How to Build a Cargo Bike

three years ago i bought a trailer to get my son to our swimming-place or to the nice playground that's a bit more far away than the small one around the corner. everything is fine with that trailer, though i always have some kind of insecure feelings:
- the trailer is quite low and altough it has a small flag attached to a stick that should make it more visible i think it can easily be overseen by cars on the street .
- sitting in that trailer the kid is around 1 meter behind me so i don't see what he's doing or how he's doing unless i turn around. not a good idea while riding.
visiting copenhagen in december 2008 i saw lots of cargo bikes there used for transporting kids so i decided to get me one. a quick look around convinced me that buying one is no option for me (much too expensive) so i wanted to build one. since this is the first bike i built i had to go through some trial-and-error situations, but in the end all came out well. after some research on the internet i decided to build a bike similar to the christiania bike. this is how i did it:

Step 1: Recycling an Old Bike

i got myself an old crappy bike and cut it in two halves along the black line.

EDIT: If you want to build this make sure you use an old bike made from steel (check it with a magnet). Aluminium won't work!

Step 2: Frame Construction

the next thing was to construct the front frame. i thought that bigger would be better so it became 100 by 100 cm. this was not a good idea, but more about this later. what you see in the pic is the frame made of steel tubes (welded) and the rear part of the old bike.

Step 3: Wheels

the idea now was to mount the front wheels directly to the frame (see detail). looking at pics of original christiania bikes i saw that they put the wheel axis not in the middle but a bit more to the front of the frame. also i wanted to have a handlebar that can be adjusted in height, thus only two short steel tubes were welded to the back of the frame where i wanted to put the handlebar in.

EDIT: the wheel axis at christiania bikes is moved a bit to the front but still behind the pivot. mine was in front of the pivot... i changed it after riding the bike for a few months and now steering is much easier :-)

Step 4: Front Frame Test Assembly

first test assembly: looked good :-)

Step 5: Rear Part

now to the rear part of the cargobike. i took the handlebar's pivot from the old bike, welded it to a steel tube and then welded the steel tube to the rear part of the bike. the angle you see in the pic between the steel tube and the pivot was again something i saw on a pic. this was the second bad idea to do - more about it later.

EDIT: after using my trike for some time with NO angle and some discussions later (see comments below) i must say it would be better to have an angle between the steel tube and the pivot. measured at a christiania bike it should be 9.5 degrees in the direction you see in the pic - which is the opposite direction of the standard castor angle on a bike.

Step 6: Connecting Parts

the inner tube of the handlebar's pivot gets welded to the front frame and then i did a ...

Step 7: Test Assembly II

... second test assembly. it looked great and i was quite happy.

Step 8: Making It Stronger

the rear part undoubtedly had to be stronger. so i added a second steel tube and a bracing.

Step 9: Handlebar

the handlebar consists of three tubes connected with 90 degree tube-angles.

Step 10: Brakes

for the brakes (old ones from another bike) i screwed two steel plates with holes to the frame.

Step 11: Test Assembly 3

test assembly 3: looked good. but as i tried to ride it i recognized i was nearly unable to turn the bike in any whatsoever direction. after some research i discovered that the angle of the pivot might be the problem. also i read that any pedal-driven vehicle above 80 cm in width has to be checked by the authorities here. since i wanted to avoid this i had to make it smaller.

Step 12: S**t...

cutting the front frame, making it smaller and building a new pivot (taken from another old bike) were the next things to do.

Step 13: Frame

finally the frame was done. what followed was to mount the brake cables and all the usual stuff to the bike. one issue that had to be solved was how to operate the two front brakes with one handle. talking to a friend he came up with a nice solution: (see next step)

EDIT: two more improvements were necessary after some time

1) mount some cross beams between the handlebar and the front frame (see pic 2 in this step) and
2) mount some more cross beams on the lower end of the pivot to stabilize it further (see pic 3+4 in this step)

Step 14: Adaptor for the Brakes

this adaptor delivers the power of one handle to two brakes simultaneously. and last but not least one needs a ...

Step 15: Final Assembly

box to transport kids and things with the bike. that's it :-)
further improvements will be some cat eyes and other security stuff.

Step 16: Edit: Adjustable Steering Damper

after improving a few things (see the edits in some of the steps above) the last thing to do to complete this battleship was to add an adjustable steering damper. since these things can be quite expensive i built my own with a spring and a turnbuckle. works fine :-)

Step 17: Edit: Final Considerations

the measurements in this pic are the actual ones of my bike. if i would build one like this again i would change some things:

1) don't make the handle bar straight. it should be bent like in the drawing. this will save some space and allows to sit more straight.
2) use 20'' wheels for the front. this lowers the center of gravity and improves the handling on sloping grounds. the problem that arises is that you can't use the simple pivot i used - there's not enough room left between the ground and the box. a solution would be to
3) use conical roller bearings (these are parts used in cars) instead of the pivot .
4) don't build that double-break-thing for the front wheels yourself. you can purchase a better thing known as "double barrel brake lever" quite cheap which allows for independent adjustment of the two brakes.
5) adopt the size of the box to your needs. for me it's fine - i need to transport two kids and stuff at the same time (some times there are 4 kids and their things in the box...). if you don't need that much space make it smaller! because even the slightest wind is a burden if you have to pedal against it... one way to go would be to build a box from cardboard and to refine it until you think it's good. then build it from wood.
6) a camber of wheels improves the handling even more.
7) before building the frame watch some of these videos, this will help a lot: http://www.youtube.com/results?search_query=Bicycle+Frame+Building&aq=f

if you ever build a bike like this or get infected by the cargo-bike-virus and build some other construction please let us all know. post a pic or a link in the comments-section!