If the Tesla Model X had the option to switch between 2WD and 4WD, could the free motor in 2WD be used to recharge the battery?

Tâm | 18/07/2014

Your front "free motor" consumes energy.

The net power you get from regenerative brakes from both front and rear motors is always a loss for a trip.

Your front motor is smaller and regenerates less power than the rear one does.

model3 | 18/07/2014

"free motor" consumes energy?
In 2WD the free motor would be recharging the battery the whole time, it might just recharge the battery for 5 extra mile in a 50 mile trip.

gfb107 | 18/07/2014

Engaging a motor to charge the battery causes regen breaking. So you have to use more energy from the battery than normal, just to keep the vehicle moving. Also, regen breaking is less than 100% efficient, you use more energy to overcome the regen breaking than you get back from it. It just doesn't work. | 18/07/2014

So much for perpetual motion:-))

Roamer@AZ USA | 18/07/2014


Alex K | 18/07/2014

I think the best way to recapture energy is to have the back wheels taller than the front, and thus the car will always be going downhill!

Sorry couldn't help myself

vandacca | 18/07/2014

Since this topic is degenerating into the ridiculous, I'll add my 2 cents...

How about attaching a fan to the radio antenna that generates electricity when the car is in motion? :*)

(I hope I don't have to return my physics degree after making this post)

AlMc | 18/07/2014

I plan on driving backwards to keep the battery fully charged.

Iowa92x | 18/07/2014

I asked the same question in this forum some time back. But it was in jest.

Tâm | 18/07/2014


It's karma!

What you asked has now reincarnated in another fantastic genius scheme!

jjs | 19/07/2014

The only true perpetual motion I know of is the posting of perpetual motion ideas. If we could somehow harness that we could all drive for free forever. (Without SCers :) )

Gen3Joe | 19/07/2014

I will attempt to explain this in simple terms.

Think about this logically. If the rear motor is producing a force to drive the car forward the front motor would be producing a force to slow it down. Thus the rear motor would have to work harder and draw more energy from the battery to overcome the force of the front motor slowing the car down.

That's how regen works in an electric motor. It becomes a generator and works against the forward momentum of the car to slow it down and capture the energy in that forward momentum. It's not as efficient at recapturing the energy during regen as it is drawing the energy to drive the car forward. Even if the regen had the same efficiency as the motor driving the car forward the car wouldn't be able to move because the force needed in the front motor to regen as much energy as the rear motor is using to drive the car forward would be exactly equal the force applied by the rear motor.

Think about what would happen if you were applying your brakes while pushing down the accelerator. The further you push the accelerator down the harder your brakes are applied. You will go nowhere.

Boukman | 23/07/2014

I know I am going to get hit for this but the hell with it...There is no need to be nasty to someone who might have genuinely thought that was a good idea. Not everyone understands the laws of physics or thermodynamics...Don't believe me? Try talking to the best educated people you know, could be your doctor or your financial advisor...many of them will think that this kind of thing is possible... as a matter of fact try Congress...and They make the laws by which we live... So why not try to be the bigger man and instead of name calling and deriding what appears to be a non informed statement, offer an explanation why the idea wouldn't work...
We all could get along...

barrykmd | 24/07/2014

Here's one along those lines, from my college days:

In the Student Union, there was a small bank branch. Because it was hot at the beginning of the school year, they set up a portable A/C unit on a TV stand in the middle of the bank. This being primarily an Engineering school, you can guess how many students informed them they were heating up their space with the A/C on.

babstude | 24/07/2014

speaking of 2WD I hope the MX will be able to be ordered with 2WD only - I would prefer that as assumption is you end up with more range with one motor - maybe it's negligible though ?? hmmm

vandacca | 24/07/2014

@babstude, it has already been verified from an Email from Tesla (and the Model X home page: that the Model X will come standard with 4WD and that 2WD is not an option any longer.

With regards to range, Elon Musk was quoted as saying that the 4WD range would be the same as a hypothetical 2WD, due to efficiencies gained by having the 2 motors geared differently. One motor would be used primarily for low speeds, and the other for high speeds.


Boukman | 24/07/2014 you said it would probably be negligible, though as vandacca pouted out, Tesla says it would be the same...( would be nice to see the actual numbers)... but even though the people in Norway have reported that the MS, with its rear drive and traction control, handles snow and ice very very well, I would tend to think that the MX AWD would be a completely new ball game under those conditions...So I think the improvement in handling the AWD would bring would be worth it...

Boukman | 24/07/2014

as vandacca POINTED out

babstude | 24/07/2014

thanks guys; i must have missed the dialogue whereby one motor would be primarily for low and one for high speed - interesting ... and yes it does make sense that the difference would be negligible when you have 2 motors doing the work of 1 - i.e. both putting in far less effort ...

still getting used to the idea of wrapping one's head around a BEV vehicle !!! take what you know about ICE vehicles and basically throw it out the window - everyone knows that AWD with an ICE is a guzzler vs it's 2WD counterpart

Tâm | 24/07/2014


You are right that there is something that EV can achieve but ICE cannot.

From the horse's mouth:

“Typical experience of AWD is that the efficiency will be worse.

We've worked really hard to not have that same effect,” explained Tesla CTO JB Straubel.

“We found some clever ways with dual motor AWD, not just mechanical linkage. To make that an efficiency neutral option breakthrough.

Flat efficiency tradeoff.”

Brian H | 26/07/2014

In the Student Union, the effect of the air conditioner would be to cool the floor level, with hot air rising to the ceiling, with a net overall average temperature increase, as you say. Depending on how high the ceiling was, it might have been worth it for those at floor level.

Red Sage ca us | 17/10/2014

After the Tesla Motors 'D' Event last week, I would hope that all doubt about the capability and superiority of dual motors is gone.

David Trushin | 18/10/2014


Man walks into the brain transplant store to find a replacement. Looks at the businessman's brain and asks how much. Salesman says $12 an ounce. Shopper looks at the physicist's brain and asks. $13.95 an ounce. Looks at the Congressman's brain and asks about this one. Salesman says $1495.99 per ounce. Person, shocked, says "why is this brain so expensive?" Salesman says, "Do you know how hard it is to find a Congressman with an ounce of brains?"

Red Sage ca us | 18/10/2014

David Trushin: LOLoLOLoLOL! A good one, indeed.


Boukman | 27/10/2014

Ha Ha Ha... Trushin.... very funny... So funny I laughed until I cried...which ultimately reminded me how sad it is for this great country...