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tuna55
tuna55 MegaDork
12/3/19 12:18 p.m.

I don't hate the idea of using existing transmissions. The 90 degree turn isn't hugely wasteful, and if you're honest, you know that re-engineering the rear subframe around a rear mounted motor is going to be hard enough that the loss of 1-2% due to the gearset will start to sound pretty good. As far as the transmission itself, I always imagined just emptying out the case of everything that you don't need. Pick a gear, strip the rest and the clutch, now it's just a well engineered gear reduction box that already more or less fits in the hole.

Keith Tanner
Keith Tanner MegaDork
12/3/19 12:21 p.m.

I actually did the math this morning. An ND with 250 miles of range and 250 hp would weigh right about 2800 lbs - a 471 lb gain. If you leave the trans and diff in there, add 190 lbs.

tuna55
tuna55 MegaDork
12/3/19 12:26 p.m.

In reply to Keith Tanner :

That's not wonderful. I know we have to expect them to be heavier for a while. Now remove gears 1, 3, 4 and 5, and also the clutch, and the pedal and the cylinder and fluid etc. 

 

Keith Tanner
Keith Tanner MegaDork
12/3/19 12:46 p.m.

Transmission is 95 lbs all up but without fluid. You can make up your own imaginary weight for one with parts removed, I don't have weights for the internals. Clutch/flywheel is 27 lbs. The pedal is plastic, I didn't remove it from the EV version. Fluid - well, if we're going there, we're measuring ounces on a back-of-envelope calculation.

My weights were based on actual measured weights for the engine (wet with clutch and all accessories), transmission (dry), driveshaft, diff (dry, open), weight of fuel (but not tank), 12v battery and exhaust system. It's actually exactly 600 lbs - the ND has a very light drivetrain. I made the assumption that the cooling system would remain much the same and did not take the weight of the fuel system other than the actual gasoline into account.

Weight was for a 62 kWh battery extrapolated from the 480 kg weight of the 75 kWh battery plus 200 lbs for the motor (rear motor from a Long Range Dual Motor Model 3). There's a higher performance version of the motor available, but the 200 lb weight came from a teardown report of the LR. I don't know how much more the 283 hp one weighs.

Of course, that new weight can be distributed so it will work well. The engine and the fuel tank (more than half of the weight "removed") are both fairly high in the chassis, the batteries can be very low. So the overall weight might be on par with an LS3 NC, but the CoG and polar moment should be superior. The transmission tunnel would be a pretty good place to put those batteries.

Jamming a motor on the end of the trans is definitely the easy button. But it will remain the hallmark of the easy button.  It removes options for controlling the weight distribution, it includes redundant components, etc. For all means, if the option is that versus nothing, it's the right option.

tuna55
tuna55 MegaDork
12/3/19 12:53 p.m.

In reply to Keith Tanner :

I understand that the Tesla stuff typically has a higher numerical gear ratio than can be accomplished by the differential alone. Thus, unless we're using the donor gearbox (and maybe you can, I don't know what it looks like), then the transmission is actually going to help you get there when combined with the differential ratio. Also, if you remove the bellhousing and clutch, can't most of the transmission and motor fit in a tunnel under the car? So you can make the driveshaft any length up to and including zero, right?

 

I may be missing something here, but it still seems like a good choice, not just a bandaid one.

Keith Tanner
Keith Tanner MegaDork
12/3/19 1:02 p.m.

The transmission is integral to the motor. Take out the stock differential, stick this thing in its place, add halfshafts. I think that's pretty typical for production EVs. The 200 lb weight included this plus the inverter, I believe.

If you start trying to move the Miata transmission further back into the tunnel, you're going to get into difficulties with the shifter location, assuming you're still using more than one gear. I'm not sure the tunnel is wide enough to go back but I have photos that would tell us. More importantly, you're going to take that transmission apart with the torque delivery of the electric motor so it's going to need to be replaced with something else or modified internally.

tuna55
tuna55 MegaDork
12/3/19 1:11 p.m.

Yeah I was planning on using just one gear, no shifter. Good call on the potential issue with torque capability of the transmission. I'm not sure what a normal transmission can handle in a medium gear, especially as it doesn't need to shift.

 

I need some more experience with the back of Miata's and the size of that chunk o' luminum to better understand how feasible that is, but I see what you mean. You may end up having to move suspension stuff apart to make enough room. You actually may have more room under a live axle car with a gas tank back there than you would in a Miata, assuming you build an IRS to suit. You may end up running out of track width though.

Keith Tanner
Keith Tanner MegaDork
12/3/19 1:17 p.m.

We've done the 3D work :) It's feasible with the Model 3 motor without moving any suspension pickup points. That thing is pretty compact.

To use the big Model S motor, we'd have to do a whole lot more work as the motor interferes with the upper control arm mounting points. We can flip the S motor if we rework the transmission oiling system. Packaging is a lot funkier in this case.

 

tuna55
tuna55 MegaDork
12/3/19 1:23 p.m.

In reply to Keith Tanner :

 

So what a company needs to do is repackage an EV motor/transmission such that it mounts to typical live axle attachments points, and a battery that looks like a transmission tunnel.

 

 

EDIT: Lost the first sentence: I suspect it will take quite a bit of engineering to come up with a frame to bolt that thing into a hole where just a differential would have been. it's likely to be nonuniversal.

LifeIsStout
LifeIsStout Reader
12/3/19 1:31 p.m.

My understanding is that the Model 3 engines are the more desirable ones anyway compared to a Model S, in terms of packaging and efficiency.  But I can see availability being a factor (and cost).  Would there be any sort of a provision to make an AWD Miata?  or does the suspension design get in the way of everything there...

