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Comment by elihu | Hacker News Reader

I've been working on converting a Mazda RX-8 to electric. At the moment, that mostly amounts to making battery boxes to go in the various empty spaces by tig welding aluminum (which I had no experience with prior to this project).

The general plan is to use about 400 pounds of lithium iron phosphate cells, spread between the spaces under the right and left rear passenger seats where the gas tank used to be and the engine compartment (mostly approximately where the radiator was). I'm using a Netgain Hyper9 AC motor (144 volt version). I haven't decided what I'll do for charging and battery management. I plan to order an adapter from CanEV to interface to the transmission so I'll be able to keep the stickshift.

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I came to this thread wondering if there would be many offline projects. Yours sounds great!

Mine was much simpler. I bought a sewing machine because I thought now would be a good time to learn how to sew and maybe I could make masks for myself and family. I never really understood how these machines work and I have to say, they are pretty amazing (even a low tech one like I got - a Singer 4423).

I also gained a ton of respect for people who are good at sewing. It's much more difficult than I thought it would be.

You will dig this https://youtu.be/4Jbk1uU_Jkk. Tim is an all time hero

Just watched the whole episode - that was fascinating - I love the human sewing machine

Whoa! That sounds like an incredibly fun project. I am not questioning your plan, as you are almost certainly more knowledgable than myself, but is there any technical reason to actually keep the manual transmission? I thought one of the biggest advantages of electric drive vehicles was a relatively linear power/torque curve.

Most EV conversions end up keeping the manual gear box because it's simply easier to build an adapter plate for the motor transmission interface than it is to build out a whole new gearbox replacement.

From what I've seen it's fine, you can choose which gear to shift to and leave it there. Cold start from 5th gear. Can even be fun to play with the gear ratios, apparently. But it is another point of failure.

One of the things holding me off from attempting an EV conversion on my old Saab 900 sitting in my shop is that the gear box in it is notoriously brittle and would break even with the torque from the (turbo) gas engine that it shipped with.

The real problem with that is weight. Because SAAB is -- well -- SAAB. Great company, great car btw.

Thanks, flat nose 84 SPG. But brake lines corroded out, so I need to run new brake lines. Which is a project I've been putting off for almost 3 years now :-)

A transmission allows you to get away with using a less-powerful motor. The motor I'm using is about 120 horsepower and has a max RPM of about 8000.

I also like having a stickshift.

Is there a website or somewhere we can track the progress of this? It would be awesome to see more details.

I haven't been blogging about it. I probably should, but I tend not to get around to writing things down until I get things into working condition.

there's a famous rx8 converted with a acura(?) motor. I only recall it was yellow and had a Pikachu stiker :) but it was well documented

Are you following the open inverter forums?

[1] https://openinverter.org/forum/viewtopic.php?f=11&t=151

No, but it's good to see another RX-8 build thread. (I've come across a few already, but everyone seems to approach their conversion a little differently.)

Really cool! This reminds of Andy Weir's The Martian (I highly recommend the book - there was a movie as well - especially the chapters that touch on some programming!) and the lead characters clever efforts to use what (bio)tech he has in order to survive on Mars.

I've read the Martian. It's kind of fun to think that electric vehicles could at least theoretically operate on Mars. (The batteries would have trouble at low temperatures and I definitely have the wrong tires. The motor is sealed, but not well enough for Mars, and sand would eventually get into and destroy a lot of the moving parts.)

It's also fun to modify machines to be used in ways they were never intended by the original designers. Fortunately a lot of the DIY electric car components are pretty flexible in terms of how you use them. For instance, you can get your motor controller, your battery management system, and your charger from different companies and reasonably expect them to work together because they each have a well-defined job and that's all they do.

