Hi MalibuMan and
to the forum.
To calculate the required gearing reduction ratio you will need to measure the outer diameter of the driven tyres.
Then you can enter this information into the
Torque and Speed spreadsheet as a custom diameter in the cell with
bold figures.
Enter your maximum Required speed in the lower section to calculate the wheel rpm at that speed for your particular wheel size.
(E.g. a 20" wheel would need to spin at 470 rpm to achieve 45 km/h)To find the required ratio, you will need to divide the maximum set motor rpm by the wheel rpm.
(E.g. 3500/470 = ~7.45:1)This means that the rear driven sprocket will need to be 7.45 times bigger than the motor sprocket.
(E.g. a 12 tooth motor sprocket would require a 90 tooth sprocket to stay below 45km/h at the maximum set motor rpm)If the wheel is not being driven directly from the motor, you will also have to consider the reduction of the gears inside the rear axle differential unit or an additional intermediate jackshaft providing double reduction gearing etc.
If the rear axle
(or jackshaft) had a gear reduction ratio of 3:1, you would only need to have a 30 tooth sprocket instead of the previously mentioned 90 tooth sprocket to give the same overall gear reduction.
This is what the spreadsheet looks like with the above figures using a double reduction gear system:
According to the
dynomometer results, the 3 kW motor has a maximum speed of less than 4500 rpm, but at this speed, it will produce very little torque
(0.7Nm) which would be less than 3kg of forward force if is was geared for 45km/h @ 4500 rpm.
I don't think 3kgs of force is sufficient to overcome wind resistance and frictional drag etc. to allow you to even reach 45km/h.
To obtain more torque, you need to place more load on the motor, so I would recommend you aim for around 3500 rpm @ 45 km/h.
This should produce sufficient torque
(~10Nm) to hopefully maintain your maximum speed and still achieve 90% efficiency.
You should be able to limit your maximum speed by setting the maximum rpm to 3500 in the controller settings, but you may need to place an official looking sticker on the motor stating that it is limited to a maximum of 3500 rpm.
The motor will still be hardware-limited as it is limited by the controller
(which I consider to be "hardware"). Admittedly this "hardware" can be adjusted by changing its software, but that should not be an issue.
You should have no problems pulling away from stationary with this gearing
(especially in The Netherlands), as it should be able to produce at least 60kg of forward force below 1500 rpm.
If both rear wheels are being driven, you will need to have some form of differential unit to allow the quad to turn corners without skidding the rear wheels. With a fixed rear axle, it will try to go straight ahead and will resist any changes in direction.
Alan 
