1974 BMW CSE

[JetDexter]

You put very succinctly what I had been trying to grasp. Thank you. My commute in the next year or so (depending on construction issues) will go from 8-10 mins to about 20 minutes. I'd been tinkering with the idea of getting a clean shell of a 2002 and doing a conversion for a DD, but I was a bit intimidated by your efforts. I need to go visit Moment, as they're closer, and try to make it out to see your efforts. Not alot of folks to discuss this with in my part of the world.

Yes, and when I say that DC motors are low-power, that is not very fair, as they can get to 200HP, but not really more than that. But the Torque is so high from 1RPM that you can expect that 200HP to feel like 300 when taking off from a standstill as compared to a 200HP gas engine which only sees 200HP at a narrow RPM range. But even 200HP in a 2002 would be a lot of power So when I say low-power that isn't very fair. It is only low compared to 485HP of a 240volt Tesla motor.

The larger issue honestly is that once you put the motor under the hood, half of your battery storage space goes away. So that's why you don't get a lot of range. There just isn't enough room for batteries. You can throw some in the trunk though where the gas tank and spare tire were. (and stay neutral in front/rear balance).

 

[JetDexter]

Making more progress on the coupe this week. My daughter finally asked if she could help which was awesome. She’s a monster with the cutting wheel. All of my gloves were far too big for her so she went without.

She was cutting out the tranny tunnel as we figured we may as well widen the space down there since there is no tranny. The tunnel is so wide in these cars as you know that the accelerator is almost under the steering wheel

Then Tyler got involved cleaning up the firewall and fabricating the additional floor space. We welded studs on for the Tesla accelerator and E46 brake pedal.

Finally, we reinforced the tunnel and mounted our inverted brake setup. To give us more room for batteries in the engine compartment we needed to relocate the brakes. We will use a lever to invert the direction of the brake pedal into the hydrobooser (powered by our 12volt power steering pump) then into the Wilwood master cylinder.

In case you are wondering, we will be capping off the bottom of the tunnel. We will actually be attempting to smooth as much of the bottom of the car as possible with plastic or carbon fiber to help with aerodynamics.

To verify the strength of the installation, we test everything using “Brett Units”. The brake setup is rated at 36BUs.

 

[Stevehose]

This is awesome

 

[Markos]

My commute in the next year or so (depending on construction issues) will go from 8-10 mins to about 20 minutes.

The next time you are on the west coast, be sure to complain to your colleagues and clients that your commute has doubled. Just don’t mention the new time.

 

[Markos]

FYI - Before you wrap up you welding,
the gusset below is a common reinforcement on e9’s, particularly with race cars. Check out the race car builds for more details. Brendan’s Gossee Beer raver would be a good start.

 

[Keshav]

Like this....

 

[Markos]

Like this....

Ha! Quick find! Here I am creating child-like drawings instead of doing metal work while @JetDexter is posting pictures of his children doing metal work.

 

[JetDexter]

Haha- awesome thanks guys. I already sent the photos to Brett and Tyler so we can take a look when I get back from my fam vacation. That makes a lot of sense.

 

[JetDexter]

I haven’t posted for a while but we’ve been making good progress. The battery box is the big story. I’ll post with more details soon, but here’s a shot of her in the car with the brackets complete (and even some branding

And for fun there’s a nod to the Tesla logo in the BMW mark

Also, Tyler did some masterful fabrication today on the upper trunk floor. Here it is on the table and then in the car:

Once we fit the two last battery modules in the trunk I will write up a post with all the details of this long process. Fitting 14 55 lb modules was quite a feat.

 

[JetDexter]

We got the last two battery modules in the upper trunk area. So that’s a total of 14 modules. We should be close to the original coupe weight distribution, just a touch heavier in the rear.

Now it’s time to wire them all up and give her a spin around the building. Sadly we still have some brakes work to complete before we can drive her, if we want to [emoji1630]

 

[dang]

What do you think the difference in CG is between the rear modules more forward up high versus behind the rear axle but lower?

