Yet another Delorean conversion

18549 Views 46 Replies 9 Participants Last post by eUKenGB, Jun 10, 2021

vauron

Discussion Starter · Nov 2, 2019

At Brian's suggestion I've started a thread on my project to convert my Delorean, VIN 6673. I'll begin with what I posted on a Chevy Volt battery thread a couple of days ago.

I have a Gen1 (2012) Chevy Volt battery in my garage that I'm about to put into my Delorean (VIN the first prime after 6666), which is now down to just a frame with no engine, transaxle, or gas tank. (The stainless steel + fiberglass body is strung up elsewhere in my garage waiting to come back down when the frame is ready for it.) This entails the following steps.

1. The cells are down to 3.45V, so 330V total. Beore I start chopping up the battery (see below) I'm planning to charge it very gently to 384V with 8 Cisco 48VDC 0.38A adaptors that I got on eBay for $39 the lot (actually 11 of them, so maybe I'll shoot for the full 400V). Later on I can figure out how to charge them faster but this is fine for the time being. I'm hoping that each of the four modules has a self-contained BMS that will keep each module nicely balanced and that I only need to monitor the modules' total voltages and not their individual cells.

2. It would be great if the whole battery would fit where the PRV V6 engine and transaxle went, but it doesn't quite fit. So I'm going to cut the front "stem" of the T-shape at the natural cut point and put the front module where the gas tank used to sit. The truncated T, consisting of two modules at the back and one module as the rear part of the "stem", turns out to fit very neatly in the engine bay. I just have to design some angle irons that will support the battery so it doesn't flex too much. My friend Michael McClure who used to race Alfa Romeos and own Ferraris is helping me on this.

3. I have to figure out the ideal climate control for the battery. Supposedly it likes a constant 70 °F for maximum life, but for now maybe it will be ok to subject it to a wider range. The Delorean has two radiators, one for the engine and one for the A/C, I need to decide which one to use to keep the battery cool. For the time being I don't care about protecting the battery against cold weather, if necessary I can warm it up in the garage somehow as needed.

4. A shipment of two in-wheel motors, inverters, and "powerbrain" arrived yesterday shortly from Elaphe Propulsion, still awaiting customs to clear it. Continuous power per motor is 50 kW, peak is 75 kW which adds up to 200 HP. This is an improvement over the 140 HP I was getting from the Peugeot-Renault-Volvo V6 engine.

5. Longer term I plan to add a supercapacitor-based KERS and a ZEF (zero-emission fuel, TBD) range extender. Also whatever aftermarket driver assistance packages are available (MobileEye?). Not sure if the Delorean can accommodate airbags.

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brian_

· #2 · Nov 2, 2019

vauron said:
4. A shipment of two in-wheel motors, inverters, and "powerbrain" arrived yesterday shortly from Elaphe Propulsion, still awaiting customs to clear it.

In-wheel motors have never been successful in normal road-going cars, for a few reasons. You're going to see lots of scepticism in this discussion as a result.

The mass of the wheel and everything that moves with it during suspension travel - called "unsprung weight" - is important to suspension performance and resulting ride and handling. Just putting the mass of the car's motor(s) and distributing it to two or all four of the wheels is a problem for suspension performance.

Without reduction gearing between the motor and the wheels, the motor needs to be very large to produce enough torque to the wheels, making the unsprung mass problem worse. An in-wheel motor with reduction gearing adds substantial weight and complexity. Whether it is a large motor without gearing, or a smaller motor with gearing, this is a problem.

People promoting in-wheel motors often point to the benefit of not needing a jointed axle shaft from inboard-mounted drivetrain to the wheels, but an in-wheel motor requires the power cables go to the wheels, flexing with every suspension movement (and turn, if on a steered axle). In addition, a motor of significant power density (like every production EV motor) also needs liquid coolant hoses.

I assume that the proposed motors are the Elaphe M700. They weigh 23 kg each (including the hub), and require liquid cooling. They also have bearings from a Smart, and apparently the brake from a Smart which is appears to be a drum; this seems unlikely to have sufficient capacity for a DeLorean.

