Electric Supercar

snowdog · 2019-06-07

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

B

brian_

· #48 · Aug 1, 2019

snowdog said:
Ha, Ha, I should have been more clear. I mean I now have the tesla motor. It is not yet mounted to the frame.

LOL oh, well, even that's progress.

snowdog said:
Here is a picture

Have you had a chance to confirm that the dimensions match the model you are using?
That's the drive unit and subframe, but you did get the suspension as well, right? My understanding is that the plan is to use the Tesla suspension.

Reply

Save

Like

B

brian_

· #51 · Aug 4, 2019

It is a little strange to see the Honda struts dangling back there, since the Telsa struts are different (in the lower mount, especially, as shown at the yellow arrow in the photo by Edmunds), and will need to mount in a different location. I assume that Tesla struts are among the various suspension components which are on the way, or that a compatible coil-over shock will be used instead.

Reply

Save

Like

B

brian_

· #53 · Aug 4, 2019

snowdog said:
The other struts were thrown on to help identify the axle position.

Thanks - that makes sense, given that the Honda struts are vertical and approximately on the axle line.

snowdog said:
I am leaning towards an alternate solution thinking that the tesla struts are meant to support a 5,000 lb car and are air struts. Still evaluating, suggestions are welcome.

The air springs could be handy because of the weight mis-match: you could just run lower air pressure. Of course coil-over shocks would provide an nearly infinite choice of springs, with some choice in length.

Reply

Save

Like

B

brian_

· #58 · Sep 9, 2019

When the still image shows a battery box, I'll assume that the latest video covers battery box design and fabrication. Will that work?

Reply

Save

Like

B

brian_

· #65 · Sep 23, 2019

snowdog said:
Hey all, Tesla rear suspension is now in place.

For those wanting more details...
https://youtu.be/pVZ_8NLtRzY

I only watched the video at 2X speed, skipping forward in jumps, with no audio... but doing all that with the Honda strut hanging in the way just seems awkward, since all the strut is doing is indicating rough axle position. I would have just put a piece of tape on the lower frame tube for that, but whatever works for you.

That's a lot of the frame tubing that had to come out, and the spring-shock strut mounts are still superfluous (since they're not placed properly for the Tesla units). It's getting close to just cutting the kit frame off at the firewall.

Reply

Save

Like

B

brian_

· #68 · Sep 27, 2019

Roadstercycle said:
Also you will probably find that the chamber will be way off and the toe in too.

That's camber and toe. I think it's reasonable to assume that any suspension which has been disassembled and reassembled would need a routine alignment... including caster if that's adjustable.

Reply

Save

Like

B

brian_

· #73 · Sep 29, 2019

snowdog said:
I have made a first pass at a frame design to accommodate the Tesla subframe. Suggestions and feedback are welcome.

https://youtu.be/ukRxEITgqyo

Maybe some day I'll take the time to watch and listen through all of that, but for now I'll just note that it seems very strange to build a big and complex frame under the subframe. Both the Tesla and the kit are designed to have the structure over the drive unit and subframe, and it's not apparent why you would not just do that; after all, all of the vertical load is taken by the struts to the two high strut perches, so that's where your structure is, anyway.

As I noted in earlier discussions, the position of the stock Model S struts accommodates large tires, so messing up the spring/shock geometry with some angled units just to use the strut mounting points on what is left of the kit frame doesn't make sense to me, either.

Reply

Save

Like

B

brian_

· #76 · Sep 30, 2019

remy_martian said:
I would just have the kit people design and fab up the framework for mounting the Tesla pieces and chop and weld what's there per their instructions.

It's a nice build so far, so why mess it up with a kludge/"bodge"? Shouldn't cost anything - it's in their best interest to provide a kit option to everyone with support for Tesla pieces....with a properly welded up frame instead of the cut and weld you'll have to do as guinea pig.

That would be an excellent plan if ordering a kit... but this one has already been purchased. Would they take it back (in the Czech Republic, where it's built) to modify it?

