# Smart Fortwo Electric Drive as Mini/MGB donor?



## brian_ (Feb 7, 2017)

My guess is that there are two reasons that the Smart ED is not a popular donor of EV components for conversions:

*Low power and low battery capacity*
Compared to other common modern mass-production EVs (which means primarily Nissan Leaf and Tesla Model S) the Smart is underpowered. Almost every auto manufacturer has a token electric car (usually a variant of a conventional compact hatchback, with the motor in the original engine location and battery under the rear floor), and the Smart is one of those; almost all have more power. This makes sense, because the Smart ForTwo is a small car. It might also work for the MGB.

*Rarity*
Although the Smart ED has been produced for several years, and will apparently become the only Smart model (as Daimler is giving up on the rest of the Smart line), it's still not common. For someone who doesn't already have a Smart ED, it doesn't make a lot of sense to go looking for one as a source of parts.

I'm in Canada, so I have have looked at the stats for EVs here. Between 2011 and 2017 there have only been 24,748 battery-electric cars sold in Canada, and only 1,195 of them have been Smart EDs; in half of our ten provinces, there are zero. I wouldn't want to be looking for one to salvage, here.


I don't know if either of these reasons would stop you from choosing Smart ED components for an MGB conversion, but they might explain why it's not a popular choice.


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## brian_ (Feb 7, 2017)

Tremelune said:


> ... I suddenly had a vision of an MGB or classic Mini with the drivetrain of a Smart ED.
> ...
> Seems like a cheap way to get a lot of components in a package that could fit any car...


I don't think there is such a thing as "a package would could fit any car", since cars have different designs.

When you say "drivetrain", what are you planning to use? The entire motor plus transaxle, which wouldn't fit anywhere in an MGB without radical modification? Just the motor (without Smart transaxle), and if so, would you use the MGB transmission?


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## brian_ (Feb 7, 2017)

Tremelune said:


> I'm casually in the market for an MGB, but I'm no longer interested in dealing with carbs or an ancient motor. My plan was to put a 90s GM V6 in it (mainly for the fuel injection), but I suddenly had a vision of an MGB or classic Mini with the drivetrain of a Smart ED.


That's essentially what brought me to this forum: we have a Triumph Spitfire with a dead engine. I have an extensive list of potential engines to swap in, and an EV conversion was one option.


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## Tremelune (Dec 8, 2009)

"Rare" and "hard-to-find" are distinct. If you have $5-7k to spend, you can pick up a Smart ED very easily in the States, and could probably recoup a grand from that, depending on your level of patience with selling the rest of the car.

I don't mean to trivialize the actual conversion costs, but how much is a Leaf or Tesla battery pack alone? Is a $5-8k Leaf just a better place to grab components?

The hardest part of installing an electric drive train is getting the motor to drive the wheels, right? Why would that be harder with a Smart motor than anything else? A lack of existing adapters?

The Smart has 120 ft-lb of torque at 0rpm. Not a powerhouse, but more than half the Miatas out there.


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## brian_ (Feb 7, 2017)

Tremelune said:


> "Rare" and "hard-to-find" are distinct. If you have $5-7k to spend, you can pick up a Smart ED very easily in the States, and could probably recoup a grand from that, depending on your level of patience with selling the rest of the car.


I'm not saying that you can't get them, only that there are fewer and so it shouldn't be surprising that they are less commonly salvaged than other EVs.



Tremelune said:


> I don't mean to trivialize the actual conversion costs, but how much is a Leaf or Tesla battery pack alone? Is a $5-8k Leaf just a better place to grab components?


The Leaf provides more battery, and a more powerful motor. If you don't need those that's fine, but for most people it does make a Leaf a better source.

You need to make the battery, controller/inverter, motor, high-voltage protective switching, and battery charging all work together. There are various approaches to that, and how much of the original electronics you want to use affects what combinations will work... and what experience from other projects can be adopted. Working with stuff that others have used is an advantage in that way, but it isn't the only valid approach.



Tremelune said:


> The hardest part of installing an electric drive train is getting the motor to drive the wheels, right? Why would that be harder with a Smart motor than anything else? A lack of existing adapters?


I don't know if that the hardest part, or if it would be any harder with the Smart components. Any transverse motor and transaxle assembly would be complex and difficult to install in the back of an MGB, which is why I asked if that was the plan.

