Atomic Zombie StreetFox User manual

Build the StreetFox Recumbent Trike
Another Atomic Zombie™ Extreme Machines Adventure
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StreetFox Tadpole Trike
Table of Contents
About the StreetFox............................................................................................................ 3
Forks, Crowns and Head Tubes.......................................................................................... 6
Axles and Mounting Tabs................................................................................................. 14
The Frame......................................................................................................................... 25
Seat Tube .......................................................................................................................... 30
Front Wheel Arms............................................................................................................. 37
Joining the Booms............................................................................................................. 45
Head Tube Angles............................................................................................................. 49
Suspension ........................................................................................................................ 59
Brake Support Arms ......................................................................................................... 62
Ackermann Steering.......................................................................................................... 70
Bottom Bracket and Derailleur......................................................................................... 79
Pulleys and Chains............................................................................................................ 89
Seating............................................................................................................................... 92
Handlebars ........................................................................................................................ 94
Adjustable Backrest.......................................................................................................... 97
Return Chain Idler........................................................................................................... 100
Front Brakes.................................................................................................................... 103
Basic Seat Design ........................................................................................................... 105
Trim Excess Main Boom and Paint................................................................................ 114
Final Adjustments and First Ride ................................................................................... 116
Showing Off Your New Wheels!.................................................................................... 123
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StreetFox Tadpole Trike StreetFox Characteristics
About the StreetFox
The StreetFox Recumbent Trike is a fast and comfortable version of
the classic "tadpole" style trike (two wheels in the front), which includes rear
suspension, three wheel braking, and 26 inch rear wheel for optimal gear
range. The StreetFox looks and handles as well as many commercially
produced trikes, and can be completely built using commonly available and
inexpensive bicycle components and some square tubing. Not one single
machined part is needed.
The StreetFox also includes an adjustable bottom bracket so it can fit
riders of just about any height from 5 feet to well over 6 feet tall. Due to the
rugged construction and use of sturdy 14 mm axle, 48 spoke front wheels,
the StreetFox can accommodate riders over 250 pounds. There is plenty of
room for customization due to the simple mono boom frame, so you can
alter the design to suit your own style or needs.
Figure 1 – A 26 inch suspension frame and rear wheel
The good news is that the entire rear of the trike is an unmodified
stock rear triangle from a typical suspension mountain bicycle. As shown in
Figure 1, you will need the complete rear triangle, the suspension spring, and
at least the part of the main frame that contains the tube that connects the
rear triangle to the frame, allowing it to pivot. The front part of the frame is
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StreetFox Tadpole Trike StreetFox Characteristics
not important, so it can be in any shape as long as the rear of the frame is
perfectly functional.
Since you can purchase an entire bicycle for not much more than
$100, I decided to work with new parts, as this would ensure the suspension,
wheel, and brake parts wee all in perfect working order. I ended up using the
front half of the mountain bike for an electric project called "The Long
Ranger", so every part of the inexpensive department store bike went to
good use. If you decide to consult your scrap pile or the local dump for parts,
ensure that the rear brakes are working, and that the rim is not damaged in
any way.
Figure 2 - A pair of 20 inch BMX wheels
One of the main concerns when designing a tadpole type trike is how
to connect the two front wheels to the steering components. The obvious
answer would be to simply find a pair of typical 20 inch front wheels then
move the threaded hub axle to one side and then bolt it to something strong
enough to support it. This answer is partially correct. The problem with this
approach is that a typical bicycle hub will not have an axle strong enough for
connection on a single side, and your axles would bend as soon as you enter
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StreetFox Tadpole Trike StreetFox Characteristics
the first corner, or before you even make it to the end of your driveway if
you weigh more than 180 pounds.
Sure, you could probably build a kid's trike using the largest mountain
bike hub axles you can find, but this would still be a risky design, as the first
bounce up a curb would certainly bend the axles. Another factor in choosing
trike wheels is their lateral strength. Since a trike cannot lean into the
corners, the two front wheels are going to be under massive stress around
any corner at higher speeds. For this reason, almost all tadpole style trikes
use 20 inch or 16 inch front wheels with at least 36 spokes due to their
excellent strength.
