PEDALEC

There are two types of electric bikes, the bikes that just help you with pedaling and the ones that drive you without pedaling.

A team of 3 students from faculty of Electrical Engineering Ljubljana had decided to enter a European competition of building a home made pedalec bikes. With help from a few larger companies and few professors from this faculty we completed the project in just two and a half months.

 The team members were Jan Božeglav, Jan Markič and Urban Bevc.

Our vision was to make the least modifications as possible to the bike, and to maintain possibility of normal bike usage.

We had so many ideas about the design so we decided on making two bikes instead of one. Because we wanted our designs to be unique and original we tried to avoid parts like hub motors instead we used a simple brushless motor found in an ordinary car as a steering servo. The engine known as Delphy was produced by company Letrika (formaly caled Iskra Auto Elektrika) for Opel. It was designed to run on 12V DC at which it would give out about 250W, 3 Nm and 3600 rpm. We increased the max speed to 7000 rpm and decided to use differential to reduce rotation speed and to increase torque.

The two designs we decided on were pretty different.

Design N°1

One idea was to put entire structure, engine and electronics on the back "trunk" of the bike and then connect it directly to the rear wheel.

With this design for reducing rotation speed of engine shaft we used a two stage planetary reducer (20:1) and a chain reducer (15:14) which gave us a total ratio of 21,4:1.

This ratio meant we would have up to 64,2 Nm of torque on the rear wheel axle which is comparable to an average biker. 

Design N°2

The second idea was based on using changeable gear ratios which help you with gaining higher speed and with driving steep terrains. The whole concept was made possible by the common rear transmission that is used on all bikes and by splitting front gear and pedals and inserting a unilateral obstruction to prevent spinning the pedals while the engine is running. The engine was mounted under the bottom of the frame using a custom made bracket and is fixed to the frame using bolts for bottle holder. The gear ratio between engine and wheel varies between ?????????? and is changeable in this area during cycling.

The project was put to the test on 19th of April 2012 in Maribor where it was entered in to the already mentioned competition. Due to a lack of testing time the bike preformed better than we thought it had just one minor glitch which was discovered on the race and it cost us valuable points in first run (endurance) and the entire second run (heavy climb). The glitch was discovered when we tried to do the second run when the bike had almost no torque and the bike barely moved. When we were putting the bike together we made a bracket for a total position sensor out of plastic and this sensor was telling our electronic the position of the motors rotor so the motor was properly controlled (we were using vector control for maximum efficiency). While the engine was running the body of the engine was heating up and it was deforming the plastic bracket which moved and caused the engine to lose torque. The solution was figured out at lunch and was abolished with recalibration of the sensor.

We finished on 5th place. Even knowing we could have done better we are satisfied with the place in which we finished.

You can find more info on the organizer's web site and other links.

Organizer's website:

http://e-bikes.uni-mb.si/

Links to other media:

http://www.youtube.com/watch?v=5IJr8_neYE0 

http://www.youtube.com/watch?v=jRFywLcuIH4

http://www.facebook.com/ebikes.umferi?ref=ts

http://mehatronika.fe.uni-lj.si/pedalec/

In the name of the whole team I would like to thank everyone who helped us with this project.