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brian_

· #3 · Nov 2, 2019 (Edited)

vauron said:
Continuous power per motor is 50 kW, peak is 75 kW which adds up to 200 HP. This is an improvement over the 140 HP I was getting from the Peugeot-Renault-Volvo V6 engine.

Elaphe says that the peak torque output of the M700 is 700 Nm, so two of them will put 1400 N⋅m to the wheels in total. For comparison, the DeLorean's engine has a peak torque output of 153 lb⋅ft (207 N⋅m) @ 2750 rpm (according to some sources).

207 x 3.36 1st gear x 3.44 final = 2,392 N⋅m to wheels up to 17 mph or 27 km/h
207 x 2.06 2nd gear x 3.44 final = 1,467 N⋅m to wheels at 27 mph or 43 km/h
207 x 1.38 3rd gear x 3.44 final = 983 N⋅m to wheels at 41 mph or 67 km/h
207 x 1.06 4th gear x 3.44 final = 755 N⋅m to wheels at 53 mph or 86 km/h
207 x 0.82 5th gear x 3.44 final = 584 N⋅m to wheels at 68 mph or 110 km/h

The DeLorean engine put out 162 lb⋅ft (220 N⋅m) @ 2750 according to Road&Track's 1982 test, which would mean more torque to the wheels at the same speeds.

The dual M700 setup will be like driving a DeLorean in second gear all of the time, so the start of acceleration driving slowly over bumps may not be acceptable. That's roughly what Duncan was saying in the other thread.

The stock DeLorean can use first gear all the way to 40 mph. Of course torque drops off after 2750 rpm, but it's still going to be out-accelerating the dual M700 setup in the same weight of car.

Is a full set of specs available for any of the Elaphe products? Given just the peak torque, peak power, and continuous power, this is a guessing game. If the peak torque can be maintained continuously within the power limits, then the 50 kW power limit will be reached at 690 rpm, and then torque will drop in proportion to speed. A Delorean's 235/60R15 rear tires turn 794 revolutions per mile, so 690 rpm is 0.87 miles per minute, or 52 mph or 84 km/h; acceleration will start dropping off more rapidly from that point.

The idea of a fixed drive ratio from electric motor to wheels is normal - essentially all production EVs have a fixed-ratio transmission, so their change in behaviour with speed is similar. But for comparison, an original Nissan Leaf (low-performance by today's standards) has a motor putting out 320 N⋅m, multiplied by a 7.94:1 transaxle, putting 2541 N⋅m to the wheels. It can only put out 80 kW, but it reaches that at a much lower speed than the M700 setup driving 235/60R15 tires.

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vauron

Discussion Starter · #4 · Nov 2, 2019 (Edited)

brian_ said:
In-wheel motors have never been successful in normal road-going cars, for a few reasons. You're going to see lots of scepticism in this discussion as a result.

The mass of the wheel and everything that moves with it during suspension travel - called "unsprung weight" - is important to suspension performance and resulting ride and handling...
...
...an in-wheel motor requires the power cables go to the wheels, flexing with every suspension movement...

I assume that the proposed motors are the Elaphe M700. ...

Ok, so the main concern is not with the battery then.

Yes, the M700. The Delorean's front brakes will remain disc, we'll see whether drums in the rear make a big difference to the Delorean's stopping ability. I never found the Delorean's e-brake terribly effective, we'll see if that's any different with drums.

With the original engine the Delorean's curb weight is 1244 kg, call it 1400 kg with two passengers. I expect the weight to be roughly the same without the engine, transaxle, and gas tank, but to be on the safe side round it up to 1500 kg.

An 8% grade at 120 kph (75 mph) raises the car with a vertical velocity of 8/3 m/s. If I can remember enough 10th grade physics, that should add 1500*9.8*8/3 = 39.2 kW to whatever drag and rolling resistance requires at that speed, hopefully less than 30 kW.

