Fabrication Manual for Chariot, Flatsy, and the “Bicycling

Fabrication Manual for Chariot, Flatsy,
and the “Bicycling Empowerment Trailer”
DRAFT
Chosing a model to build
The first set of plans here are for Flatsy, the next for Chariot, and the third for the “Bicycling
Empowerment Trailer” designed for fabrication and use in Namia while I was working for BEN
Namibia. Deep and Short plans can be downloaded from bikecart.pedalpeople.com, and set of bolt
together plans, created by Nick Lobenitz, can be requested at carryfreedom.com
Flatsy
This trailer is very easy to build, partly because itʼs all made in one plane, on a flat surface. Stored
on end, it has a small footprint, and it tracks behind the pulling bicycle very well due to its low
hitch point. Both Flatsy and Chariot use 20” wheels, which are generally stronger but often harder
to come across second-hand.
Chariot
After focusing on trailers pulled from an axle-mount based on pulling stability and fabrication
simplicity, I have a rising interest in high-mounted trailers, stemming from my work designing bicycle-pulled ambulances in Namibia, where the roads are often too sandy to cycle. Often the cyclist
must dismount and pull the ambulance trailer by hand, walking the bicycle. A high pulling arm or
a separate handle is necessary for this sort of operation. Similarly with smaller bicycle trailers, a
manual handle can convert the trailer into a hand cart and increase the utility of the trailer tremensously. The Deep and Short (DS) model has a separate pushing handle, but Flatsy does not. Chariot
is less stable at low speeds and around corners with a high mounting point than with a low (axle)
mount, and is slightly more complex to make than Flatsy and doesnʼt store as well., but it is slightly
lighter and less expensive to build, but does not store as compactly.
BEN Namibia “Bicycling Empowerment Trailer”
I designed this trailer to be built in the welding shop that are common throughout Namibia, Africa,
and other less-developed nations. Because of the intended auduence, the plans for this trailer are
written with metric units. The trailer is designed for heavier applications, including medical transport of people and supplies, and vending goods. It uses 1” OD tubing and is consequently heavier,
but also much more durable and repairable by any welder, blacksmith, or bicycle mechanic. It can
be pulled by hand or with a bicycle. This trailer can be modified to fit 20”, 24”, or 26” wheels, depending on availablilty. Contact me if you are working or living in the global south and would like
more information about the design and implementation for healthcare, income generation....
October 10, 2007
[email protected]
two designs for a 200 lb capacity bicycle trailer
details, photos, and fabrication manual at
thatʼs inexpensive and easy to build
http://bikecart.pedalpeople.com
$30 US in parts, 5 to 10 hours to build
Deep and Short (DS)
This model is designed for 26” (or 700c) wheels. It is much more complex to build than Flatsy or
Chariot, but it does have the advantage os using a more common wheel size. For an extra-sturdy
trailer that uses 26” wheels, look into using 3/4” mild steel for the fubing, or look at the I-bike
trailer design. (see links section)
Ben and Jimmy test ride a trailer built at a
workshop in Washington DC in July, 2006.
Chosing a Welding process:
I teach brazing in workshops because itʼs easy to get a good joint with only a few minutes of
practice, and tubing remains stronger and less brittle. Arc welding processes have a steeper learning
curve, Iʼve found. Stick welding will be very hard with thinwall EMT, but a wirefeed MIG would
work OK. You might want to gas weld or TIG weld if you have the experience. Just be careful to
avoid the zinc oxide fumes.
Units: Use 10mm to replace 3/8”, 51mm to replace 2”, 25mm to replace 1”, and 3mm to replace
1/8”. there are 25.4 millimeters in an inch.
please support my work: bikecart.pedalpeople.com/support.html
Creative Commons License: ByAttribution, NonCommercial, ShareAlike 2.5
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FLATSY PLANS
Material List All prices in USD
Trailer Body ($19)
(4 lengths) 1/2” thinwall EMT conduit or 3/4” OD tubing
(6”) 1” X 1” X 3/16” angle stock
(1) 3/8”-16 X 2” long bolt
(3) 3/8” -16 nut
(1) 3/8”-16 wing nut
(8) 3/4” self taping screws
Flatsy Hitch ($10)
1/4” rod (18” per cart) *
rod end ball joint (zinc plated, oiled bronze 3/8”-24)
3/8” - 24 nylon nut
3/8” threaded female coupler, 1 1/2” long (2 hitches)
(3”) 1”X 3/16” bar stock
Jig for Dropouts (use for future carts) ($4)
(1) 3/8” -16 threaded rod, 3 feet long
(8) 3/8” -16 nuts
(8) 3/8” washers
Dropouts
Tools
Cut four pieces from the 1” X 1”X 3/16” angle iron, 2” long. (Some photos here have 1” flat stock,
but use angle, or strengthen the joint with reinforcemet rings.
1/2” thinwall EMT conduit bender
hack saw
tape measure
marker
punch (or nail)*
hammer*
vice
1/8”, 3/8”, and 1/2” bits
drill
8” half round file
oxy-acetylene torch (or MIG setup)
brass brazing rod, brazing flux
goggles, and gloves
bricks or flat metal surface
Punch a small dent in the cener of the material 1” from the ends and 1/2” from the edges. With the
dropout in a vice, drill a 1/8” pilot hole, and then enlarge to 3/8”. Cut in from the end to meet the
hole with a hacksaw. The slot should be 3/8” wide. Make sure your wheel axles fit in the slots. Finish the slot with a file. File or grind off the sharp edges.
Miscellaneous and often free:
plywood for bed: 1/2” thick. 20” x 35”
exterior enamel paint for metal and wood
two 20” wheels, (front BMX wheels)
The underside of the
Hold the main frame
original
“Flatsy” trailer
together for brazing
Flatsy bending diagram for the mainframe and wheel-wells.
