[VicBee]

As I consider the options for my future conversion of a 1969 Citroen DS 21, it was suggested to do something novel and do a 1 per wheel motor conversion and do away with the transmission altogether... What are the good and not so good ramifications of such an idea? While this probably has nothing to do with that decision, I will be using Tesla batteries regardless.

 

[scottherrington]

Whilst that does sound like an interesting concept it sounds to me to be a lot more complicated, you also have to consider the additional stresses that will be placed on the hub motors.
If you don't want the original gearbox why not just use an OEM motor and gearbox then go straight to the drive wheels?

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[PacEmaker]

Being a front wheel drive vehicle could I suggest you look at transplanting a third generation Prius transaxle with inverter/converter into the Citroen in place of the existing engine and gearbox? You can utilise either one or both electric motors in this transaxle to provide traction for driving the car. To maximise the 'grunt' available you would weld the planetary gears in the power split device and use the new 'dual' inverter control board being developed by Damien Maguire of EVBMW. This requires some competence in electronics and general fabrication of course, so if you haven't any of that kind of experience just forget it, but the result could be very impressive and very practical if you have these skills. The availability and cost of a suitable lithium battery bank might be the most challenging part of the project.

 

[brian_]

As I consider the options for my future conversion of a 1969 Citroen DS 21, it was suggested to do something novel and do a 1 per wheel motor conversion and do away with the transmission altogether... What are the good and not so good ramifications of such an idea? While this probably has nothing to do with that decision, I will be using Tesla batteries regardless.

That doesn't do away with a transmission entirely, unless the motors are directly connected (by just a shaft) to the wheels and so run at the same speed as the wheels... and that's a problem because reasonably-sized motors won't produce enough torque - they need reduction gearing.

If you have a reduction gearbox for each motor, that eliminates the differential, and is a valid design approach, now being used by a few EVs and hybrids. If you want to use readily available salvaged parts, that's not really an option, but if you can get the right parts together it would work well.

The most straightforward way to eliminate the Citroën transaxle is to replace the engine and transaxle with the motor and transaxle (drive unit) from a production EV (or even a hybrid, without the engine). Since the Citroën engine sits behind the axle line, the Tesla Model S/X drive units are an obvious choice, but they're wide and may not fit in the available space. Any of the front-wheel drive EV drive units are possibilities, and would leave a significant space (the original engine space) between the drive unit and the firewall for a battery pack.

One caution: everything about the DS and other Citroëns of that era is so weird that nothing is guaranteed to fit or to work without careful examination of how it would fit in the car. For example, the steering rack is mounted unusually high, and just ahead of the axle line, so it goes over the transmission but is likely to interfere with many front-wheel-drive EV drive units. Another example: the brakes are inboard, meaning that the disks are on the transaxle end of the axle shafts, and the calipers are bracketed to the transaxle. While in general I see little benefit to keeping the original transmission in most conversions, a Citroën may be a case in which messing with as little of the original design as possible would be wise.

 

[rfletch]

Hi VicBee,

I'm currently in the planning phase of my EV conversion and have settled on the same idea. My donor car is a Daihatsu Feroza (called a Rocky in some countries) and I saw this design as a way to solve several problems. Removing the transaxle would remove diff slip, save weight and increase space. It will also reduce drivetrain losses. The disadvantages are that you will need a controller for each motor and it will add some complexity to the build.

My design is 4 permanent magnet (brushless) motors, each connected to a 7:1 single speed gearbox driving each axle shaft.

 

[louismoulton]

I also have a Feroza I am considering converting. I was thinking an AC induction motor as it would probably be easier to seal up for 4WD. I am thinking of keeping the whole drive chain so I would still have low ratio.

I notice the brakes will need a vacuum pump, but no power steering makes that bit easy.
Not got any further. Might look at a leaf motor.