If the idea is to use just the Smart motor with the MGB transmission (so I'm still asking: _is that the plan?_) then a Leaf isn't easy either... yes, because of the lack of an available coupler for the shaft (and an adapter for the housing, but that's probably easier than the coupler). That's true of almost any production EV, since they have splined motor shafts designed to work with dedicated transmissions, not with the transmission which happens to be in a gas-engined car to be converted. Readily available conversion parts are designed to work with motors from forklifts, and similar motors from conversion suppliers which follow industrial face-mounting patterns and have plain shafts.



Tremelune said:


> The Smart has 120 ft-lb of torque at 0rpm. Not a powerhouse, but more than half the Miatas out there.


That's probably more torque than a gasoline or diesel Smart ForTwo, but that's not the issue. It's also not the right value: the second-generation Smart ED motor put out up to 120 *newton-metres* (that's 89 lbf⋅ft), and the third-generation puts out up to 130 newton metres (96 lbf⋅ft) (according to specs quoted in Wikipedia, which seem plausible and are supported by references).

The issue for many conversions would be power:

second generation
20 kW (27 hp) continuous; peak power output of 30 kW (40 hp) for approximately 2 minutes
this is really not very much

third generation: peak power output of 55 kW (74 hp)
this is comparable to the diesel Smart ForTwo, but low by current EV standards

No Miata (or MGB) in reasonable running condition would be comparable in power output to either generation of Smart ED, although an early Miata's or MGB's torque at low engine speeds would be inferior to these electric motors... which is why there's a transmission.


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## brian_ (Feb 7, 2017)

*Mini*

While the drivetrain configuration discussion here has been mostly about an MGB, because that's a problematic scenario, the situation for a Mini would be quite different. The entire Smart ED drive unit (motor and transaxle) could probably be planted in a BMC/BL/Rover (not BMW) Mini (if it doesn't extend too far forward), entirely replacing the original engine and transaxle. That seems like a natural fit, in a similarly small car. Of course, substantial design and fabrication would be required since the mounting points will not be the same.

The gearing wouldn't be as intended for the Smart, because Mini tires are substantially shorter than Smart ForTwo tires, but that just means a lower top speed and more drive force available (both as compared to the Smart ED)... which is probably a fun combination. 

The challenge might be getting in all of the battery without shifting weight distribution too far rearward.

With stock-sized tires, if the Smart ED top speed is limited by motor speed (not power), then:

a second-generation Smart ED powertrain with a maximum speed of 100 km/h would have an 85 km/h maximum speed with Mini tires, and
a third-generation Smart ED powertrain with a maximum speed of 125 km/h would have an 106 km/h maximum speed with Mini tires.


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## rmay635703 (Oct 23, 2008)

MB Products are notoriously bad for aftermarket tuner and utility support.

That said the Smart cars self contained engine cradle is ideally packaged to throw under any old thing with minimal effort , just lift the body and a couple simple removals later you have a self contained EV/suspension/drivetrain you can set any old body on.

Sadly you would need to repackage and reuse all the modules and dash so the car thinks it’s still a smart car as there has been zero effort to program smart parts.

Take a look at the gasser, nothing this simple to repackage since the original VW Bug

https://m.youtube.com/watch?v=UPnoFS2NApE


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## brian_ (Feb 7, 2017)

rmay635703 said:


> That said the Smart cars self contained engine cradle is ideally packaged to throw under any old thing with minimal effort , just lift the body and a couple simple removals later you have a self contained EV/suspension/drivetrain you can set any old body on.
> ...
> Take a look at the gasser, nothing this simple to repackage since the original VW Bug...


If you really want a complete drive unit and suspension assembly to put under the rear of something, I would say this is much better than a VW Bug, which doesn't have a usable subframe... you had to use the whole chassis or build your own structure for suspension.

The Smart setup (at least the first two generations) is especially nice for this purpose because the springs and shocks mount to the subframe; often the subframe only supports the suspension and powertrain components, while spring and shock loads bypass the subframe and go directly into the body. A publicity image of the Renault Twingo (which is on the same platform as the third-generation Smart) suggests that the layout and suspension are similar, but a subframe is no longer used.

On the other hand, the rear suspension from a Smart is mediocre at best. It is a beam axle, with a goofy lateral location system that bends the beam.


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## Tremelune (Dec 8, 2009)

Yeah, it seems like the #1 reason is simply that Leaf stuff is similar money, and is a better platform for swaps. I hadn't realized they'd come down so much as well.


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