Monday, 27 July 2015

DIY Long Tail EBike - Chapter 1

DIY Long Tail EBike - Chapter 1- Intro

It has been a few year now since I built my first DIY Long Tail Cargo Bike, and it has been very handy for the right sort of trip. (Skip to Chapter 2?)

A long tail cargo bike is excellent for transporting large bulky items that are light in weight think planks of wood, big boxes and christmas trees. But although I regularly use it for transporting my two children on short journeys (combined load of 40 kg), carrying a heavy load really reduces range.

The main problem is that I live in a hilly area, and any journey involves lots of hills, and lots of sweating. Anything over 15 mils carrying two kids means you will want a day or two off, there is also the the problem of gearing, as typical MTB gears just aren't low enough to pedal up the steepest hills, and pushing a heavily loaded bike is no fun (its actually more strenuous than pedaling). 

The Result

So . . . an electrified long tail will enable me to carry kids around in hilly terrain, for useful distances, more quickly, and if I need some exercise I can always hop back on my "analog" bicycle.

As with all by builds I like to keep budget way low, so I am starting off with bits I have in the garage. Which is a BMX frame!

DIY Long Tail EBike - Chapter 1- Why Use a BMX Frame?

So why use a BMX frame?

  1. Smaller Wheels = Low Center of Gravity
  2. I happen to have a BMX frame spare.
  3. BMX parts are cheap.
  4. Small Wheels equal lower gearing (motors are typically for 26" wheels).
  5. Many have 14mm axles for heavy loads
Humble Beginnings - A Mission "Grave Digger" Frame

DIY Long Tail EBike - Chapter 1-  Getting Started

You will need a welder and a hacksaw a a minimum. Do not be put off by welding, it is very easy. I would recommend a gas less MIG welder for the how user it is cheap and simple.  One can be had on ebay for less than £100, and they are handy for all sorts of things.

Before you start draw a scale drawing of you proposed bike on a sheet of graph paper, a 1 to 10 scale is good and will allow you to use a normal ruler to draw  and scale off with. 1cm = 10cm. So a BMX wheel at 50cm diameter will be 5cm.

A Scale Drawing can help you decide on dimensions and order enough steel.

A rear deck length of  As well as all the normal considerations you will need to leave spaces in the frame adequate for batteries and motors.

To preserve the bottom bracket height measure the gap between the base of the shell and the floor, after you have welded everything back together this will have to be the same as when you stared.

Draw a Line on the floor to help line things up.

Cut the frame (wear gloves) to separate the rear triangle, this frame has wish bone stays which is ideal and saves much faffing. To help get everything lined up draw a line on the floor using a straight edge, this can be used to line everything up. Once welded, it is hard to get everything apart again. 

Again you can see the line on the floor is useful for lining things up. To check for uprightness, hold a spirit level against the bottom bracket shell. There are not many points on the bike were you can put a spirit level without getting a false reading.

Here she is with the lower strut welded in place. Next up is to check that the bottom bracket is at the right height. I will need a front wheel to do that which is in the post!

We are a fair way from mounting the motor and batteries! That's for sure, but you should have already have an idea of what to use so as to leave room for them in you design.

The frame starts to come together in Chapter 2. . . 

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