Drive
From Trevipedia
The drive system comprises the motor and transmission. Motor control is discussed elsewhere.
The UniSA prototype drove the single rear using synchronous belts in two stages:
- a 3:1 reduction from the motor to the swing arm axle
- a 2:1 reduction from the swing arm axle to the rear wheel.
In the prototype car, the motor was inside the tub chassis under the rear seat and the belts passed through a hole in the back of the tub to the rear wheel. A better design would have the motor and rear wheel assembly completely outside the tub; the drive assembly could be built out of the car, then the car lowered onto it.
The process for selecting a motor is:
- determine torque and power requirements for hill climbing, high-speed travel and acceleration
- select a motor and transmission that can deliver the required torque and power to the drive wheel.
You should select your motor before designing the battery.
Motor performance requirements
The design requirements for the UniSA prototype assumed that the laden mass of the car would be 410 kg. The torque and power required at the road wheel were
| torque (Nm) | power (W) | duration | |
|---|---|---|---|
| driving slowly up a 20% grade | 290 | - | 10 seconds |
| climbing a 50 mm curb | 230 | - | 10 seconds |
| driving at 90 km/h up an 8% grade | 150 | 13000 | 10 minutes |
| 100 km/h on a level road | 48 | 4700 | continuous |
Accelerating to 100 km/h in under 10 seconds requires even greater torque and power. Furthermore, getting the required power to the road through a single rear wheel is a challenge.
Selecting a motor
Some general principles for selecting a motor are:
- Trev needs high efficiency at city speeds and low loads.
- A high-speed motor will be smaller and lighter than a comparable low-speed motor. The UniSA prototype used a motor spinning at 6000 rpm, with a 6:1 reduction to the rear wheel.
- A motor with permanent magnets will have greater power per mass and power per volume than a motor without permanent magnets.
- Increasing the motor diameter will increase the torque.
- Air-cooled is simpler than liquid-cooled. Trev does not require a lot of power, so air cooling is usually adequate.
Motor options include:
| motor | type | torque (Nm) | power (kW) | speed (rad s-1) | voltage (V) |
|---|---|---|---|---|---|
| Perm PMS 156 | PM S BL | 6.5 / 18 | 100 / 600 | ||
| Agni 95 series | PM B | ? / 52 | ? / 26 | ? / 500 | 72 |
| Agni 143 series | PM B | ? / 60 | ? / 22 | ? / 370 | 84 |
- Motor types: PM = Permanent Magnet, S = Synchronous, BL = Brushless, B = Brushed
- torque values are continuous / peak
- power values are continuous / peak
- speed values are rated / maximum, 100 radians per second is about 1000 rpm
- voltage is the maximum motor voltage.
