Electric bikes in education

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Ebikes offer interesting opportunities for education:

• Technical design and STEM principles: An ebike as learning object can be used to study mechanics, physics and electronics.
• Technical design (advanced): At least one of the better designs was made in collaboration with an engineering school
• Technical design and fabrication (DYI): E-bikes can be hand-crafted, i.e. be used as ambitious object in a design and fabrication class
• Teaching evaluation methodology: Evaluation of e-bikes is relatively easy, and could be conducted as a class project

Designs

Types of designs

We could distinguis roughly types of e-bikes

• So-called Pedelecs, i.e. the motor only turns when the user pedals. In most systems (see legal restrictions below), the motor will fade out and cut assistance at 25km/h or 45km/h (s-pedelects).
• So-called Power-on demand. The user will turn a throttle and can either pedal or not. Such designs are illegal in most countries, although some models like the Ezee were modified to require the user to pedal and therefore become legal. Others will cut assistance at 20Km/s when not pedalling.

Power system

Motors Motors can be front or rear wheel hub motors or in the middle. All decent motors are brushless, i.e. there is not friction that would reduce its lifetime.

• Front wheel: cheapest solution, a bit dangerous when breaking on wet roads
• Rear wheel: Most possible raw power, some 500W moters do have overheading problems. Requires crank shifts.
• In the middle near the bottom bracket: The motor interacts with the bracket and then the chain.

Main makers: Panasonic, Bosch,

Batteries: Battery position is most often somewhere in the middle. Some high-end models integrate the battery in the frame. Others on top of the rear wheel. Many models offer a choice of batteries, i.e. smaller/bigger and also with respect to quality.

Currently, most batteries are either NiMH or lithium-ion batteries.

Main makers:

Electronics and motor control:

All pedal-assisted ebikes offer to control the degree of assistance (from none to high), usually about 3-5 levels

The motors can be controlled in various ways. According to Wikipedia (March 2013):

For switching or control of the motor, there are several possibilities:

• Measuring the force or torque on the signal of a force sensors on the pedals, the pedal crank, the chain or at the wheel
• Measurement of treading on the signal from a revolution counter or threshold switchs on the crank, or at another suitable location
• Measurement of both force and the speed
• Measurement of acceleration or drawbar force at the push trailer
• Measuring electrical values in the serial hybrid (pedal generator)

In addition, the speed of the vehicle are measured on the wheel, in particular, for example, to drive the motor from 25 km/h off. The measurement can be further processed mechanically or electronically and is used to control the motor on and off or to regulate a control function based on continuously.

The fed power is based on the sensor data (force sensor, crank speed, ground speed) is calculated based on the chosen level of support from the motor controller. The so-called support levels, that is, how much the motor supported in addition to the driver's performance lie in horizontal drive 5-400 percent.

Examples:

• Stöckli E.T. Urban: Force and speed sensor
• TDS Impuls Trekking XT: Force, Speed, Pedal rotation frequency, inclination
• Flyer R-Series: Force, Speed, Pedal rotation freqency
• Stromer: Force and speed sensor
• Dolphin Express: Pedal rotation freqency

Bicycle part

Frame

Frames are usually made from aluminum since both the motor and the battery will add weight.

Gears

Gears are either in rear hub (typically for models with a motor in the middle) or derailleurs (for models with a rear hub motor). Nearly all models require manual shifting, but some models exist that will select a gear to match your cadence.

Brakes:

Ebikes should have strong brakes, either disc brakes (preferrably hydraulic) or hydraulic rim-brakes. Some models offer regeneratic braking, i.e. an interface with the motor and the battery to generate energy when you break.

Suspension

An ebike should a least have some kind of front suspension, i.e. be able to cope with potholes a higher speed.

Legal restrictions

Most countries put restrictions on specifications of e-bikes:

• Switzerland defines two categories of so-called Pedelecs: 25km/h (16mph) and 45km/h. Both require that the user pedals. Limited non-pedaling assistance is allow for the second category (S-Pedelecs) that is assimilated with mopeds and require a vehicle permit and wearing a helmet. Germany has a similar solution.
• France, Australia and the UK only allow 25km/h bikes.
• In the USA, each state has a different regulation. For faster models, a driving licence, helmet, etc. can be required.

Standards:

• EU: EN15194 (EPAC – Electrically Power Assisted Cycles) defines the use pedal-assisted less than 25k/h bikes: "Cycles with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of 0.25 kW, of which the output is progressively reduced and finally cut off as the vehicle reaches a speed of 25 km/h or if the cyclist stops pedaling.”

Hacking

• Most 25km/h bikes can be easily hacked to go a bit faster. This can be very easy, e.g. a few seconds for the Panasonic middle drive and some hours for others. This is particularly interesting if you got a 350W motor.

Some interesting designs

Commuter bikes

Below a list of good designs for bikes that are suitable for both city traffic and communing and that are legal in some countries in specific versions.

• BH Neo Nitro, made in Spain.
• Stöckli E.T. Urban Confort, made in Switzerland. In the USA, a similar product is available as Currie eFlow e3 Nitro (different motor and electronics)
• Stromer ST1, made in Switzerland.

Both Swiss bikes (the Stromer and the Stoeckli) are very nice designs and - it seems - easy to handle. Reliability for both does not seem to be up to Swiss standards. I don't know about the BH Neo Nitro. It may be the best buy in this category, and Spain's industry does need some help ;)

Bibliography and links

Overviews

• Electric bicycle (Wikipedia, as of 4/2013 needs some updating)
• Pedelec (Wikipedia)