EI Electric Scooter
The Story of the Electric Scooter
The project was motivated by a general fascination about the natural high efficiency of bidirectional conversion between mechanical and electric power. The aim of the project was to produce a low cost but practical means of transport. The Scooter makes no concessions to the requirements of aesthetic design, rather caters for all the practical requirements, as well as providing a mobile battery test facility.
An Overview of the Overall Design Philosophy.
- DC PM motor used for simplicity of control
- Switching IGBT Regenerative
- Sealed Lead Acid Batteries used for convenience/cost
- The standing position was chosen but could use seat
- A low centre of gravity helps disguise the battery weight
Specifications of the Finished Product
- Motor Power 1.5 kW
- Weight 64 kg
- Cruise speed 34 kph
- Running cost 0.4c/km 115 kJ/km
- Fun to ride, steers easily with throttle only control
- Regenerative brakes are progressive and anti lock
- The scooter has travelled in far away places (see pics)
Performance
The range with new batteries is 30 km. With its current efficient single chain ratio gearing it cruises at 30 kph with top speed not too much higher due to the constant speed nature of a PM motor.
Longest distance travelled was 40 km with the 13 batteries and 1.5 kW motor option. Top speed recorded on that run was 46 kph down a steep hill, charging batteries hard!
The scooter has currently travelled 2,650 km at an average recharging cost of 0.45c/km.
Handling
The relatively high mass of the batteries are offset by the very low centre of gravity, allowing it to be handled easy.
Regenerative braking guarantees maximum economy, and a degree of antilock braking into the bargain.
The weight, combined with no suspension, suggests smooth riding surfaces however!
Cost
Since a practical, low cost transport method was a high priority in this project, the various parts have been obtained at bargain prices. The motor at $200, the batteries second hand used ones from UPSs, the speed control donated by Electronic Innovations, and the materials, welding, construction and mechanical design by Gary Pryor.
What are the Individual Components of the Scooter
The Motor
This is a Permanent Magnet DC servo motor rated at 1.5 or 1.1 kW and 180v. It has a high power to weight ratio, high peak torque, overload capacity and can be efficiently powered from a semiconductor controller.
AC motors could also be used, either Permanent Magnet or induction, the latter being favoured due to its constant power range, though in small sizes the efficiency is not as good as a PM motor.
The Batteries
11 or 13 off 12v 7 Ah fully sealed Lead Acid batteries. This type of battery is not ideal for a deep discharge usage but excellent in terms of ease of use and peak power output. They provide in excess of 2.6 kW for short periods when accelerating. (132v @ 20 amp).
For cost reasons the batteries chosen are the same as the batteries that are used within several APC UPSs. Electronic Innovations has a ready supply of these batteries by making use of the best second hand batteries that come from our UPS Service Center.
To maximise the life of the batteries, they are charged slowly at the C/7 rate overnight (up to 7 Hrs to charge). In Lead acid, the flooded cell is a better proposition for long life but has the disadvantage of potential acid spill.
The Electronic Speed Control
The speed control uses state of the art IGBT switching techniques with de-saturation protection, to provide smooth controllable power. The entire control unit was designed and manufactured by Electronic Innovations. It is a good example of the custom electronic design that is carried out by Electronic Innovations on a daily basis. The design used in the speed control has become a very mature and thoroughly tested product due to its use in a wide variety of industrial jobs throughout Brisbane.
The motor current is monitored and incorporated into the control to give an optimum throttle feel. Regeneration on braking occurs naturally as the throttle is turned back.
By operating at an optimum 4.5 kHz for this motor the controller efficiency reaches 97%.
The controller can also provide the 160v charging voltage necessary to charge the battery from a lower voltage source, even 12v DC.
Who is Responsible:
- Mechanical Design and Construction by Gary Pryor
- Electronic Design, Construction and Testing by Ross Pink and the staff from Electronic Innovations