# Off-road 4x4 based on Tesla drivetrain.



## riwe (Nov 17, 2011)

Hi!

I’m planing a conversion of a 4x4, using a defender 110 as reference.

The defender has a transmission and a transfer box/case and a final drive in the front and rear axle.

I wanted to get some feedback on the idea of replacing both the transmission and the transfer box with a Tesla model s drivetrain. The drive shaft to front and rear axel would be connected directly to the tesla unit.

I attached two pictures of the transfer box and it contains a diff which allows the front wheels to spin faster than the rear and a transmission.

Looking at the tesla unit it also contains a diff but it is built to be connected to each wheel not to the front and rear axle which also contains a diff.

I googled and found that the wheel, 
245/45R19, on a Tesla model s spins at 1881 rpm at 155mph. 

The defender comes with a 3.5:1 ratio in the final drive (in the front rear axle).

The default tire diameter on the defender 110 is 31.7”

That would, if I got it right, give the defender a top speed of 51 mph which is a bit to low, I can live with 60 mph but my guess it that the drivetrain should not be designed to reach that speed a max rpm. 

Some questions:

1. Is it possible to use the tesla unit in a setup like the one I described above?

2. I worked with permanent magnet motors and in order to push them to high rpm’s we use field weakening which has an impact on efficiency. Is this true for the tesla model s unit as well?

Thank you

Br

Rikard


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## riwe (Nov 17, 2011)

Here is a picture of the defender 110 transfer box attached to the original transmission. Flanges for front and rear drive shafts are also In the picture.


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## Tomdb (Jan 28, 2013)

'easiest' option is to get new gear sets for your axles.

Anything is possible, you just need to throw money and time at it.


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## eminemam (May 10, 2018)

It seems you will be losing the 4x4 then. You will end up with three open diffs which will result in giving more power to the axle and wheel with least available traction.
I may be wrong since I am not familiar with the drive train on this vehicle.


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## Tomdb (Jan 28, 2013)

you can fit the ATB that Zero-EV or EVTV offers to solve that.


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## brian_ (Feb 7, 2017)

Yes, it can be done. A similar arrangement - but with a transverse engine and transaxle turned 90 degrees - has been used for custom off-road vehicles. The main issue is gearing, but you have realized and considered that.

Yes, every mildly competent PM AC motor controller manufacturer has implemented phase shift (called "field weakening") to handle high speeds. The Model S does not use synchronous motors - it has induction motors - but the control is managed appropriately for high speed. I wouldn't expect to make a Model S motor run faster than designed, as it is already a high-speed motor and the transaxle gears and bearings may not handle much faster.


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## riwe (Nov 17, 2011)

Thanks you all for your reply. 

Brian_, you got a link for that conversion?

So in theory:
If it was possible to fit 2:1 gears in front and rear axle I would have a theoretical top speed of 87 mph.

In real life this could possibly get me 60 mph on highway.

I like the idea of replacing motor, transmission and transfer box with one unit but in this case it might not be feasible.

Thanks 

Rikard


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## brian_ (Feb 7, 2017)

brian_ said:


> A similar arrangement - but with a transverse engine and transaxle turned 90 degrees - has been used for custom off-road vehicles.





riwe said:


> Brian_, you got a link for that conversion?


Sorry, this sort of thing has been done a few times, but I don't recall a recent example which would be shown on a web page.

I hope this isn't too confusing, but the Peugeot 205 T16 rally car used a longitudinal engine and transaxle, turned 90 degrees so the left and right "axle" outputs were used to drive the front and rear final drives:








You can see from the size of the bevel gears in the transaxle (which would be the final drive gears in a normal 2WD application) that the gear reduction ratio there is low (near 1:1) so the overall gearing ratio doesn't have too much reduction.


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## retrEVnoc (Mar 23, 2019)

Theoretically I think you could lock up the Tesla diff so that the drive unit sends equal power to the front and rear stock diffs. Right? So depending on your differential and front axle setup you would have AWD, or maybe you'll have locking hubs and 4WD.

