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Depending on your motor weight, you might get a better weight distribution by locating the spare wheel under the bonnet/hood, and using both halves of the under-trunk space for batteries. You'll definitely shift the CoG downwards.
An interesting idea. It would also shift the CofG rearward... maybe too much? I think it would make sense to calculate the new CofG - at least front-to-back and ideally vertically as well - before committing to component locations.
 

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Discussion Starter · #24 ·
Happy New Year folks! Here's another blog post update from bmwcse.com:

Swiss Cheese and the Rebar Method


Last week the coupe arrived back from the glass blaster. We knew that we were going to discover hidden issues, so we weren’t surprised to find quite a few areas with poor metal work and plenty of filler covering things up. The car had been repainted 10 or so years ago, and one can hide a lot of sins under a fresh coat of paint.

Now that all is exposed, we have plenty of Swiss Cheese holes. Behind the sunroof (where the water drains had clogged decades ago). On fenders, behind rear wheels, doors and more.


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The Rebar Method



What we were not prepared to see was rebar. Inside the driver’s front wheel well was plenty of fiberglass, reinforced with rebar and more fiberglass. Scott, our faithful blaster said that in his years of blasting restorations he has never discovered rebar as a structural component. I never thought that Home Depot would have many parts for auto restoration.

As bad as this is, we already knew of a lot of repairs in the strut supports, so we won’t let this beat us down too much. We will source new metal and get it cleaned up properly. It’s too early to get beat down yet.
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Battery Module Placement




Now that things are finally clean and free of grease, we took an opportunity to dry-fit some foam models of our Tesla battery modules. Through our research we know that we can run these units vertically with very little gap between them - as little as 3/16” if we configure mounting rails just so and our wiring setup doesn’t push the bolts to the next module. In this photo, we have 9 units across the engine bay (but we may need to reduce this to 8 to allow a bit more room for reality). The far left and right unit are sitting on frame rails, but the center units are extremely low in the bay.

We then add 2 more where the radiator sat, and finally up to 4 more can stack flat on top of the main cluster of modules. This gets us 14+ all in the engine bay, and the bulk of the weight will be much lower than the engine weight which sat much higher in the compartment.

To keep the center of gravity the lowest, we would prefer not to stack that last 3-4 modules on top of the base cluster. One module does fit under the rear seats with some modification to the tunnel. We would have to perform a lot of modification to get one or two where the transmission sat. Finally we could easily get 2 or more in the trunk, but we prefer to not add the weight back there, as the drive unit is as much weight as we like back there.

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Raspberry Pi for dessert


We picked up a Raspberry Pi with dual isolated CAN Buses and a 7” touchscreen to begin programming our control system. This system will control most of the basic functions of the car from blinking the turn signals, setting the interior to 70 degrees and more. It won’t perform critical motor and braking control, but it will push to the Tesla control unit what preset we are running (i.e. Standard, Sport or Valet modes) I will describe more of these details in a future post.

Well, that’s all there is to report this time around. Happy New Year!

Paul
 

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Discussion Starter · #26 ·
Here's another update from the Blog

Cut, Weld, Smooth, Repeat.

After ordering up a truckload of sheet metal and a 50 gallon drum of perseverance, we dove head-first into rust repair. We started in the rear of the car going spot by spot through the simpler areas. Below are some photos of one spot of the trunk. We cut a section out, weld a fresh section in and smooth it out. Good as new, right? Well yes, after we do this process a hundred or so more times.

Cut out the cancer…Weld in a fresh section…Then smooth it out.

Then there are the floors

While the bodywork is happening up top, we also began work on the floors. The passenger side sub-frame rail underneath was rusted through. We sourced a pair of new replacement rails, but they didn’t really match up to the angle and length at the front. After some debate about fabricating from scratch, we decided to modify these units which wound up working out well. A bit of smoothing will still take place after the floors go back in, and we will move to the driver’s side.

