For my mechanical engineering senior design project, we are designing a cargo transporter electric vehicle for off-road conditions. The vehicle needs to transport loads weighing up to about 22,000 N or about 5000 lbf.
The transporter will have a very slow speed (about 6 in/s). Using a coefficient of rolling resistance of 0.35, I calculated that the total power requirements would be about 5 hp. To calculate this, I took the rolling resistance force times the target speed of 6 in/s (P=FV).
Assuming that we use four electric motors, one for each wheel, I found a per-motor horsepower requirement of about 1.25 hp. For large wheels of about 3 ft diameter at the speed of 6 in/s, the wheel rotation rate is about 2.5 RPM. This yields a large torque requirement of around 3700 N-m or 2700 ft-lb.
I'm having trouble finding the right combination of DC motor and gearbox to fit this application.
How can I size a DC motor for a high torque, low speed application? The torque load per motor is about 3700 N-m and the nominal rotation speed is about 2.5 RPM, yielding a power requirement of about 1.25 hp per motor.
I can find DC motors rated for this power, but definitely not for this torque requirement or rotational speed. Would I need a special gearbox? How do industry people normally solve this problem?