My club is building a 1/4 scale utility tractor (around 800 lbs) and for the past couple of years we have been using an electric hybrid drivetrain. Our system has been a 32 hp gas motor powering a DC generator which we convert to 3 phase AC to power our independent wheel motors with an operating voltage of 72V AC. My question is would we be better off using a DC motor considering we don't require high speeds but need very high torque for our pulling competition.
The motors we are currently using are rated at around 40 ft*lbs at 5,000 RPM and go through a 31:1 gear reduction which we thought was plenty but when they start seeing a high load, the current spikes and faults out our controllers.
The first year we ran this system the controllers faulted out because we didn't limit the amount of current the motors could have, we changed the system this year to have a current limit so the controllers wouldn't fault out and it basically shut our motors off under a high load, I guess the question isn't necessarily which is better but is one more efficient under high load to make the most out of the current we can generate.
RPM: Our final drives have a 31:1 ratio so anywhere between 3000 to 5000 RPM, HP our gas motor is 32 hp so we sized our current motors to be 15 hp peak per motor so we could equal the power capability of the gas motor, Budget is hard to gauge, we have a decent amount of funding but sometimes companies sponser us or give discounts, Torque: we initially thought 1200 ft*lbs per wheel was plenty but now it is looking like we would need more around 2000 ft lbs per wheel to be able to compete with the other teams at our competition. The pull lasts maybe a minute or two maximum so we are pulling peak current that whole time but we have long rest cycles between pulls and events so the motor doesn't see prolonged current draw. We have a .66 F Capacitor in our system to smooth the DC current we provide to our controllers.