I don't know of any kit car company offering a kit set up to install a powertrain from an EV donor. The time has probably arrived for that. B-racing supports multiple unrelated powertrain donors (rather than being dedicated to one donor as most kits are), so perhaps they're the ones to do it, if it's not already out there.

Reply

Save

Like

B

brian_

· #80 · Oct 17, 2019

snowdog said:
The system can monitor up to 96 cells (with satellite systems). Can this BMS monitor 2, 96 cell packs in parallel?
...
This would mean I have 192 cells to monitor, however the dilithium BMS system it can only monitor 24 cells each and only up to 96 with satellite systems. Or is there a different way to monitor parallel packs?

How would I wire? Or would a different BMS be a better option?

With 192 cell voltages to monitor, you need a 192-point BMS. The fact that you will have two string of modules with the strings in parallel doesn't change that.

You could connect every cell level of every module to the corresponding module in the other string, so that you would effectively have 96 groups in series of 2 cells (or 2 times whatever is paralleled in a module), instead of strings each with 96 cells in series... but the module's BMS wiring connections are not suitable for parallelling cells.

I see four options:

a different BMS which can handle 192 points
two 96-point BMS, each independently handling a string
rewire modules internally to 8S instead of 16S (difficult, if even possible)
use different modules

There are reasons that production EVs generally do not use parallel strings of modules.

See less See more

Reply

Save

Like

B

brian_

· #84 · Oct 27, 2019

snowdog said:
Finishing up the steering column and starting to design the battery boxes.

https://youtu.be/wvJ_ACsmO-8

While it is true that any connected set of cells forms a battery, it is typical in EV discussions to refer to a cell group which is only part of the whole system and forms a unit with housing and internal wiring - particularly one which is interchangeable with other groups - as a "module", not a battery. A group of modules assembled in an enclosure with a common electrical connection is a "pack"; on that basis you have a battery consisting of a front pack and a rear pack, each pack consisting of several modules.

When the structure was first shown and battery module mounting was discussed, my comment was that the design didn't allow useful space for modules in the front, largely because of the diagonal bracing (which in turn is there due to the unnecessary but aesthetically desired inboard suspension position). I see that the solution is to put the modules way out front; while making the modules part of the crush structure is not ideal, my first thought was that is undesirable from a mass distribution viewpoint. It is, on the other hand, part of the fine DIY conversion tradition of stuffing bits of battery way out in the nose to fit it all in. At least they're not filled with lead.

The rest of the modules stack in what is normally engine space, which is the logical location (and the best place for the mass, front to rear)... just like an original Tesla Roadster. The rearward (of the axle) motor mounting enables this, again as in the Roadster. The only unfortunate thing is that they need to be stacked so high to fit in, so the centre of mass of this performance car will be higher than a sedan of the same size would be with an underfloor battery... I don't know of any good way around that, because no one wants to perch the occupants up on top of a layer of battery modules in this style of car.

At first it sounded like these modules were going to be mounted without any enclosure, and I was glad to see that they're going in boxes - some DIY builders seem to believe that no enclosure at all is required. The boxes are to be some sort of plastic sheet; I find it interesting that every EV manufacturer decides that the cost and weight of a metal enclosure is justified, but most DIY builders don't.

If the cables go through the box without interruption, the fitting would be a "grommet" or "feed-through bushing"; if a connector is installed in the box wall, it's a bulkhead connector.

See less See more

Reply

Save

Like

Reactions: 1

B

brian_

· #92 · Oct 27, 2019

dtbaker said:
probably partially left over from lead-acid days.... polypropylene lasts way better when exposed to acid (or water from underneath) and has the added benefit of not acting as a giant ground path for any frayed insulation or loose ends that touch the box.

I don't think that the construction of battery enclosures on modern production EVs has anything to do with lead-acid batteries or traditional practices. Also, the box for the lead-acid starter/accessory battery in essentially any modern car is moulded plastic.

There are not frayed or loose bits in a production EV battery box. Terminals have insulating covers.

Reply

Save

Like

B

brian_

· #93 · Oct 27, 2019

snowdog said:
My initial thought was to secure the battery packs to the vehicle and then to provide some insulation as you mentioned.