Since Elaphe specs the two motors at 100 kW continuous, and 150 kW for 10 seconds, I figured that 70 kW would be enough power to feel reasonably confident about hill climbing ability, otherwise I would have used some other motor.

As for unsprung weight, this will be a learning experience for me. If it proves to be unbearable I'll look into active suspension options. (Since the front suspension is unchanged, information about bumps can be measured there and fed to the rear suspension before it hits the bump.)
However this won't be a priority because the purpose of this conversion is to have a test platform to explore renewable (zero-emission) fuel technologies for use as a range extender, e.g. ammonia. At some point I'll start fleshing out details at https://7leaguewheels.com.

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vauron

Discussion Starter · #5 · Nov 3, 2019

brian_ said:
the 50 kW power limit will be reached at 690 rpm

Yes, and the 75 kW power limit will be reached at 1035 rpm, which using your arithmetic is 78 mph.

So acceleration will still be constant at 60 mph = 26.8 m/s. If the curb weight is 1244 kg, an 80 kg driver brings that to 1324 kg. I measure the rear wheel's radius at 0.30 m (you were working with 0.32 m), which converts 1400 Nm to 1400/.30 = 4666 N, hence an acceleration of 4666/1324 = 3.52 m/s2. So to reach 60 mph = 26.8 m/s should take 26.8/3.52 = 7.6 seconds, well within the time allowed to use the motor's max power 75 kw.

Road & Track measured the Delorean's 0-60 mph time at 10.5 seconds. If my math is correct the M700 should shave about 3 seconds off that. Nowhere near ludicrous of course, but respectable.

vauron

Discussion Starter · #6 · Nov 3, 2019

brian_ said:
The dual M700 setup will be like driving a DeLorean in second gear all of the time.

I seriously doubt that the acceleration of the Delorean in second gear at below 5 mph is remotely near 3.52 m/s2, which is what I'm expecting from the M700. The PRV V6 is wonderful but not that wonderful.

As long as you can keep the M700's magnet below 65 °C and the windings below 180 °C it has a torque constant of 2.12 Nm/A. Maximum phase current is 350 A; as long as this current is sustained you should get a torque of 350*2.12 = 742 Nm as soon as you hit the accelerator. (This is actually a tad over their quoted max torque of 700 Nm, I'm guessing they rounded down to be conservative but I can check.)

brian_

· #7 · Nov 3, 2019

vauron said:
I measure the rear wheel's radius at 0.30 m (you were working with 0.32 m), which converts 1400 Nm to 1400/.30 = 4666 N, hence an acceleration of 4666/1324 = 3.52 m/s2. So to reach 60 mph = 26.8 m/s should take 26.8/3.52 = 7.6 seconds, well within the time allowed to use the motor's max power 75 kw.

Road & Track measured the Delorean's 0-60 mph time at 10.5 seconds. If my math is correct the M700 should shave about 3 seconds off that. Nowhere near ludicrous of course, but respectable.

I didn't work with a radius at all; I used the specifications for a P235/60R15 tire. Unfortunately I copied the revolutions per mile incorrectly, presumably picking off the number for the wrong size - it should be in the range of 715 to 745 revolutions per mile, depending on tire brand and model. The same specifications show an overall diameter of 28", which would be 71.12 cm, for a radius of 35.56 cm, but the loaded radius is less. A radius of 30 cm would be a flat tire of that size, but okay...

The logic of acceleration calculation is fine, except that it ignores all rolling and aerodynamic drag; that's a substantial difference. If you make the same assumption with the output of the gas engine (which is much more difficult because it varies with speed), you'll get an acceleration time much quicker than reality, too.

During that acceleration with a constant 700 Nm the motor's output power isn't 75 kW; it is zero at zero speed and increases linearly with speed. Using the undersized 0.3 m radius, the tire turns 854 times per mile, so 854 revolutions per minute at 60 mph (a mile per minute). 700 Nm times 854 rpm is still only 62 kW, so the motor's burst power limit is not a concern.

