Introduction: Building a Recumbent Bamboo Trike Frame
Before building this trike, I had never built anything that moved or worked on bikes. I had also never constructed anything using bamboo, carbon fiber or epoxy. Needless to say, I needed a lot of help and resources to get this project done. My primary source of information on trike building was www.atomiczombie.com. Brad and Kat at Atomic Zombie sell plans for building recumbent trikes from old bikes. Brad has put together an entire library of picture and video tutorials on bike building and maintenance. The AZ online forum is filled with DIY builders ready to give advice on every aspect of recumbent trike building. Without these folks, I'd still be doodling. I purchased a set of plans from AZ (Warrior trike) to learn how to build the steering, front axles, hubs, and disc brakes. Since these specific details belong to Atomic Zombie, I’m not going to divulge their plans, but I highly recommend purchasing a set for building out the rest of the trike. They are very easy to follow, well illustrated, and reasonably priced.
Other good bike websites I use:
Bamboo resources I found invaluable:
Step 1: Safety First
Don't forget to be safe. It's easier to put on a gloves than skin. Wear gloves, safety glasses, earplugs and masks where appropriate.
I also want to warn you that I'm not an engineer, a bike professional or certified in any way to do what I've done here. I'm completely self-taught by reading as much as I can and I certainly don't know it all or have much experience. My goal is to build a safe trike which will provide safe enjoyment for years to come. Read and educate yourself as much as you can and I look forward to getting your comments on how to improve my techniques. Let's stay safe out there!
Step 2: Try Try Again -- Designing the Trike
Using the plans from Atomic Zombie, my first bamboo trike was configured very similarly to the Warrior Trike. I had doubts about whether it would be rigid enough since bamboo flexes much more than square metal tubing, but it seemed like a good place to start. In the end, it didn’t work well as the main beam would twist and the rear wheel tip to the side a bit when turning hard in a corner. While it was comfortable and nice to ride, I didn’t consider it safe. Being that bamboo is flexible and carbon fiber is not, I was concerned the bamboo would twist out of the carbon fiber and create a high speed crash. I did learn a lot about joining bamboo and wrapping carbon fiber so all was not lost! This frame now hangs on the wall of my woodshop;)
Step 3: Rethink & Redesign
My primary design goal was to use 3 bamboo poles as the main frame and interconnect them to create a “truss”. Tying the three long poles together as a unit minimizes the bamboo’s inherent flexibility creating a rigid frame. Design #2 is a variation of the popular Catrike Expedition recumbent (pic 4). http://www.catrike.com/catrike_expedition.html
Step 4: Anchoring the Wheels
This type of trike is called a tadpole and has two 20" wheels in the front and a 26" wheel in the back. Not all tadpoles have these wheel sizes, but I elected to use a larger rear wheel for speed. The distance between the front tires is 30" on center and the distance between the front and rear tires is 48" from where they contact the ground. Since I built this trike from the ground up, the first thing was to lay out where the wheels go and anchor them to my work table. To accomplish this I made some wooden L-shaped channels that were slightly narrower than the inflated tire. These wheel "holders" were bolted to the table in their appropriate spots where they remained until the frame was complete (pic 2). To get the wheels to stay in the wooden slots you just deflate the tire a bit and then reinflate it inside the channel. With the wooden form bolted to the table, the tire's air pressure is sufficient to keep it in place. Since this frame is 3 dimensional, I struggled to come up with a jig and just fit my pieces to the wheels as I put it together. Worst case....the wheels are straight;)
Step 5: A Plastic Trike
Rather than waste bamboo figuring out angles and lengths, I build a full-scale trike out of PVC pipe. I had purchased the bamboo in 1 1/2" and 2" diameters so I used the same size PVC. Very cheap and you can make a lot of mistakes. This proved to be very helpful later on as I could simply cut my bamboo pieces to match the PVC and eliminate errors. It also taught me that I needed a method for maintaining the plane in which the PVC was cut. I'll show how that works in the next step.
