I have taken the petrol motor out and split the gearbox away, the question now is, do I need a clutch? the weight of the flywheel seems a bit redundant but will I be able to change gear while moving if take the center spline out of the clutch and attach use it to directly link the electric motor to the gearbox?
Yes, in an electric motor installation the flywheel's mass is superfluous; the only reason it is used is as one of the faces for the clutch (the counterpart to the pressure plate). Flywheels can usually be substantially lightened - even when used with an engine in racing applications - and with the starter ring gear not needed and no inertia required to smooth out power pulses (or desired), lightening for an electric car could be radical. I had half the mass of our Honda's flywheel machined off for competition use with the stock engine, and one could go further with an EV. Despite this, I see a lot of stock-looking flywheels in build threads.
Flywheel inertia means energy stored as rotational motion of the flywheel, instead of forward motion of the vehicle. While not a big factor in a typical EV project, it is best minimized. Some EV design discussions consider the effect of energy stored by motor inertia on performance and driving feel (and higher inertial energy storage is always bad); flywheels substantially affect that inertia.
That depends on the gearbox
When you change gear the syncro cones change the speed of the gearbox input shaft so that the drive dogs can engage
With the clutch disengaged they only have to change the speed of the input shaft and the clutch disc
With the clutch engaged they have to change the speed of the engine and flywheel as well
The largest inertia by far is the flywheel
With an EV you will have to change the speed of the motor and your coupling - this is a LOT less than the engine and flywheel but more than the clutch disc
I think this is a good summary. Of course shifting with the clutch engaged with an engine is not normal, and is affected by engine power and drag... which is a different situation than with an electric motor.
The real alternatives are:
- with flywheel and clutch, disengaging clutch to shift: shifts like the original car (assuming that in the original car you don't use an advanced technique such as double-declutching)
- without flywheel or clutch: shifts like shifting the original car using the clutch (no use of power to affect shifting), but with motor inertia making shifts much more difficult (vastly more inertia to overcome). Downshifts are especially difficult because the motor must be sped up by the synchro, but even an upshift is slow because the motor coasts relatively freely compared to an engine, and the synchro much slow it down.
The rotational inertia of some electric motors is very high, particularly the larger-diameter, higher-torque, lower-speed designs. Others are much lower. Flywheel inertia varies, too, although any engine with few cylinders will have high inertia (an 8-cylinder is usable with no flywheel, but a 4-cylinder absolutely needs substantial inertia). Motor specs (for serious modern EV motors, not so much for the updated-forklift brushed DC units) often state rotor inertia; engine specs don't but a rough inertia value can be calculated from diameter and thickness. So I don't know if "the largest inertia by far is the flywheel", but maybe it doesn't matter much...