I like this approach because you end up with fewer moving parts (no transfer case). However I think the AWD might bring range reductions when highway driving.

Maybe you could mate Tesla's stock drive axles to your front and rear driveshafts


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## eminemam (May 10, 2018)

Indeed you could put a Quaife diff in the center replacing the tesla drive unit diff but still you wont fix all the issues. You will still need EDL to lock one spinning wheel to give power to the other wheel on the same axle. 

Picture an Audi Q7 with self locking quattro center diff. It still has EDL to compensate for the lack of per axle manual locking diff. 

Not that you need EDL every day 

I would just put the Tesla drive unit at the rear and use Quaife diff. This would give the "remove as many drive train parts as possible" solution and will give good traction. Then there is more space under the vehicle for batteries.

cheers


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## retrEVnoc (Mar 23, 2019)

EDL = electronic differential locking?

Putting the Tesla drive unit in the rear is the typical and simpler approach given you have some welding and fabrication skills. However, it does not leave you with a 4x4 vehicle, which I (and the OP) are interested in.


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## brian_ (Feb 7, 2017)

retrEVnoc said:


> Theoretically I think you could lock up the Tesla diff so that the drive unit sends equal power to the front and rear stock diffs. Right?


No, that would drive front and rear axles at the same *speed*, not the same power. It would be the same as any part-time 4WD system with 4WD engaged: unusable on a paved surface as the front and rear tires fight each other and the shafts get overloaded with torque as a result. And you wouldn't have a transfer case in which you could disengage the drive to one axle, to provide 2WD on the street.



retrEVnoc said:


> So depending on your differential and front axle setup you would have AWD, or maybe you'll have locking hubs and 4WD.


You would literally have all-wheel drive, but most people expect a system labelled as "AWD" to be usable on pavement. If you used locking/unlocking hubs or an axle disconnect, you could use those to disconnect one axle (presumably the front) when on pavement.



retrEVnoc said:


> I like this approach because you end up with fewer moving parts (no transfer case).
> ...
> 
> Maybe you could mate Tesla's stock drive axles to your front and rear driveshafts


Yes, replacing the stock engine, transmission, and transfer case with a Tesla (or other brand) complete drive unit (motor and transaxle) would be a simple AWD configuration. This would require mating the Tesla drive axle outputs to the axle inputs; there are few ways to make that connection.


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## riwe (Nov 17, 2011)

Thanks for the input. Having 4x4 is a plus but if is to complicated I can live without it.

When you say “putting the tesla unit in the back” do you imply that the tesla unit is rebuilt, diff welded, and then connected via propshaft to rear axle?


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## riwe (Nov 17, 2011)

Regarding:

This would require mating the Tesla drive axle outputs to the axle inputs; there are few ways to make that connection.

The plan was to weld the flanges from the original transfer box to the tesla “outputs”. I might need some type of support bearing since the propshaft is longer/heavier than the original driveshaft.


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## brian_ (Feb 7, 2017)

retrEVnoc said:


> Putting the Tesla drive unit in the rear is the typical and simpler approach given you have some welding and fabrication skills. However, it does not leave you with a 4x4 vehicle, which I (and the OP) are interested in.





riwe said:


> When you say “putting the tesla unit in the back” do you imply that the tesla unit is rebuilt, diff welded, and then connected via propshaft to rear axle?


Not likely. I assume that retrEVnoc is referring to using the Tesla drive unit in the back of your vehicle just the way it is used in a Tesla. Of course this is impractical in anything like a Defender, since it would require a completely different (and independent) suspension and a subframe to hold the drive unit. I have no idea why anyone would want to do this with a Defender or similar 4X4, but if you want a Defender body on a completely custom frame and chassis, you can use Tesla (or other brand of EV) drive units front and back... essentially putting a complete Model S or X AWD under an old British SUV body.


