Introduction: The Choprical Fish: a Human Powered Party Bike

About: Fossil Fool, the Bike Rapper, a San Francisco street performer and bicycle entrepreneur. Invented the Down Low Glow, a neon safety light for bicycles. Develop high-end sound systems for bicycles used by bicycl…

Bikes and music are both amazing ways to experience community. Combining them takes the whole thing to a new level.

I've been creating bicycle sound systems since 2002. My friends and I use them for impromptu Halloween parades, Critical Mass rides, and smaller Cruiser Rides that I organize on

After building four different "Soul Cycle" party bikes, as I call them, I decided to go off the deep end and build my ultimate bike, to my highest, most exacting standards for visual details, sound quality, ease of use, features, and overall cosmic qualities. The Soul Cycle Chopper is now almost complete after 2-3 years of hard work. I'll be taking you through the overall process of making this bike at a fairly high level, and diving deeper into a few techniques that I think are cool or useful.

Step 1: Concept Phase.

This is the inspiration stage, the brainstorm. Have fun. Pull out your notebook when you're on the subway and draw your ideas. Later on you'll have to deal with dimensions, components, and techniques, but at this point you're just drawing.

Fill up your notebook, identifying which are the key features, thinking of the overall visual look. One of the key features I was going for with the Choprical Fish was a laid-back cruiser / chopper look that was still capable of carrying a powerful sound system and climbing hills.

Step 2: Design or Acquire Your Base Bike.

The most important part of your Soul Cycle is the base bike / frame. It has to be a good looking bicycle, well maintained, with working brakes and gears. You can't put 40-60 pounds of music equipment and a passenger on a rickety bicycle and expect to have a relaxing ride. Everything has to work. Period.

The Soul Cycle Chopper wasn't my first Soul Cycle, so I was able to compare the geometry to my previous one, the Soul Cycle ClassicSoul Cycle Classic.

I took a profile shot of my Xtracycle, and overlaid my drawing for the new chopper frame in Illustrator.

The major new feature of the Chopper frame is the dual seating position. It allows the rider to climb hills in a power position with full leg extension and then cruise in a chopper position, by employing a parallelogram seatpost system. The parallelogram keeps the seat flat when you 'drop and chop'.

I've seen many people use bicycle trailers as the way of carrying bike sound systems. It can be an easy way to get started, but there are some disadvantages to bike-trailer-based systems that I discuss on this blog entry.

I recommend a long-wheelbase load-carrying bike such as the XtracycleXtracycle or MundoMundo. They're designed to carry loads with ease, and they'll leave you room to carry a passenger.

Step 3: Prepare Full-scale Drawing of Frame for Welding.

I got large craft paper from a packaging store and began to draw out the curves of my frame. I started with the crucial points: the bottom bracket, the centers of the front and rear wheels, and the seat. These are the parts that affect how your bicycle will ride.

If you don't have direct experience with designing bikes, I recommend copying the geometry on a bike you like riding, and making, perhaps minor changes to crucial elements like the head tube angle.

Step 4: Weld the Bicycle Frame.

I don't know how to weld at the quality level required for bicycle frames. So I chose to work with a very skilled welder, Curtis Inglis. I chose Curtis because he already was highly familiar working with curved tubing. And his shop was in the Bay Area so I could work directly with him.

Some people would say that this isn't a DIY project because I didn't do the welding. They may be right. My friends Ross and Adam have been talking about DIT projects -- "Do It Together." DIT is more fun than DIY because you have people to keep you positive and focused.

In any case, I can't offer too much wisdom about the welding phase except to say that it will take longer than you expect to do good work on a new bicycle design.

Step 5: Create Custom Seatpost System.

I used a bamboo lamination to create the custom seatpost assembly on the Soul Cycle Chopper. I experimented with different methods of bending the bamboo until I found a steam bending method I liked. As it turned out most of the curves I wanted to do were gentle enough to not need steam. Rather than using a steam box, I soaked the pieces of bamboo in water, then bent them around a hot pipe.

The Rock the Bike workshop is in a shared workshop community in Berkeley called the Tinker's Workshop. I raided my neighbors clamps for a few days to get the most thorough clamping job possible.

Step 6: Prototype the Sound System With Some Household Kool Herc Speakers.

If you're taking on a long-term project like the Soul Cycle Chopper, it really helps to build in a few milestones that can help give you the ongoing motivation you'll need to finish out the project at a high quality level. For me that really meant that as soon as possible, I needed to preview the cruising experience on my new bike by cruising with my friends.