Obtaining Parts
The best wheels for this trailer are front BMX wheels with aluminum hubs and rims and at least 32
spokes. Next best are rear single speed wheels, without a coaster brake. Get 2 tires of similar size.
Hardware stores carry the EMT conduit and hardware. You can order the ball joint from mcmaster.
com. It is part 6072K64 for the oil-impregnated bronze race with a chrome plated steel ball and
right hand threads. It costs $5.92 without shipping (about $4). You might consider getting a welding
respirator ($12) from McMaster-Carr at the same time.
hitch brace
Not Pictured:
self-taping screws (replace pipe straps)
reinforcement rings for flat dropouts
self-tapping screws
dropouts
Hitch plate
Flatsy Frame:
Miter one end of the main frame tube.
female coupler
nylon
lock nut
hitch pin
Bend main frame following the diagram, so that the miter is in the parallel to the frame tubing
where it intersects 2” before the end of the tube. Tweak the main frame by hand to make sure itʼs in
one plane.
Braze the miter on the main frame 2” before the end of the tube, holding it in place with locking
pliers, as shown above. Cut the inside wheel wells to fit inside the frame, after mitering, so that the
wheel well tubes are 4” center to center from the side tubes of the main frame.
ball joint
3
4
Dropout placement
Pulling Arm--Flatsy
Measure the hub spacing on your wheels between the locknuts on the axle. If youʼre using front
BMX wheels, the spacing will be 105mm, or about 4 1/8”. If youʼre using rear BMX wheels, the
spacing will be 110mm, or 4 5/16”.
Cut a new piece of piece of tubing to 29” and bend a 45 degree angle 11” back from one end. Buttweld the top pulling arm (with the 11” mark) to the main frame tube, making sure that they are in
the same plane and aligned.
Braze the wheel wells in place so that the wheelwells and main frame side tubes 4” apart, center to
center.
Cut the bottom arm so that it extend all the way to the dropout. This piece should be 23.5” longer
than the top pulling arm. It will be about 52.5”. Bend at the same 45 degree angle, at 10” from one
end. Achieve the same angle by under-bending slightly and stacking the two pulling arm pieces to
sight the angle. Continue to bend the tubes until they are the same angle.
Make a dropout jig by threading 8 nuts onto a threaded rod, to hold the dropouts in place and in
line. The jig should hold the dropouts centered on the wheel wells. The flat part of the angle iron
should face the wheel.
Place the cart upside-down on a flat surface, with the dropouts on top, slots facing up. The dropouts
should be 13” from the back of the cart, to leave room for the 20” wheels. (Flatsy: make sure that
the 2” extention of tube will be on the left side of the bike when the cart is rightside up.)
Tack-braze all the dropouts in place on the edges. Youʼll need to focus the flame on the thick
dropouts to achieve even heating and strong joints. Finish brazing the dropouts. The strength of the
brazes is very important here. You shouldnʼt see any convex bumps, which indicates too little heat.
Make a large fillet braze.
Squash the end of the bottom pulling arm tube flat in a vice, so that the end can butt against the
dropout. See the diagram below. Cut off the bit that protrudes on the top, preventing good arm contact. Cut again if necessary to line up the pulling arm bends. The front of the top pulling arm should
extend 1” beyond the bottom arm. Braze the two pulling arms together every 8” or so, and braze the
end of the bottom arm to the dropout.
Use a 18” scrap of tubing to make a brace between the center front of the main frame and the bend
in the top pulling arm. Cut, miter, and braze as needed to attach the arm brace to the cart.
***If youʼre using flat dropouts: Bend a piece of 1/4” rod into four circles of 3/4” ID, each with
a 3/16” gap. Braze these rings around the frame tubes where they hold the dropouts for added
strength and resistence to dropout failure. (No photos here; check bikecart.pedalpeople.com/gallery.
html for photos and updates)***
Jake places the dropout jig 13” forward from the back of the mainframe.
Two brazed dropouts,
held by dropout jig
One side of the dropout jig: 8 nuts and 8 washers. This
one uses wing nuts, but regular nuts work better. 5
end of top
pulling arm
end of bottom
pulling arm
arm
bra
ce
Connection of bottom pulling
arm to left-side dropout
6
Hitch--Flatsy
Finishing Flatsy
The hitch clamps onto the left side of the rear axle. The trailerʼs hitch pin drops through the ball
joint and is attached with a wing nut. There is a slot cut for the wheelʼs axle, a tube to allow the ball
joint to pivot, and a rod that is braced against the chainstay to keep the hitch from twisting around
the axle. The hitch plate is a 3” piece of the 1” X 3/16” flat stock. Drill a 3/8” hole for the axle 1/2”
from the end and 1/2” from each side. Cut towards the hole from the sides to make a 3/8” wide slot.
Cut the other end at a 30-degree angle as shown below and cut a notch for the nut.
Hitch pin: Drill a vertical 1/8” starter hole 1/2” from the end of the pulling arm, and enlarge to 3/8”.
Crush the end of the pulling arm slightly around the bolt hole so a 3/8” nut just slides inside. Slide
a 2” long 3/8” bolt through the arm, from the top to the bottom, threaded through the nut inside the
arm. Slip a 3/8” split-ring lock washer on, and then thread another 3/8” nut onto the end of the bolt
and tighten it until the tube is crushed around the interior nut. Thread one more 3/8” nut onto the
bolt. Make it tight. Option: Braze the nuts and bolt together, and to the arm. Braze a 2” long tube,
4” back from the hitch pin, facing down, as shown below. This will protect the hitch piu from the
ground.