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## riwe (Nov 17, 2011)

brian_ said:


> Not likely. I assume that retrEVnoc is referring to using the Tesla drive unit in the back of your vehicle just the way it is used in a Tesla. Of course this is impractical in anything like a Defender, since it would require a completely different (and independent) suspension and a subframe to hold the drive unit. I have no idea why anyone would want to do this with a Defender or similar 4X4, but if you want a Defender body on a completely custom frame and chassis, you can use Tesla (or other brand of EV) drive units front and back... essentially putting a complete Model S or X AWD under an old British SUV body.


Ah, thats not my route.


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## riwe (Nov 17, 2011)

Did some googling and correct me if I'm wrong. It looks like the Tesla drive shafts rotate anti-clockwise when drive the car forward:








When looking at the defender, from the front, I was told that the prop-shaft rotates as indicated in this picture:









It would be awfully nice to put the tesla unit where the transmission is and “just” connect the two prop-shafts to it, yes they need to be longer than original but that’s the least of my worries. 

Since the tesla unit is rotating in the wrong direction I have some options: 
1.	Flip the tesla unit up-side down.
Is there an oil-pump and pickup in the unit? Can it be flipped?

2.	Run it in reverse. 
My guess is that all gears are made to rotate in one direction and 
running it in rev will break it. 

3.	Place the tesla unit on the other side of the prop-shaft. 
Since there is not so much space I would have it sticking up through 
the floor which is not optimal. 

4.	Change the angle of the prop-shafts so the tesla unit fits on the left side. 
I don’t know much about prop-shafts but what I did pickup is that 
messing with angles will have an great impact on wear and vibrations. 

Any thought? 

Thank you 

Rikard


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## brian_ (Feb 7, 2017)

riwe said:


> Did some googling and correct me if I'm wrong. It looks like the Tesla drive shafts rotate anti-clockwise when drive the car forward:


Yes, but "anti-clockwise" is only meaningful if you specify from what perspective. Any drive unit will rotate the output shafts anti-clockwise if you are looking at the left output, and clockwise if you are looking at the right output.



riwe said:


> When looking at the defender, from the front, I was told that the prop-shaft rotates as indicated in this picture:


Again, the rotational direction only means something when you specify the perspective. In this case, it would be clockwise if viewed from the front. Not all vehicles are the same, but this direction of rotation is very common, perhaps almost universal.

Since from the front you would be looking at the right-side Tesla output (given the Tesla motor on the centreline and the differential on the right side of the vehicle to match the stock propeller shaft location), the rotational directions do conflict.



riwe said:


> Since the tesla unit is rotating in the wrong direction I have some options:
> 1.	Flip the tesla unit up-side down.
> Is there an oil-pump and pickup in the unit? Can it be flipped?


Yes there are, and flipping it would keep the lubrication (which is also important for cooling) from working properly.



riwe said:


> 2.	Run it in reverse.
> My guess is that all gears are made to rotate in one direction and
> running it in rev will break it.


This has been discussed a few times in this forum. The gears don't really have a direction (although loading these helical gears in the opposite to normal direction changes the direction of axial thrust, which is potentially important to bearings and clearances), but the lubricating/cooling oil pump does. You could use an external pump, but scavenge flow (off the gears to the sump) still won't be ideal with the gears spinning in reverse.



riwe said:


> 3.	Place the tesla unit on the other side of the prop-shaft.
> Since there is not so much space I would have it sticking up through
> the floor which is not optimal.


This packaging does seem problematic.



riwe said:


> 4.	Change the angle of the prop-shafts so the tesla unit fits on the left side.
> I don’t know much about prop-shafts but what I did pickup is that
> messing with angles will have an great impact on wear and vibrations.


That would be a huge and very likely unacceptable angle.


There is a straightforward solution: the Tesla Model S and X drive units all place the motor behind the axle line, but almost every other EV drive unit places the motor ahead of the axle line, with a few (GM's Chevrolet Spark EV and Bolt) having the motor on the axle line. Instead of using a Tesla unit, you could use any of the motor-ahead-of-axle units, such as the one from a Nissan Leaf (which is being used by some other DIY builders, so there is more known about using it than other brands).