Remember this photo from a few posts back? Looking a lot better now.

Some toys showed up

Our Tesla drive unit, controller, and battery modules have arrived. We have to hand it to HSR Motors/057 Technologies for terrific communication, education, support and packing (thought you wouldn’t know it from these pictures, as it looks a little like Christmas morning just happened). We chose 057 Technologies after a lot of consideration - and I know there are more opinions here than there are stars in the sky. We tossed around buying a totaled Tesla at auction, and stripping her ourselves of all her goods. We considered saving a few bucks and buying from any number of cut-rate dismantlers. Lastly, was the idea of buying from a shop that specializes in Tesla and EV conversion support. After visiting some, and chatting with others, I felt like I bought into not only the passion, but the engineering approach that 057 has taken with their controller, but also the drive units themselves.


We will surely see if we made the right call once we can dive into this gear in the coming weeks. In the meantime, it is back to Cut, Weld, Smooth, Cut, Weld, Smooth, Cut, Weld Smooth…
 

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Discussion Starter · #28 ·
Re: 1974 BMW CSE

Hi all,

While this post isn't related to the EV portion of the build, I just want to continue to paste over the updates from the bmwcse.com build blog.

Here Comes the Sunroof

You might remember that one of my requirements for the coupe was that it have a sunroof. Of the 60 or so cars I have owned, a majority of them have been convertibles - I simply crave the open air. While this car was not going to be a convertible, it was most certainly going to have a sunroof.



But our story takes a turn with the little tube shown in this photo. The photo shows a new tube, but imagine one just like it that was plugged inside like a clogged drain. This tube, along with 3 comrades, takes the portion of rain water that makes its way through the sunroof seal, and passes it into hoses that run to the bottom of the car. This is a great plan so long as the tubes aren’t clogged, and in our case, the tubes had become very clogged, very long ago. Water would come in and take up permanent residence - turning our roof and the sunroof frame mechanism to rust.

We were unaware of this rust until the car came back from the media blaster. We were then faced with three options: 1, we simply fill in the roof. This is the course that any sane person might take. But since a sunroof was an early requirement, this was not an option. 2, we could fill it in, then install a very nice modern OEM electric sunroof. Our car is a “resto mod” after all, so a blend of modern elements is not out of the question. However, another goal is to retain the classic styling of the car, and the original steel sunroof is an important part of that. So our 3rd option was to painstakingly rebuild the roof and frame. This took a few good weeks to do, and here is the story:


Here is the roof from inside the car. Rust on all four sides.


The damage to the frame (the sunroof track) was even worse than the roof itself.

Let’s make a new roof:


Trace the sunroof hole and prep it for cutting.


Cut along the line- this part seems a lot like elementary school art class but with steel.


Begin the process of bending the edges to form our thick and smooth final edge.


Continue the bending and shaping process with the panel setting on the car.


Finally we have a panel which is looking like a final product.


Weld the piece in, then smoothing, smoothing, smoothing.



We also found that we had to strengthen the sagging steel behind the sunroof as well. We then smoothed and smoothed and smoothed some more.

In the end we now have an entire roof that is better than new.

Continued...
 

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Discussion Starter · #29 ·
...Continued due to the limit of 10 photos- all of which I have hosted elsewhere 🤨

Repairing the Sunroof Frame

The jig is up. Well, in the photo the jig is on the bottom and the frame is up, but you get the idea.


Our frame attached to the jig.


With the frame on the jig we can cut out sections and start replacing them.


Tyler is a patient craftsman. Give him some steel and some tools and he can turn out just about anything.


Here’s a fun, rusty rounded corner,


And here’s the new replacement piece all clean and tidy.


All the new sections welded and smoothed into the frame.


The restored frame receives a fresh black coating.


Installing the frame back into the coupe. Tyler loves crawling around grinding things in the car.


It’s looking good from up above.

