Bob's EV SLC Build Log

Bob, thanks to your ambitious undertaking, i've started some research on my own about tesla motor usage, battery management etc.
Couple of questions to understand your decision making: You were talking earlier about changing the inverter controller. I'm reading there are not that many different options around (still) as per website "Which Tesla LDU should I use". You were contemplating the use of the EVBMW opensource controller, correct? Are you still going down that path, and if not: what route are you taking?
 
Right now, I have decided to give the open inverter hardware a try. For me, I already have all the inverters off the drives, and swapping boards is easy. I linked up with a guy who has a lot of experience with them who is local. He is getting about 15% more HP out of his drives with it.

That said, the rumor is the Aem is going to get their Vcu to work with tesla inverters. If they do I will be going with them. It has all the add ons and controls I need. They have a unit that can control 4 motors, and I am back to planning to have 4 motors now. I figured a way to get 2 small drive units up front. Going to have a crazy transmission, but should work. Best part is I don't have to cut the chassis to do it, just bolting a subframe up front, well lots of bolts.
 
That sounds awesome. The more I learn about the EV world, the more fascinating it becomes to me. I'm so happy to see a 'hotrod' type of community is starting to form around this, just a whole diffent type.
Also, i'm surprised to learn it does sound look doable for an ICE guy such as myself. As long as you are interested to dive in, learn, and stand on the shoulders of giants that do the actual reverse engineering etc.
In Europe (my side), I think I'm going to look into Model 3 battery/motors, as they are much more affordable and available. We never had many model S/X's on the road. Also I'm very not-sure about the registration/regulation around road registering EV vehicles in my corner of the world yet.

Please keep us updated on your progress, really cool to see your work here, and inspiring as you can tell.
 
So batteries really are the one area where the current automotive offerings are not really tailored to performance/racing. I would think hard about using the model 3's. They re going to be hard to fit...

Batteries are really tailored to the application. Most automotive batteries are really optimized for range over powder. For performance/racing it really comes down to peak and continuous amps the pack can put out. Tesla, which really have the highest amp out of any commercial pack, save the LG chem from the pacifica, (which are almost impossible to find now) have to make a huge battery (100kw) to get the ~1200 amps they need to power a small and large drive unit at max power, to get to the "plaid" 3 motor configuration ~2100 amps, they had to double the pack size to almost 200 kw, but it really is two 100 kw packs in parallel. The problem is the cells tesla uses to make the packs are capped at abut 6.5 C (1500 amps) discharge for 3 seconds, and 4 C (1000 amp) for 10s sec, and 1C (233 amps) continuous. The tesla pack can just make the amps needed, but it is also heavy (625 kg) to be able to achieve these amps.

To race with a single tesla drive you are going to be running at ~500-700 amp for ~20-30 min. Using tesla batteries, you are putting the pack and the drive into over heatting scenarios, and you have to lug around 625 kg of batteries, of which you are only going to use maybe a 1/3 of the Kw during a race. Not to mention it is very hard to fit a full pack into most chassis, as they are really designed to be in the "skateboard" layout.

For me, I need 3300-3500 amps peak at 360 V. No automotive OEM battery is going to get me there, unless I want to use like 3 full tesla packs or 24 LG chems. No way to fit it all safely, and I don't want to add 1500 kg of weight to the car. My solution is to use high discharge pouch cells 30C continuous/60 amp peak, and immersion cool them. You get the high peak amps with a small ~50 kWh pack. I am going to have to use a very aggressive BMS strategy, every pouch with have a monitor, but it can be done. I think a custom pack is really the only way to go if you want to keep the weight of the car down.

Bob
 
I hear what you're saying there. And I see the racing scene for EV's is an extremely difficult environment, and very different than the 'high performance' street car such as the 'performance' range of the Tesla's. I admire your highly ambitious targets, and you're going all the way to get that to work.

To be honest, I'm not necesarily looking to build a race EV, but more interested in a decent performance EV-swap or kitcar build. I want to learn and get experience in working on EV powertrains and control, and would like to do that on one that Id get road legal etc.

Love to see your progress here.
 
So big update. The rear mounts for the large drive units are at the welders. Was supposed to have them back this week, but he's backed up. Really wanted to show the rear motors mounted in the frame, but that will have to wait.

I have been working on the mounts for the two small drive units, and the pushrod suspension for the front end. My work flow is about the same as the rear mounts, draw in sketchup, laser cut in 1/4 mdf, and then final in 0.25" 6061. Slot and tab for assembly. I picked up a 150 watt laser so I can cut my own mdf, it has been a real nice addition. Turns out there are two kinds of MDF out there, light and dark colored. Get the light, I cut this first mock up out of the dark and it chars way more than the light. I think it is something to do with the iron content. Below are the pictures of where I am going for the front end. It is basically a bolt on subframe that slides over the front tub. It is exactly the same length as the existing radiator mount. Originally I was going to triangulate the center frame to the sides with 2x2 tube, but I think I am going to use I beams like I did in the center frame. There are removable I beam pieces that go horizontally from the side frame to the center, you can see them in the sketchup plan. They have to be removable for the drives to slide in. You can see the mounts from them in the MDF. The frame will hold the two small tesla drives opposed to each other. Power from each drive will be transmitted to front drive shafts via short 1:1 enclosed chain drive gear boxes. I am going to use the sprockets and chain from a Nissan GTR differential.

