Will this ebike project work?

Discussion in 'Electric Bicycles' started by primetime2020, May 13, 2015.

  1. primetime2020

    primetime2020 New Member


    I live in an area that is very hilly. I was looking to buy an ebike kit and a battery to go along with the kit but it is beyond my budget at the moment. So, I decided to build my own ebike kit. I was thinking of stripping a brand new cordless electric string trimmer and using the motor to chain drive the back wheel. I am thinking of attaching the motor to a rack in the back. I would have to take the throttle from the stripped assembly and attach it to the bike's handle bar with a twist-on wire connector to extend the throttle far enough to reach the handle bar.

    Here is a drawing I made of the setup:


    I am looking at this trimmer as a possible choice for this project:


    Is 40v enough for my needs? Will it reliably ride up steep hills without burning out the motor and making it unusable?

    where can I get the chain sprocket that I would need to attach to the motor arm?

    Which type of chain should I use?

    Looking at the picture on that homedepot product page, it seems like the motor is within the trimmer shaft next to the throttle. Will it be compatible with the setup I want to achieve?

    Last edited: May 13, 2015

  2. jaguar

    jaguar Well-Known Member

    I would think that such a light duty motor wouldn't have enough torque to propel a bicycle (well, maybe without a rider it could)
    libranskeptic likes this.
  3. libranskeptic

    libranskeptic Member

    I second that you are trying to make a silk purse from a sows ear with that motor. Very different intended tasks.

    hilly and cheap, tough combo. Assuming you are not really heavy anyway, a light bike helps. maybe an old but good 28" dropbar (wind is easily the biggest hinderance at ebike speeds) chrome moly roadbike (~12kg vs ~20kg for an alloy MTB) with a hub motor, and resign yourself to some light pedal assist on the steepest bits.

    The simplicity of a front hub geared (much lighter) motor appeals. There are 2 speed hub motors from china which sound well worth the premium

    a lighter bike means another riders upgraded battery may be had cheap, yet be OK for you.

    Start by deciding on the most expensive and important bit, the battery. Once thats done, you have a sense of proportion about what spend on the rest.

    I would consider 24v, but its a long story. I prefer 8x 3.4v 20ah = 480watt hr pouch cells, to say, 12 smaller 15ah cells for 36v = 540 watts

    fewer bigger cells sounds cheaper and better.