Step 6: A Tip for Cutting and Assembling Pieces
When you consider that bamboo doesn’t have a flat surface to orient it, it becomes difficult to precisely join cut pieces together in the same plane. One or both pieces of pipe is always slightly rotated which changes the joined angle. As I mentioned earlier, bamboo is not perfectly round across its diameter. On a 2" diameter piece of bamboo, the diameter may vary 1/8". If you cut an angle and then roll the bamboo a bit to make your next cut, the difference will be even greater when you try to join the pieces. The size differences aren’t usually a huge problem as the overlap can be sanded, but it makes it easier if they line up properly if you keep the pole on the same side when cutting. It also looks better as lines and defects in the bamboo will match once joined together which improves the appearance.
So to accomplish this and make life simpler, I rip lengths of plywood similar in width to the bamboo's diameter. With my cuts marked on the bamboo, I then hot glue the bamboo to the plywood and press it against my miter saw fence until set. For each piece that will be cut, it needs at least 2 dime sized globs of glue (pic 1). e.g. if you're cutting 3 pieces, you need at least 6 glue globs.
When you make your miter cuts, move the saw blade and not the bamboo (pic 2). If you flip or rotate the bamboo, the pieces won't be oriented the same. If you make your miter cuts this way, you simply line up the plywood pieces to each other and the bamboo will matches perfectly (pic 3).
Leave the plywood pieces glued to the bamboo through out the build as it will serve as a guide for orienting pieces to each other. At times during the build, I laid a level across the wood so I would know when it was perfectly horizontal or vertical. Trust me, it gets difficult to know which ways up at times. When your ready to remove the plywood (your frame is assembled), just use a hot air gun to melt the glue and it comes right off. Don't worry about burning the bamboo, you won't (pic 4). The rest of the glue is removed during sanding.
Step 7: Another Little Glue Trick
On a few of the pieces with compound miter cuts on each end of the bamboo you will need to flip the bamboo. For these cuts you will want the plywood and bamboo to match each other in height as closely as possible (pic 1). Takes a bit of finesse with the irregular bamboo, but on short pieces it's possible. This is only necessary for compound miters on both ends of the piece.
So while you're cutting a piece of PVC you miss cut one end the wrong way or it is a little short; instead of starting over here's a little trick. Just cut off your mistake end square (pic 3) and get another little stubby piece and a scrap of plywood as a spacer. Loctite makes a great 2 step plastic superglue (pic 4) that will quickly give you a new end (pic 5). Use the "highlighter" to prime the ends, wait 60 seconds, apply superglue and you can try again. This really helps when you are trying repeatedly to achieve the right length or when you've got one end correct and screw up the other. This trick saves a lot of time recutting and also a lot of wasted PVC. Since no one is going to ride the PVC model, we're not worried about strength so this works great.
Step 8: Getting Started
Let's get some bamboo and get started. There are 1600 varieties of bamboo and a lot of them would work. I ended up using a timber variety called Blue Hennon. My choice was based on what others had used successfully for their bikes and conversations with bamboo nursery staff. There is a lot of variety between species in wall thickness and rigidity so investigate a bit. You can buy Blue Hennon on ebay from Charlene (AKA rainbowsatoz). I purchased my bamboo from her and was very pleased. http://myworld.ebay.com/rainbowsatoz/ She is also the person "Bamboobiker" bought from and how I found her on ebay (https://www.instructables.com/id/Bamboo-Bike-2/). I also used the same resin as "Bamboobiker" -- Max CLR hp (pic 2) -- which you can buy here -- http://myworld.ebay.com/polymerproducts/. Since I knew so little about carbon fiber, epoxy resins, etc, I went with Bamboobiker's suggestions and was very happy. A lot of good info in his Instructable!
The first step to preparing the bamboo is puncturing the nodes inside the bamboo to allow air to escape during heating. When my bamboo arrived, I broke every node or diaphragm in every piece so I wouldn't have to worry about it later. You can break it with a metal rod or drill it out with a long (36") electrician's drill bit. Puncturing the nodes allows air to escape when you are heat treating the bamboo. If you do not break the nodes, there is no place for the trapped air to expand to and the bamboo will explode. Do this step first on your pieces and you won't have to worry about having an accident. From what I've heard, it's not something you'll do twice.
