Brushless Motor From Computer Parts




About: I wouldn't say I'm a knowitall but people who know me ask me before they Google

My aim is a completely DIY brushless hubmotor for electric assist on bicycles based on recycled parts.
This is prototype 2. Prototype 1 was just a quick lashup and 3 will be full scale testing.

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    28 Discussions


    8 years ago on Introduction

    Im thinking of doing similar thing for my bicycle to generate the power. I dont have the HDD magnets yet but ill try to find these. What do you think how does the size of coil matters much? I mean is the bigger coil better then smaller?

    1 reply

    Reply 8 years ago on Introduction

    Couldn't really say about the coils but I suggest matching their size as close as possible to the magnets.


    9 years ago on Introduction

    very nice here in the us we have a festival called tour de fat which is a celebration of alternative vehicles and im building a very heavy bike so thank you for this

    1 reply

    9 years ago on Introduction

    those magnets that are used in hdd's are usually (when they are the size he is using) actually two magnets butted up to each other, insofar as they have more than 2 poles
    each one has (im not sure) a NS-NS arrangment could make a bit of a difference if that were taken into consideration


    Reply 9 years ago on Introduction

    I might do that, actually. Hadn't planned on it but with one thing and another it's been growing in my mind. Can't promise anything but keep a lookout.


    9 years ago on Introduction

    that would make a cool generator ,but would not be strong enough to power a bicycle. I once used a starter motor and a 12volt SLA battery from one of those kids power wagons,and that barely crept along,,I do plan on trying again with a ten speed ,so maybe the gears will help.

    I think on your Idea it may work if the magnets were placed along the hub ,and a series of coils were placed on a hemicircle outside the rear tire,as stated ,it would not self start but in theory would sustain the momentum you are going for some time.Thats the only way i see any amount of torque coming from such a motor ,the thing would need to be almost the same diameter of the wheel itself


    10 years ago on Introduction

    Here is an idea : Could you use this as a generator instead of a motor ? If you have it on the wheel as you described then when you pedal it should be able to output power to a battery bank. If used this way with another motor you could probably charge the batteries while they push the bike for a range extender. I am learning about this stuff, so I could be wrong.

    1 reply

    Reply 10 years ago on Introduction

    Yes, it does work like a generator if you bypass the electronics and add a rectifier (diode-bridge) and that could indeed charge a battery. Doing this while using another motor for powering the bike however runs into the laws of thermodynamics .. basically you can't get more out than you put in. Powering a generator which powers the motor powering the generator sounds like a good idea until you try it ;) I'm still experimenting with this motor to learn more about timing, switching and practical uses while I look for more magnets for the final project. I regret every harddrive I ever threw away.

    Could you use the sensor as your accelerator? mount it on a rail and slide it back and forth over the coil, to change speed and possibly direction of your bike.

    1 reply

    That sounds like a logical non-programming approach. Much like an internal combustion motor this motor need it's point of "ignition" at the right place. The right place is often a compromise. One position could give more torque while another gives higher speed. It's possible that this is less effective though. As a reverse I think it is the only possible solution except for using a microprocessor. However .. this would only alter the point of activation of the coils and not change the amount of power used for the motor.