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Renard's BMW

Posted: Tue, 31 Jan 2012, 20:49
by Renard
It is now over a year since I joined the AEVA forums, and I have finally bought my host vehicle and would like to share my conversion process with other readers who may be interested.
I do not claim any particular adventurousness for my work: I have only general familiarity with mechanics, electrics and electronics, and I'm deficient in the area of software and microcontrollers. So I'm not in a position to roll my own with regard to motor controllers or BMSs.

I live in the country, and am intending to move to a fairly hilly region where a trip to the nearest town and back may be of the order of 100km, so I want regeneration and good range, and I'm not interested in zippy acceleration.
To be up with the times, I've chosen an AC conversion.

To make things simpler for myself, I've bought Tritium's Wavesculptor and the induction motor they have explored: the SEW-Eurodrive DRE 132MC4. This is a 132 frame, 4-pole, copper rotor motor. Tritium have tested this motor and have concluded that with a 380V DC bus and at a motor current of 300A(rms), it achieves 240Nm of torque and 70kW peak power at 2700rpm, while also being capable of 20kW continuous running at 75A(rms).
The motor is wound to 100/175V delta/star, and weighs 67kg. Efficiency is 90-91%. There are three modifications to the motor: replacing the fan with a 12V electric fan mounted on the NDE shroud; machining down the NDE shaft to fit an encoder; gluing a 100k thermistor onto the windings. These mods, along with the performance data, are described in files available from Tritium.
TRI85.001v2 Mech.ModsDatasheet.pdf
TRI85.003v1 Mech.Mods.pdf
TRI85.005v1 Mech.Mods.pdf
In its simplicity and durability, the induction motor is one of the truly great inventions of the industrial age.

While I was mulling over the kind of vehicle to convert, I was assembling various bits and pieces: the controller and its cooling system, the motor and its modifications, the Tritium driver controls unit, contactors and some enclosures and circuits, DC/DC converter, vacuum pump, and minor items.

Eventually I reached a point where I needed to move on the car itself, and before Christmas I called my car buyer -- EasyCarSearch P/L -- who trawls through the wilds of Sydney buying cars to order. What a nightmare that would have been for me if I had had to do it myself!

I ordered a late 90's six-cylinder E36 BMW. I wanted a six cylinder version as I figured that, being heavier than the four cylinder one, it would permit more battery weight to be installed. It doesn't have the vehicle weight stamped on the VIN plate, but I think it weighs 1385kg, including a nominal driver. I will check it at a weighbridge. The car has a manual gearbox which I intend to discard.

So this series of posts may be of interest to those without special expertise who wish to tread a more conventional and less exploratory path, buying items off the shelf -- well, it's not quite as straightforward as that.
I should say that there are only three or four BMW AC conversions listed on, two of which are semi-commercial with cost no object. Of course there are more elsewhere.
As far as I know, it's the first published Wavesculptor-plus-SEW-motor conversion.

Yesterday, I finally took delivery of the donor car, which was very exciting, but then I had an anxious dream last night. I had been allocated Room M52 in a hotel of faded glory. It was an old ball-room with tools littered everywhere. And I had paid up-front for several nights. (The car has the M52 engine.)
Oh well, here it is. Image to follow later.
It's a 1997 323i and has done only 132Mm, and seems very clean. Indeed it seems a shame to take the knife to eviscerate the well-functioning vital organs. Still, I will drive it a while first, and get it re-registered for another year before operating.

The next big step on the journey!

Renard's BMW

Posted: Wed, 01 Feb 2012, 02:15
by BigMouse
Very nice! I'm planning a similar conversion (in my 1992 E36 Coupe), but with my own motor controller, if I can get it to the point where it can drive a car.

Was your motor purchased with those windings from the factory, or was it custom wound? Mind if I ask what the motor cost? I'm also using a 132 frame motor, but the one I got is custom wound to 48v for a high redline on my planned pack voltage (I'm keeping the transmission). I'll make a thread about it on here someday.

Which final drive are you going to use? I originally planned to do dircet drive in my conversion as well, but even with the highest final drive ratio available for these cars (4.44:1), I wasn't going to be able to produce enough torque to climb the steepest inclines I was likely to encounter. The exit from the local Woolworth's underground carpark is 16 degrees (measured with an inclinometer app on my phone). 260Nm from the motor into a 4.44:1 final drive is enough to push a gross-weight E36 up a 10 degree incline, just barely. This math convinced me to retain the transmission in my conversion. The last thing I want is to find myself stuck at the bottom of an underground carpark, unable to develop the torque to climb out.