I call these Kool Herc speakers, because they remind me of the ones that DJ Kool Herc used to roll around Brooklyn withroll around Brooklyn with back in the day when he was breaking hip hop.

Step 7: Design a Resonating Chamber.

OK, now the bike you've designed or acquired is ready to ride. It's time to turn your attention to the resonating chamber. It needs to be rigid, attractive, and large enough to have adequate bass response.

On the Classic Soul Cycle, I had used a bazooka bass tube for bass. But on the Choprical Fish, I wanted all the lines to flow, so I needed to build the subwoofers into my cabinet. I used SketchUp to create an accurate scale model of my bike and design the speaker cabinet.

At this point in the process I didn't know how I was going to build the cabinet. So I thought it was important to do the design work in a 3D CAD program in case I would use CNC tools to fabricate it.

Had I known more about custom fiberglass fabrication, I wouldn't have spent so much time in this phase. I would have done more drawing and less CAD work, knowing that I was going to sculpt the form by hand anyway.

Step 8: Create a Positive Form for Fiberglass Layup

I purchased a 4x8 sheet of 4" household insulation foam for a lumber store and removed the foil sheets from the outside by peeling and then sanding. Note that whenever you sand foam you need a good dust mask. Take your health seriously when doing fiberglass work! If you find yourself coughing or getting headaches, you need to stop working and figure out how to improve your workspace and safety equipment before continuing.

I made a sandwich of three large pieces of this foam. I cut the wheel profile out of the middle layer before gluing up the sandwich with polyurethane glue. The seams were difficult to work with during the sandind and shaping process. I would probably use 30:1 expanding foam next time. Doing so requires building a large box to contain the foam as it expands and hardens. Still, I think this might have been slightly better than using the household insulation foam.

I used a variety of wood shaping and sanding tools to reduce the crude shape to one I began to like more and more. I snapped lots of pictures so that I could compare it to my drawing.

Step 9: Create a Speaker Port in the Positive Form

I mentioned the Bazooka bass tube earlier. It's a ported subwoofer with excellent thump for its size and cost. Ported speaker cabinets can sound up to twice as loud at certain frequencies as sealed cabinets. However, if you don't tune the port correctly, you can have a system that sounds boomy or damages your woofer. The length and cross-sectional area of your port need to be calculated to the woofers and cabinet size. The manufacturer of the subwoofers you use should be able to provide you a data sheet on recommended port settings. Use it!

At this point in my process, I didn't know the exact volume of my cabinet. I measured it later by filling it with styrofoam peanuts.

So I created a port that was longer than I needed it to be. Later I would cut it down. I created a foam plug (again, longer than I needed). I made sure the port and the plug matched perfectly.

Step 10: Create Translucent Side Panels and Mate Them With the Foam Shape.

Back in step 6 you guys saw the flat side panels in the cabinet design. These are made of fiberglass/aluminum honeycomb sold by PanelitePanelite. I love the lighting effects that are possible with the honeycomb material, so I figured out a way to use it as a structural side panel, even though it's not really meant for that. It involves pouring resin into the cells near the periphery of your shape, and then cutting through the filled cells with a jigsaw. The dark areas in the flat panel are those filled with epoxy resin.

I don't recommend working with the honeycomb because it's a very expensive material. Frosted acryllic panels would also be very beautiful when backlit properly. Or you could just use the fiberglass itself, which stays pretty translucent, and can be dyed with translucent color dyes. The advantage of using the fiberglass is that there is no mating process between side panels and the main form. The disadvantage, is that you would then have limited access to the inside of your cabinet unless you create a parting line. You'll have to reach through the woofer holes. Not a big problem if all the objects you're planning on putting inside your cabinet (amplifiers, lighting, etc.) are smaller than this hole.

Step 11: Create Subwoofer Retrorockets and Midrange 'eyes'.

In the design for the cabinet, I wanted the subwoofers to emerge from the form like retrorockets. I saw this as a way to add significant volume to my resonating enclosure, without making it look like one big bubble. The other thing it accomplished was angling the sound forward and out, so that the ears of the rider are within the dispersion cone of the speakers.

Similarly the midrange 'eyes' increase the volume of the overall cabinet slightly and angle the sound forward. I like the eyes, because they play into the tropical fish theme of this cabinet. It's not a literal reference, but the end version of the cabinet looks a bit like a tropical fish. It fits with my mission of getting more people on bikes --> less global warming --> more coral reefs and tropical fish mission.

