Electric Supercar

117045 Views 525 Replies 38 Participants Last post by snowdog, 9 d ago

snowdog

Discussion Starter · Jun 7, 2019

Hello all,

I thought I would start a build thread. I have ordered a K1-attack kit car. I have started the assembly. My plan is to have a Tesla drive train. I am sourcing from EV-West. Hopefully that was a good company to partner with. I am waiting on batteries until the build is further along. I will definitely reach out to the forum for advice along the way. I am also documenting in YouTube. Feel free to follow along.

https://www.youtube.com/channel/UC-Uk13BnLTGAO5APsfuT9uw

Reactions: 2

21 - 40 of 526 Posts

brian_

· #21 · Jun 14, 2019 (Edited)

remy_martian said:
IMO, the Tesla strut suspension sucks. As Brian points out, the load point is way high. It'll be interesting to see if and how they ditch this with Roadster II, and even the pickup truck (if it actually is a truck vs an electrified Honda Ridgeline).

The high body mounting point for spring/shock loads is quite compatible with unibody structural design, so I doubt they'll change it for car models. The pickup truck, though, will likely have a different structure, with different spring/shock mounting... but it's all speculation at this point.

remy_martian said:
Why have the Tesla subframe at all -- seems to me like it's a lot easier to just mount the drive unit itself (IIRC Damian, a <gasp> Youtuber, did that with his BMW), and run your axles to something with a more sane and/or conventional geometry?

Damien couldn't make the Tesla drive unit work with the BMW 850 suspension, so he ripped it out and downgraded to an older BMW semi-trailing arm suspension... the only type that typically fits easily with the Tesla drive unit; the tendency for Tesla-powered conversions to be older Porsches and BMWs is not just by coincidence. The K1 Attack suspension (presumably from the front of an old Accord, but they also offer an MR2 version which uses the donor's rear McPherson struts) is not semi-trailing arm, is designed specifically to work with a transverse engine ahead of the axle line, and will not easily work with the Tesla drive unit.

The Tesla Model S/X rear suspension geometry is entirely sane and quite conventional. It is not a McPherson strut; it is a multilink design, of the "integral link" type also used by Ford and Jaguar. The spring/shock unit's lower end mounts directly to the hub carrier, providing a desirable 1:1 motion ratio, but it connects though only a single bushing so it does not control the suspension geometry at all (unlike a McPherson strut with its rigid lower mounting to the hub carrier, so it controls caster and camber). Both the 1:1 motion ratio (at the rear) and the mounting of springs and shocks to the body rather than the subframe (at both ends) are characteristics shared with the current Mazda MX-5 (Miata). Edmumds has a good "walkaround" tour of the Tesla suspension.

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brian_

· #22 · Jun 14, 2019 (Edited)

remy_martian said:
I'd want a CAD model of the frame vs measurements. This one's a case of cut once, order a new frame from Eastern Europe if you F it up.

It also sounds like they have the means to mod the frame as needed -- why not have them do the Tesla drive unit mounts and fitting vs bodging a bodge? I'd even have them mod the chassis to accommodate a floor pack between rocker tubes. It's not like they couldn't sell a bunch of these for their initial investment of effort...

This makes sense to me. Their options list includes "electric drive", simply meaning that they leave out bits specific to any of the engine options, but there is still provision for a rear suspension (presumably CB-generation Accord front). They could offer a real electric drive option, to fit the drive unit and suspension of a specific donor EV (which would be Tesla Model S in this case).

brian_

· #23 · Jun 14, 2019

snowdog said:
I am not planning to change the tesla suspension the only modification that may be required is where the shocks are mounted to the frame.

My guess is that you are concerned that the spring/shock units will interfere with the K1 Attack frame tubes. Only very limited change is reasonable with this, since the spring/shock struts attach directly to the hub carriers (you can't relocate them on a control arm), and if you even tilt them you change the progression of the spring and shock stiffness with travel. They could probably tilt inward a bit without problems, but it would certainly be better to modify the frame to work properly with the suspension.

brian_

· #24 · Jun 14, 2019

remy_martian said:
Tuck a Tesla drive unit into an XKE rear suspension assembly and you have the makings of a sportscar.