Renard's BMW

Posted: Wed, 01 Feb 2012, 14:39
by Renard

The motor came wound 100/175 from the factory, though being a special wind, it was not quite 'off-the-shelf' but needed an order with a delay of a month or two. Cost from SEW Brisbane was $2300 incl GST last year.

About the torque, thanks for bringing this up as I had just assumed I'd have enough torque for normal use. And maybe so, but calculations are always good.

T x d /r = mg tan A            where d is diff ratio, r is wheel radius, A is slope angle.

So for your case, and assuming my wheels ( r = 0.295) we have 260 x 4.4 / 0.295 = 3878

Divide by g gives 396. Tan 16° = 0.287 that's 1:3.5 pretty steep. So m = 1380.

I can see your point. I have to consider whether allowing for such severe slopes balances the virtue of removing the gearbox. Hmmmm. Take a run at it?

Renard's BMW

Posted: Wed, 01 Feb 2012, 17:11
by BigMouse
Renard wrote:Hmmmm. Take a run at it?
I considered that too, but one place I encountered was a property I was considering renting. It was a unit at the back of a complex and had a VERY steep, quite long drive with no run-up room. I measured it to be around 14 degrees with my phone. It was then that I made the decision to stick with the gearbox. I decided that even if direct drive was fine 99% of the time, the first time I got stuck at the bottom of a hill needing a tow to get to the top, I would regret it.

Also, my wheels radius is 0.315m. I don't think the coupe and sedan have different wheel sizes. It makes about 18Nm difference on a 10 degree slope.

So you can expect to be able to hold on a 12.5 degree slope, but not quite climb it. That's assuming the 240Nm is available at 0rpm. If not, your steepest slope will be shallower.

I spent a fair amount of time trying to source an approx 2:1 gear reduction in order to retain direct drive, but it seems it would have to be custom made. When talking to Malcolm on the subject, he mentioned plans to use the planetary reduction out of a turboglide transmission, but there is a lot of fabrication involved in such a project. Chain drive could work, but would be noisy and high maintenance. None of the bolt-on c-face industrial planetary reduction drives can handle the power or RPM.

The manual transmission from an E36 weighs about 30kg, only a bit more than I'd expect a suitable single gear reduction to weigh. It also greatly improves performance. I'm expecting 0-100 in about 9.5s (assuming constant 175Nm to redline). My spreadsheet estimates 16.5s for your 240Nm (again, assuming a constant value), a 4.44 diff, and direct drive at gross weight.

I'm not trying to sway you, but just sharing my thought process on the subject.

Note: my formula for torque is a bit different than yours. After doing a free-body diagram, I get T x d/r = mg sin(A). I did most of the calcs above using your formula though.

Renard's BMW

Posted: Wed, 01 Feb 2012, 19:30
by Renard
" It was then that I made the decision to stick with the gearbox. I decided that even if direct drive was fine 99% of the time, the first time I got stuck at the bottom of a hill needing a tow to get to the top, I would regret it."

Yes there are pros and cons. I will hold off deciding for a while.

(Incidentally, is there a straight-through gear in the gearbox?)

My tyres are 205/60R15. Calculation gives r = 313.5mm, but standing on a firm horizontal surface, r measures as 295mm.

The tangent is strictly correct, but of course the sine is almost the same at small angles.

No, I was wrong. Sine is more accurate. Woke up in the night and drew the diagram in my head. Ooops.

Renard's BMW

Posted: Wed, 01 Feb 2012, 21:34
by Sheany
There is a straight through gear, or 1:1 is 4th gear.

Renard's BMW

Posted: Thu, 02 Feb 2012, 16:05
by PlanB
Love the line about the faded glory hotel squire. I've had a 42kg drive masquerading as a door stop this past year, part of me really wants to do something with it but the thought of an EV that never goes & the shame of not pulling it off fills me to my old fashioned TTL core with the most mesmerising rabbit-in-the-headlights fear. Those of us that wonder just when it was that resistive pot throttle pedals became CAN bus nodes salute your endeavour.

Renard's BMW

Posted: Thu, 02 Feb 2012, 19:41
by Renard
PlanB wrote: . Those of us that wonder just when it was that resistive pot throttle pedals became CAN bus nodes salute your endeavour.

I had thought that by getting a 90's car, the electronics would be simple.
But alas, the beemer has a CAN bus and heaps of control modules. I fear that if I do something to it, it will take revenge, and I'll have to go all the way like Dave with HAL in Kubrick's 2001. "Stop, Dave, my mind is going…"

Renard's BMW

Posted: Thu, 01 Mar 2012, 16:13
by Renard
Since the last post, I've managed to find the BMW Electrical Troubleshooting manual for this model and year, ( and the only CAN bus is between the ECU and the auto transmission module, which, since the car is a manual, is not there. So there should be no CAN problems.
By studying the wiring diagrams, it seems that there is almost no connection between the SRS (airbag) system and the rest of the wiring, so no great troubles there. The only other possible difficulty is the ABS system, but as long as the ASC is switched off, it looks as though the ABS requires no inputs apart from the wheel sensors, and only outputs to the ECU.

