I tend to agree. Trying to weld a hot thing to a cold thing never works well. The process is touchy and unreliable.
I think I may of replied to you before, but parts from my Solidoodle are very strong. The heat transfer from the extruder when printing at 0.3mm is more than enough to slightly melt the previous layer and fuse them. Printing at 0.1mm makes an almost seamless print. When printing with a heated bed, in an enclosed space the whole print is slightly tacky and soft. The prints do have a grain, and that is the weakest part, but you can design items with that in mind. If you are worried about printing something out of ABS/PLA that is going to fail due to stress, having it injection molded isn't going to increase the strength factor by enough margin to stop it breaking.
Combustion engines typically have very poor efficiency at low rpms, so you'll spend far more Watt-hours worth of gasoline to generate a Watt-hour of kinetic energy until you get into the relatively narrow "optimal efficiency" power band.
What gave you that impression? I have been doing a lot of reading/research into this lately and there is no reason you can't make an engine efficient at low rpm. There are 2 terms related to engines/cars. Efficiency which is what you stated, measured in g/kWh (or lb/hph) and economy. An engine with good efficiency != a car with good economy.
How efficient an engine is, generally follows the torque curve (but not always). As the torque curve measures how good the engine is at being an air pump. If it manages to pump more air each revolution, it can make larger bangs for the same friction and other ancillary overheads. So an engine tuned to make a lot of torque in low rpm ranges, will be just as efficient (if not a little more, due to less heat causing more friction overheads, but I suspect that is actually quite minor).
The problem with designed engines to make a lot of torque down low, is to get any appreciable amount of power you need large capacities. This destroys the economy. The major contributing factor for this, is to maintain 60mph (100km/h) a car only needs around 6-10kW. For a big engine this is an issue, as you do not need to open the throttle very much to achieve this. Thus the engine spends most of it's engine sucking a vacuum against the nearly closed throttle plate, and your efficiency goes out of the window. With a smaller engine it will have the throttle at a wider more open position, so the engine is not fighting as hard to be able to breathe.
Putting a smaller motor on there would not increase battery life magically.
That was my point, a smaller motor was not going to increase battery life. The parent Gordonjcp seemed to be under the impression that you could shrink the motor, and make up for the loss of power by gearing. I was trying to state (in my saturday night drunken state), that gearing will make up for the loss in torque, but not the loss in power. 1) & 3) Electric Motor Basics Top Graph is for an ICE, torque is more or less flat over the rev range, they are torque constant devices. Electric motor, torque slides down, power goes up to a peak, stays there for a bit and drops off. They just work in fundamentally different ways. Power = torque * rotational speed. With an ICE, you form explosions that push a piston, connected to a conrod that provides leverage on a crank shaft that produces torque. The torque is equivalent to the size of the explosions produced. Power is how many explosions you produce a second (directly tied to crankshaft speed). The torque stays relatively constant throughout the rev range (although this changes quite a bit based on intake shape/resonance, cam lift, duration and overlap, exhaust resonance, head swirl dynamics), so therefore power increases with Revs. With an electric motor, power comes in, power goes out. Power = torque * rotational speed. So if a motor is drawing/given 300kW of power. Either rotational speed or torque (or a whole load of heat) has to go up to keep the equation balanced.
4) " I am talking in terms from the engine/motors perspective." So motors don't follow the rest of the laws of physics?
Of course they do, but you don't just look at the torque output from an engine (see my hand crank example), you need to look at work done (i.e power).
Happiness is twin floppies.