Introduction: Dinabike

Electric Bike with energy generator.
This project was developed by students from 12th of a vocational Course of Computer Maintenance at EPFelgueiras (Portugal), as part of PAP project under my orientation. The goal was to build an electric bike under European legal rools but with a good performance and autonomy that could be used daily in a frequent up and downhill area, not realy appellative for bikes uses. Half year after, dinabike as over 2600 Km (1600 Miles) with no problems at all, except for regular maintenance: brakes, tires and a few tunings.

Step 1: Stator Windings

After a logic option for a electric bike convertion kit with 250W brushless motor, rear gear and 36V 10Ah Ion-Lithium power, left to profit downhill to produce energy to improve the autonomy of the bike. After some wrong options and consequent changes we've come to this solution. We decided to Build a new axis for the front wheel, wich was able to support, inner rays, magnets and the stator. 
 We began by  the stator building a gadget to do the copper winding. 
 For a correct placement of the coils we designed and cut with a computerized milling cutter a polyester mold as shown in the picture.

Step 2: Rotor Build

The magnet were glued with epoxy on aluminum discs, side by side of stator. Once again for a correct placement we've built a polyester mold, using the some technique us we used with the stator. For a perfect fixation of the magnets, after removing the mold we gave more epoxy in the outline of the magnets as shown in the picture. As you can see, in the center hole, there's a pair of spheres ready to attach the axys. But it would be better to use bearings. See next step.

Part List:
2 x 12 neodymium block Magnets Q-30-10-05-N42 
18 cm diameter aluminum disc for magnets support
Epoxy for instant glue the magnets in aluminum discs
18 cm diameter polyester mold disc for a correct magnet position (made in CNC cutter)

Step 3: Axys Build and Mount

The front wheel axys was designed in AutoCad and build in a numerique mechanical lathe. This is the innovative part of the project
 For a correct system to function we have implemented a double pair of spheres side by side underneath the rotors. As i said before, today i will use bearings because the mounting with spheres is not so easy. You have always to be aware not to lose any sphere in a moment where you have to grip the rotors by attempts, leaving the minimum space between rotors and stator. This is fixed in the middle of the axys. Afterwards, you assemble one side, giving the needed grip. Next you have to tight by attempts because the magnet doesn't leave space to use a tool to attach the nuts even if it was on plastic, there's no space. Interior nuts have to be tight before mounting the rotor.
 Unfortunately we don't have any pictures of that assembly.

Step 4: The Tilt Controller

It was important that this dynamo could give us energy without growing friction. That's why we've included a tilt controller in our project. This dynamo is intended to work only at downhill conditions. The timer included grants that any irregularities on the roads don't revert the system state. Although it's advisable to add a on/off switch that habilitates to disable the dynamo/generator in very bad condition roads. The last two pictures in this step, show the electronic system used to double the voltage of the energy generated at the dynamo/generator using star type connection.

Step 5: Summary

In summary, I must confess that after increasing the voltage to 40 volts, there is very little amperage left. Still, it was enough to be able to increase the autonomy of the bike from 15 to 20%. I think it would be a good idea to try to put a generator on the type of brushless motor but with progressive income.
Many things were left unsaid, but I hope to answer all the questions raised by those who are interested on the subject.
For finish I leave some more pictures...



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    34 Discussions

    Looks very nice and clean !

    Is it abble to provide power to a brushless motor ? ( charging a battery ) and if so, do you know how much time is it needed to pedal ?

    1 reply

    As you may know in Europe we use the PAS system. That means you have to pedal for motor to work. If you stop pedal the motor stops too. It's much healthy I think. So, if we always have to pedal the goal was to extend the time (ou space) during which the motor can assist you.

    No. I would like to have used bearing races, it would be much easy, but not. It's really, in each side, we have 2 pars of 9 steel spheres, that we put together, one by one.

    Para além de se tratar de um projecto PAP de 4 alunos de uma escola profissional, que sempre têm alguns Euros para estes projectos, Já devem ter reparado que foi colocada publicidade nas decorações da bike que também serviu para tapar os fios. Todos ajudaram e a obra fez-se. Sem ajudas seriam precisos 1000 Euros e muitos dias de trabalhos.
    Agora em Inglês senão ainda somos castigados.

    With none publicity and if it wasn't a School project, you will need about 1000 € and a lot of days of work.

    Aluminium is better in atmosphere conditions, it is rust resistant material.

    1 reply

    I agree. the only other concern is a bimetallic reaction between stainless spokes and a allumium disk. This can make both parts oxidize.

    The glass mercury tube worries me a little.The EPA in the US is not ok. Is there another solution?

    If you increased the diameter and number of copper coils would you increase the output?

    hi im colombian, i am interesting to build this great machine, i want to have more information about how to make the alternator and how put it in the well of the bike. could you write to my mail: speaker_3746@hotmail.com

    So "loose bearings" as opposed to "cartridge bearings"?

    Not to put a damper on your product, which I think is a great idea, but
    I read in this morning Atlantic City Press, That some Towns within the State of N J, consider Electric Bikes a Motor Vehicle. And as such must be register, Insured and be operate by a Licsensed Driver.

    The city is Ocean City N J.

    Did I read that you are using alluminium for the rotor discs?
    You would get considerably better performance using mild steel to focus the magnetic flux path. Nice idea though, well done.

    2 replies

    Yes! Steel has 100X the magnetic permeability of aluminum. Think about the magnetic circuit, how the field lines pass from the magnet through the coils and back to the magnet. Use steel to follows these field lines wherever possible, every little bit of magnetic field passing through steel instead of air or aluminum boosts your efficiency dramatically.

    That's it. You are right. But if we used steel provably the bike not even moves. The idea was to reduce the tork even we use strong magnets.
    Better idea would be to have 2 or 3 combinations of windings that could be used automatically in a progressive way, giving more magnetic force in a more speed conditions. At the beginning we have thought on that but in just a school year we have no time for more. They have not only the technical disciplines, but also the Math, Portuguese, English, and so on.

    I notice that you didn't use steel core windings, or steel backed plates to increase flux density between the rotor and stator. is there any particular reason that you did it this way?

    Also, I was wondering if you did any analysis prior to building it? or was this more of a build and test approach?

    In any case, excellent writeup and a very cool build!

    1 reply

    The plates are originaly not in steel, by option. For all we knew from wind generators, if we used steel, we will have a great force to move de plates, knowing, that we'l have between 100 and 300 rpm. The option was too use stonger magnets instead of steel plates. In project we have thought on put steel plates, from old transformers in the middle of each coil but the space was very reduced.