The process for creating the retrorockets was similar to the process of making the main form. I sculpted foam until I liked my shape and then glassed it. In this case I had some assistance from Wen, who was quite skillful wetting out the fiberglass.

Step 12: Mate Subwoofer Retrorockets With Side Panels.

I hollowed out the foam inside the retrorockets with various picks and brushes.

Next I positioned it properly in the plane of the side panel, then tacked it in place with some 5 minute epoxy. Once it was tacked I created a very strong epoxy fillet on both sides of the side panel.

In order to create epoxy fillets you have to have an understanding of epoxy thickeners. If you don't use thickeners, the epoxy will run down your form like maple syrup. I used two thickeners on this project: cabosil and microspheres. Both are very lightweight powders. Cabosil is the better of the two for thickening epoxy to the consistency of vaseline or smooth peanut butter, while microspheres are better if you want more of a lightweight paste. They can also be used in combination, but I am still an intermediate/beginner at this and can't offer any rules of thumb.

In any case, I wanted a nice, glossy fillet was translucent, so I used cabosil to thicken the resin. I applied packing tape to my side panels beyond the glue line, to avoid smears.

Step 13: Create Midrange Enclosures.

MIdrange speakers and subwoofers respond to different frequencies. You don't want them to share the same airspace in a cabinet. If you do, the bass hits coming from the subwoofers will distort the vocals.

Because of this, I needed to create cups for the midrange. Pretty much any size would do. But they do need to be rigid, just like the subwoofer enclosures.

I had never tried vacuum-bagging before, so I decided to try it for the midrange enclosures. The process is pretty basic. You lay up the fiberglass in the usual way. Then, while the glass is still wet, you wrap the form in saran wrap, followed by a layer of 'breather cloth', and finally and outer plastic bag that you then tape to your vacuum tube. I used a regular vacuum cleaner and used the port to reduce the strength of the vacuum.

The outer bag did indeed suck the curing fiberglass to the inner form, making a nice, strong midrange cup.

Step 14: Glass Main Cabinet and Install Speaker Port.

After dealing with the side panels, it's time to lay up the fiberglass on the main cabinet. As you can see I used a red dye in with the epoxy resin. This was mostly decorative. I wanted red light to give the cabinet a special glow that other colors can't do.

Step 15: Stiffen Flat Fiberglass Panels With Ribs

After finishing the fiberglass layup of the main cabinet, I wasn't satisfied by the stiffness of the rear panels. If the panels aren't stiff, you are losing power from your amplifer into heat and vibration of the material. You want every watt to go into producing clean, crisp bass hits. So I stiffened the panel by creating ribs. Using ribs was better than simply adding more fiberglass layers, because it triangulates the surface, similar to the corrugations in cardboard.

Step 16: Create 'flight Deck' Control Panel.

Up to now, I was working on the back of the bike... But any good party bike needs to have knobs and swiches on the handlebars. I can't begin to tell you how crucial this is. You need to be able to respond to the moment, turn the music up or down, pump up the bass, add some lighting, fast forward to the next track in your playlist. If you design your bike without front-mounted controls, you're only setting yourself up for a stressful ride.

I decided to continue working with fiberglass for my 'flight deck.' I used the actual pair of handlebars to create a curved form that will clamp to the bars. Then I pecked, shaved, and whittled it away until I liked the shape. Then I glassed it.

Step 17: Integrate a Rechargeable Battery As a Power Source.

A Soul Cycle needs a rechargeable battery to power the various devices: lighting, amplifiers, and audio devices like microphones and mixers.

For previous Soul Cycles I've used Sealed Lead Acid batteries and NiMH batteries. For the Soul Cycle Chopper, I decided to go with the best battery available, Lithium.

The closest voltage to the devices I used was a 4-cell lithium pack producing 14.4 volts. Some of the devices I planned to run off the battery were really designed for 12 volts. So this means that in wiring up the system I needed to include a couple 7812 voltage regulator chips.

Choosing how large of a battery to use is a judgment call. Unfortunately, you really can't just use a formula, like multiplying your amplifier power by the number of hours you want to perform / ride. This would work for some devices, like lighting, that have a steady current draw. But for a music amplifier, the current draw fluctuates according to the music. So you have to go with estimates. I chose to use 7 x 4 cell packs. I run them all in parallel.

As you can see, I wanted the battery pack to fit in the empty space between the rear rack tubes. The music cabinet fits over the battery enclosure. So, you can separate these, to be able to service the battery.

