Tuesday, 4 August 2015

DIY Long Tail EBike - Chapter 2

DIY Long Tail EBike - Chapter 2 - The Frame


The mechanical elements and the electrical elements of an e bike overlap some what. You may have to add in extra mechanical elements (extra rear sprockets & battery storage) to allow for conversion.

I have ordered most of the electrical parts needed, but some are coming from Germany etc. so  for now I am concentrating on the frame. In Chapter 1 we saw the basic concept of the bike, and the initial welds, over the last few weeks I have been "sourcing" some thinner tubing and building the rear seating and battery housing section. If you would like to learn about the electrical system the please go to chapter 3.

The main consideration is a large area in which to place the batteries. I had originally looked at using leisure batteries at around 50ah, but these were very heavy and so have opted for 22ah AGL Lead Acid Batteries, which seem to offer a good compromise. I am opting for a 24 volt system.

I have opted for a  a brushed motor, rather then a hub motor. So there is a space requirement for this too. Below is shown the space allowed within the frame for the batteries and motor. Note Duplo Brick for scale, or size 10.5 plimsoll trainer if you prefer.

A large area needed for batteries and motor.


The whole design of the bike is based around allowing enough space for large batteries, which should give very good range during use. For more detail on specification of electrical systems please see Chapter 3 (coming soon). The width of the rear seat makes it look as though it will be comfy.

Do not Underestimate Heel Clearance
Another major factor is heel clearance. It is amazing how much space you need between the bottom bracket and any protrusion further back.

Rear Frame (needn't be this complicated)
You rear frame needn't be as complicated as this one. I was working with thin tubing (10mm), and so I had to allow for frequent supports. After this ran out I switched to thicker 15mm tubing (galvanised electrical conduit), for the lower rack sections. The result is very strong.

The main tubes (dark grey) are a strong carbon steel  tube around 25mm in diameter, with a 2mm / 3mm wall. These were left over from my other cargo bike build and so they are tried and tested as strong enough.

Allow for chain routing. Run a string from the top of the chain cog to the place where the rear sprocket will be, this area needs to be kept clear. I have opted for a smaller front chain ring to allow for a lower rear deck.

For welding I have been using by old gas-less MIG welder, which is cheap and reliable. TIG welding would be neater, as would brazing, but both are more expensive. and TIG welding I have found tricky to master. A gas-less MIG welder can be had cheaply on ebay, and is useful for so many things, particularly if you like fixing things.


The supports rear of the rear axle - Not so good.
The supports to the rear of the rear axle, did not go so well. I am happy with them strength wise, but the design is poor. Vertical drop outs would allow for a stronger rear facing join in this area, but as they are slot drop outs have to be kept clear to allow for insertion of the wheel.

After welding and brushing of joints comes painting. I had some orange metal paint left over from the last bike I built so I used that. TEMAC Howard Rotovator Orange from Mole Vally Farmers.




DIY Long Tail EBike - Chapter 2 - Kit List


Ingredients for frame:











  1. BMX Frame
  2. 15mm Metal Tube Mild Steel (Galvanized Electrical Conduit £11 for 6 meters)
  3. 10mm Mild Steel Tube (sourced from child's play pen, or similar)
  4. 25mm Carbon Steel Tuve (bought from steel stock holder)
  5. Gasless Mig Welder
  6. Gloves
  7. Wire Brush
  8. 4" Angle Grinder with flap disc
  9. Tape Measure
  10. Permanent Marker
  11. Spirit Level
  12. Straight Edge
  13. 2 roles of 0.8mm MIG wire
  14. Hack saw
  15. Approx 12 hours of time.

DIY Long Tail EBike - Chapter 2 - Lessons Learned


  • Always wear gloves when working with metal. Sharp edges can delay things if you cut your hands.
  • If your garage floor is flat then assemble the parts on the flat floor and then add them to the main assembly. 
  • Once you have a few parts lined up using measurements or spirit levels, line up the other parts by eye, it is quicker.
  • Cutting tubes badly and filling with weld is quicker than filing tubes to fit curved edges.
  • Even thin tubing can be very rigid is the framing supports are closely spaced.
If you have question please ask away in the comments section below.

Learn about the electrical system in CHAPTER 3.

Flood Risk

Waste Transfer Station Permit

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