Clamp the slotted end of the hitch plate in a vice at a 30-degree angle from vertical. Hit the plate
with a hammer so that the hitch moves the ball joint about 1/2” away from the side where the bike
will be located. See the diagram below.
Holding the 3/8” female coupling firmly in a vice, carefully drill out the threads with a 3/8” drill
bit. Cut its length in half with a hacksaw and file the edges smooth. This tube will hold the ball joint
loosely so it can turn freely. Alternative: cut a 3/8” ID tube to 7/8” long. Line up the tube along
the angle of the hitch plate, so that the ball joint and nut on either end of the tube can rotate freely.
Braze securely.
Cut a piece of 1/4” rod 8 inches long. Bend the end in the shape shown in the diagrams (a hook to
go around the chainstay). Use a hammer and vice to make the bends. Braze the rod onto the opposite side of the hitch plate, at the same angle as the cut, making sure that it does not hang over the
edge of the cut. Bend the rod with a vice, hammer, pliers, or your hands until the hitch fits well on
the chainstay. The 3/8” ID tube needs to be parallel to the ground and the hooked arm should rest
on the chainstay without interfering with the spokes of the wheel.
Braze a 2” long piece of rod to the two wings of a 3/8” wing nut. This will attach the cart to the
bike, and the wing nut extension allows removal without tools. (Alternative: use a 3/8” nut with a
wrench for theft-resistance.)
Clean it all up with a wire brush, sand with course sandpaper, wash it with water and soap, let dry,
then paint the cart. Attach the wheels to the cart. Use washers if there is space between the dropouts
and hub.
Make tie-down straps out of old bicycle tubes, with the valve cut off. Use bowline knots to attach
them to the main frame, or reappropriate bungee cord ends. A nice option: Add something unique
and special to the cart. Try a pole with space for art and signs. “One less car” “Yes, Iʼm moving by
bike” “One less car; make it two?” Please send me pictures and the measurements that you used,
and tell me about your ideas--can you tell this is a passion of mine?
File everything smooth. Paint the hitch. Once dry, attach the rod end ball joint through the tube, and
secure it with a nylon nut. Make sure the ball joint can spin freely, but without play.
Wheel Guards-Flatsy
One way to make wheel guards is with two 35” pieces of tubing, bent at right angles 5” from each
end, mitered, and brazed onto the main frame tubes. This will guard the wheels, and with some
plastic, wood, or sheet metal you can protect the inside of the cart from the spokes and make a
fender as well.
The two wheel wells/guards protect cargo from the spokes.
Use 8 self tapping screws to secure the plywood to the frame.
Hitch pin assembly diagram
Make another guard that will hold the cargo to the front of the trailer. As with the wheel guards,
bend and miter from both ends. Bend at 6.5” from each end on a piece 37” long. Braze it to the
frame at a forward-slant, so that the top of the guard is at the same height as the tops of the wheel
guards.
Add a plywood bed, 20” by 35”, with small notches for the wheel guards. Use 1/2” thick painted
plywood, and attach it with six conduit clamps or self taping screws. I recommend sliding strips of
bike inner tubes between the tubing and the plywood to prevent the plywood from rattling.
7
Add a 2” long tube to the bottom of the pulling arm to protect
the hitch pin from the ground. Protect the end for user safety.
8
CHARIOT PLANS
U-joint Seatpost Hitch for Chariot and the Bike Bakki
Charriot has a pulling arm that attaches to the bicycleʼs seatpost, allowing the trailer to be used as a
hand cart as well.
Make a clamp for the seatpost with two pieces of 1”X 1” by 3/16”” angle iron, each 2” long. Cut
two pieces of the angle to 3” and weld them together to create a rectanglar tube, or use 3/4” X 1
1/2” rectangular tube. Weld one end of this tube to the center of the outside of one of the angle iron
pieces. Drill out two 3/8” nuts with a 3/8” bit. Create 2 identical bolt assemblies of 3/8” X 1” bolt,
threaded with a matching nut after the drilled-out 3/8” nut is slipped over the bolt threads. Use a bit
of 1” OD tube or a spare seatpost to holt the angle iron clamps evenly spaced, and clamp the boltnut assemblies on either side of the seatpost, in the center of the angle clamps..The result will be a
clamp that tightens around a seatpost securely. The drilled 3/8” nuts act as a stop for the bolt head
to tighten the pieces together.
Tools: Same tools for Flatsy
Material List:
Trailer Body
(4 lengths) 1/2” thinwall EMT conduit or 3/4” OD tubing
(9 1/2”) 1” X 1” X 3/16” angle stock
(8) 3/4” self taping screws
Weld two 5/8”X 1” bolts with their HEADS are touching and the shafts perpendicular. Weld two
1/2” nuts together concentrically. Drill out these nuts to 1/2”. Thread one 1/2” nut onto a 1/2” X 2”
bolt, then slide on the drilled nut assembly, then thread on another nut, leaving a 1mm gap. Weld
the outside nuts to the end of the rectangular tube on the hitch. Remove the bolt, and drill out these
nuts as well. File to allow the welded nut assembly to spin freely inside the outside nuts when the
hitch pin (1/2” bolt) is in place. This hitch pin should should slide from the nuts freely, without
turning.
Chariot Hitch
(2) 5/8” nuts
(2) 5/8” X 1” bolts
(4) 1/2” nuts
(1) 1/2” X 2” bolt
(10”) 1” X 1” X 3/16” angle stock
(4) 3/8” nuts
(2) 3/8” X 1” bolts
Remove the inside nuts, and weld a 5/8” nut to one side of the 1/2” nuts so that the holes are perpendicular. Thread this whole assembly onto one of the 5/8” bolts. Thread a loose 5/8” nut to the
end of the other bolt. Weld a small bump onto the threads at the very end of each bolt to keep the
nuts from coming off. The loose 5/8” nut should now be welded to the top of the angle iron on the
pulling tube. (Bike Bakki: Weld this nut to the end of the pulling tube, concentrically.)
