Electric bikes in education

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Introduction

Electronic bikes (ebikes) most often refer to some kind pedal-assisted bicycles.

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

Ebikes in technical design classes

A good example is the Swiss [ Stromer].

Ebikes in fabrication classes

Ebikes in evaluation of design classes

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 since it doesn't need to interact with the gears, 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.

Power output:

  • Pedelecs: 250-350W (in some countries only 200-250W are allowed and the output is electronically locked)
  • S-Pedelecs: 350-500W
  • Other: Up to anything ....

Torque:

  • 20NM (Pedelects)
  • 30-40NM (S-Pedelecs)

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 the lighter Ion-lithium batteries.

  • Energy: between 250Wh and 500Wh
  • Voltage: typically 36V
  • Capacity: typically between 8 and 20Ah.

More output means more weight and more money. A high-end battery costs at lot. E.g. the big Swiss Stöckli 23.2Ah costs 1800 CHF (1400 Euros). The small 11Ah is 990 CHF.

Main makers: Panasonic, Samsung

Electronics and motor control:

All pedal-assisted ebikes offer to control the degree of assistance (from none to high), usually about 3-5 levels. Support ranges from 50% extra power to 300%.

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

Controllers:

A decent controller should offer at the least the following

  • Energy display: charge level
  • Speedometer
  • Selection of output:

Optional:

  • Boost mode and push assistance
  • Regenerative breaking, current comsumption, kms to go, etc.
  • Trip data,

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

(As of spring 2013, i.e. it maybe be totally outdated sometimes in the near future)

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.

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

Tests

User communities and websites

All in German (sorry, but Germany is the Pedelec country together with Switzerland)
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