What heat transfer are you trying to reduce with insulation? Your modules are designed to be mounted on a thermal management plate, with circulating liquid which can cool them when they run hot due to use, and can heat them to prepare them for use in cold weather. Without the active thermal management systems, heat transfer through the enclosure is all they have to get rid of excess heat, or to warm up if stored in a warm place. Most of the time, the outside temperature is probably more desirable than the temperature they would reach on their own in an insulated box.

The front of the front pack is going to be blasted by warm air from the radiator, so that might be a place for insulation.

Reply

Save

Like

B

brian_

· #96 · Oct 28, 2019

dtbaker said:
you asked why DIY builds usually don't use metal boxes.... I gave you my opinion. production builds are different than DIY tons of ways OBVIOUSLY.

Fair enough, but the question remains of why production EVs seem to need metal, and DIY builders think they don't. Also, the same straightforward methods used in production EVs to prevent accidental short circuits are suitable for DIY construction. Sure, a DIY builder probably won't injection-mould polymer terminal covers, but insulating covers are still practical and used.

Reply

Save

Like

B

brian_

· #106 · Dec 10, 2019

joekitch said:
i wonder, does this suspension geometry criticism extend to the model 3? or is it specific to the model S?

These concerns have been addressed in previous posts in this thread, including #21 and #24. Other than the height of the struts when used in applications with limited height available (not a concern in this case, as mentioned in post #28 and illustrated in #30), I don't see any valid concerns.

Whatever one thinks of the Model S/X rear suspension, nothing other than the height of the spring/shock struts applies to the Model 3 rear suspension, which is an unrelated design. The Model 3 is a five-link of the type popularized by the Mercedes W201 series, and currently used in various other cars as well, such as the Mazda Miata/MX-5, previous generation Camaro, and Cadillac ATS and CT5. The suspension links of the Model 3 are visible in the overhead ghost views of the car published by Tesla. Published reviews of the Model 3's handling are generally favourable, as I would expect from the suspension design, low centre of mass height, and good front-to-rear mass distribution.

Reply

Save

Like

B

brian_

· #117 · Dec 30, 2019

Re: cell monitor wiring

kennybobby said:
You may already realize this but i'll point it out for the next guy. When you have the modules tied together with the large lug jumpers and the BMS wires plugged in, then there can be a large voltage between the ends of the BMS cell monitor wires.

In the wiring video it looked like those monitor wires were just cut off flush on the loose ends. If the tiny exposed ends happen to accidentally touch chassis metal and short together it might cause a fire from melted insulation and wires.

Good catch!

kennybobby said:
Be aware that they are hot when it comes time to cut, strip and crimp the loose ends.

... or unplug the BMS harnesses from the modules before working on the the other ends, or even better don't plug the harnesses into the modules until they are properly terminated on both ends.

Reply

Save

Like

B

brian_

· #123 · Jan 5, 2020 (Edited)

I agree that the diagonal frame tubes all seem to be in the wrong places; it would have made more sense to me to cut off the original tubing further forward, and rebuild with fewer diagonals running to where they really need to be. On the other hand, it doesn't need to be optimal, it just needs to work.

MattsAwesomeStuff said:
... the ones that look like the crossed legs of a 4 year old who has to pee... is that going to transfer the load properly? Or just untwist?
...
What about the little brace thing between the two crossed legs. Why is it there? What load is it helping to support?

If I understand what Matt is saying, this is about how the frame tubes meet the plates at each of the four subframe mounts.

I think that I understand what happened here: the tubes were run to a flat oval plate at each mount, with the mounting bolt in the middle. With no way to make a tube hit the middle of the mount without blocking access to the bolt, the solution chosen was to land on two separate points around the bolt. That leaves the crossed legs, and a tube as a gusset to keep everything from twisting more or untwisting, or perhaps to keep the tubes from deflecting different amounts and bending the plate.