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## riwe (Nov 17, 2011)

Thank you Brian, the pictures I attach show the rotation reference.

Just watched a quick video of the leaf package and it looks really neat. I love the
“boxed” approach. I also heard the motor is well oversized can handle a lot more power than stock.

I need to do some more reading on gearing and power to know if it could be used on the defender. 

This one is for reference, http://www.evalbum.com/4655. 50kw 200nm nominal, 70kw 300nm peak. 

Thanks again


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## riwe (Nov 17, 2011)

In regards to flipping the drive unit up side down. What about adding more oil and fixing a vent/catch tank to keep lubrications working?

Does anyone know if there are oil channels in the shafts that needs to be pressurized or is it a matter of taking oil from the bottom and spraying gears from the top?

Even if messing with the lubrication is difficult, I still feel it’s easier than going the leaf-route.

The leaf package is nice but it revs approx 10K and that’s way to low.

Br

Rikard


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## brian_ (Feb 7, 2017)

riwe said:


> The leaf package is nice but it revs approx 10K and that’s way to low.


Why do you think that is too low? The Leaf motor runs more slowly than a Tesla Model S/X motor, but it comes with different gearing to suit. The motor can run at one rpm or a million rpm and all that matters - given that you are using the complete drive unit - is the range of output shaft speeds that are possible.


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## dain254 (Oct 8, 2015)

Aside from the Tesla drive unit being non ideally used as a transfer case - I would say pump the brakes and work out the rest of your functional requirements of the vehicle before getting set on that. If top speed not acceleration is your only performance parameter, the Tesla unit is overkill. What range are you looking to achieve? What is your budget for the project?


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## riwe (Nov 17, 2011)

brian_ said:


> riwe said:
> 
> 
> > The leaf package is nice but it revs approx 10K and that’s way to low.
> ...


Well that sounds promising, are you talking about available kits? Is it internal gears or an external gearbox? 

Since there is a 3,54:1 reduction in the front and rear axle I need a high rpm from the drive unit.

The idea was to minimize the number of components in the drivetrain.

Thanks

Rikard.


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## riwe (Nov 17, 2011)

dain254 said:


> Aside from the Tesla drive unit being non ideally used as a transfer case - I would say pump the brakes and work out the rest of your functional requirements of the vehicle before getting set on that. If top speed not acceleration is your only performance parameter, the Tesla unit is overkill. What range are you looking to achieve? What is your budget for the project?


The plan is:
250km range all year, +20C to -15C. Heating/cooling of battery is in scope.

Speed and acceleration needs to be moderate. Not building a performance car or an off road monster.

I would like to be able to do 90kmh in the highway without pushing to many limits.

Budget is set to what and tesla drivetrain plus 75kwh battery costs from a scrapyard in Norway 🙂

Thanks

Rikard


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## brian_ (Feb 7, 2017)

riwe said:


> Well that sounds promising, are you talking about available kits? Is it internal gears or an external gearbox?


I'm not suggesting changing the gearing in a salvaged EV gearbox, or adding another gearbox, just pointing out that Leaf gearing is not the same as Tesla gearing.

There is usually a choice of final drive ratios for an axle assembly, and often some choice even for the final drive ratio in a transaxle, since the same axle or differential is used for various models of vehicles with different requirements. At this point there are so few variations of EVs from the same manufacturer that this choice does not exist... and even if it did, a radically taller (less reduction) ratio would not rationally exist.

The early Leaf ratio is widely quoted as 7.9377:1, but I've seen higher reduction for later years; an article says that for 2018 it is "8.193, which spins the motor faster than the 7.8366 in pre-2018 models". I suspect that it was unchanged from the first Leaf through 2017 and the "7.8366" is a typo.

The Tesla small drive unit ratio is 9.465:1... or something close to that, since I didn't search all sources for an authoritative number.

That means that the Leaf motor (pre-2018) driving through its transaxle will only turn about 84% of the speed of the Tesla motor driving through its transaxle.



riwe said:


> Since there is a 3,54:1 reduction in the front and rear axle I need a high rpm from the drive unit.


