[brian_]

If you are starting assembly, does that mean that you have worked out the placement and mounting of all of the EV components?

I've seen the advertising material on the kit manufacturer's website, but I didn't see any technical details. Do you have an illustration or clear description of the rear suspension? That's critical to fitting the Tesla drive unit in.

Update:
After some online research, I see that the kit uses the front suspension of the FWD donor at the rear, which is normal practice for mid-engine kits of this century. In this case, this means the double A-arm system of the donor Accord.

That's generally a good thing, but it is designed to fit around the conventional transverse placement of the engine, ahead of the axle line. In this case it seems to include the cross members from the Accord, to locate and mount the lower control arm and the steering rack (which is presumably replaced by fixed track rods). The rear cross member will probably go right through the bottom of the motor and inverter of a Tesla Model S or X drive unit (because they are behind the axle), although the Tesla front drive unit places the motor higher to clear the front of the battery case, which might help.

Your post in another forum says that you have motor mounting information from another builder; what's the plan to make the drive unit fit with the suspension and structure?

 

[brian_]

I normally don't watch anyone's YouTube videos, since they are black holes for time providing little if any value. I did watch the intro, hoping for an overview of the technical plan. Sadly, there is no plan provided... but a viewer's note: the music adds nothing and is louder than your voice. Turning the volume up enough to hear the words means getting blasted by the noise at the end. Does anyone listen to their own videos when they're done, or do they just toss them into the YouTube pile of junk?

Anyway... Nice garage.

 

[brian_]

I did look through (no audio, 2X speed, skipping ahead) the front suspension video. Combined with some forum reading, I see that the bits are a VW/Audi McPherson strut system converted to double A-arms. This type of conversion is relatively common for this sort of car, although it seems like a strange choice for a car using Honda components at the rear, since there are stock double A-arm Honda front suspensions... they are using the one from the Accord at the rear.

More importantly, despite using rocker arms to place the spring/shock units roughly horizontal across the top, it looks like they still managed to occupy the space behind the axle line which could be a nice battery pack space with frame tubing.

Do you expect to be able to put any of the battery up front?

 

[brian_]

Brian, thanks for all the kind words . My first YouTube attempt ever. Obviously I have a lot to learn.

Please don't take the YouTube comments personally - almost nothing in YouTube from anyone is worth the viewer's time, and I'm far from the only person who feels that way. Lots of people have posted dozens of videos, and have never produced anything worth the time it takes to watch. In most cases, a couple paragraphs of text and a few still images would be more informative. If it must be video, then just leaving out background music would help.

 

[brian_]

I obtained the frame dimensions from the kit manufacturer. I sourced the Tesla dimensions from GrabCad. It will fit.
...
I am waiting on the battery purchase for now as it will take me some time to assemble the car. I am planning on ~30kW. Batteries can fit up front as well as between seats and behind the seats. Much of the other electrical, contactors, DC-DC converter, Tesla controller, etc. will be in the back.

It sounds like you're well along in planning. I think I understand the general intent and approach, although it sounds like Tesla components were the only option considered; was that because a ready-to-run product is required, and EV West and others promise that with Tesla drive units?

I assume that you meant 30 kWh (not kW). That's not much capacity for a high-powered application, so range (assuming aggressive driving, given the nature of the vehicle) will be short. It is difficult fit in more in a car not designed to accommodate battery volume.

I'm impressed that the kit manufacturer provided frame dimensions. That's helpful. I see that their order options include "electric drive"; I assume that just means that (compared to their Honda and Toyota options) they just omit the fuel tank, cooling system, and shift linkage. Since the others are set up to bolt in suspension parts from the donor, and there is presumably no donor for the electric drive, does it just have plain frame tubes with no mounting points for any suspension?

 

[brian_]

Obviously I will need to modify the frame to meet up with Tesla subrame and I may need to modify the suspension points. I may need to widen the rear fenders depending on what size tires/rims I end up going with.

Also, maybe I wasn't clear. I will be sourcing the entire tesla subframe (control arms in all). I just need to mate it with the frame.

I wondered when you mentioned the Tesla subframe earlier if you were planning on using it, complete with the whole Tesla suspension (like Chris Hazell's drift car project - see Tesla Powered Nissan r32 skyline). That can make sense and avoids several compatibility issues, but it will involve substantial frame modification and will result in a very wide car. Chris discussed the details of the width issue; fortunately, the K1 Attack body is designed to fit over an Accord front end which is a little wider than the Skyline, so the additional fender width won't be as extreme.

Keep in mind that to "just mate it with the frame" is not trivial, since the frame needs to support and locate the subframe at four specific points (relatively low in the vehicle), plus the rear suspension spring and shock struts (relatively high in the vehicle). The subframe will pull down on the frame at the four mounts (with the weight of the subframe and drive unit), while the struts will push up on the frame with the entire weight of the rear of the vehicle.

This is a reminder that the Tesla "skateboard" idea is nonsense: the car is a conventional unibody (the tube frame will take the place of that in this case) with front and rear subframes that support nothing but themselves, and a battery in between which supports nothing but itself.

I suggest taking suspension modification seriously. Pickup points can't just be moved without consequences, and most people in this forum don't seem to realize that. On the other hand, if you use the complete subframe with suspension, I don't know why you would need to modify the Tesla suspension (other than changing to softer springs and shocks for the lighter vehicle); the Honda (or Toyota) suspension likely would require modification.

 

[brian_]

Strut suspension works incredibly well which is why 99% of cars use it

The spring/shock "struts" are not part of the Tesla suspension geometry at all. The spring is just packaged on the shock. When people refer to "strut suspension" as a type, they normally mean McPherson strut designs, in which the strut controls the caster and camber. However,

• while McPherson struts are the most common front suspension design, particularly in front-wheel-drive cars, they are not in 90% of all front suspensions
• McPherson struts are now (in this century) rarely used in rear suspensions (although the MR2-based version of this kit uses them because it gets them from the donor)
• neither front nor rear of any Tesla model uses McPherson strut suspension

 

[brian_]

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.

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.

 

[brian_]

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_]

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_]

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

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).

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_]

Jag IRS sidetrack...

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_]

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.

 

[brian_]

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.

 

[brian_]

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_]

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.

 

[brian_]

battery placement: side tunnels?

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.

 

[brian_]

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.

 

[brian_]

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.

 

[brian_]

Tesla motor is in!!!

Congratulations on a substantial milestone.

Photos?