 

The other question is if there is a difference on the front AWD motor compared to the rear motor, and a possible sizing/packaging gain there as well.

Keith Tanner
Keith Tanner MegaDork
12/3/19 1:42 p.m.

I would love to see a drop-in electric replacement for a Ford 9 inch. 

The Model 3 is a better motor, at least one generation more advanced than the S. Also considerably more compact. But the S motor is a beefy creature that puts out north of 400 hp and there are more of them on the used market, so that's what you'll be seeing most of the time to start.

The front Model 3 motor is rated at 197 hp. I don't know physically how big it is by comparison to the rear. Photos make it look a little narrower.

AWD would not be easy. The Miata is not a modified FWD platform, the front spindles do not have any provision for a driveshaft and IIRC it's the only non-strut front end in the Mazda family. There is no interchange without welding.

Now here's a fun thought I was kicking around with a friend - the X1/9 is a FWD Fiat 128 with the motor installed in the back seat. And from what I can see of pictures, it retains a set of stock 128 front uprights with the bearings held together by a couple of washers. In other words, an AWD EV X1/9 would be quite possible from a packaging standpoint.

TurnerX19
TurnerX19 Dork
12/3/19 1:53 p.m.

In reply to Keith Tanner :

The X1/9 does indeed use the 128 front hub, but to reduce the height of the nose they moved the strut cartridge down so that there is no path from the hub to the center of the chassis.

sleepyhead the buffalo
sleepyhead the buffalo Mod Squad
12/3/19 2:19 p.m.
tuna55 said:

In reply to Keith Tanner :

 and a battery that looks like a transmission tunnel.

that sound like the existing Volt packs... but I don't recall their kWh/power

also... are there power/rpm curves (or torque) for either the model S or 3 motors.  With them, we'd have enough to plug into OptimumLap to give some performance estimates.

Keith Tanner
Keith Tanner MegaDork
12/3/19 2:21 p.m.

There are dyno charts out there in googleland.

nimblemotorsports
nimblemotorsports Reader
12/3/19 2:24 p.m.

Netgain has offered a motor that has a driveshaft attachment for years, so it is a drop-in replacement for a GM transmission.

sleepyhead the buffalo
sleepyhead the buffalo Mod Squad
12/3/19 2:43 p.m.
Keith Tanner said:

There are dyno charts out there in googleland.

I was putting the sleepykids to bed, and was looking for a shortcut to "good data"...

take this and divide by 2 for one motor?

Keith Tanner
Keith Tanner MegaDork
12/3/19 2:47 p.m.

Not really, because it has a stronger motor at one end than the other. Depends on just what you're trying to figure out - the shape of the curve? The actual power to the wheels? The P85D is rated at 463 hp, so it looks like 15% loss. Look up the rating for the motor and take away 15%, and you'll get the wheel power. Note that the car can't deliver maximum power to both motors at the same time (stupid physics) so one motor will perform better than half of two motors.

tuna55
tuna55 MegaDork
12/3/19 3:25 p.m.

In reply to nimblemotorsports :

That's delicious

barefootskater
barefootskater SuperDork
12/3/19 3:30 p.m.

In reply to nimblemotorsports :

That is a serious bit of hot-damn-where-do-I-get-one.

Keith Tanner
Keith Tanner MegaDork
12/3/19 3:44 p.m.

Based on the sticker, I'll bet that go-ev.com might be a good place to start.

Rons
Rons Reader
12/3/19 6:57 p.m.

This company is a dealer for the net gain motor and has adapters to various transmissions https://canev.com As an interesting aside I have a move being planned which in the next year should but me about 10 minutes away from can ev. I can hear rusty gears beginning to turn.

MrJoshua
MrJoshua UltimaDork
12/3/19 9:26 p.m.

Wow-that model 3 motor is a pretty batch of packaging. It is perfect for stuffing in the front or back of almost anything without a solid axle!

2GRX7
2GRX7 Reader
12/4/19 10:11 a.m.
amg_rx7 said:

In reply to 2GRX7 :

You might be interested in checking out the Rich Rebuilds YouTube channel 

https://www.youtube.com/channel/UCfV0_wbjG8KJADuZT2ct4SA

Ha-I 've been watching him lately. I'll need to go back and check out his earlier episodes.

kb58
kb58 SuperDork
12/4/19 10:14 a.m.

I've been halfway toying with the idea of designing something around an electric drivetrain, but the challenge is cost. As an example, a used LS driveline is maybe $5K. Right now, an S drivetrain is around $11K without batteries, so that's around $20K ready to go. So, "the extra $15K gets you what, exactly?" Tire shredding torque off the line (LS has that already), no noise, limited range, and being "different." Right now I think the "being different" factor is overriding the cost. Once that settles down, such a build/conversion will have to stand on its own for being a good idea cost-wise. I realize that prices will keep coming down, but right now, its still just an idea rolling around in my head. (And I'm ignoring the corner cases where someone gets hold of a $2000 Model S to prove it's a great idea.)

Keith Tanner
Keith Tanner MegaDork
12/4/19 10:26 a.m.

I think the pricing is simply a reflection of supply and demand. There literally millions of LS motors out there after more than 20 decades of mass production by one of the biggest manufacturers on the planet. There are not that many Model S motors. Ferrari engines are expensive to buy, too.

If you're looking at the simple cheapest way to go fast, it's going to be hard to beat a good ol' Murican bent 8 for a long time. If you're looking for different attributes - low CoG, instant torque, silence, the howl of a flat plane Italian V8, whatever - then you may make different choices.

BTW, my hypothetical EV ND has more range than the LS ND unless you're on the highway :) Fuel economy of LS engines around town is just ridiculous, and you've only got about 10 gallons to play with.

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