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Electronics newbie needs help with power assist scooter

Discussion in 'General Electronics Discussion' started by thegiantpeanut, Jun 18, 2013.

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  1. thegiantpeanut


    Jun 18, 2013
    So I am making a power assist kick scooter for a project at collage. The main focus will be its lightweight, carbon layup structure but I wanted it to have a power assist feature. This means having a dynamo connected to the front wheel charging a battery (when going downhill) then flicking a switch driving a motor when wanting a bit more "kick". An alternative ac power port would be nice to add so you can charge the scooter from the mains.
    I hope to use a basic dynamo with 6V output and a motor with 6V input. I am struggling to see what components I need to get for the battery and this is where I need help. Can someone please help by saying how I would go about having a charging battery which can have power inputs as well as outputs. What components would I be using?

    I have added a simple flow chart to try and sort out any confusion.


    The questions do not stop here I am afraid. If I connect up a motor to a cog with a chain running to the rear wheel, how would this help? Say the motor is 7000 rpm... the wheel will never be turning that fast so will the motor actually do anything or just lock up with insufficient torque? I know I could gear the cogs so a higher motor rpm = a lower wheel rpm but still could not get anything close to an equal ratio. As this is an assist function I want it to act when you "kick", effectively making your "kick" last longer. This does not need to maintain a constant speed purely from the power of the motor. (I know this isn't really a circuit question but hey ho)

    More questions! After all this (probably not that much), how hard would it be to integrate lights into the equation? So the motor and a pair of lights running off the battery but operated independent of each other. (assist will be a push button/trigger, lights would be a switch). If I get my poor physics head on, if this is a series circuit then my dynamo output p.d. will have to be equal to the light input and motor input.

    I know these are noob question but I am a noob at anything with wires so I hope you are a patient bunch!

    Last edited: Jun 18, 2013
  2. duke37


    Jan 9, 2011
    Some comments.

    A dynamo can be used as a motor so you will not need a separate motor.

    The amount of energy reclaimed will be low.

    You will need a complex circuit to adjust the dynamo voltage to the battery voltage.

    You will need a complex circuit to adjust the battery voltage to the motor (dynamo).

    The faster the dynamo runs, the smaller it can be but the gearing will be more lossy.
  3. thegiantpeanut


    Jun 18, 2013
    Thanks for your help.
    Reading a bit more, I have heard that a motor can act as a dynamo? Is this true?
    If so I could have the motor fixed to the wheel to when it turns freely without assistance it will charge the battery a little.
    You are quite right, after a little maths I realise that little charging effect would actually be given. Its more to have something so I can blab on about sustainability/eco-friendliness in my portfolio.
    I think charging it from mains would be the best way to go.
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