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brian_

· #8 · Nov 3, 2019

vauron said:
With the original engine the Delorean's curb weight is 1244 kg, call it 1400 kg with two passengers. I expect the weight to be roughly the same without the engine, transaxle, and gas tank, but to be on the safe side round it up to 1500 kg.

My suggestion would be to add up the weight of all of the parts to be removed, and all of the stuff to be added, to get a realistic estimate. EV conversions only end up lighter than the original car if they are very short-range (small battery), or if the original engine and transmission were abnormally heavy.

vauron

Discussion Starter · #9 · Nov 3, 2019

brian_ said:
I didn't work with a radius at all; I used the specifications for a P235/60R15 tire. Unfortunately I copied the revolutions per mile incorrectly, presumably picking off the number for the wrong size - it should be in the range of 715 to 745 revolutions per mile, depending on tire brand and model. The same specifications show an overall diameter of 28", which would be 71.12 cm, for a radius of 35.56 cm, but the loaded radius is less. A radius of 30 cm would be a flat tire of that size, but okay...

The logic of acceleration calculation is fine, except that it ignores all rolling and aerodynamic drag; that's a substantial difference. If you make the same assumption with the output of the gas engine (which is much more difficult because it varies with speed), you'll get an acceleration time much quicker than reality, too.

During that acceleration with a constant 700 Nm the motor's output power isn't 75 kW; it is zero at zero speed and increases linearly with speed. Using the undersized 0.3 m radius, the tire turns 854 times per mile, so 854 revolutions per minute at 60 mph (a mile per minute). 700 Nm times 854 rpm is still only 62 kW, so the motor's burst power limit is not a concern.

Good, it looks like we're basically on the same page. I was wrong to ignore rolling resistance and drag for 0-60 mph quickness, it will be interesting to see what the real quickness is. Hopefully I'll know this in December.

No need to point out that power is low at low rpm for both electric motors and ICEs, obvious for both from elementary physics. The huge difference is that, like power, torque is also low at low rpm for ICEs, but not for electric motors, which is why a Delorean in 2nd gear is the wrong comparison. The acceleration figure I gave for two M700s on the Delorean should be correct at low speed and gradually decrease at higher speeds because of drag and rolling resistance as you say.

The rear wheels are currently off the car, and their circumference is 2.13 m, making their unloaded radius 34 cm. I believe I'd correctly inflated them back when they were supporting the whole car, will recheck when it's back together.

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vauron

Discussion Starter · #10 · Nov 3, 2019

brian_ said:
My suggestion would be to add up the weight of all of the parts to be removed, and all of the stuff to be added, to get a realistic estimate. EV conversions only end up lighter than the original car if they are very short-range (small battery), or if the original engine and transmission were abnormally heavy.

At some point I'll try to estimate the weight of the Delorean's engine, transaxle, and half-axles.

Don't most conversions only remove the engine and not the clutch or transaxle/transmission and half-axles? I've removed the lot. And I'm not aiming for long range using just the Volt's battery, which is somewhere around 400 lbs, a lot lighter than the batteries in Teslas, Bolts, etc. I'll be happy if I get 60 miles of range before I get around to the range extender.

MoonUnit

· #11 · Nov 11, 2019

4. A shipment of two in-wheel motors said:
I didn't realise one could buy Elaphe motors, I thought they were only available to OEMS. Can I ask how you were able to purchase them?

vauron

Discussion Starter · #12 · Nov 11, 2019

MoonUnit said:
I didn't realise one could buy Elaphe motors, I thought they were only available to OEMS. Can I ask how you were able to purchase them?

It's for a research project they're interested in. https://7leaguewheels.com will have more details in due course.

rmay635703

· #13 · Nov 11, 2019

How much does the hub motor set you back?

I was looking at an s400 to drive a rear wheel on a micro car and will watch your progress carefully

EVmattyP

· #14 · Nov 11, 2019

rmay635703 said:
How much does the hub motor set you back?