Jig for Dropouts (from Flatsy Plans)
Optional Sheet Metal (for wheel guards and fenders, with self-tapping screws)
1. Create dropouts as described in the “Flatsy” plans.
2. Using a 10ʼlength of conduit, create the mainframe by and bending at 2”, 34”, 60”, and 92”.
Bend the sides in, as needed, torque the frame to make it lie flat, and cut off the remaining 4” of
tubing. Attach the ends with a coupler made for 1/2” EMT conduit. Be sure to get one made from
ferrous steel (check by bringing a magnet into the hardware store). The set screws will help hold
the coupling in place, but you should give it a bit more brazing to secure it in place.
This is your Universal Joint for the hitch.
3. Next, make a handle tube by cutting a piece of conduit to XXXXX, and bending at XXXX and
CXXXX from the ends. The end is mitered to fit on the main frame. With the mainframe flat on the
ground, hold the end of the handle 22” off the ground if you are using 20” wheels. Add 2” for 24”
wheels and 3” for 26” wheels. Braze the handle to the main frame. Create a pulling tube with two
pieces of conduit, 12” long each. Miter one end of each, and braze them to the center of the handle,
extending forward parallel to the main frame. The tubes should be touching, and be brazed together
at the ends and middle. Cut a 1 1/2” piece of angle, and braze it over the top and ends of these pulling tubes to close them and provide a surface to which the hitch will be attached.
4. Cut two wheel guards to rise from the end of the main frame at the intersection with the wheel
wells up vertically, and forward to meet the handle. This part creates a box for the cargo and reinforces the handle. Cut two pieces of conduit to XXXXX, and bend at XXXX from one end. Miter
the back end to fit the intersection of the wheelwell and main frame, and the front end to meet the
handle. Braze together, taking care to keep these parts vertical and in line with each other.
5. Weld the dropouts in place as you would for “Flatsy”.
9
10
Finishing Chariot
BEN Namibia Empowerment Cart
Use your choice of plywood, sheet metal, mesh, or fabric to fit to fit the trailer bed, wheel guards,
and backrest. Use self drilling sheet metal screws to secure the plywood in place. Complete the
trailer with sanding, painting as you chose, and create tie-down straps. Attach wheels. experiment
with accessories and be sure to let me know how this trailer and set of fabrication plans work for
you.
The Bicycling Empowerment Trailer (Bike Bakki) is designed for use and manufacture in Namibia, to address transport problems in rural Namibia and to help meet the needs of disadvantaged
Namibians through improving access to healthcare and offering income generation opportunities.
The appearance is similar to “Chariot”, but this design uses materials which are stronger and more
commonly available in less industrialized economies.
This bicycle trailer may be adapted to meet many needs—this trailer is designed to use 20” wheels,
but may be adapted for any size. Attachments may be created for the trailer, including locked
boxes, signs, sun shades, beds, and display racks.
Some possible uses
Transporting water
Shopping trips
Vending prepared food
Transporting sick passengers
Carrying bricks and cement
Rickshaw for tourists
Alternative hitch that does not require drilling, and consequently does not have a quick release.
U-joint nuts are M12 (1/2”). Seatpost clamp nuts and bolts are M10 (3/8”), sliding inside M12 nuts.
When the bolt in the center is removed, the hitch segments come apart to leave no loose parts on
the bicycle seatpost
Technical details:
Most tolerances are low, 2 mm or so, but a few are 0.5mm. The dropouts, dropout placement, and
hitch must have the most accuracy. Most steel suppliers and bike shops in Namibia carry the materials needed. The trailer is designed to be pulled by standard adult mountain and road bikes from
the seatpost of the bicycle.
Bending: all bends are done from the center of the tube, and specified for kink bending in a vice.
All bends are 90 degrees, except for two bends on the wheel guards/handle tube. To follow the diagrams, cut the tube to the overall length, mark the center, then mark the “First Bend Distance” on
each side of the center line. In the case of the outside frame, where there is a second set of bends,
itʼs still measured from the centre line.
Eliaser (left) ,Michael (cycling), and I test ride the rickshaw adaptation I created from Michaelʼs
first BEN Namibia Bicycle Ambulance prototype. Michael created the organiztion Bicycling
Empowerment Network, Namibia to coordinate the donation of bicycles to health care workers in
Namibia to improve heathcare access in rural areas.
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Tool List:
Welder (Stick, MIG, TIG, Gas, or brazing) and chipping hammer for stick
Safety equipment: gloves, clear glasses, welding mask, ear protection
Hacksaw and blades
Vice
Drill
3.5mm, 10mm, and 12mm drill bits
Sheet metal shears
Phillips screwdriver
Hammer
Permanent Marker
Scriber
Tape Measure
Grinder with cutoff wheel
Sand paper
Dropout jig: 10mm threaded rod, 1meter long, with eight M10 nuts
File
Square
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Trailer Frame:
Cut the Main Frame tube and mark the center. Measuring from the center, mark the bend lines
on each side. There will be progressive bends from the center, in each direction, to minimize
fluctuation in bending.
Bend the Wheel Guards/Handle tube in the same manner, first cutting the tube and marking the
center, then marking the bends from the center in each direction. Bend from the center out for
each side, and then bend in a perpendicular plane downward at _____ degrees, following the
included template.