You may be thinking that this project calls for a pair of expensive
rims mounted to a set of custom made hubs, but the good news is that you
can purchase a pair of sturdy 20 inch trike wheels from any bicycle shop in
the form of 14 mm axle, 48 spoke BMX wheels like the pair shown in
Figure 2. Unless you have an unlimited budget, or really know the dynamics
of bicycle wheels and plan to make your own hubs, the BMX wheel route is
the best way to go. You can expect to pay between $100 and $200 for a pair
of suitable wheels complete with smooth tread tires from a bicycle shop.
Figure 3 - Hub axles. Yes, size does matter
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StreetFox Tadpole Trike StreetFox Characteristics
As you can see in Figure 3, the difference in axle size between a
common bicycle hub and the 14 mm BMX hub is amazing. The 14 mm axle
on the BMX hub is made for serious abuse, and if you have ever seen a
BMX freestyle competition, then you know what I mean when I say these
wheels are indestructible. The smaller axle would be barely enough to hold
up a kid's stroller if held by only one side, but the BMX axle would easily
survive trike use with a rider at roughly 250 pounds. I have made several
trikes using these hubs, and I can assure you, the crazy stunt riding I did
went far beyond what most "sane" riders would ever consider doing on a
trike! So as a general rule, do not use any threaded axle less than 14 mm in
diameter, and do not use a wheel with less than 36 heavy gage spokes.
Follow this rule, and you will never bend an axle or "taco" a wheel.
Forks, Crowns and Head Tubes
Figure 4 - Finding two identical head tubes
When you are sourcing steering parts for the front of a tadpole trike,
you will basically need two of everything when it comes to the front wheels.
As you can see in the completed StreetFox photos, the steering system is
made using bicycle components so you do not need any expensive machine
shop work done, and the resulting steering system is much smoother than the
traditional kingpin bolt style steering system often found on go-carts. Your
goal is to find two identical head tubes and the fork hardware to match.
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StreetFox Tadpole Trike Front Hardware
When I say identical, I am not referring to color or brand, but the overall
length and width of the head tube so that both front wheels will be at the
same height when the parts are installed. As shown in Figure 4, I have two
identical head tubes and two matching fork stems that fit into the head tubes.
All of my parts are from at least three different bicycles, but they are
all the same size, and that is all that really matters. If you don't have access
to a large bicycle scrap pile, then you could trim a head tube down an inch or
two to match the other one, but keep in mind that you will also need to cut
the fork threads, and could end up with not enough thread to install the fork
hardware by cutting away too much of the threaded tubing. Also, do not
worry about the condition or size of the fork legs, as they are not being used.
Just make sure that the fork stem is not bent.
Figure 5 - Checking the fork hardware
It doesn't matter if the head tube is from a 1960’s beach cruiser and
the forks are from a competition BMX bike as long as the hardware fits
together properly and the forks spin around without friction. I ended up
using a 20 inch and a 26 inch fork, but again, this doesn't matter, as the fork
legs are soon to be cut from the fork stem. As shown in Figure 5, fork
hardware consists of two bearing cups, a pair of bearings, and at least two
locking nuts. Bearings are inserted into the cups "balls first", and the fork
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StreetFox Tadpole Trike Front Hardware
stem should spin without friction of the bearings and cups are the correct
size. There are at least three different cup sizes, so the wrong bearing will
cause friction, making it difficult to spin the fork stem.
Figure 6 – Removing the bearing race
Before you start amputating the fork legs from the fork stem, first tap
off the small bearing race (Figure 6) installed just above the fork crown by
tapping it with a small hammer. Tap all the way around the ring until it falls
off so you can work on the fork legs without risk of damaging the bearing
race with our hacksaw or angle grinder.
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StreetFox Tadpole Trike Front Hardware
Figure 7 - Cutting the fork legs from the stem
How you cut the fork legs from the fork stem is up to you, but do try
to avoid cutting into the fork stem when you are doing this job on both forks.