Finally we set the sunroof back in and check the fit. The gaps are cleaner than when we bought the car. With our new drain tubes and fresh hoses, as well as a new seal in place we should be good for another 45 years of open air, rust-free enjoyment.


While all this sunroof work was going on, there was a lot of junk going on in the trunk. Next week I’ll post an update on all that.

Cheers!

Paul
 

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Discussion Starter · #30 ·
Here is another post from my bmwcse.com Blog

While all of that sunroof work was being done Brett and I started to have some fun with the Tesla drive unit.



We are not the first people to retrofit a Tesla unit into another car. We leveraged some of the engineering, trial/errors and successes from some of the more graceful projects that we have followed.

We started by clearing out the trunk floor. We want the motor to sit no lower than the original differential, but also no higher than necessary - leaving us with a good amount of trunk space.

Getting off the Ground

Our Tesla unit weighs 291 pounds, so I can’t exactly hold it in place while Brett bolts it to the car. We welded up a rolling stand that could safely hold the unit under the car, then we would use the car lift to lower the coupe to the unit.

Here’s our Tesla motor stand. I am going to reach out to Elon to see if he wants to put an order in for several:)


A forklift is the closest thing we have to an engine hoist, so here we go.


The unit feels secure in its temporary home.


Reinforce and Fabricate

With the unit on the rolling stand we put it into position to verify our mounting design and overall clearances. We strapped the rear wheel into a relative ride height, so that we could check the axle angles.

While we had done our homework I am not going to lie - there was some relief when everything fit without obstructions.


Tesla Unit in Position


Regarding the mounts: There is a front mount which was a simple matter. The side mount can be tricky since there is suspension right there, and the rear mount has nothing to hang from.


We plated the front and rear of the wheel well to distribute the loads and to give us something to attach to.


Brett welds in the horizontal plating, which will support our front mount.

continued below...
 

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Discussion Starter · #31 ·
The Front Mount

(Sorry I don't know if I figured out how to present YouTube videos)
Cutting the thick stuff is like cutting warm butter when you have a plasma torch.


The front mount had the trickiest shape to it and required some bending of the center plate.


The front mount welded into the car.

The Side Mount


We created a side mount plate with a compound bend by notching, then smoothing out.


Welding the side mount sections to our plate.

The Rear Mount


The rear mount suspends from a beam which spans between the wheel wells.


Reinforcing the hanging points with gussets. It was just an opportunity to take a photo through the taillight hole.

Clean Things up and Hang the Unit


With the welding done, we cleaned up any rough edges and applied etching primer to everything.


Finally the drive unit is hanging in it’s final home! We strapped the front of the car down to the lift just in case things got a little back-heavy:)

The moment of truth when the Tesla unit is successfully raised off its stand.


The placement leaves plenty of usable trunk space. We have a large and deep rear section, then an upper forward shelf (with perhaps a plexiglass floor for any Cars & Coffee events we may find ourselves at).

Next we connect the axles from the drive unit to the hubs. So that we don’t twist the old BMW axles we opted for Tesla performance axles, which will mate (somehow) to the BMW hubs.

That’s it for now- until next time!

Paul
 

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We started by clearing out the trunk floor...
It looks like a lot more than the trunk floor went. :eek:

In the middle, at the front of where the original final drive (differential) housing would have been, there appears to be a bracket which was likely bolted to the nose of final drive, and likely goes forward to a beam that the suspension arms mount to. In later photos, it looks like that bracket was cut off of the beam. The back of the final drive would have been supported by a mount. If that's how it was done, the beam and the final drive with its brackets formed a T-shaped subframe for the suspension, and the rear leg of that is now gone. With only two mounting points of the remainder of the subframe (the beam) to the car, the subframe is no longer properly supported and will twist under loads.

Ideally, the structural role of the bracket, final drive housing, and final drive rear mount, would be replaced by a tube arching over the drive unit to the new rear mounting point.