Cut the two Wheel Wells to length, then miter the ends with a hacksaw, to fit inside the main
frame. Weld the Wheel Well tubes to the mainframe, ensuring that they are parallel, square, and
have an inside spacing of 90mm (105mm on centre).
Prepare the Handle Welding Jig by placing a support against a wall. Two nails spaced at 500mm
horizontally work well. This holds the center handle at 530mm above the ground. Once you add
the radius of a 26” wheel, with the dropout, the handle will rest at 815mm above the ground, a
good hitch height for most bicycles. Lay the trailer frame on the ground and place the ends of the
Wheel Guard/Handle at the back welds of the mainframe and wheel-wells. Mark the angle on the
handle, then cut and miter the handle to fit the frame. Weld in place.
Cut the Pulling Tube to 300mm, miter one end, and weld it onto the handle, parallel with the
trailer frame, and in the center of the handle.
Cut Backrest tubes to length, and miter as needed to fit from the corners of the Wheel Guards/
Handle to the
Prepare Dropouts by cutting a 10mm wide slot, 15mm deep, in 30 X 30 X 3mm angle iron.
Make a dropout jig with a 1-meter length of M10 threaded rod and eight M10 nuts. Use the jig
to hold the dropouts in place, with each pair centered on the wheel wells on the underside of the
trailer, and 100.5 mm apart (standard hub spacing is 100mm for a front hub, for the 26” mountain bike wheels that youʼll use.) Weld on the dropouts, using a 40mm long piece of 10mm rod
to reinforce each on the inside of the wheel well. The wheel well is so wide to accommodate
double-wide tyres for sandy conditions.
Cut the Tailgate Pivot Tube to length and bend as before. Miter the ends to fit the Tailgate Pivot
Tube, and weld together. Cut the Tailgate Hinges to length with a hacksaw, slide over the ends of
the Tailgate Pivot tube, and place the Tailgate in the “closed” position. Weld the hinges to the end
of the Mainframe.
Weld the chain to the tailgate and Wheel Guard/Handle tube so that the chain is tight when the
tailgate is open flat. Slide a short piece of bicycle tube over the chain to prevent it from banging
against the trailer in use.
Cut, miter, and weld on Fender supports to the sides of the Wheel Guard/Handle tubes, XXXXXmm back from the front bends.
Strngthen the kink joints by welding bits of 10mm OD rod, 20mm long, in the corners.
Finish welding the trailer frame together as needed.
13
Finish welding the trailer frame together as needed.
14
Trailer Bed:
Cut a piece of mesh (or plywood) to fit the floor of the trailer. Use a cutoff wheel on a grinder to cut
through the intersections of the mesh. Cut another piece to fit the backrest, inside the handle.
Cut the corners of the mesh to fit on the trailer frame. Weld the tailgate and bottom of the trailer bed
in place. Bend the mesh into the corner of the backrest by hitting it gently with a hammer along its
length. Weld the mesh to the backrest. Fold the top over for safety. Bend all the edges over with a
hammer and grind or file smooth as necessary.
Hitch: See directions for Chariot Hitch.
Using Bicycle Trailers
Community cart programs:
I would like to see community bike cart programs with user accountability. Imagine this: a group of people get
together, obtain some funding from the town for a community development project, and build a few bike carts.
They advertise the program in the town/neighborhood, and offer the use of these carts to anyone. For a small
deposit of money, barter equivalent, trust, etc, you get a key that unlocks the bike carts from wherever they are.
You have designated locations where they live, where you might expect to find a cart. In this way, many people
can use a few carts. The carts could either have designated bicycles, or you can attach the hitch to your bike
when you get the cart. Carts from workshops are in Northampton, MA, San Francisco, and Washington, DC.
Weight capacity
I recommend a 200 pound weight limit. You will be able to load more weight if you donʼt ride on steep sideslopes or turn corners quickly. Balance the load just in front of the wheel axles. Secure the load with straps,
especially on bumpy roads. When pulling, donʼt go around corners too fast when the cart is empty, because it
could flip over. Donʼt go around corners too fast when itʼs heavily loaded, because the sideways force on the
wheels could cause them to buckle. Donʼt jack-knife the trailer when backing up or turning.
Finishing:
Sand, clean, and paint the trailer.
Trace the outline of the wheel guard/handle tubes onto a piece of sheet metal, 0.6mm thick galvanized. Add 25mm to the bottom, Cut out the shape, and bend 10mm up at the bottom.
Cut out these two pieces of sheet metal, bend the bottom up 10mm. Drill holes and use self-tapping
screws to attach this fender to the trailer frame. This sheet will be positioned on the outside/wheel
side of the fender tube.
Cut two more sheet metal pieces to be the top fenders. Bend one long edge in 10mm, and bend the
other twice for stiffness.
Attach wheels.
Apply grease to the hitch threads and backrest pivot tubes.
Attach the hitch to a bicycle seatpost.
Weld a M10 nut vertically onto the end of the hitch pin, and tie string around the first bolt from the
pulling tube, and through this hole. The hitch pin slides through all the M12 nuts to connect and
disconnect the ambulance without taking off the hitch from the bicycle.
Test ride.
Investing in an alternative to cars
There is a significant amount of embodied energy and chemicals involved in the fabrication of these trailers.
The steel industry has a long history of chemical pollution and labor exploitation. I donʼt know whatʼs in brazing flux, or what the process of galvanization is like. Brazing conduit releases zinc oxide and other chemicals.
The paint used to protect the joints is dangerous, and paint cans have a disposal problem. Recognizing all this,
bicycle trailers can replace a technology that is much more chemical, energy, and exploited-labor intensive: the
automobile. The health benefits from transporting oneself by bike are significant. I encourage you to treat this
project as an investment in an alternative to cars, and as such its usefulness will outweigh its social, environmental, and financial costs.
