WEEK 7: Researching Electric Motors + Cars

This week, I began to look into all the different types of electric motors that could be used to propel an electric car.
These are the different motor types I found:

• DC Brushed Motor (series/shunt)
• Permanent Magnet DC Motor
• Single Phase Induction Motor
• 3 Phase Induction Motor
• Brushless DC (BLDC) Motor
• Stepper Motor

I found each has their own advantages and disadvantages for use in an electric car. Here is some stuff I researched: 

DC Brushed Motor (series/shunt):

As stated before DC motors use a DC current source, this could be from a constant voltage source like a DC wall adapter or a battery, etc. This is the most simplest motor type to power as it can come straight from a DC energy storage like batteries.

However, a DC motor construction uses a mechanical commutator to invert the DC power source for the stator coils to get an AC current. With series and shunt wound DC motors, the field coils are electromagnets that are either wound in series or parallel with the DC voltage source to create the magnetic field to cause the rotor to rotate. These motors have carbon brushes which are designed to wear to protect the commutator, so these will have to be serviced and replaced sometimes. Another downside is the increased friction and less possible RPM because of arcing at high speeds and friction/resistance losses to heat. But on the upside, DC motors are very simple to control and RPM scales with increased voltage and more torque is achieved by increased current. These give DC motors an advantage over simplicity but at a cost of efficiency and service life.

Permanent Magnet DC Motor:

These are the same to series/shunt DC motors but instead of electromagnetic fields they are created from permanent magnets (generally ferrite/ceramic for cheaper cost). These are simpler to series and shunt DC motors due to not having to power a field coil as well as the rotor. The magnetic field is fixed by the strength of the magnets, therefore a maximum torque spec is produced. Torque is determined by magnetic flux per pole (coils) of the rotor, from voltage and current, and the strength of the magnetic field. Some advantages include the simpler working mechanism, but still the friction of carbon brushes on the commutator causes less efficiencies. The permanent magnets (particularly in large DC motors) begin to take up a lot of weight and space to achieve good magnetic properties. This also begins to cost more and mould the magnets into the right shape. Therefore most larger DC motors are typically series or shunt wound (no magnets). This helps reduce weight and the electromagnetic field can be increased by variation in voltage and current to achieve better torque spec than typical permanent magnet DC motors.

Also there are several cars I have looked into so far on TradeMe:

- Mazda Lantis 1994:

 Located in Auckland:

Uses Manual Transmission

Has failed water pump - would require towing

Rego on hold, No WOF

Body in fair shape, clear coat peeling in places.

Cost would be approximately just over $1000 in total with towing, but would require a fair drive and fuel burnt to tow the car back here in Whakatane.

- Toyota MR2 1993:

Located in Whakatane (within a km)

Uses Manual Transmission

Engine is rough and running rich

Rego on hold, no WOF

Paint fading a little, primer in places, couple rust spots

Cost will probably end up around $2000 (auction) but may be less if I am lucky.

This car would be ideal to get and has a low profile and has a relatively efficient design.

The car is located a street away which makes transport very simple and no cost.