Step 18: Wiring!

Wiring is one of the most time-consuming steps, and it really demands a lot of experience. Things that seem simple to me now, like how to use a single ground plane for your entire system, were very foreign when I wired my first soul cycle. When I wired that one, I though each circuit needed its own ground wire to the negative terminal of the battery. This means I was running many feet of wire that were redundant. Trial and error is really important to developing good practices.

The big fat connectors are 8-way connectors from Neutrik. This means that with a single twist lock motion I am connecting 8 different wires to each other, and allowing 8 different circuits to function.

Why would you want to use connectors in the first place, let alone 8-way connectors? Because, presumably, you're going to want to remove your Soul Cycle from your bike at some point (perhaps each night after you've used it). Having a quick-disconnect capability that separates the controls from the main cabinet means you won't have to be walking with one big rats nest of wires. you can undo the connectors, coil the wires and lift the cabinet off the bike for storage or service.

Same with the batteries. It's nice to be able to charge them with a quick-connect charger.

The more complicated the system you're trying to build, the more crucial it is that you start on paper. I drew several drafts of the wiring system in my notebook before moving to full sized paper.

The wiring step also encompasses coming up with elegant ways to pass the wires into the music cabinet. By this point in my project, I was getting a strong tropical fish vibe from the cabinet shape. So I decided to accentuate it by passing the wires into the cabinet near the 'mouth' of the form to give it a whisker-like appearance.

Step 19: Create Cargo Racks

With an Xtracycle based Soul Cycle, your cargo needs are met by the FreeLoader bags. But with a custom Soul Cycle like the Choprical Fish, you'll need to create a way to carry cargo. On the Choprical Fish, the cargo racks support the passenger seat and backrest. They had to be sturdy, so I made them out of the same 8-ply bamboo lamination as the seatpost system.

I also carry percussion instruments, spare microphone and cables, my laptop if I'm DJ'ing somewhere, a little food, something to drink, and a jacket in case it gets cold.

Step 20: Create a Passenger Seat With a Backrest.

OK, this really shouldn't be buried down here at step 17. Carrying a passenger is sooo important to the Soul Cycle experience. I can't believe how many chopper bicycles I see without a passenger seat! It's one of the best feelings in the world to have your girl on the back with her arms around you as you cruise down a mellow hill, listening to Marvin Gaye, flanked by your friends on both sides, all grooving to the music, YEOW!

I should note that using an Xtracycleas a base bike is the easiest way to add passenger capabilities to your Soul Cycle.

After mounting the bamboo cargo racks to the Soul Cycle, I carved a foam block into the shape of the passenger seat, then glassed it and mounted it to the racks using stainless steel hardware.

Step 21: Customize the Backrest With Your Electronics

The backrest on the Choprical Fish is a sophisticated electronics hub that includes 3 repackaged elements: a Rolls MX56c 4-Channel mixer, a Shure Wireless Mic, and a Shure Wireless transmitter for bike-to-bike surround sound while cruising.

The actual backrest surface is slightly curved, for lumbar support. The acryllic reveals the circuit boards behind it for a decorative look. During a performance, I'm able to plug a guitarist into the bike, hand a wired microphone to a backup vocalist, click a track on the iPod, and lay down lyrics over it using the wireless mic . The guitarist, backup singer, and I can all set our levels using the knobs of the mixer.

On my first soul cycle I used a two channel mixer. It allowed me toperform over the iPod perform over the iPod, but I didn't have the ability to bring in other performers.

If you do go through the trouble of purchasing expensive items like wireless microphones, don't stuff them in a bag somewhere. Design your bike so you'll be able to access them while cruising / performing.

Step 22: Design and Prototype a Beefy Dual Kickstand.

If you really want to rock a party on a Soul Cycle, you need a solid kickstand. I put many hundreds of hours into my bike, and I didn't want some drunk guy knocking it over. Not to mention the fact that I will be integrating a drum machine into the performance system, and need a flat surface to mount it on. The dual kickstand takes lots of engineering, but it's worth it for things like Human Power and bike-based performance.

Of course, it would be easier if I only wanted the kickstand to function as a kickstand. But of course I wanted it to function as a passenger footrest also. This is especially challenging because it has to have both a locking 'up' position and a 'down' kickstand position.

Here are some of the prototyping stages that led to the current aluminum, water cut design.

Step 23: Build Center Kickstand

I used flat aluminum plates and bamboo laminated sides to create a box structure kickstand. I used a stainless steel strut that pivots off the rear dropout to triangulate the kickstand.