I like to cut around the fork leg using a cut-off disc in my grinder, leaving
about 1/4 inch as shown in Figure 7. I then finish up the surface grinding
with a rough grinder disc and then clean the area with a flap (sanding) disc.
Keep the fork legs around for some other project; they make good head rest
supports or seat frames.
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StreetFox Tadpole Trike Front Hardware
Figure 8 – Mark the crowns for trimming
At this point, you have two perfectly clean fork stems as shown in
Figure 8. The length of the crown area may not match on both fork stems,
but this does not matter since we will be cutting them down to 1 inch to
remove the excess crown area. A bit of tape around the crown area will
make a good cutting guide, or you can draw a line around the crown using a
marker. The cut line should be 1 inch from the top of the crown where the
underside of the bearing race would have been sitting.
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StreetFox Tadpole Trike Front Hardware
Figure 9 – Fork crowns trimmed to 1 inch
Figure 9 shows the two fork stems after cutting each crown down to 1
inch. The bearing races have been reinstalled by tapping them down the
same way they were originally removed. Now both fork stems are exactly
the same length and have the same amount of crown material. If you look
closely at the bottom of the original fork crown piece that you have just cut,
then you can see that it has a small bead of weld around its edge (shown in
Figure 9). This is because the crown is actually made of two pieces of tubing
that fit together, which might be apparent if you look closely at the area that
you just cut. You should run a small bead of weld around this area as it was
done on the part you just removed on order to secure the two pieces of
tubing back together. If you look ahead to Figure 11, you will see that I have
done this as shown on the underside of the fork crown.
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StreetFox Tadpole Trike Front Hardware
Figure 10 – Cleaning up the head tubes
The head tubes can now be cleaned up by grinding away the excess
tubing leftover from the original bicycle frame. As shown in Figure 10, a
little work with a grinder disc and flap disc will bring the metal tubing back
to its original, ready to the weld state. Removing the paint will spare you
from the horrific smell that will fill your garage when welding painted
bicycle tubing, so it is worth the extra effort. Again, avoid cutting into the
head tube metal when cleaning up the area, and take this opportunity to weld
up any holes that have been drilled into the head tube where the other tubing
was welded. A few passes around the outside of the hole will fill it with
weld metal so you can grind the area flush.
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StreetFox Tadpole Trike Front Hardware
Figure 11 – Reinstalling the fork hardware
Now you can clean all the fork hardware and reassemble the parts as
shown in Figure 11. Notice the small bead of weld on the underside of the
fork crown where the cut has been made. Now you have two identical parts
to make your lightweight and friction free steering system. This steering
kingpin system is far superior to the bolt and bushing system, which often
has unacceptable play and friction. The bicycle head tube was designed to
steer a bicycle wheel in a friction free manner, so it only makes sense to use
it to do this job on our trike. The bolt and bushing system is easier and
would be less expensive to manufacture, but you don't have to cut corners
when it comes to your own quality work.
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
Axles and Mounting Tabs
Figure 12 – Cutting the axle mounting tabs
The 14 mm axles will be held to the head tubes by a pair of axle
mounting tabs (one for each wheel). Originally, I had made a pair of
machined tubes to do this same job, but that increased the cost of building
the trike, and my goal was to keep the cost down and not use machined
parts, so I came up with this system, which I think is easier to work with.
Your goal is to make two 1.75 inch by 1.25 inch tabs with a thickness of 1/2
inch so you can secure the axle to the fork crown. Drawing 1 shows the
exact dimensions and drilling for these two tabs.
Since half inch thick plate is hard to come by as well as cut, I decided
to make my axle mounting tabs by welding two 1/4 inch parts together to
form the required 1/2 inch total thickness. You can use any scrap metal,
plate or flat bar to make these tabs, as long as the required dimensions and
thickness are met. Figure 12 shows the four pieces I cut from the scrap 1/4
inch plate to make the two 1/2 inch axle mounting tabs.
