According to our plan we will use dual motor setup for RWD configuration. To maximize the performance of the car within the rules the motor will need to have at least 40 kW of power each, but preferably higher to allow sufficient torque vectoring capabilities.
From our search we found three motors that are suitable for our use. The first is the EMRAX188 from Emrax, a common brand in FSAE competition. The second motor is the REB60 from MGM Compro which has a lot of background in large RC vehicle. Our last candidate is the MP202150 from FRC this motor is for general use.
We calculate the acceleration time of the car with a dual motor setup with these variables.
gear ratio: we used the highest gear ratio that can achieve a 130 km/h top speed
weight: we used 280 kg plus the motors' weight (the final weight included the driver's weight)
torque: torque is multiplied by the efficiency rating specified by the manufacturer
neglect traction limits
NONE
All motors can theoretically achieve better acceleration time than the target time of 4.23 seconds and all motors' acceleration time fall within a one percent range of each other.
every motor is equal in the acceleration criteria.
EMRAX 188
the hypothetical weight of the car with a dual motor setup is used to judge the motors' weight.
EMRAX motor is a clear winner with over 3.5 percent weight reduction over other motors.
EMRAX 188
the specified efficiency is used to compare the motors
EMRAX has the highest efficiency with iver 8 percent improvement over pther motors.
MP202150
the maximum voltage is used to judge the motors. this criteria is important because the maximum motor voltage will limit the maximum circuit voltage since all components must be rated for the maximum circuit voltage. lower motor voltage will limit not only the drive voltage but also the charge voltage.
REB can withstand the highest voltage with EMRAX falling into the acceptable range but MP motor will be eliminated since it can not withstand at least 450 volts
In conclusion we choose the EMRAX188 for its light weight and high efficiency rating. The EMRAX188 in dual motor configuration with a gear ratio of 4.8 can output 60kW and 480 Nm at each wheel and can saturate the 80kW power draw limit. The motor will be air-cooled with no additional aerodynamic equipment since from observation many teams with inboard motor setups, even with an Emrax unit, has no heating problem with an air-cooled setup.
Indicator: Net Energy*
Overall Range = 22 km** (approximate) [D.12.2.1]
Our Team uses Net Energy from FSE22 Efficiency Scoring Results to define Battery size.
From the results, The maximum energy used is around 6 kWh so we will use 7.67 kWh from the maximum first because we don't know an Actual Motor Specification and Regenerative Performance.
Then when we got Actual Motor Specification, we can simulate energy consumption with Regenerative Braking to get more accurate energy consumption. So maybe we can reduce Battery Capacity to make vehicle weight lower.
In short, we will use 7.67 KWh and reduce it when we know the energy consumption
*Net energy is the energy used at the end of the event compared to before the event start.
**We have to approximate the range because we don't have actual racing track information.
For Battery Benchmark Indicators
Maximum Pulse Discharge Rate - can provide 80 kW for motor power used
Total Energy - More Total Energy ==> More Energy Receive from Regen ==> Longer Motor Operation Time & Range
Total Mass - Lower Mass ==> Higher Acceleration
Total Volume - Lower Volume ==> More Space ==> More Cooling ==> Low Cells Temperature