Step 24: Integrate Lighting.

A soul cycle is best experienced sunset or at night. Think about it. Throughout the ages, people have come together around fire and music, as night falls, to tell stories, dance, and connect with other humans. In our age of televisions and dense cities, we no longer use campfires as the source of light, but a soul cycle can have a similar effect. To neglect the importance of lighting would be to miss out on the mesmerizing campfire effect.

I like to use CCFL lamps, similar to the one we use in the Down Low Glow. CCFL lamps provide a very even glow when compared to LED's. They're less energy efficient but not unacceptably so. I glue them into the inside of the music cabinet, and try to create beautiful color fades that are accentuated by the honeycomb side panel material.

Step 25: Sand and Smooth Fiberglass Surfaces Using a Gel Coat.

By this stage in the process, you have finished the structural and functional aspects of your party bike. It's time to work on the visual details, like smoothing out the surfaces. If you use fiberglass on the outside of a positive form, as I have done, then the exterior surface will have the texture of the fiberglass fabric, similar to the texture of a cast on someone's broken arm. This is generally considered 'unfinished'. It's strong enough to use and test, but it will not look good, either painted or unpainted. In order to have a smoothly faired surface that you can polish or paint, you need to use a gel coat, and then sand till you're satisfied.

A gel coat is basically a thicked epoxy coat that includes no fiberglass. You paint or smear it on the fiberglass. Then 24 hours later, you sand it down. In my case I repeated this procedure 3 times. In the photo you can see that in a couple spots, I was sanding all the way through the gel coat to the fiberglass fibers. This is a no-no, since it means you are sacrificing strength. If you aren't happy with the curve yet, and you're sanding down to the fibers, you have to add more gel coat, then repeat the sanding process.

Most fiberglass products handle the gel coat a little different. Take a fiberglass boat, for example. Instead of laying up the fiberglass over a positive form, they would lay the fiberglass inside a negative mold. Before adding fiberglass, they'll paint in a gel coat. This way, once the glass hardens, they can pop it out of the mold. The gel coat, which was touching the inside of the mold is now the exterior surface.

In my case, the complexity of dealing with male - female molds, was greater than I wanted to take on for my one-off Soul Cycle. So I had to deal with sanding and gelcoating repeatedly.

Step 26: Get Your Friends Together and Go Cruising.

We premiered the Soul Cycle Chopper on Bike to Work Day in May of this year. We met at Lanesplitter's Pizza in Oakland, a local bike community hangout, and went on a beautiful 5 mile cruise that ended at Luka's Tap Room for late night dancing. The bouncer at Luka's let me bring my bike inside so I could enjoy the night stress free. Music and bikes are both so important to a strong community that when you bring them together, you can't help but have amazing things happen. I encourage people to choose positive, uplifing, groovy, dance music, rather than the typical thrashing music associated with bike culture. But hey, if thrashing music floats you and your friends' boat, go for it.

Here are some of my all time favorites:

Anything from Marvin Gaye funky years, including Sexual Healing, and Got to Give it Up.
Stevie Wonder, Innervisions album.
Curtis Mayfield, Move On Up.
DJ Sergio's House Mixes.
The entire The Harder They Come soundtrack
Bill Withers, Use Me.
David Bowie, Let's Dance.
Diggable Planets, Dial 7.
CIrque Du Soleil, Delirium Album.

Step 27: Host Human Powered Music Performances in Your Community.

Use your Party Bike to host music events in your community. I co-organize the Bicycle Music Festival and do lots of street performing in the Mission District.

Step 28: Human Power Your Party Bike!

Integrating Human Power wasn't on my radar screen when I started working on the Choprical Fish, my shopmate Nate and friend Gabe's enthusiasm was infectious.

I had my welder weld a pivot point for a motor that swings to hit the tire as it spins. This only happens when the bike is up on the beefy center stand.

A 23 farad ultracapacitor from Maxwell Technologies buffers the charge so that you can stop pedaling for a few seconds and not have the music and lights turn off. As you can see in the video, the battery system and the human power system are independent on this party bike.

When you integrate human power, you have to deal with the fact that the human pedaling the party bike can pedal too hard or too slow. If the pedal too slow, the amp and other devices will sound distorted or turn off. If they pedal too hard, you can risk ruining the ultracapacitor.

At the very least you need some kind of display that shows people what they're currently generating. Better still, you'd create a shunt that dumps excess voltage into a heat sink (fog blaster?)