While waiting for a Bentley Manual, I whiled the time away with some vehicle dynamics.


Renard's BMW

Posted: Tue, 06 Mar 2012, 21:28
by EV2Go
I'm still partial to the idea of the Black Box discussed here...


Renard's BMW

Posted: Tue, 06 Mar 2012, 22:35
by Johny
I liked that when it was discussed but it looks like it's built to handle way more torque than EVs usually provide. It also looks like it shares the transfer case oil. I'd like a less-bulky version - kind of like an overdrive unit with a self contained oil supply.

Really what I'd like most is a two-speed diff.
Dream on John.....

Renard's BMW

Posted: Wed, 07 Mar 2012, 02:07
by Renard
Yes, a simple, light, two-speed gearing would be ideal.
But my mechanical and engineering resources are fairly basic, and so I think I will go with keeping the gearbox, probably minus the clutch. (Since I wouldn't expect to change gears while moving, and even if I wanted to, the small angular momentum of the motor's rotor should not stress the synchro.)
I could always change my mind in the future, though given human inertia I probably won't
With the gearbox, the engineering requirements are very modest: just a coupling and adaptor plate.
Thanks to Coulomb and Weber for advice.

Renard's BMW

Posted: Tue, 03 Apr 2012, 21:09
by Renard
Movement at the station!
Ten days ago, I brought the car back on a flatbed from the mechanic I had employed to take the engine out.
Here is a picture of the great beast, and the gaping hole. I'm sure every converter breathes a sigh of relief when finally all the superfluous stuff is stripped out and the car is ready to measure up and one can start designing the parts to go in.

I have just discovered that the propshaft, gear box and motor will fit such that the base of the motor just clears the engine mount crosspiece (seen in the bottom of the second photo) and steering element. The engine shaft centre is about 90 - 95mm above the engine mounts, and so for the 132 frame motor, that leaves the motor base 37 - 42mm below the engine mount base. I had been worried that the motor would clash with the crosspiece.


Renard's BMW

Posted: Tue, 03 Apr 2012, 21:15
by Johny
Great stuff. I think removing the ICe stuff, fuel lines, exhaust, petrol tank was one of the most satisfying moments in my EV build.

Renard's BMW

Posted: Wed, 04 Apr 2012, 01:50
by Renard
Today I weighed the stripped down car. The gearbox and prop shaft and clutch were not installed, but together those items weigh about 40kg.
So with three sets of bathroom scales ($8 each from bigW) I weighed each wheel in turn. The rear half weighed 580kg and the front 460kg making 1040kg in total, or 1080kg with gearbox, clutch and shaft. This compares with a total of 1380kg -- 700 front, 680 rear -- for the original vehicle. That's 300kg less. I'd hoped for a greater reduction, but the engine though large is all alloy and weighed only about 175kg.

I've added some graphs and a range calculation to my Vehicle Dynamics file, providing a little more maths for those who like that kind of thing.


Renard's BMW

Posted: Wed, 04 Apr 2012, 20:30
by woody
Loving the maths, much more elegant than my brute force spreadsheet.

Renard's BMW

Posted: Wed, 04 Apr 2012, 20:45
by Richo
I found it just as easy to measure the rolling resistance and drag then plug real numbers back into the maths.
Nice work though.

Hopefully your 132 motor has mounts on each side for easy mounting to the cross member

Renard's BMW

Posted: Thu, 05 Apr 2012, 15:05
by Renard
Richo wrote: Hopefully your 132 motor has mounts on each side for easy mounting to the cross member

The first photo (31/1/12) shows the motor on its side. You can see its baseplate. This will be bolted to an angle member running between the engine mounts with a horizontal middle portion of length 246mm offset down about 44mm. The engine mounts slope towards the centre at 14° so the angle member follows that slope down to the middle part.
The BMW files require a deviation from linearity at the transmission/prop shaft junction of no more than 30 minutes (half a degree). The distance from the rear mounts of the transmission to the foremost mounting holes on the motor baseplate is 800mm. So the deviation should be no more than 7mm in any direction from the line of the prop shaft. The horizontal position is easy to get right by referring to the crosspiece. I calculated the vertical position by parking the car on the concrete floor of the shed and measured the height of the final drive input, measured the engine shaft height above the engine mount points (not too difficult with the engine removed), measured the engine mount height above the floor, and referred that to the 132mm height of the motor shaft above its baseplate.
Next thing to do is to buy some steel, crank up the welding gear, and think about an adpater plate and flywheel replacement. The existing dual mass flywheel weighs 10kg.