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
Drawing 1 – The axle mounting tabs
Drawing 1 shows the size and thickness of the axle mounting tabs as
well as the drilling for the 14 mm axle hole, which is placed 3/8 inches from
the end of the tab. Obviously, a 14 mm drill it is about as common as a
comfortable upright bicycle seat, so rather than try to find one, just use a
9/16 drill bit for the 14mm hole. 14mm equals .551 inches, and 9/16 is .563
inches, so the resulting hole will be perfect for the 14 mm axle. If by chance
you have a bit of scrap 7/16 inch thick plate, you can make the axle
mounting tabs from that, but do not make them any less thick than 7/16 inch.
1/2 inch thickness is your best bet as the weight savings is almost zero.
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
Figure 13 – Welding the two ½ plates together
Since I made my axle mounting tabs from 1/4 inch plate, I had to weld
two pieces together in order to achieve the required 1/2 inch thick result. As
shown in Figure 13, the axle mounting tab on the left has been welded and
ground clean and has a pilot hole drilled for the axle hole. The axle
mounting tab in the right of the photo is fresh from the vice and has yet to be
ground, but you can se that it is nothing more than two bits of 1/4 inch scrap
plate welded together to form a 1/2 inch part.
Figure 14 – Drilling the 9/16 or 14mm axle holes
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
To drill the 9/16 axle mounting holes, start by drilling a small pilot
hole using a 1/8 drill bit and then gradually work your way up to the 9/16
bit. I work my way up the drill bit set, skipping every third bit, so the final
hole is exactly where it should be. If you try to go straight for the big drill
bit, your holes will probably not be in the same place on each axle mounting
tab, or you will jam the bit and end up with the part flying out of the vice. I
only own a hand drill, so a drill press is not required, although it would
certainly make the job easier. Figure 14 shows the two axle mounting tabs
with the 9/16 holes drilled.
Figure 15 – Test fit the axle mounting tab
With a 9/16 inch hole drilled in the axle mounting tab, it should fit
snugly over the 14 mm axle with just enough play to not have to force it on.
The tab and the axle should form a 90 degree angle, and there should be
plenty of axle length to get the axle nut installed as shown in Figure 15.
Another advantage of the axle mounting tab system over the hollow tube
mounting method I previously used is that the axle does not need to be taken
out and moved to one side of the hub. Not all axles are threaded all the way
through, so this became a bit of an issue.
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
Figure 16 – Trimming the unused axle
The other side of the axle can be cut flush with the locking nut as
shown in Figure 16. There is no point having the axle sticking out past the
outer side of each front wheel, as this would be a hazard to pedestrians in a
close encounter, and also very annoying while trying to move your trike
through a narrow doorway. Just use a hacksaw or zip disc and cut the axle
flush with the locknut. Now would be a good time to make sure that all of
the axle nuts are tightly secured as well. You may also want to paint the bare
metal where the axle has been cut, or add a bit of lock-tight just to be safe.
Figure 17 – Mounting the axle tabs to the fork crown
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
There are a few angles that we need to get right concerning tadpole
trike steering, so take your time and fully understand the next few steps
before doing any welding. Nothing here is rocket science, so if you take your
time, and fix any obvious errors, the trike will handle like a dream. Shown in
Figure 17 is one of the axle mounting tabs tack welded to the base of the
fork crown at some weird angle. This angle is no mistake, as it creates what
is called "center point steering" so that the wheels turn directly on their axis
when touching the road.
This concept is shown in Drawing 2, with the line that travels down
the fork stem directly to the center of the tire as it hits the road. Without this
center point geometry, the vehicle would swing from side-to-side as you turn
the front wheels, causing a dangerous inertia at high speed that could launch
you from our seat. Only extremely slow moving vehicles can operate
without center point steering, but since it is generally good practice, even
lawn tractors and many kid's toys seem to have it. Read ahead a bit so you
can understand how this axle mounting tab angle is derived directly from
your wheel.
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StreetFox Tadpole Trike Making Axles and Mounting Tabs
Drawing 2 – Center point steering geometry
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