 

[JetDexter]

That’s a great question. I’d asked a few race drivers and designer buddies I respect about it and the opinion was generally forward verses low and behind the axle.

It’s true I have no fuel tank and spare. Those two items were flung as far back as possible, yet low. But our drive unit is heavier than those. So the consensus was that the combined weight of the drive unit and 110lbs of batteries would be best where they are.

I am sure more engineering might prove otherwise. I’m very interested to see how it behaves, and possibly make some adjustment back there. While the front battery box is pretty fixed, it will be fairly easy for me to adjust these guys in the rear.

 

[JetDexter]

It’s been slower progress on my car now that we’ve taken on another car, splitting up our time. But we are getting closer to driving this thing!

I’ve posted before about our relocation of our brake booster and master cylinder into the tunnel to make room for our batteries.

We have been making progress on the new brake lines and should have those done next week.

Our biggest challenge is transferring power from the brake pedal to the inverted booster. A couple guys really recommended a small booster in the footwell transferring to the main booster through a hydraulic line. I really didn’t like the idea of more systems and fluids to monitor. So I forged ahead with my lever idea. We named it Greg.

Greg started out as a 3/4” piece of plate. Brett cut it to shape in record time with the plasma torch.

We then heated Greg up to twist the bend which extends Greg Into the tunnel some. We could have heated and hammered the bend in, but cutting the shape then twisting was actually simpler. We then heated Greg up evenly to strength up the particles so he’s nice and strong all around.

He’s just tacked in for now for some testing and today we clean things up and finalize the welds.

We’ve got the full travel into the booster from the pedal- and it only takes up a couple of inches of space in the “battery compartment”.

We’ll probably give Greg the full treatment with some orange powder coating while the car is getting painted.

 

[Bmachine]

Fearless.

 

[JetDexter]

Brett did a fantastic job of finishing Greg today. He looks terrific polished.

And he was overseeing some planning work later in the day.

 

[JayWltrs]

Amazing. From 3/4” plate to a lever that looks like a Nambe’ mustache handlebar. This week I burned through two pieces of sheet metal, fouled some tungsten & burned my hand learning to TIG weld. You two are just showing off now.

 

[Stan]

Could send to the museum of modern art

 

[JetDexter]

The last couple of weeks we finally got the battery box all wired up for high voltage.
As Jeff mentions in his thread, electric cars seem very simple compared to internal combustion. It’s still generally true, but for example this is but one of three major things that have to be handled inside this box. In addition to the high voltage wiring (done with 2/0 wire which is probably thicker than what powers your house) there is also small low voltage lines that provide feedback from the batteries, and finally coolant hoses to cool or warm the batteries. We will be doing the latter two elements while the car is in for paint as we can do controlled, light runs with just the voltage.

Here’s the box wired up- with a couple of electric E9s in the background

The wiring is a blend of the 2/0 stranded wire and custom bus bars sourced from an outfit in the UK that has been doing a lot of EVs the last few years.

After making the 12 module loop we terminate everything to this under-car terminal box where we will connect to the two leads that run to the trunk batteries and the motor. The 12 modules create 273 volts of DC give or take based on the state of charge. Well have 320 volts total. What is more stunning is the total watts of these packs.

Finally the junction box seals up nicely for the road. Right in front of Greg

Next week we drill our exit holes and run to the trunk!

 

[JayWltrs]

The last couple of weeks we finally got the battery box all wired up for high voltage.
As Jeff mentions in his thread, electric cars seem very simple compared to internal combustion. It’s still generally true, but for example this is but one of three major things that have to be handled inside this box. In addition to the high voltage wiring (done with 2/0 wire which is probably thicker than what powers your house) there is also small low voltage lines that provide feedback from the batteries, and finally coolant hoses to cool or warm the batteries. We will be doing the latter two elements while the car is in for paint as we can do controlled, light runs with just the voltage.

Here’s the box wired up- with a couple of electric E9s in the background

The wiring is a blend of the 2/0 stranded wire and custom bus bars sourced from an outfit in the UK that has been doing a lot of EVs the last few years.

