Drive system

I've been looking at how to connect the motor and gearbox so that I can get the adapter plate made ready to bolt it all in to the frame soon.
I've modeled the gearbox, motor, curtis controller and gearbox mount so far, I'll model the rest of the frame and main parts just to get an idea of how it fits together as it seem like a good opportunity to draw it up and when I was looking into doing this I couldn't find any information or dimensions for any of the Smart components. The gearbox is representative and the casting shape not accurate, although the holes and shafts positions should be close enough to make sure things line up.

This is the mount plate, Dia 290mm and 70mm thick, this thickness is needed to move the motor far enough away to prevent the motor shaft and gearbox spline clashing. I'm hoping to track down a clutch spline cheaply but the Smart clutch is a whole assembly which I don't need. The cutout is for the drive shaft, so the motor couldn't be much larger diameter.

Section of the mating parts, just need to sort out a coupling but I think this will be a taper lock plate bolted to a clutch spline, some compliant connector would be good to prevent excess wear on the bearings.

Schematic

Seems like a good time to get a layout of the system drawn up to make sure I'm covering everything.

This schematic shows the layout of the main parts and how they interconnect, it breaks down the physical areas of the car and shows what will go where.
Blue boxes are things that already exist in the car and the Green boxes show components that will need to be added.

As I haven't touched the car yet I'm sure some other things will present themselves but it seems a good place to start.

The Curtis controller has a 'typical' wiring layout...

The datasheet is here http://curtisinstruments.com/index.cfm?fuseaction=Products.home#/motorcontrollers/64

I've also stumbled across this one page wiring system in a forum, this was marked as 'free to share'. Not exactly as I intend to use but a useful reference that makes some sense of the curtis diagram, for example the Pot2 appears to be used on the Brake peddle to provide regen during braking.  

Drive components

So these are the parts I have so far for the drive.

• HPEVS AC35 motor
• Curtis 1238 6501 controller - 80v 550A
• A load of good quality pre-terminated cables
• Curtis throttle pot with switch
• Chunky solenoid
• 2 used chunky fuses
• Curtis 840 battery gauge
• The 35 way Curtis cable connector pre-wired

Coupled to this will be a standard Smart 450 gearbox/transmission. I got this from ebay, unfortunately the person used another photo from someone else's listing so the one I thought I was getting looked in better condition, but this one should do the job. More on this to follow next..

The subframe

This is sort of where it starts, the subframe is built completely independently of the rest of the car and contains all you need to make a self contained driven unit. It's fairly easy to remove from the car so it's the easiest way to swap out the current petrol engine (ICE). Ideal for this kind of project. It turns out the Smart fortwo 450 has the same subframe as the Roadster 452 apart from the 450 has an anti roll bar and a slightly different hand break cable position, but the 450s are much more readily available so easy to find, I've bought this one from someone from the Smartz forum, it's in good condition and after a quick jet wash it's ready for a qui
ck sand and a coat of paint.

Smart Roadster

This is the car I'm going to convert, it's a 2004 Smart Roadster Coupe.

It's a great fun car to drive but is renowned for having an interesting gearbox, although in many ways ahead of it's time, but due to the motor controlled clutch and gear selector being fairly new it is slow off the start and the semi-automatic gear change causes the car to be a bit unpredictable with few people driving it in full automatic mode... although semi auto helps you are never quite in control of the clutch. However, the car looks great, and the feeling of being wrapped in the confined cockpit makes you feel a part of the experience. The petrol engine has a great power to cc ratio providing up to 80BHP from a 698cc engine (100BHP with the Brabus), scaled up that's better than most modern cars.
What would it be like as an electric car... perhaps with the light weigh and small space this is what it always should have been. I guess I'll find out.
But enough of the car, I won't be doing anything to it for a while as the intention is to get the running subframe finished first.

The plan

I don't intend on dismantling the Roadster and then starting the conversion. Instead, as Smarts have a subframe with the rear suspension, gearbox and engine all mounted on it which is then bolted up under the car it makes sense to buy a set of subframe parts and build a fully working electric drive version, once it's all finished and running this can then be easily swapped with the petrol version so it should then only require minimal effort to finish it.
I'll be using a full AC motor system as they have a wider rev range, regenerative braking and are more efficient than a simple DC motor. The cost will be higher but the effort will be more or less the same so it would seem to be the better option.
Normally you wouldn't need a gearbox with an AC electric motor, they have a wide torque range and are high revving but the one I plan on using with a controller with a 80v limit means I'll probably need to be able to change gear ratios so that I have some acceleration at lower speed and it won't rev out at the top end.

Summary

I've always been interested in electric cars, ever since being involved in the Battery Vehicle Society in the 80's racing home made electric cars around various kart and bike tracks for hours, seeing who could go the furthest on 2 car batteries.

Many years have passed since then but more recently I leased a Nissan Leaf through my companies green car scheme for 2 years. Leaf's aren't exactly the best looking cars and living with a car with a range of 70 miles can be frustrating, but the feeling of driving something now which we will all be driving in the future was great. The pull from a standing start, continuous acceleration and lack of maintenance is great, unfortunately some EV's are slow or people drive them slowly, but they don't need to be. I also got to drive a Tesla Model S, without doubt the best car I've ever driven in every way, but unfortunately at cost few can afford.

I bought the Smart Roadster 4 years ago, I love the looks and the fun handling but ever since owning it I've though this car should be electric. So after a lot of thought, a lot of searching for parts and too much time seeing what other people have done, it's time to make a proper start on planning the conversion.

Finding good information on conversions that have been done so far is quite difficult, so I figure I should try and document it properly in case anyone else might be interested. I've never blogged before but I'm assuming this will be the best way to do it.. time will tell. I hope you find it useful and interesting.