The extra stage of reduction (compared to the stock EV for which the motor and transaxle were intended) is certainly the challenge. It can be moderated somewhat with a change of ring and pinion gears in each axle, but it will still likely be close to 3:1.

One factor which is fortunate because it will help slightly is that the Defender presumably uses taller tires than a Leaf (although perhaps comparable to a Tesla). For a given road speed, the motor speed is inversely proportional to the tire diameter (or actually, the loaded radius).

With any configuration of a drive unit intended to drive the axle shafts directly, but instead driving the inputs of live beam axles, there will be more overall reduction than desired (even with tall tires) and the vehicle's top speed will be severely limited.


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## brian_ (Feb 7, 2017)

As appealing as it is to take advantage of the differential built into an EV drive unit as the Defender's centre differential, it might be more practical to give up on that and use the stock transfer case instead. That means

using the EV motor without the original transaxle (not straightforward, especially with Tesla components), and
providing a more moderate gear reduction between the motor and the transfer case.

There are single-ratio reduction boxes intended for use between an electric motor and the rest of the drivetrain of a vehicle. A compact and lightweight (but expensive) choice is the ev-TorqueBox, and if you can find one there are suitable units which were used in commercial trucks such as those from Smith.


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## riwe (Nov 17, 2011)

brian_ said:


> As appealing as it is to take advantage of the differential built into an EV drive unit as the Defender's centre differential, it might be more practical to give up on that and use the stock transfer case instead. That means
> 
> using the EV motor without the original transaxle (not straightforward, especially with Tesla components), and
> providing a more moderate gear reduction between the motor and the transfer case.
> ...


You are right, I will pursuit both solutions and make a pro/cons summary. 

Love the planetary gearbox, I use the same type in my homemade electric hydrofoil board, but muuuch smaller.

Got to have helical gears to minimize noise.


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## dain254 (Oct 8, 2015)

Based on those functional requirements of 250km, 90kmh top speed you could easily get by with a lot less power than even the smallest Tesla unit's output. My recommendation would be to look into the new Netgain Hyper 9, which would make connecting to your existing transfer case easy. That motor I believe is around 150V - so utilizing 6 Tesla Modules will give you a 30kwh battery at that voltage. To get your range you will need at least double that - so a person could parallel another 6 modules - OR have a switchable power bank like having two fuel tanks (to avoid complexities of paralleling batteries that aren't meant to be paralleled). No bias against a Tesla drive unit, but for this project it seems like more work than is needed and overkill!


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## leman2112 (Dec 2, 2018)

Why not just use the stock transmission or upgrade to a strong 2 or 3 speed? Weld the tesla diff.

https://www.youtube.com/watch?v=wgpXy8FTvPE

If I could afford the quaife diff I would just do that and gear the axles accordingly.


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## Olphart (May 25, 2017)

Welded tesla diff:
https://www.youtube.com/watch?v=wgpXy8FTvPE


4.5:1 gears should allow for good speeds -


https://www.youtube.com/watch?v=_GigD0s47RI&feature=youtu.be



https://zero-ev.co.uk/product/tesla-large-drive-unit-gear-set-4-51/


You can see I have been researching/dreamgeneering my own AWD project!


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## Lowcoe (Jul 3, 2020)

This has been done now. Vintage voltage season1 episode 6. If I recall they ran the motor in reverse, used limited slip differentials in both axles as well as the Tesla motor. Changed the gearing in the Tesla motor to alter the gear ratio by 50% and installed an oil pump which would run in reverse...


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## Lowcoe (Jul 3, 2020)

Lowcoe said:


> This has been done now. Vintage voltage season1 episode 6. If I recall they ran the motor in reverse, used limited slip differentials in both axles as well as the Tesla motor. Changed the gearing in the Tesla motor to alter the gear ratio by 50% and installed an oil pump which would run in reverse...


That guy from zero ev was in the episode. That’s the conversion of which I spoke.