Duncan said:
Have you ever done anything with an XKE rear suspension setup? - I mean it's cutting edge technology 70 years ago! - I like my driveshafts to drive the rear wheels and NOT have to resist suspension and brake loads as well

I'm with Duncan on this one: not so much about braking torque, but I certainly don't want axle shafts as suspension links in anything but a classic car (my Spitfire has them, but I wouldn't build anything that way).

remy_martian said:
I'm not tickled by the bazillion rubber bushings and no parallel link on the Tesla rear knuckle to keep it where it needs to stay in free space. Rube Goldberg and it's no wonder it clunks.

The integral link design has fewer joints and fewer parts than classic double-A-arm and multilink designs, and a typical number of them are bushings (since in this case it doesn't use any ball joints). I'm not sure what link you think is missing, but I suspect that you don't understand the function of the vertical caster control link (the one that leads to the "Integral Link" trade name). The classic five-separate-links design (Mercedes W201 and many subsequent, Mazda RX-8 and NC/ND MX-5, for instance) is a more elegant solution, but the integral link style packages a little more easily.

brian_

· #25 · Jun 14, 2019

Jag IRS sidetrack...

x.l.r.8 said:
To be fair from hot rods to drag racers it does do it well, increases the unsprung weight and is highly adjustable, easily modifiable and pretty damn strong, is way better than a fixed axle and had LSD’s in most of the cars with wide final drive ratios. For a track car I’ll take a jag IRS over a 9 inch.

Of course you mean decreases unsprung weight, but any IRS does that and the additional reduction due to inboard brakes comes at a high cost in maintenance. Any reasonable IRS is better than a beam axle (which is presumably what you mean by "fixed" axle), but a bad design of any type is still bad... and most newer IRS designs are better than the classic Jag IRS in just about every way.

brian_

· #26 · Jun 14, 2019 (Edited)

snowdog said:
Several electric powered options were considered. I was not keen on options that would require clutch and shifting. I also liked the available power for the small size and weight. I know there were other options, however this is the one that I landed on.

Any motor with sufficient operating speed range could be used without a multi-speed transmission, eliminating the clutch and shifting of the traditional DIY conversion approach (although the right total gear reduction ratio is still required). Any complete drive unit (motor with transaxle) salvaged from an EV would be a suitable motor and single-ratio reduction gearing system, and most of them would fit with the stock K1 Attack suspension, because they are designed to fit in place of a typical transverse engine mounted just ahead of the axle line.

Of course those are not the only factors, and I do understand the appeal of the promised "plug and play" of the Tesla packages.

x.l.r.8

· #27 · Jun 14, 2019

You are correct. Long night and way to much excitement in the past 24 hours. I only played with older IRS units because I’m older. After the late 80’s I thankfully moved away from Jaguar.

brian_

· #28 · Jun 15, 2019 (Edited)

Following up on the spring/shock unit height...
The car is designed to work with the Honda front double wishbone suspension, which has a spring/shock strut which is quite tall because its entire working length is above the axle shaft. The available alternative MR2 McPherson struts are similarly tall for an equivalent reason. The Tesla and Honda (or Toyota) strut tops are probably comparable in height, so in that dimension (but not in width) the Tesla suspension is likely reasonably compatible with the K1 Attack frame.

snowdog

Discussion Starter · #29 · Jun 17, 2019

Great discussion guys. You all have a wealth of knowledge. When the Tesla subframe comes in I will post some pictures with potential mounting options. I would love for the feedback.

snowdog

Discussion Starter · #30 · Jul 8, 2019

2

So I have a couple of screen shots of the tesla rear subframe with the K1 frame overlay. The designed placement of the coilovers for the K1 look like they will be ~2in inboard of the stock tesla location. My plan is to change the mounting point of the coilover to match the location and angle of the stock tesla struts. The plan for the frame is all weld on (no cutting) to bring the frame to the four motor mounting points.

You can see a little more in the last 3 minutes of this YouTube video.
https://youtu.be/eqOIkSRNeFY

Suggestions?

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remy_martian

· #31 · Jul 8, 2019

Seems like you could get a wider rear tire on there if you ditch the Tesla springs.

In any case, I thought the company did bespoke frame design as well? If it were me, I'd have them build a new rear frame section (everything aft of the rear bulkhead, properly triangulated and including a crush zone, cut off everything and weld that new rear piece in place of the old. If your Tesla models are accurate, you've done a lot of the CAD heavy lifting for them.

brian_

· #32 · Jul 9, 2019 (Edited)

remy_martian said:
Seems like you could get a wider rear tire on there if you ditch the Tesla springs.

Ditch them for what - small-diameter coils on custom shocks?

