1993 Rx7 + Tesla Motor

[ccsdo5]

Definitely a cool build, I'm all for Rx7 content and EV stuff. Would eventually love to do an EV conversion in something.

[rjmcdermott81]

Small progress. I have the motor mocked up at the right level and it allowed me to figure out how much more to cut out. I have one small bit I'm going to cut tomorrow and then I'll move on to fortifying the subframe so I can take it out of the jig.

I mocked it up with the tesla axles - these things are beefy. I didn't insert them all the way but I am concerned that it's sitting pretty far back. The only way to really tell will be to get the suspension on here and look at it.

[rjmcdermott81]

Progress this weekend. I now have the two top lateral support bars completely welded in. I still need to clean up the welds more after I take it out of the jig but they are pretty much done.


My son always seems to show up at the end to check my work....

Next I'm planning to add some bar stock on the bottom that will bolt in. I'm sort of just using whatever I have around the house....since we're on lockdown. You can see it mocked up in the pick below.

[NORBY]

Seriously cool project, i'm interested to watch someone go through this process, I'm thinking of doing similar in an old 911

[rjmcdermott81]

Alright - now I feel like this thing will have the structural integrity it needs to pull it out of the jig. This is going to hurt ground clearance so I may come up with a better design when I get it all together. Last thing I'm going to work on before I do that is installing the front motor mount.

[rjmcdermott81]

Motor mount is tacked in place.

[Metallated]

Great thread so far!
Are you planning to box in that mount any more? I'd be a little worried about it's strength, especially side to side.

[rjmcdermott81]

Great thread so far!
Are you planning to box in that mount any more? I'd be a little worried about it's strength, especially side to side.

Yes definitely. I want to test fit it in the car before locking it in place. I was planning to add a plate on both sides and possibly adding gussets on each side. I’m also open to suggestions since this is my first time doing this.

[mikey.antonakakis]

Get those welds hotter! (a little hard to tell without close-up pics, but looks like you're not getting good penetration).
Awesome project!

[rjmcdermott81]

Get those welds hotter! (a little hard to tell without close-up pics, but looks like you're not getting good penetration).
Awesome project!

Will do. I need to turn it up for this thicker stuff.

[rjmcdermott81]

Progress! and the next hurdle - the axles.

Here is the subframe out of the jig


Test fitting the motor/suspension/axles for clearance - all good here




At this point I'm going to start finishing up the subframe so I can mount it.

Now, on the axles. I don't know squat about axles so looking for advice. This is the first time I've ever taken CV joints apart...pretty easy. The RX-7 axles are actually the right length, but the knuckle that goes into the inboard flange is obviously different. I took the knuckle off the tesla axle but it is a different spline count so no-go there.

Here is the inboard Tesla knuckle - 35 splines


The outboard splines on the Rx7 - 26 splines


Length - 20.5 inches


From some quick research it seems like I have several options. Does anyone have experience with any of these?

1. Find an axle from another car that is 20.5 in, 35 spline inner, 26 spline outer. I'm guessing this is a longshot because of the huge difference in splines and it seems to be relatively long. I looked through this interpart catalog but is anyone familiar with another?
2. Have the Tesla axle machined down in length and splines to fit the Rx7 outer hub. The Tesla axles are super beefy and much longer. I've seen a video of this being done but I'm just not sure how much it would cost. If it's <$500 this might be the best option because they are so beefy.
3. Have a custom axle made. Maybe expensive.
4. Have someone cut, weld, and sleeve the two axles together. I've read this isn't the most reliable option plus they are different diameters so it might not even be an option.
5. Have someone somehow marry the Rx7 inboard flange with the Tesla inboard flange.

I'm going to hunt for a stock axle but in the meantime I may run it by a machine shop to find out the pricing for option 2.

[Metallated]

Definitely far from an expert on this, but when I was part of an electric vehicle team at college we had a similar axle problem.
Even though our axles were also different diameters it was easy to have a shop sleeve and weld them. They were plenty strong enough for our needs.
I think this would be cheaper than having the Tesla axles machined, I can't see that being less that $1000, at least in my area...

[varg]

It's not an uncommon problem to run into, needing shorter or longer CV axles for a project like this. Plenty of shops and companies offer re-splining and custom axles. If the Tesla shaft is not narrower than the splined section at the point it has to be cut down to to be the appropriate length it is definitely the better and easier option to have someone with the correct machine hob some new splines in the correct involute profile. You do want that feature of it being stronger than the FD axle since you're going to be dealing with more torque and the potential for very abrupt loading than an FD's engine is ever likely to produce. If you're not going to be drag racing the car on sticky tires it's possible the sleeve or chamfer and weld method may hold up just fine, but it's probably not something you want to try to weld yourself, and it will significantly weaken the axle in most cases because it will locally ruin the heat treatment. You could always use this option to just get it on the road while you sort custom axles or re-machining out. I think it's very unlikely you'll find something existing that will fit, and in any case there is much more to a splined shaft than the number of splines. If you find one that is the right spline count but a different profile or spline type it could cause wear issues. If the Tesla axle is narrower at the new end point than at the existing spline a new custom shaft will likely be your only option to do it right.

[rjmcdermott81]

Metallated and varg - thanks for the insight. I sent some emails out and have some responses back. The DriveShaft Shop can custom make the axle bars based on length and spline count for $999. Another option is to have them fabricate Porsche 930 inner CVs onto the existing Tesla inner cups and the they fab up billet outter cups which starts at $1,799. That sounds much more complicated and expensive.

[NORBY]

I'd be confirming what torque rating those custom drive shafts are rated to as well. Electric motors obviously have crazy torque numbers from standstill which most drive shafts never see.

This is honestly one of the coolest builds I have ever seen, keep it up!