The conventional solution to this would be to put a short large-diameter vertical tube around the bolt (centred on the bolt hole), then fishmouth the tubing to meet the side of that vertical tube, then probably fit gusset plates between the frame tubes. This is a mediocre example (the first I could find); you have to imagine the tube angled upward (and properly fitted) for the subframe mount in this car:

This example is part of the brace shown (about 2/3rds of the way down) on this page: Automotive Welding: Tube Steel Projects Step-by-Step, in case anyone wants to see it in context. I'm not recommending this guide, just using it to illustrate this joint design.

See less See more

Reply

Save

Like

B

brian_

· #130 · Jan 15, 2020

snowdog said:
I will go through a couple of my thoughts, then I would like to explore more of the concerns...

The PDF document attached to this post describes the approach nicely. For the subframe mounting points, everything seems to have followed from choosing an oval plate with a tube landing on each side of the subframe mounting bolt, and a set orientation of those plates. The odd tubing directions result from that; it would have made more sense to start with a plate big enough to accomodate the tubing on any side, place the tubing to make sense structurally, remove the extra plate area, and finally gusset appropriately. But again, if the stresses on those oval plates don't excessively flex them, it will all work.

I had suggested - perhaps for future projects - a fabrication technique:

brian_ said:
The conventional solution to this would be to put a short large-diameter vertical tube around the bolt (centred on the bolt hole), then fishmouth the tubing to meet the side of that vertical tube, then probably fit gusset plates between the frame tubes.

In reading an unrelated discussion, I ran across a video in Instagram which shows this technique. It happens to be another project using a Tesla Model S drive unit, and apparently the suspension and subframe, but not the complete stock subframe (probably because it is mixing a large rear drive unit with front suspension).

See less See more

Reply

Save

Like

B

brian_

· #133 · Jan 19, 2020

I never understood why the modules installed earlier were mounted with rails in the slots on the module sides, since that's not how they are mounted in the production vehicle (Chrysler Pacifica Hybrid). These behind-the-seat stacks are now using a similar method to the Pacifica, clamping them down with frames... but with much heavier welded angle instead of the stamped brackets of the production car, and with threaded rods instead of brackets which extend down to the mounting plate.

Although there were various references to battery "boxes", these are brackets - I assume that enclosing boxes are still to be built.

So, two questions...

What is the total battery configuration up to? If I recall correctly (it's way too slow to re-watch videos) there were three in a horizontal row in the front, plus one on top of them, there are four here (in two stacks of two), and there are some (2? 3? 4?) on end in the box to the rear of these latest stacks. That would be 10 to 12, presumably to be used in parallel pairs or strings for a suitable pack voltage.

What normally goes in this space behind the seats in this kit car? The fuel tank, or storage, or nothing? The location works well for battery from a mass distribution perspective.

See less See more

Reply

Save

Like

B

brian_

· #135 · Jan 19, 2020

snowdog said:
12 Battery modules in total. There are 4 up front, 4 in the middle (2 behind each seat), and 4 in the back (just in front of the motor). I will need to put 2 sets of 6 in series and then join the two sets in parallel.

Thanks

So, presumably front pack plus left or right behind-seat pack in one string, and rear pack plus the other behind-seat pack in the other string.

snowdog said:
I had to ask the kit company what this space was used for. It is simply storage.

That makes sense, assuming that there is no front or rear trunk. Do your battery modules limit how far the seats can go back? Will you have a trunk over the drive unit?

Reply

Save

Like

B

brian_

· #139 · Jan 26, 2020

MattsAwesomeStuff said:
That "manual". Wow. It was generous of you to stay so positive and upbeat, but, jeez. What a joke. (First 6 minutes of video).

That's utterly unprofessional and unacceptable....

It's certainly unprofessional. Anyone wanting to buy a kit car may need to accept this, as good detailed instructions are probably the exception.

To understand how this situation might come to be, have a look at the Wikipedia page for the K-1 Attack.

As for the lack of assembly specifications... I doubt that anyone associated with manufacturing this kit (or many other kits) has any idea what a suitable bolt torque might be; they don't even know what size the bolt should be, as they just put something in that looked reasonable to them.

Reply

Save

Like

Top Contributors this Month