Glossary
•EMT Conduit: The kind of tubing used for the cart frame. It is used to protect electrical wires. You want
“Thinwall EMT conduit.” The outside dimension (OD) for 1/2” EMT is about 3/4”.
•Jig: A device to align the dropouts and hold them at the correct spacing.
•Miter :A fitted connection between two pieces of metal. In this case, it is a 3/4” diameter half-circle cut out of
the end of a tube.
•Dropout: The slotted piece that holds the wheel axles.
•Hitch: The connection between the bike and the pulling arm. It is a piece of flat metal with an arm that hooks
around the chainstay. There is a ball joint on the bottom of the hitch.
•Rod-end Ball Joint: A universal joint that spins freely around two axes and about 15 degrees in the third. It
allows the bike to lean, turn, and go over bumps independently of the cart.
•Oxy-Acetylene Welding/Cutting/Brazing torch: This setup burns oxygen and acetylene in a hot flame from a
welding tip. There are a lot of oxy-acetylene torches around. Check with farmers, automobile and equipment
repair people, neighbors... If you find an arc welder that you want to use instead, seriously consider buying mild
steel tubing instead of galvanized EMT, because welding galvanized tube is difficult.
Test of double-wide tires for ease of use
in sand--these wheels are used on some
bicycle ambulances in Namibia. (Anyone want to help quantify their usefulness? We need to test force to pull
trailer in deep and shallow sand, and on
firm ground, with different loads.)
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CarryFreedomʼs bamboo trailer. Plans are available from Nick at carryfreedom.com/bamboo.html
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Design principles for bent-tubing welded bicycle trailers
Safety Considerations:
Many different styles of trailers can be made to be safe and stable. This section will help you design
your own trailer.
Ventilation:
Braze outside, and keep air moving across the work, with a fan or align yourself with wind so that
the smoke blows sideways. (If your back is to the wind, your body will stop the airflow in front of
your face.) Donʼt breathe the smoke plume, and keep your head back from and never above the area
that you are brazing.
Hitch point: Do you want a hand cart in addition to a bicycle trailer? You will either need a
seatpost-mount hitch or a separate handle. Seatpost hitches are a bit trickier to build, but save having a separate handle. After years of thinking that they destabilized the bike, Iʼve used them now
extensively with bicycle ambulances, and donʼt have problems with them, for weights under 200
lbs. Design the trailer to be flat when it is on the bike, or slightly angled down towards the bike.
Rule of thumb: 32” is a good height for the hitch on the seatpost, that will work with many different
bicycle geometries. Grab the seatpost for a highh hitch, and the left side dropout plus chainstay for
a low hitch (or left side chainstay AND seatstay for a heavy-load hitch. U-Joint mechanism: I donʼt
personally like rubber or springs for this, but theyʼll work. Use threaded nuts and bolts to make an
elegant and inexpensie U-joint
Length: Leave enough clearance for the bicycle wheel, but not so far that itʼs unweildy, or requires
a massive pulling arm to eliminate flex. The farther back the wheels from the bike axle, the nicer
the ride is--a good consideration if youʼll have passengers or delicate cargo (thanks to all the people
who asked for advice to build trailers from which to sell pastries, choolocates, and sweets.
Wheel size: Use 20” if theyʼre available (and can be replaced--bike ambulances are limited to 26”
wheels. A smaller wheel keeps your cargo low, while using a simple design, and the smaller wheels
are stronger laterally (for corners and sideslopes).
Frame size: If youʼre using conduit, you might be limited to 10 foot lengths--Flatsy and Chariot
are designed with this in mind to minimize waste. If youʼre using steel tubing from a steel supplier, 20 feet is a common lenth, and you can be creative. A 1/2” EMT conduit bender works with
3/4” OD mild steel tubing, up to 0.065” wall, but itʼs more difficult. 7/8” tubing is an ideal size for
slightly larger trailers, but good luck finding a bender for it. I havenʼt experimented with 3/4” EMT
conduit benders for 1” OD pipe of larger wall thicknesses, but I imagine it would be a struggle.
The bend radius on a 1/2” EMT bender is 4 1/2”, which is about the width needed for the wheel
wells. The 3/4” EMT bender (1” OD) has a much larger bend radius, and so is not ideal for simple
frame design. Try to avoid lengths of tubing longer than 18” that donʼt have joints or bends, for
structural stability.
Frame design: Find the radius of your bender, by taking a 30” long piece of tubing, marking the
center at 15”, then marking and bending at 5” to each side of the center to make a “U” shape.
Meausure the distance of the legs, center to center. Subtract 10” for the center section, and divide
by two to get the bend radius. Multiply by pi, 3.14, and divide by two to learn the amount of pipe
taken up by a bend. For a 1/2” EMT bender, the radius is approximately 4 1/2” and the bend length
is 7. When designing your frame, consider the total length of tube, and the desired width, then determine the length. If you have access to a Hossfeld-style tubing bender, you can be more creative
with your frame design. I like a two-piece design for the frame, consisting of one backward facing
“U” piece, and an outer piece bent four times to close the “U” and make the wheelwells.
Load Balancing: Locate the wheels slightly back from where the center of gravity of a loaded
trailer will be, by about 4”
About Kink Bends: You can also bend tubing with a kink in a vice. Generally, youʼll make your
bend mark 1/3 of the tuning width inside of where you want the
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Respiratory Protection:
If you cannot ensure adequate ventilation, wear an N95 (or higher) type respirator. You can buy a
N99 filter respirator from McMaster-Carr for $11.34 (Part #53565T2). The instructions say itʼs only
good for 8 hours of breathing through, or until it gets hard to breathe through.
