[robertsdiy]

Been thinking about building an electric car for a number of years. I started building custom electric bikes and mopeds and now ready to take on the electric car. I purchased a Nissan Leaf a few years ago and liked the car but ended up with the car in the dealership more often than at home. The complexity of the Leaf was too much for me to feel comfortable. I recently purchased a non-running Smart Fortwo electric car as a base for a DIY project. My intention is to cannibalize the Smart battery and to purchase an AC motor in the 96-128V range. The Smart electric car has a differential that is 9.91:1 reduction and may not be appropriate for an aftermarket AC motor swap. My question would be is it possible to configure an AC motor to directly drive one of the rear axles?

 

[brian_]

Why wouldn't you use the original Smart motor? Anything that you substitute for less than tens of thousands of dollars will be inferior to the original equipment.

Yes, you can drive a wheel "directly" (via a jointed shaft, but with no reduction gearing) but the resulting performance would be horribly poor.

Are you actually considering just driving one wheel?

 

[robertsdiy]

I had a bad experience with the complexities electrical systems with modern electric cars. I purchased a Smart car knowing the battery was bricked. Previous owner of the Smart car also had a bad experience with the car and dealer.

I would prefer to simplify the electrical design and mechanical design to something that I could maintain. I doubt it possible for me to interface to the original engine and have no problem purchasing and aftermarket motor and building a cradle to accommodate. Just need to sort out the gearing and selecting the right motor to replace the original.

 

[MattsAwesomeStuff]

At this point, I would:

1 - Buy a Gen2 or Gen3 Prius inverter.
2 - Buy a drop in replacement control board from either OpenInverter.org or EVBMW.com
3 - Junk their controller and substitute the Prius.
4 - Replace the battery.
5 - Leave everything else exactly the same or it'll probably never work again as everything branches off into less and less interesting tangents of basic functionality.

 

[brian_]

I would prefer to simplify the electrical design and mechanical design to something that I could maintain. I doubt it possible for me to interface to the original engine and have no problem purchasing and aftermarket motor and building a cradle to accommodate. Just need to sort out the gearing and selecting the right motor to replace the original.

Okay... although there is no complexity or maintenance on the mechanical side. Then if you are using fixed gearing the gearing choice is easy: choose the gearing that makes your motor run as fast as is permissible when the car is at the maximum desired speed. That's about 10:1 for the Smart forTwo ED; if your motor runs half as fast you would want about 5:1, and so on. Unless you buy an expensive motor, the one you buy will not be able to run as fast as the original Smart motor, so you will need a different gearbox... which will either be from another EV or will be more complex than the original gearbox.

If you're looking for similar performance, you'll need to buy the biggest motor that you can afford and can fit, since the reasonably priced and reasonably sized aftermarket motors are not as powerful as the Smart's original 60 kW motor.

 

[robertsdiy]

That is helpful. Most aftermarket engines run 5000 rpm continuous and 10000 max rpm. The Smart ED engine can operate at 15000 so the Smart differential at 10.1 will not work. Onto researching a gearbox or differential for next steps.

 

[brian_]

That is helpful. Most aftermarket engines run 5000 rpm continuous and 10000 max rpm.

If you are referring to aftermarket electric motors... no, 10,000 RPM is not typical of the low-voltage motors. The higher-voltage stuff such as BorgWarner (formerly Remy) HVH motors can run faster, but one of those motors alone would be worth more than this entire project.

The Smart ED engine can operate at 15000 so the Smart differential at 10.1 will not work. Onto researching a gearbox or differential for next steps.

Yes, that makes sense (except that it's 10:1, not "10.1").