Maybe my guess about the structure is mistaken - maybe BMW decided to make one model different from all of the others - but do you have a photo of the suspension arms and what they are mounted to?

Until you're sure this is structurally right, I would encourage you not to support the car on the rear suspension, and certainly not to drive it.

The attached images:
  1. image of cut out trunk floor, showing the bracket
  2. later image, showing the subframe cross beam and where the bracket was probably cut off of it
  3. suspension and subframe from a BMW 2002 (not a CSE), but is shows what the corresponding parts of the CSE likely looked like:
    (somebody else's image from Photobucket, plus annotations)
 

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Discussion Starter · #34 ·
Brian,

Thanks for the thoughts. You are correct that we did cut off the bracket that held the front of the Diff, and the rear of the Diff did connect to the car forming the tee you mention. We do plan to reconnect this tee structure in some form.

It is a bit of a strange setup, as the point of isolating this front unit (in my estimation) was purely to isolate the differential vibrations from the car. Front drive cars often simply attach the trailing arms to the car itself. So we are doing a bit of research to determine the best course modifying this. Either we reverse the tee shape forward and connect it with a mount (with bushing) in the tranny tunnel, or we simply shorten the tee and attach closer to the Tesla front mount.

Thanks again for your thoughts and concern - it's what I love about this group!

Paul
 

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Hi Paul

Don't forget that the Tesla unit will see wheel torque not motor torque

The further apart (fore/aft) that the mountings are the lower the loads that your mountings will see
 

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You are correct that we did cut off the bracket that held the front of the Diff, and the rear of the Diff did connect to the car forming the tee you mention. We do plan to reconnect this tee structure in some form.
Good :)

It is a bit of a strange setup, as the point of isolating this front unit (in my estimation) was purely to isolate the differential vibrations from the car. Front drive cars often simply attach the trailing arms to the car itself.
The T-shaped subframe has the same purpose as any other rubber-mounted subframe: to isolate the components on it from the vehicle structure. Yes, lots of vehicles do not use a subframe like this... they mount powertrain and suspension components directly to the structure at either at the front, or the rear, or both. Both differential gear noise/harshness and road noise/harshness through the suspension are handled by the rear subframe in this case; that's typical for rear-wheel-drive vehicles with an independent rear suspension, but not a universal practice.

So we are doing a bit of research to determine the best course modifying this. Either we reverse the tee shape forward and connect it with a mount (with bushing) in the tranny tunnel, or we simply shorten the tee and attach closer to the Tesla front mount.
Logically the Tesla drive unit would be mounted to the rear subframe; that's what Tesla does (both front and rear), and what probably every other current production EV has at the driven axle(s). Ideally, perhaps the existing CSE subframe could have been extended to two new rear mounting points to the unibody (replacing the differential case mount), and the Tesla drive unit could have been mounted to it instead of directly to the body. The Tesla front mount would be bracketed off of where the diff bracket was, the Tesla side mounts would go to the subframe ahead of the new subframe mounts to the body, and the rear Tesla mount would go to a new crossmember of the subframe. But that isn't the only way to go and it's not what you have been building.

Assuming that you want to stay with the direct-to-body mounts that have already been built for the Tesla drive unit, all that remains is to restore a third mounting point for the subframe, which now handles only the suspension. To be effective, it must be significantly away from the axis formed by a line between the mounts on the crossmember beam; the diff mount was well behind that (and a long and awkward S-bend tube could go all the way back to your new crossmember), but a replacement could be significantly ahead as you described, or even above. Maybe back and up to your Tesla unit front mount would work. The point is primarily to keep the subframe from rotating around that axis between the remaining mounts.

Thanks again for your thoughts and concern - it's what I love about this group!
Good. :D Some people really only want to share what they have done, rather than have a discussion of possible designs.
 

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Don't forget that the Tesla unit will see wheel torque not motor torque

The further apart (fore/aft) that the mountings are the lower the loads that your mountings will see
That brings up another reason for subframes: to spread loads further apart on the body structure.

