little worse too. The way I drive there is very little slippage happening. Also, Tesla AWD uses two motors, one on each front and rear axle. SMK uses two motors on two front axles so the slippage saving is only on turns or strong acceleration if anything. I avoid both of those as much as possible.
My blog is an eclectic list of rants and commentary about things for which I care. See MrPogson.com It's been around a decade...
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)