The Model S hardware fits 245 mm wide tires, and this is a much lighter car, so I don't see a need for wider tires. The Tesla struts have, I assume, air springs; that would be handy for tuning the rear stiffness.

brian_

· #33 · Jul 9, 2019

snowdog said:
So I have a couple of screen shots of the tesla rear subframe with the K1 frame overlay. The designed placement of the coilovers for the K1 look like they will be ~2in inboard of the stock tesla location. My plan is to change the mounting point of the coilover to match the location and angle of the stock tesla struts. The plan for the frame is all weld on (no cutting) to bring the frame to the four motor mounting points.

That all looks good. The new strut mounts can be just like the current ones, but outside the frame rails rather than inside.

Keep in mind that the four subframe mounts take all of the horizontal forces (of cornering, acceleration, and braking) plus support the weight of the drive unit... the frame extensions will need to be well-braced.

snowdog

Discussion Starter · #34 · Jul 15, 2019

2

Question on battery placement. The kit that I am building (https://www.youtube.com/channel/UC-Uk13BnLTGAO5APsfuT9uw) has large channels that run along either side of the car length wise between the front and rear tires. This seems like it might be a good place for battery locations, right? Any draw backs?

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brian_

· #35 · Jul 15, 2019

battery placement: side tunnels?

snowdog said:
The kit that I am building (https://www.youtube.com/channel/UC-Uk13BnLTGAO5APsfuT9uw) has large channels that run along either side of the car length wise between the front and rear tires. This seems like it might be a good place for battery locations, right? Any draw backs?

I think you'll find that by the time you put any available module in an enclosure, with room for wiring and cooling, it's too bulky to fit in spaces like that.

Have you ever seen the battery setup in AC Propulsion's tzero? It had packs down each side, but wouldn't meet modern expectations of safe battery pack design.

Duncan

· #36 · Jul 15, 2019

Re: battery placement: side tunnels?

If I build another EV That is exactly where I would put the batteries -
It's always a problem finding space for the batteries - I would design the chassis right from the start to hold the batteries

Those two spaces are the best place - the only things that need to be in between them are the driver and passenger - and they don't need anywhere near as much space as they usually get

The Tesla is what 77 inches wide? - you need 16 inches for each bum and 8 inches between them - 40 inches - leaving 37 inches for the two battery modules - my Volt modules are about 11 inches wide - and they are wider than most

snowdog

Discussion Starter · #37 · Jul 15, 2019

I was planning on using using LG Chem 16S 2.6kWh Batteries. The drawings seem like there should be plenty of room. Maybe I am missing something.

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brian_

· #38 · Jul 15, 2019

snowdog said:
I was planning on using using LG Chem 16S 2.6kWh Batteries. The drawings seem like there should be plenty of room. Maybe I am missing something.

Or maybe I am underestimating the size of those spaces.

My suggestion would be to build a cardboard box, wide and tall and long enough for the module plus whatever you need for cooling plus the enclosure structure plus cabling, and stuff it into those cavities to see how it fits.

Keep in mind that you probably don't want to use your battery modules as a crushable structure in a collision, so steel tubing around them would be appropriate.

snowdog

Discussion Starter · #39 · Jul 18, 2019

Any fundamental problems with standing batteries upright instead of laying down?

brian_

· #40 · Jul 18, 2019 (Edited)

snowdog said:
Any fundamental problems with standing batteries upright instead of laying down?

In lithium-ion cells, typically not. Those LG Chem modules are presumably stacks of pouch cells; in this type of design (which is by far the common design in current EVs) the pouches are clamped together, and the clamping force is much more important than gravity. They don't typically have top vents, so which side is on top doesn't matter.

Do you have a link to any information about those modules? LG Chem has made a lot of cells and modules. I'm guessing that they are the ones sold by EV West, which appear to be made for the Chrysler Pacifica plug-in hybrid (although the Pacifica is not mentioned in the LG Chem battery overview). They lay flat in the Pacifica simply to fit under the floor.

If these are the modules, you can find substantial discussions of them in this forum by searching for "Pacifica". I don't know offhand what mounting orientations have been tried.

You haven't asked about cooling, but I'll toss in my comment anyway...
For "supercar" performance, or even to use the full stock output of even a small Tesla drive unit more than very briefly, these modules will likely need cooling. If they are the modules that I am guessing, they are cooled with a plate against the large (14"x8") side with the exposed aluminum. That means building cold plates (presumably with coolant circulating in them), or adapting the plates from something like the Pacifica. Just finned heat sinks and lots of airflow might be adequate, for less-demanding use.

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