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I hope that “drivetrain” is the correct term - it actually stands for “motor mount, motor, clutch, adaptor plate and gearbox”.


The motor is a surprisingly heavy, brushless three-phase AC squirrel cage variant with nominal 24kW peak power. Depending on the controller settings and the squirrel's physical constitution, it can temporarily be “overboosted” by some 50 per cent.

The diagram shows torque (grey line) and power (violet line) vs. rotational speed. As you see, the full torque near 120Nm is available between 0 (!) and 2000 rpm, while the power peaks between 2000 and 4000 rpm.

In practice these characteristics widely depend on the controller settings. Please see chapter "motor controller setup"!

Forced cooling of motor and controller is described in chapter "cooling system" below.

why do we still need a gearbox?

Ideally, an electric motor would have a hyperbolic characteristic of the torque over the full range, i.e. torque equals peak power, divided by rotational speed. Then it would render a gearbox unnecessary. Practically however, as we see above, the hyperbolic characteristic applies within a limited rpm range only. The top speed can only be reached in one of the “higher” gears, while going uphill a steep slope (or regeneratively braking downhill) requires a low gear. So we are still dependent on the gearbox as in a conventional car.

Practically, there would anyhow be no other way to fit in the motor with manageable effort!

Note that “native” electric cars indeed come without a gearbox. This however requires a motor+ controller with much higher power. For a “conversion”, such devices seem not available (or affordable) yet.

assembling and mounting the drivetrain

When I received the motor from Rainer and Marco Lorey in their workshop in Offenbach, Germany, it was already pre-assembled with adapter plate (custom-made by Rainer and Marco), clutch and gearbox and connected to controller and accelerator potentiometer, so that the function of the assembly could be demonstrated.

For the transport, the devices were disassembled again.

New clutch, pressure plate and clutch release bearing.

Gearbox and motor with flywheel and clutch before joining.

The clutch initially tended to slip at moderate torque already. After some forced “grinding in”, this slowly improved and after a few kilometers of driving the clutch now behaves as it should. I cannot tell whether the slipping was caused by improper contact between the surfaces of flywheel respectively pressure plate and clutch disk, or by contaminants such as e.g. coolant liquid (washing with water anyhow had not helped).

The drivetrain is assembled again.

Norbert, showing off with his professional white gloves, helps to lift the drivetrain into the engine bay.

The drivetrain is provisionally mounted - the red belt is a makeshift substitute for the yet missing motor mount.

A section of the adaptor plate is cut away to leave more space for the front battery box.

motor mount

The drivetrain is suspended in rubber bearings at three points. Two of them connect to mounts that are directly attached to the gearbox, and they were left unchanged. The third one required a dedicated mount to fit the backside of the motor.

This is a mounting plate that was actually fitted for a different motor type. I had to cut away a few extra sections.

The first parts of the motor mount are tack-welded together.

After welding, the motor mount is heated by a gasoline stove together with a torch lamp, so that internal tensionings are reduced.

Damage due to inexperienced welding: The faceplate is warped. With sanding paper sticked to a flat surface, I identified the yet embossed areas and marked them with red Edding. With the help of the angle grinder and numerous repetitions of sanding, marking, cursing and grinding, I could finally get the faceplate flat again.

The motor mount is joined with the original rubber bearing, which is bolted to the car's frame.

One of the two other rubber bearings carrying the gearbox.

The speedometer bevel is inserted again.

Drivetrain now complete with motor mount, the half-shafts are already in place.

Some time later - the engine compartment is already tidied up, next the front traction battery box will be inserted.

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astra_conv/conversion/drivetrain/drivetrain.txt · Last modified: 2014/05/09 16:00 by richard