I was looking at an s400 to drive a rear wheel on a micro car and will watch your progress carefully

same... I did the math on the S400 and it looks like top speed with my wheels would only be 50mph but that may be fine for you.

I've also reached out to them, re-purposing my business to something that may allow me to get a quote.

vauron

Discussion Starter · #15 · Nov 12, 2019

EVmattyP said:
same... I did the math on the S400 and it looks like top speed with my wheels would only be 50mph but that may be fine for you.

I've also reached out to them, re-purposing my business to something that may allow me to get a quote.

Seems like DIYelectricCar is quite divided about in-wheel motors. Duncan and Brian were pretty pessimistic. I'd be interested to know who's tried them and been disappointed. Me, I like to balance theory and practice, and this is a big experiment for me. For all I know I'll have proved Duncan and Brian right.

Bear in mind that if you're planning to attach a motor to a suspension that Elaphe hasn't worked with before, the engineering costs are likely to dwarf the parts costs. When it comes to your budget, think Roadsters, not volume-production Model 3's. Stephen Wynne's Delorean operation in Texas would hit you up for over $100K if ever the NHTSA lets them go forward with their idea of selling electric Deloreans, even though Congress is fine with the concept and gave it the green light years ago. And those would still be using the Delorean's clutch and transaxle with just one motor, not the fancier pair of M700's with no transaxle.

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brian_

· #16 · Nov 12, 2019

vauron said:
Seems like DIYelectricCar is quite divided about in-wheel motors. Duncan and Brian were pretty pessimistic. I'd be interested to know who's tried them and been disappointed. Me, I like to balance theory and practice, and this is a big experiment for me.

I would be interested in just seeing someone try them with a normal road car (not a microcar or low-speed vehicle, or a heavy truck or bus) and complete the project to a running state. Then, it would be interesting to see an objective suspension performance comparison, but I really don't expect to ever see that.

I am looking forward to seeing this DeLorean reach completion (at least to the battery-electric stage) - it should be interesting.

brian_

· #17 · Nov 12, 2019 (Edited)

vauron said:
Bear in mind that if you're planning to attach a motor to a suspension that Elaphe hasn't worked with before, the engineering costs are likely to dwarf the parts costs.

Elaphe's in-wheel motor page gives only the barest minimum of information. Is there anything more available, such as drawings showing how the unit is mounted?

ishiwgao

· #18 · Nov 14, 2019

vauron said:
Seems like DIYelectricCar is quite divided about in-wheel motors. Duncan and Brian were pretty pessimistic. I'd be interested to know who's tried them and been disappointed. Me, I like to balance theory and practice, and this is a big experiment for me. For all I know I'll have proved Duncan and Brian right.

I, for one, am actually very interested in In Wheel motors, and not just the low-powered ones for low speed vehicles. I have been looking at high powered in-wheel motors and seeing how to fit super high powered motors (200-300kW) into normal wheels to use in sports car applications.

It's been about 3 years since i started, and still no concrete method yet. But I'm not giving up soon.

brian_

· #19 · Nov 14, 2019

ishiwgao said:
I have been looking at high powered in-wheel motors and seeing how to fit super high powered motors (200-300kW) into normal wheels to use in sports car applications.

By "fit in", I hope you mean "make light enough" more than just "find space for". The only space problem is getting the motor (possibly with reduction gearing) and the brake both in. Excessive unsprung mass is a bigger issue, especially in a sports car.

ishiwgao

· #20 · Nov 15, 2019

brian_ said:
By "fit in", I hope you mean "make light enough" more than just "find space for". The only space problem is getting the motor (possibly with reduction gearing) and the brake both in. Excessive unsprung mass is a bigger issue, especially in a sports car.

I try to look at this problem from a different perspective, to say that unsprung weight is a big issue with low downforce. What do you think?

If we can make the wheels have enough downforce so that the "sprung" (so-called) to unsprung weight ratio is kept, then it wouldn't be a problem anymore?

of course, how to implement this is another topic for discussion, but at least now we found a solution to the first problem

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