Eye protection:
Use #5 shade eye protection for brazing (and clear glasses for drilling). If you look at the flame for
a second, youʼre not going to lose your sight, but itʼs bright and bad for your eyes. Iʼve heard that
your eyes are safe 10 feet back from the flame.
Heat Protection:
Use gloves when you might come in contact with hot metal or a flame, but never for a grinder, drill
press, or other spinning tools.
Metal Fume Fever Information
You are heating galvanized metal, which is coated in zinc. The zinc will burn off and oxidize in
the air, creating zinc oxide. Breathing zinc oxide can cause Metal Fume Fever. According to the
American Welding Society, Metal Fume Fever is an illness caused by exposure to zinc oxide, a
chemical present in fumes from welding and brazing galvanized metal. The symptoms of metal
fume fever are flu-like, including headache, nausea, fever, fatigue, and chills. Symptoms start several hours after exposure and last 6 to 24 hours, although total recovery might not be for 48 hours.
High levels of exposure may cause metallic taste in mouth, dry and irritated throat, and coughing.
Several hours after exposure, you may have a fever (lower than 102 degrees F, then chills before
returning to normal). The OSHA standard for zinc oxide exposure is 5 miligrams per cubic meter of
air averaged over an 8 hour work shift. NIOSH uses the same 5 mg per m^3 (cubic meter), but suggests that it is permissible for 10 hours per day, or 40 hours per week. They further permit a STEL
(short term exposure limit) of 10 mg/m^3 averaged over a 15 minute period. There is no published
information about long term effects of zinc oxide exposure. (American Welding Society. Safety and
Health Fact Sheet No. 25)
Even though there are no known long term effects, it doesnʼt make sense to expose yourself to zinc
oxide and potentially suffer from Metal Fume Fever, because itʼs easy to prevent exposure. Brazing,
as opposed to welding of galvanized metal, produces fewer fumes because of the lower temperaures.
In the process of designing and learning to build bike trailers with galvanized conduit, I got metal
fume fever twice, through carelessness. You should be careful, and I think it is possible to braze
EMT conduit safely. The sickness felt like the head and body ache that are symptoms of influenza. I
felt dehydrated and tired. I felt fine the next morning.
Protect yourself from exposure.
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Using the Tools
To use a conduit bender, line up your bend mark with the arrow on the bender. Step
on the foot plate, while pushing down and pulling back on the bender handle. Bend
until the bubble level reads level with no force on the handle.
Use two hands on a hacksaw, and the full length of the blade with gentle but even,
forward cutting force Cutting happens on the forward stroke of hacksaws and files.
Pulling back with downward pressure on the file will only dull the file or blade. File
and cut close to the vice.
To drill into metal, make a starting dent with a nail, and drill a small hole at high
speed with a sharp metal bit. To enlarge it, use a lower speed and watch out for the
bit catching as it breaks through the material. Always drill into material secured in a
vice or by clamps.
General safety: Wear gloves when things are hot, donʼt wear gloves with spinning
tools. Wear safety glasses when there are chips flying (drilling, cutting). Wear shoes
or boots and long non-flammable clothes when working with the torch. Donʼt
breathe fumes from cutting, heating, or painting. Have fun and take care of yourself
so you can ride your bike and pull your bike cart and tell your friends how great it is
to not use a car.
How to braze:
This description is not meant to replace instruction by someone with experience with torches.
Brazing is the welding process of bonding surfaces by heating them to a temperature above the
melting point of the filler material, but below the melting point of the base material; the filler material is drawn into the joint through capillary action. To braze a joint, heat up both metal surfaces to
a temperature hot enough to melt the filler material (usually brass). Brazing is more effective than
welding for galvanized steel because is compatible with the zinc coating.
Put on gloves and number 5 shade goggles. Ensure adequate ventilation and use a respirator. Turn
on your oxy-acetylene torch setup. First close the torch valves and make sure the regulators are
disengaged (counter clockwise). Open the fuel (acetylene) tank valve 1 turn, while looking away.
Usually, you will set the regulator to 10 psig. Open the oxygen valve all the way, and set the regulator to 10 psig. Bleed the gasses out of the torch handle by opening and closing the acetylene, then
the oxygen valves. Open the fuel valve on the torch handle, and light it with a flint striker. Adjust
the flame so that it almost creates a gap (without a flame) right at the tip of the torch. It is too low if
it produces a lot of smoke. Add oxygen until the two visible flame cones come close together. For
fine work, you will want the cones to merge. For general heating, keep them separate.
Coat the surface to be brazed with a brazing flux paste. Heat the two base materials with the flame,
just beyond the inner cone. When the metal starts to shimmer a little, touch the brazing rod to the
hot metal. The filler rod will flow into the joint. If the metal is too hot it will spark. If it is not hot
enough the rod wonʼt melt. Go all the way around the tube, creating a good fillet. The strength of
the joint comes from the surfaces joined in close contact with brass and from the fillet (smoothedout corner) between the base materials. DO NOT BREATHE THE FUMES FROM BRAZING
GALVANIZED METAL (EMT conduit). Use good ventilation and a welding respirator.
Turn off the torch by first closing the fuel valve on the torch handle. Then close the oxygen valve
on the torch handle. Close the valves on the tanks, and open the torch valves to bleed the lines.
Unscrew the regulators until they are loose. Close the valves on the torch handle.
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images from microcosm publishing
Philosophy and Social Theory: bike carts are political
Iʼve been designing carts that people can build in their communities for a low cost, with fairly basic
fabrication skills and access to common tools. Through making carts, people can build community,
and extend that farther by sharing their skills or starting community cart programs, in which a lot of
people can use a few carts/bikes.