I re-read Artemis now that I know something about welding, and was kind of disappointed it was all oxygen-acetylene, which I know next to nothing about rather than TIG, which is usually the recommended way to weld aluminum. (I'm not sure if you'd even need a shield gas like argon in a vacuum environment?) Maybe there is a good technical reason for that, but it wasn't explained in the book (nor does it really matter to the story except to the 3% of readers who care about welding trivia).

No, you wouldn't need a shield gas, and if I remember right Jazz is forced to borrow a tank of argon from her dad so as to not tip him off that she'd be welding outside, even though she wouldn't be using it.

Ohh.... One of these things that on Europe we aren't allowed to do by regulations.

Is a thing that I would like to do, on the future, with my 90's Nissan Micra.

Neat! I'll be extra impressed if you make it a rotary electric.

Well, any typical electric motor could trivially be considered a "rotary".

I did save one of the rotors from the engine. Maybe I can think of some whimsical use for it, like cut a thin slice off it and weld it to something as a sort of decoration.

Would love to follow your progress - are you sharing it somewhere?

I'm not, sadly.

Come on over to The Car Lounge please!! We’re an eclectic group of enthusiasts, don’t take anything too seriously, and would love to see something like this.

https://forums.vwvortex.com/forumdisplay.php?1#/forums/1?pag...

Very cool! What do you expect the range to be with that setup?

Maybe a hundred miles if I'm lucky. Lithium iron phosphate isn't as good as, say, modern Tesla batteries in terms of energy density, but they're a good choice for conversions because they're much less likely to catch on fire if something goes wrong.

I could get better range with more batteries, but I also didn't want to increase the total weight of the vehicle by more than a few hundred pounds, just to stay within design tolerances.

(The RX-8 is about 3,000 pounds normally, which is pretty light for that sort of car. A Miata would probably be an even better choice, as it's around 2,000 pounds. It's hard to find newer Miatas for a reasonable price, though. RX-8's can be had pretty cheap because the rotary engine is easy to destroy if you don't maintain it properly and even in the best case usually needs to be rebuilt every 100,000 miles or so to replace worn apex seals. So, there are a lot of used RX-8's on the market that need engine work.)

What resources did you use to learn tig welding?

Youtube mostly. I also discovered that one of the people at a local regular tech meetup teaches welding at a community college and he critiqued my welds and gave me some useful advice.

I've been using an AHP AlphaTIG 201xd, which seems to be a good machine for the price. It seems that the hard part initially is mostly just figuring out what settings to use to get a good weld. Beyond that, it's about getting used to how aluminum behaves, and figuring out how to position yourself and your work piece so you can keep your hands steady.

My welds aren't anything I would mistake for art, but they get the job done.

are there any regulatory hurdles to overcome doing this yourself, or if it passes a test (like in Ireland, we have the NCT) is it ok?

In many US states, there are no vehicle inspections, so as long as it has the basics like turn signals, wipers, brake lights, headlights, etc. it can be driven on the street and nobody will care.

Yea, I did not realize the huge difference moving from the east coast living in a few cities there going through the detailed inspection. I moved to the south, a different city, brought in my car, they told me to turn on my signals and hazards, asked for some money, and gave me a sticker. Very different.

I don't think there should be any regulatory problems. I'm in Oregon. I think I just have to tell them it doesn't have an engine anymore to be exempt from DEQ testing.

what are you going with for the motor controller?

The motor comes with a controller. It's made by SME, and is surprising small and light.

Who makes the motor, then? Where did you get the electronics side of it?

I want to design an electric formula car and am having some trouble deciding what parts to go with.

I used a Netgain Hyper9, which is a pretty decent AC motor. There are smaller, more powerful AC motors out there, but they can get pretty expensive. AC is nice for the regenerative braking. (When applied to electric cars, AC generally means 3-phase AC, synchronized with the rotation of the motor.)

On the other hand, series wound DC motors are cheap and popular for drag racing applications. Check out the White Zombie if you want an extreme example. The guy that built it lives nearby and he's been giving me advice on my (very different) conversion.

Man this is super cool!

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