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Discussion Starter · #1 · (Edited)
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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'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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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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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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Discussion Starter · #7 ·
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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A similar arrangement - but with a transverse engine and transaxle turned 90 degrees - has been used for custom off-road vehicles.
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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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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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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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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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.

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.

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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Discussion Starter · #13 ·
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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Discussion Starter · #14 ·
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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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.
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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Discussion Starter · #16 ·
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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Discussion Starter · #17 ·
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:
tesla_unit.png

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


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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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.

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.

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.

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.

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.

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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Discussion Starter · #19 ·
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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Discussion Starter · #20 ·
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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