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Discussion Starter #1 (Edited)
New user here and at the very beginning of an EV conversion idea with a French car called the Secma QT500. It might take a year or two just to find the car because only one or two come up every year or two so it will be a long project.

The car has a 12hp (21Kw) 2 Cylinder engine in rear. Once removed the total kerb weight is about 300kg. The key challenge will be the battery pack space, because these vehicles have no bonnet space, the body is rotomoulded polyethelene and difficult to modify as is a structural pod onto of a tubular chassis. The only space is the engine compartment and this is tiny anyway.



So far the plan/idea is:

Look into feasibility of building a ~30s20p 18650 5kwh 72v battery pack that would slide into the length of the main chassis spine which is a 5 or 6" Hollow Steel Tube (Chassis will be rebuilt anyway). A second pack will fit around the motor in the rear motor area, hopefully gaining another 5-10kwh

The current gearbox (Peugeot 106 I believe it is) is not being used. I plan to use a belt or chain drive going through a Mazda MX5 MKI (Miata) Helical LSD made by Westgarage in Scotland and simply connect up to hubs with drive shafts as the vehicle currently uses. Using a Chain/Belt Drive LSD will allow different sprockets to be switched and makes the gearbox redundant anyway. I will then use a DNR control dial switch where the gear knob currently is.

Motor choice is undecided at the moment until I have the actual car to measure from and look at directly, but, given it might take a year or two to find the right car to buy, I'm half hoping Saietta (Cedric Lynch of Agni Motors fame) might released what looks like a liquid cooled Axial Flux Motor called E-Drive. If not, I'm not sure. The traditional Agni Motors I don't think would be powerful-enough as I want to improve the 21hp performance by maybe 20-30% if possible.

Comments welcome. For some reason if I attach pictures, the post ends up in moderation???
 

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Hi hokinsk
Welcome, I'm a fan of the little QT500. Never seen the chassis bare though, interesting.
That motor looks very appealing to me, and I'd agree with a belt drive. Can you use the original drive shafts? Keeping the motor and diff offset will give more space for batteries. And Nissan Leaf modules would be my choice as you can stack them about and fit in most spaces. Also robust and reliable so don't have to use a BMS. Plus they can be quite affordable.
Where is the fuel tank location?

Cheers
Tyler
 

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Discussion Starter #4
The Saeitta motor isn't yet available unfortunately. I've switched idea to using a dual motor now and will connect directly through a reduction gear to the axles. Battery pack will be custom built by me as it will need to fit inside the main spine of the chassis and where the petrol tank is. Hoping to begin this project in earnest in the spring.
 

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That sounds interesting, though dual motors seems complicated. How will you achieve this? Is there a drive system you can buy for this? What benefit does it give you for your build?

Cheers
Tyler
 

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Discussion Starter #6
Half the rear engine space is taken by the Peugeot 106 gearbox which is about 65kg, by removing this I save some weight, but mostly free up much needed space for batteries & controllers. It's really just an additional controller for the second motor.
 

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Separate left and right drive motors

It's really just an additional controller for the second motor.
... and coordinating the two motors so that they deliver the same torque, or appropriately proportioned torque. It can certainly work, and in sophisticated systems works better than any other solution, but the control isn't entirely trivial.
 

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Discussion Starter #8 (Edited)
The motors will be controlled using the same torque demand of each motor, so the car will behave exactly as if there were an open differential and exactly what is inside the Peugeot 106 transmission already, it isn't complicated in this car which is essentially a large go kart anyway. Sure, if I wanted more than basic traction control and limited slip differential performance or even torque vectoring it would be complex though.
 

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Discussion Starter #9
I'll be using controllers that support both Master>Slave set-up over CAN and and also allow motor torque output at a constant value for a given throttle position rather than speed output. e.g. Sevcon support this mode and is designed for dual motor highway traction.
 

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The motors will be controlled using the same torque demand of each motor, so the car will behave exactly as if there were an open differential and exactly what is inside the Peugeot 106 transmission already...
Almost. In an open diff, the torque to each wheel is limited to the same value as the other wheel. With two motors if one tire loses traction the other is still able to deliver the full requested torque, which is good for not getting stuck but can be difficult to handle.

I'll be using controllers that support both Master>Slave set-up over CAN and and also allow motor torque output at a constant value for a given throttle position rather than speed output. e.g. Sevcon support this mode and is designed for dual motor highway traction.
Excellent. :)
This is significantly different from just giving two independent controllers identical torque demand inputs.
 

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Discussion Starter #11
The second controller is a slave controller to whatever torque is provided by the master Brian, but when cornering will behave as an open differential exactly the same as a standard (unlocked) differential. The controllers also have individual torque control however, so if one wheel slips, the controller power is reduced to prevent that. With the Sevcons, you can even add a steering position potentiomoeter and calibrate each controller to steering angle/radius.
 
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