Renard's BMW

Posted: Sun, 15 Apr 2012, 02:48
by Renard
On Thursday 12th I took the gearbox and motor drive end flange into Lismore to have an adaptor plate made up. It will be 10mm steel. I also bought steel for the motor mount -- 50 x 50 x 5 angle; and today I cut it and bent it to make the mount. The photos show the process.
Two cuts were made in one side of the angle, and then it was bent out to 14.5°. One photo shows a piece of 3mm flat that I used as a template to get the angle and dimensions right.
In order to regain the strength lost in the cut I have cut a piece of the same angle which will be welded onto the mounting piece as shown.

Renard's BMW

Posted: Tue, 24 Apr 2012, 22:14
by Renard
Sometimes progress seems painfully slow. As has been observed, one spends a lot of time lying prostrate, gazing up at the underside of the car working out how items will fit.

So a small achievement is satisfying: I'm very pleased that I was able to install the controller's coolant radiator in an otherwise unused space just behind the front grille, as the photo shows. It's held in place with some brackets and straps I made out of some stainless steel sheet I had in the scrap box. It was necessary to cut away some of the plastic cowling around the auxiliary fan to get the radiator in.

I also mounted the coolant pump on the bracket that had previously borne the battery positive connection point. (The BMW battery, a 22kg hulking beast, sat in a hard-to-get-at spot in the right hand side of the boot.)

The vacuum pump fits in the position that had been occupied by the cruise control motor. Unfortunately, although this pump seemed quiet enough, when I put my head inside, there was a strong low frequency sound permeating the whole car. I will have to re-mount the pump on vibration isolators.

In a day or two, with some trepidation, I take the plunge and order the batteries: 112 Sky 100Ahr with a nominal weight of 350kg. (That's 23% more amp hours than even Weber and Coulomb's pack.) I'm going for a large pack because I'll never live in a city again if I can help it, and country distances call for more than the usual 100km or so. But the cost is higher of course. I console myself with the thought that it will pay off in future savings.




Renard's BMW

Posted: Tue, 24 Apr 2012, 22:39
by weber
Well done! It looks like the same vacuum pump that we have. I hope you have the blue wire as positive. We are delighted with how quiet it is, but then we mounted it using the rubber standoffs it came with, and we mounted it to the traction motor with its huge mass and its own rubber mounting. So all that's left is the air exhaust noise which seems well muffled despite the small size of the mufflers.

Renard's BMW

Posted: Tue, 24 Apr 2012, 23:33
by Renard
Thanks Weber.

The vacuum pump came without any rubber mountings, and I have ordered isolators from Mackay Rubber through Blackwoods. (Mackay part M1164, to be precise.) I agree that the pump itself is quiet, but the transmitted vibration was surprisingly strong.

I want to keep the ancillary items off to the side as much as possible and keep the central space clear for all the cells.

The architecture is becoming clearer to me: the power steering pump will sit beside the motor to its left, and the right hand space is reserved for a future electric A/C compressor. I have drilled a few holes in the motor mounting bracket in anticipation of further mounting needs. Then almost all of the volume above and forward of the motor is available for cells.

You showed the bracket mount for your motor but I don't recall seeing any pics of the rubber mounts. What did you use?

I don't have much room at all for rubber mounts since the motor has to sit not much more than a centimetre above my mounting bracket. I was thinking of using a flexible rubber pad type separation.

Renard's BMW

Posted: Wed, 25 Apr 2012, 05:30
by weber
I've just added a photo and description here:
viewtopic.php?title=weber-and-coulombs- ... 439#p34439
Your rubber pad idea should work fine if you make it impossible for any of the bolts to contact the motor foot, up down or sideways. i.e. a piece of rubber tube on the bolt where it passes thru the foot, and pads above and below the foot.

Renard's BMW

Posted: Wed, 25 Apr 2012, 14:42
by coulomb
Renard wrote: You showed the bracket mount for your motor but I don't recall seeing any pics of the rubber mounts. What did you use?

If you mean the rubber mounts for the motor bracket itself, as opposed to the mount for the vacuum pump, we used the original engine rubber mounts.

Renard's BMW

Posted: Thu, 26 Apr 2012, 16:31
by Johny
When I mounted my controller (big), I wanted to use these Ring and Bushing mounts but I did not want to buy 20 of them when I only needed four. Their advantage is that they are intrinsically secure and only take up 6mm of height.