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## brian_ (Feb 7, 2017)

Lowcoe said:


> This has been done now. Vintage voltage season1 episode 6. If I recall they ran the motor in reverse, used limited slip differentials in both axles as well as the Tesla motor. Changed the gearing in the Tesla motor to alter the gear ratio by 50% and installed an oil pump which would run in reverse...





Lowcoe said:


> That guy from zero ev was in the episode. That’s the conversion of which I spoke.


Yes, since this discussion was active Zero EV has addressed all three issues which we had discussed, using parts which they offer for sale:

a reverse-rotation oil pump allows the desired drive unit placement and the corresponding operation in reverse of the normal forward rotation;
a gear-type LSD replaces the drive unit differential, which becomes the centre differential of the 4WD system; and,
the first stage reduction gearing is changed to lower the overall reduction ratio.


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## Lowcoe (Jul 3, 2020)

On that episode they also spoke of changing the differentials in each axle as well. Plus I believe they replaced each individual axle rod with stronger versions. Is that correct. I’m not sure if they were skimping in the details to shorten the air time or protect trade secrets. 
Where would these parts typically be sourced? A 4x4shop for rovers like old man emu or just a Rover part supplier? 
and in essence the car would be all wheel drive all the time correct? Would there be any reason ( range) to disconnect the front hubs?


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## Lowcoe (Jul 3, 2020)

Parts are back ordered...


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## brian_ (Feb 7, 2017)

Lowcoe said:


> On that episode they also spoke of changing the differentials in each axle as well. Plus I believe they replaced each individual axle rod with stronger versions. Is that correct. I’m not sure if they were skimping in the details to shorten the air time or protect trade secrets.
> Where would these parts typically be sourced? A 4x4shop for rovers like old man emu or just a Rover part supplier?


While not part of the EV conversion, it is routine for 4X4 customization projects - especially ones that involve spending tens of thousands of dollars and ones that increase available power - to upgrade the strength of axle components. This doesn't change how they work... just how likely they are to break, and possibly the gear reduction ratio and/or differential slip limiting action. This is aftermarket stuff, not standard Land Rover part sourcing.



Lowcoe said:


> ... and in essence the car would be all wheel drive all the time correct? Would there be any reason ( range) to disconnect the front hubs?


Yes, it would be full-time all wheel drive. You would not be able to disconnect the front hubs, because without a locked centre differential or a transfer case that can be shifted to a rear-drive-only mode, doing that would leave the shaft to the front axle spinning freely and the shaft to the rear axle unable to transmit any drive torque.


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## Lowcoe (Jul 3, 2020)

Could hearing in axles be changed rather than the gears in the Tesla motor? Seems like it would be simpler.


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## Lowcoe (Jul 3, 2020)

Gearing


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## brian_ (Feb 7, 2017)

Lowcoe said:


> Could gearing in axles be changed rather than the gears in the Tesla motor? Seems like it would be simpler.


Yes, but you probably can't change it enough. For instance, if you have 4:1 ring-and-pinion gear sets in the axles, and you want half as much gear reduction, you need 2:1 gears... and they don't exist. 

If you can get the overall ratio you need with an axle gearing change, that's the obvious way to go... but it may still not be cheap and it's not entirely trivial to do (there's typically some shimming involved to set suitable gear tooth mesh).


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## Niels60 (May 11, 2021)

riwe said:


> The plan is:
> 250km range all year, +20C to -15C. Heating/cooling of battery is in scope.
> 
> Speed and acceleration needs to be moderate. Not building a performance car or an off road monster.
> ...


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## Niels60 (May 11, 2021)

Hi Rikard, did you carry out this conversion?


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## ryolse (2 mo ago)

@riwe, did you ever find your project coming to fruition?

Being that I'm extremely late to this party, I'm assuming you've already seen what Electric Classic Cars has been up to proving that it's possible for your application



https://youtube.com/playlist?list=PLBHm9Yo2w2bYPU02xSB873iOs88Irk7lJ


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