After making the 12 module loop we terminate everything to this under-car terminal box where we will connect to the two leads that run to the trunk batteries and the motor. The 12 modules create 273 volts of DC give or take based on the state of charge. Well have 320 volts total. What is more stunning is the total watts of these packs.

Finally the junction box seals up nicely for the road. Right in front of Greg

Next week we drill our exit holes and run to the trunk!

I understand ~40% of this, but fascinating nonetheless.

 

[JetDexter]

Here's another blog post from my bmwcse.com website. I always appologize for it because all of this has already been discussed in this thread. Yet some of you have told me that you enjoy reading these organized stories of particular aspects of the project. That being said, here you go. (Oh and yes, this blog is written to my family and non car-friends, so I explain how brakes work. Feel free to skip that part

Turn the Brakes Around

Remember all the work we went through to convert our steering from the bulky original setup to compact rack and pinion? You may recall that this was not done simply to modernize the car. On the contrary, the factory setup had a wonderfully classic BMW feel. We made this change in order to make way for batteries. The same is true with our brake setup…

Car Brakes 101
For those of you not familiar with how car brakes work, here’s the basics: In most cars the brake pedal on the floor pushes a rod through the firewall (the wall that separates the humans from the engine compartment) and into a booster. This device adds the power so that a modest touch of the pedal can give hard braking action. Most cars use a vacuum-style booster, which is a fairly large round tank. Vacuum supplied by the engine enhances the pedal input, creating an output which has several times the power.
Connected to the back of the booster is the master cylinder. This device takes input from the booster and converts that energy to hydraulic fluid pressure. This fluid makes its way through small tubes to the brake calipers on each of the four wheels.

Here is a photo of a stock brake setup. To the left is the passenger compartment. Outlined in Pink is the brake setup. First the tube containing the rod, pushing into the large vacuum booster, then finally the master cylinder at the end of the line.
Now you can see our problem. We really need all this space for our Tesla battery modules. We needed to reconfigure things in a major way.



It all Started with Child Labor

My daughter Maggie had been asking to help with the project so this was her perfect opportunity. There were no gloves small enough in the shop but I did have a face mask. She did a terrific job cutting away the steel!

After the floor was cut out Tyler welded in some sections and smoothed it out.

Now we have a very comfortable space for both feet. I’ll go ahead and say it: No more two left feet. (You’re welcome).

Now, Back to the Brakes


Since we have no transmission, we have no need for a transmission tunnel. My idea is to install the brake booster here - backwards. We sourced a new Bosch Hydro-boost unit which will feed a new Wilwood master cylinder. Notice in the photo you can see where we took out some of the tunnel.

Another issue we have with the BMW brake booster is that it requires vacuum. We have no engine to provide us vacuum. We could install a vacuum pump, but it makes more sense to move to a hydro-boost style booster. With hydro-boost, the power comes from your power steering pump. Since we have a 12 volt power steering pump to power our steering rack anyway, this becomes a very elegant and unified solution. In the photo you can see the brake setup installed securely, backwards, into the tunnel.

Enter Greg

At this point we have one huge gap in the essentials of braking. Connecting the brake pedal to the brake booster. This is where Greg comes in. My concept is to build a lever which will receive the rod from the brake pedal and invert that motion backwards into the booster. Essentially a brake teeter-totter. While I may have brought the idea, it was Brett that brough the magic. I kept calling our device a lever, but Brett didn’t see that as the correct term. He just decided to name it Greg.

Brett started with a piece of 3/4” inch steel plate and a plasma torch. He had made a guide and could just ride the torch along for a perfect cut.

The plasma torch provides some terrific looking metal artifacts.

We heated Greg up a few hundred degrees where he gave up his strength and we could twist him into the compound shape we needed. Once the shape was achieved, we evenly heated Greg up to get his particles all in harmony for strength.

After the cutting, cleaning, twisting, heating was done Brett welded ends on it, and the pivot point. He attached a very strong receiver to the firewall and we now have a terrific braking solution which takes up less than 2 inches of the engine (battery) compartment.

Cheers,
Paul