The suspension system is pretty unique. I took inspiration from the new ford GT cars that use 2 springs (torsion bar and coil spring) and a lock out mechanism so that you can run two truly different spring rates and ride heights on the car, one for street and one for track. In my setup I am using a penske 8760 for the damper, a 7/8 x 14 inch torsion bar from a sprint car for one spring, it is inside the bell crank axle, and a spring keeper from a off road truck to hold the original 8 x 2.5" coil spring. The keeper looks like it has a shock in there, but it is just a guide. Axle is held with pillow blocks that have not arrived yet, but I made MDF dummies to just get everything on the car. The pictures show the suspension in full extension. As you can see there is alot of room on the keeper for the hydraulic lift puck. I never liked how the spring is almost fully compressed on the stock system when the pucks are extended. I am going to do a custom controller for the ramliftpro, so that I can use ride height sensors, and really do custom presets. The setup gives the ability to easily swap out the torsion bar or the coil springs, without having to jack the car up, and I can run up to a 12 inch spring in the keeper. A wide variety of spring rates are available with this setup. The lockout mechanism is not shown yet, but is a short hydraulic cylinder that lifts to push the front bell crank arm, when locked out the coil spring will not be able to compress and the torsion bar rotates inside the bell crank axle. The push rod to the lower front A arm comes off at a 6.5 degree angle, sort of like the rear pushrods, and give a nice straight shot for front CV joints. Suspension movement through the bell cranks is all 1:1 ratio. You can also see a mount point on the damper bell crank for a sway bar. I may clock the reservoirs on the dampers, but everything fits and works as shown. The only issue is the bell cranks are going to come though the stock front clam, if I keep the stock from end, it will have to have bump outs like some LMP cars have, or I might do a custom from end. There is some really interesting work being done with large format 3d printers.

If the front end comes together and the suspension works as designed, I will do the same dual rate setup on the rear. I designed mount points for it into the rear motor subframe.

The spyder is going to have to be trimmed in the front to fit on the set up. I may end up mounting the spyder a little high on the body to get another inch of clearance on tires.

I just ordered a upgraded steering rack and electric steering from Hill at Agile automotive. Shout out to Scott for the connection. Hill is incredibly knowledgeable about SLC's. I spoke to him for a good 2 hours in the early design phase of the front end. Everyone should buy a steering rack and electric power assist from him, the units he has are skookum. I am going with the exact same setup Scott put together. Probably going to wait for that to come in before I cut everything out of aluminium. I am going with the x-tracker hubs front and rear. My uprights are the "gen 1" flat billet pieces, so I can just drill new mounting holes for the adapters. I am really thinking about getting a set of used z06 carbon ceramic brakes and rotors, with Z06 rims. I have a line on a lightly used full set for a killer price. Has anyone done this yet? I would like to talk to them prior to pulling the trigger.

There will be two small radiators on either side of the frame, one for each motor, and a small condensers in front of one radiator for a ev hvac unit, it will be used just for the AC. Battery and rear drive unit cooling will happen in the rear. As it stands right now there will not be cooling lines running front to back on the car. Each motor cooling system is self contained unit.

Anyway, that's it for now. Open to all suggestions and comments. I'm finishing up a really big work project and on the road, so nothing is going to happen for a month or so. I may start drawing up the battery. We will see.

Bob
 

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hey guys, update soon. I have been down in kentucky finishing off a very large project for work the last 2 months. It gets commissioned tomorrow, and I will be back in MA wrenching on the car. The rear sub frame is at the welders, just waiting for me to pick it up. Front one goes to get welded next.


bob
 
Update:

So the rear subframe is back from the welder. Fitted to car and to the drives. Have a little more weld grinding to take care of to get everything to clear, but we are home on this part. Basically the angled vertical pieces you see attach with three bolts, once the drive is in the lower frame. It is a very very tight fit. The cross piece of the original frame, that sits under the transmission can now come out, and get moved up to the center of the transmission frame area. Front part of the subframe will get welded in too at that time. Should really stiffen up the rear frame i think, not that it needed it. The rear subframe slide onto stainless steel adaptors that mount to the rear frame uprights. Fit is perfect, slides right together. For as complex as a a job it was, everything came out really well. Took 90 days longer than i wanted because my welder was backed up, and them I was out of town, but here we go.

Next design piece is the battery boxes, which i can now do with the subframes in. Also have to just finish messing with the front end and send it out for laser cutting. Im not 100% happy with it, but I'm nit sure I ever will be at this point.

More pics after this weekend when I mount the drives.

Bob
 

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Thanks, i am sort of upset that I completely over estimated the amount of time I would have to work on it. The delays with welding and work really put a dent in my momentum. But, it not a sprint, it a marathon.

On the upside, battery technology has moved on in the last year, and I probably shaved 200 pounds off the battery by waiting a year. If I wait a bit longer semi-solid sodium cells will be readily available.

Bob
 
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