Thread: The "New" Defender, ...Your Thoughts?

Originally Posted by Beery

A drive system involving a motor at each wheel, be it fully battery powered or diesel-electric would be phenominal in its flexibility for use as a 4wd. Imagine being able to drive each wheel independantly.

I was at an electric car seminar a few weeks ago and one of the speakers was asked why this 'one motor in each wheel' hasn't taken off. His answer? Its really hard to calibrate and control four independent motors to handle differing speeds around a corner. He told a story of being in a car that had four separate motors when one wheel decided to do is own thing and spun the vehicle across to the other side of the road at speed (not sure what speed).

A single motor front and rear with conventional diff is much simpler, safer and easier to program.

Cheers

Dan

Originally Posted by Disco-tastic

I was at an electric car seminar a few weeks ago and one of the speakers was asked why this 'one motor in each wheel' hasn't taken off. His answer? Its really hard to calibrate and control four independent motors to handle differing speeds around a corner. He told a story of being in a car that had four separate motors when one wheel decided to do is own thing and spun the vehicle across to the other side of the road at speed (not sure what speed).

A single motor front and rear with conventional diff is much simpler, safer and easier to program.

Cheers

Dan

Did they happen to mention cars future construction. I was at an air show recently and the NZ air force has operational attack/support choppers are something like 60% plastic. It was much lighter so was more economcal and could carry 1/3 more, but still performed as good or better than the predecessor. The French air force has them as well.

Was there any talk of no gears reading the motor, just one long variable speed. Bit like a variable speed drill I guess, or something like a low and high.

double post

Originally Posted by Disco-tastic

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A single motor front and rear with conventional diff is much simpler, safer and easier to program.

and heavier and more expensive.

There does not seem to me to be any good reason why, if we accept software control of power, brakes, steering and collision avoidance, as is the case with many current cars, there should be a problem with this. Unless I am mistaken there are mine vehicles in use with a single hydraulic motor at each wheel, and they seem to go OK without any software!

And as for being difficult - the advantage of doing it in software is that you only do it once and the cost of duplicating it is negligible - if you use a conventional drive setup with a single motor front and rear, you still have the problem of coordinating power from front and rear, but you have to build the differential and axles for every vehicle you make.

I think the answer was a non-answer. I am sure there are multiple problems with it, but I rather doubt there is a single show stopping issue.

John

Originally Posted by JDNSW

and heavier and more expensive.

There does not seem to me to be any good reason why, if we accept software control of power, brakes, steering and collision avoidance, as is the case with many current cars, there should be a problem with this. Unless I am mistaken there are mine vehicles in use with a single hydraulic motor at each wheel, and they seem to go OK without any software!

And as for being difficult - the advantage of doing it in software is that you only do it once and the cost of duplicating it is negligible - if you use a conventional drive setup with a single motor front and rear, you still have the problem of coordinating power from front and rear, but you have to build the differential and axles for every vehicle you make.

I think the answer was a non-answer. I am sure there are multiple problems with it, but I rather doubt there is a single show stopping issue.

John

You beat me to the punch with that one John. My sentiments exactly.

Yeah fair points john. Just passing on his tale of his experience.

Cheers

Dan

I can't tell you why the guy at the conference told you that, probably so he could share his spin out story.

I'm no expert on EVs but from what I know, the electric motors used are more efficient at high RPM. That is to say, you can make electric motors generate adequate power at lower RPM but they need to be of a larger and heavier design (much like ICEs). For light vehicles, a lightweight (high RPM) motor is the most efficient way to go. So seeing as you need gear reduction to have good acceleration, a differential fits the bill nicely and also means you need less motors.

Originally Posted by Dervish

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I'm no expert on EVs but from what I know, the electric motors used are more efficient at high RPM. That is to say, you can make electric motors generate adequate power at lower RPM but they need to be of a larger and heavier design (much like ICEs). For light vehicles, a lightweight (high RPM) motor is the most efficient way to go. So seeing as you need gear reduction to have good acceleration, a differential fits the bill nicely and also means you need less motors.

Yes, electric motors have a better power/mass ratio if they are high rpm - but having them in the wheels saves a lot of mass. And gears are probably more expensive than motors, although design as in any vehicle is a matter of balancing these factors against each other.

Certainly the cost of electric motors a hundred years ago would have been a major factor in the failure of the idea then. In 1919 for example, Morris found it more economical to use a combined starter/generator or dynamotor when offering electric lighting on his Oxford - and even then, this optional extra was 10% of the total cost. But the costs of electrical equipment have almost certainly dropped a lot more than the cost of mechanical parts.

John