How to find out the right DC motor

[slick123]

Hi guys, I am a bit confuse on how to calculate the power of the motor, the torque and the speed of the motor shaft + how to find out the rpm. Basically, i want to buy a motor which will be able to travel 100miles with a min speed of 55mph and have a total load of the vehicle of 600kg. if someone could please help me with the calculations because I am not sure to start the calculations from. thanks

 

[rcgldr]

You would need to figure out the total power it takes to move the car at 55 mph (aerodynamic drag, rolling resistance, drivetrain losses, ...) and to achieve a resonable amount of acceleration. Then you'd probably want a bit of power to spare, perhaps an additional 25%.

DC motors maximum power output occurs at 1/2 their no load (peak) rpm, so you'd need to select a top gear ratio so the motor would be running about 1/2 it's no load rpm at 55 mph or the targeted top speed.

 

[slick123]

so the total power will be Power = Torque x radian speed is that right?? but how do i start the calculation?? it will be a belt drive thou

 

[slick123]

Rolling Resistance: Froll = uroll x M x gravity ,
Where: uroll - is the rolling resistance coefficient. Typical values for the rolling resitance coeffiecient (uroll) range from 0.010 to 0.015
M - is the mass of the vehicle (kg)
gravity - is the force of gravity (9.8 m/s2)

Please what's the formula for the total power it takes to move the car at 55 mph?? thanks

 

[mheslep]

This reference should answer your questions. Read the 6-7 pages starting here; its quite clear:
http://www.inference.phy.cam.ac.uk/withouthotair/cA/page_254.shtml

Generally speaking for the rolling resistance and air drag of a sedan traveling at 55mph you'll need ~25HP (mechanical power output from the motor) to maintain that speed on level grade.

 

[koolraj09]

Hi
This might help you a bit:
http://www.micromo.com/n390290/n.html