In some case there is no isolation at the points where the subframe bolts to the body (it's just solid), which indicates that the subframe is being used to carry loads to suitable points in the body structure... or in some cases to allow a large assembly of components to placed into the vehicle on the assembly line in one operation (such as an entire engine, transaxle, half shafts, hubs with brakes, and suspension into the front of many vehicles... or the drive complete drive unit and suspension into the rear of a Tesla).

In this case, the stock Tesla mounting points (where the drive unit mounts to the subframe) are being used, and they're at the extreme front, back, and left side of the drive unit. During acceleration the front mount will push up on the body mount bracket, which looks quite substantial. Presumably that beam added for the rear mount can handle a similar downward force. The left mount (assuming there's no right-side mount) will basically just see a small share of the weight of the drive unit vertically because the motor is on the left side (plus all mounts take lateral force in corners and longitudinal force when accelerating and braking due to the mass of the drive unit).

Assuming 601 N⋅m (443 lb⋅ft) of motor torque, and 9.73:1 gear ratio, the axle or wheel torque could be 5800 N⋅m (4300 lb⋅ft), so if the front and rear mounts are about 60 cm (2 ft) apart, the difference in vertical force at those mounts could be 10 kN (2000 lb... one ton).
 

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Discussion Starter · #38 ·
Yes, we considered quite a bit the idea of attaching the front motor mount to the suspension subframe. In the end we saw a lot of well done cars where the drive unit was attached to the car directly- using the Tesla motor mounts as the isolation. Naturally them (and us) all created distribution for the loads of those mounts.

To use the subframe for even one of them would mean not using the Tesla motor mount as it would require a multi-bolt setup (in the same manner as the 4 bolt setup to the differential- which was acting as a bridge to the rear mount to the car).

We decided on this route as the simplest and most robust. We did certainly plan for the 2000lb. We aren't auto engineers, but we do a lot of structural work where we have to account for 7x the maximum expected load for rigging. You can probably tell by the type of steel beam we used in the rear :) It looks more like we are hanging speakers above an audience in a fine arts center...

Regarding that subframe 3rd mount, I am doing a bit of research on just how much torque she will see. The 20" back or so that it attached in the past was because she experienced a lot of torque to spin the wheels. Now she does nothing but go along for the ride. The main thing is to lock her in so that the two main bolts aren't expected to do all the work- they would shear eventually. So I thought of going perhaps 12" or so forward in the tunnel and attach with a generic isolated motor mount, or even as you mention, straight up to our front Tesla mount (other than it being crowded up there).
 

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We decided on this route as the simplest and most robust. We did certainly plan for the 2000lb. We aren't auto engineers, but we do a lot of structural work where we have to account for 7x the maximum expected load for rigging. You can probably tell by the type of steel beam we used in the rear :)
Yes, the structural work looks good. :) My comments were mostly for those other forum members who dismiss mounting these components are trivial, and don't understand the forces involved.

Regarding that subframe 3rd mount, I am doing a bit of research on just how much torque she will see. The 20" back or so that it attached in the past was because she experienced a lot of torque to spin the wheels. Now she does nothing but go along for the ride. The main thing is to lock her in so that the two main bolts aren't expected to do all the work- they would shear eventually. So I thought of going perhaps 12" or so forward in the tunnel and attach with a generic isolated motor mount, or even as you mention, straight up to our front Tesla mount (other than it being crowded up there).
While torque reaction from the final drive housing would be the major torque about the lateral axis, that's not that's going on. The subframe takes all of the horizontal load of the suspension; while the suspension arm pivots and the subframe mounts are nearly in the same plane, that alignment isn't perfect so any cornering, accelerating, and decelerating forces will tend to twist the subframe around those two mounts. The third leg doesn't need to be anywhere near as long as it was (to the rear of the final drive), but something is needed, and it sounds like you're headed in a viable direction.
 
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