Car Independence: In my opinion, cars are problematic because they support global industrial capitalism and the outsourcing of manufacturing to the people who are hurt the worst by industrialism.
They also support militarization and environmental degredation of oil-rich areas of the world for
access to cheap energy. Our use of cars releases greenhouse gases into the atmosphere, and burns
dirty fuel in inefficient engines where the combustion byproducts poison humans, other organisms,
and the land. Additionally, the automobile paradigm takes us out of small centralized communities
where we could work, live, and play, and spreads us out to the far reaches of sprawling development where we use our cars to go everywhere and isolate ourselves from our neighbors, local small
businesses, and family.
Why bike carts? Too often people complain that they would ride a bike except they canʼt carry what
they need for work, that they canʼt bring their children, that they have to pick up a bag of potting
soil that they couldnʼt possibly fit on their bike with the groceries...sound familiar? Bike carts are
a great solution, but most are expensive (for a cart that can haul 200 pounds, $300 to $500 USD).
This cart weighs 25 pounds, costs $30 to build, and will carry more weight more securely than
many commercial bike carts. So this is a zine about making bike carts, but itʼs also about finding a
way to gain independence from our cars and to build community by fabricating, playing, and biking
together. Reclaim transportation technology and empower ourselves by taking technology choices
and development back into our own hands.
Cars teach us that to get around, we need to spend lots of money to buy something which is environmentally damaging. They teach us that when something breaks, we need to take it into a shop,
send away for parts, and pay lots of money, and eventually start all over again with a new car. You
canʼt build them, fix them very easily, grow fuel for them (for the most part: read on vegetable oil,
ethanol, and biodiesel), or reuse their parts efficiently.
If we question cars, we learn that we can lessen our impact by buying a less-bad car (small car,
hybrid, grease, biodiesel), and that less-bad is a fine way to be. Make that choice for yourself.
One Less Car
make it two?
azuki bean: my 2-speed break-away bike frame for travel.
the coupling plates are 1/4” flat stock with two 1/4” bolts.
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The images on these two pages may be under copyright.
CycleTote
Bikes At Work
BicycleR Evolution Shopper
Bob Yak
summer, rebecca, dan, lillian, and aaron
drumbent.com conduit trailer
my first prototype
Joe Bielʼs trailer,
used at Microcosm Publishing
Burley Flatbed
Koolstop Kool Mule
Ingrid fitting a modified bicycle trailer to a wheelchair
Koolstop Wilderbeast
Burley Nomad
Carryfreedomʼs
Y-frame
Radicaldesign Cyclone
donna picking up hay bales in deep and long
Cancart by Bikecartage
I-bike trailer
Bikes at Work
Human Powered
Machines: Hauler
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from cyclecircus.org ... another design for a weldless bike
trailer. the chain in the hitch is a free version of a universal
joint, but it allows the cart to tug on the bike. the design could
be strengthened considerably with a little bit of welding.
Extracycle
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commercial bike carts:
http://www.bikesatwork.com/bike-trailers/
http://blueskycyclecarts.com/
http://www.burley.com/
http://www.bobgear.com/
http://www.bykaboose.com/
http://www.efn.org/~equinox
http://www.bikerev.com/
http://koolstop.com/trailers/beast.html
http://www.xtracycle.com/html/home.php
http://www.cycletote.com/
http://www.karstilo.net/bike/trailer/index.php
http://www.radicaldesign.nl/
http://www.efn.org/~cat/hpm/
links
Bicycle Pulled Ambulances in Namibia
Bicycling Empowerment Network, Namibia
home made bike carts:
http://carryfreedom.com/bamboo.html
http://www.re-cycle.org/trailer/
http://www.ibike.org/economics/trailer.htm
http://www.cyclecircus.org/cyclecircus/diy.html
http://drumbent.com/trailer.html
http://home.clear.net.nz/pages/joecolquitt/0trailer.html
http://www.motherearthnews.com/arc/6645/
actions, social theory, economics
http://benbikes.org.za/namibia
http://bikesnotbombs.org/
http://bikekitchen.org/
http://pedalpeople.com/
http://www.carbusters.org/
http://www.carsrcoffins.com/
http://www.bikesatwork.com/carfree/
http://www.guerillastickers.com/
http://www.critical-mass.org/
http://bikeforpeace.org/
http://www.carfree.com/
paying my respects...
http://www.communitybike.org/
http://www.workbike.org/
http://www.worldcarfree.net/
http://www.carsharing.net/
http://www.kenkifer.com/bikepages/
http://www.catoregon.org/
http://www.journeytoforever.org/biofuel.html
This bicycle ambulance is in use by Obome Oto HIV/AIDS Home Based Care volunteers in Oshandi, Ohangwena region in namibia. These heath care workers use bicycles to reach their patients
in the rural areas, and when further medical attention is required but traditional transport unavailable, they collect their patients on the bicycle ambulances.
aaron on his first tallbike, 2004
metal-working and supplies
http://www.handyharmancanada.com/TheBrazingBook/bbook.htm
http://www.mcmaster.com
Paulina and Josh test ride the Bicycle Ambulance
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From October 2006 to October 2007 I was working in Namibia with the organization Bicycling
Empowerment Network Namibia, designing a bicycle ambulance appropriate for use and repair
in rural areas of Namibia, and training local fabircators in the design and manufacture of ambulances and trailers. BEN Namibia also facilitates the donation of bike to Namibians working as
HIV/AIDS home based care volunteers, and coordinating programs for Orphans and vulnerable
Children (OVCs). We also provided training on safe use, operation, repair, and management.
To find out more or to support this project, visit Aaronʼs blog at
http://namibikes.wordpress.com
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and BEN Namibia at http://benbikes.org.za/namibia