Next is to heat treat the bamboo which caramelizes the sugars in the walls and makes the culm harder and stronger. You need a regular propane torch to gradually heat the bamboo over a fairly large area. You'll also need leather gloves, safety glasses, and old bath towels or rags. It takes a lot of heat to accomplish this step and a hot air gun isn't enough to do it efficiently. I typically heat the bamboo until the waxy outer layer becomes shiny (pic 2) and wipe off the wax. Repeat this step until the pole looks dull and then continue heating a smaller area about 3-4" long all the way around. Suddenly the bamboo will switch to a brown color (pic 3) and you want to continue heating where the green and brown bamboo meet each other until the entire culm has been heat treated. You will be able to shade the bamboo darker or lighter as you go along. Since you'll be sanding the outer layer off it's best to go a little darker than you want your final color to be. I prefer to heat treat all of the bamboo before I start so it's ready to go. The other option is to cut your pieces and then bake them in the oven. I've not tried this technique but it's described in various places on the web. Baking in an oven would probably give you a more uniform color, but that's my guess.
The last thing I do before I begin cutting is to sand all of the poles. To me, it's just easier to get the bulk of the sanding done on the entire culm than to sand small pieces later. And since I hate sanding, it's nice to get the worst of it out of the way!
Step 9: Making the Center Beam
The build starts by making the center beam out of 2" bamboo. The front joint is 22° so each end is cut to 11°. The rear joint is 30° so each end is cut to 15°. Using the plywood pieces as a guide, the 3 bamboo pieces are glued together (pic 1). There are a lot of different glues I've heard people use including gorilla glue, wood glue and 2-part epoxy resin. When you are gluing the end grain of 2 pieces together, it's weak regardless of the glue you use. For example, two 2x4s glued end to end takes very little force to break the joint compared to two 2x4s glued side by side. In this case, you're gluing 2 rings of end grain together so the strength of the joint is the carbon fiber & resin and not the glue. So I personally don't think it matters which glue you use, but most builders seem to use epoxy resin.
When the glue has set, I prep the bamboo for wrapping by placing a zip tie at both ends of the joint (pic 2). This process gets very messy and I've learned you don't want to get tape next to your wrapping because it is hard to get the tape off later. It gets stuck under the carbon fiber or in the resin and you have to sand the bright blue painters take out which is a pain. So the zip tie creates a buffer to which the resin won't stick and makes a nice distinct edge. A small amount of resin will leak under the zip ties in places, but it comes off pretty easily. Once the zip ties are in place, I wrap the rest of the bamboo with tape. Typically I just leave it on throughout the build since you end up with resin all over the place as you assemble the frame. The tape is a real time saver as the resin is hard to get off of bamboo which has been dewaxed and sanded. Once the taping is done, I sand the area to be wrapped with 60-80 grit sandpaper until the surface is rough. This insures all the wax is removed and a good surface is present for bonding. If wax remains on the bamboo when you apply resin it will easily just pop off. Not good. Use a tack cloth or acetone to remove all the dust before wrapping.
Wrapping carbon fiber tow (tow=ribbon) is an acquired skill and it gets easier with practice. Don't worry, there's a lot of practice found on this trike. The idea is to keep the carbon fiber wet with resin while wrapping as evenly and smoothly as possible. This limits the amount of sanding and rewrapping you'll have to do to make the joint look good. On my first frame, I used 3K tow which is carbon fiber containing 3,000 strands on cross-section. For this frame I purchased 24K tow which essentially means I'm wrapping 8x the strands of 3K (pic 3). This made the wrapping go much faster and saved a lot of time. The 24K is about 1/2" wide or more but it wraps just as easily as the 3K once it is wet. The build up of carbon fiber is faster with 24K than 3K and with the amount that needs to be done on this trike it saved me a lot of time.
Carbon fiber's strength is only along it's length so you want to wrap pieces which are as long as you can manage. I usually wrap pieces which are 9-12 feet in length. I begin by wetting the clean, sanded surface with resin using a foam brush. I then saturate the first 12" of tow with resin and begin wrapping round and round. As I use up tow, I wet another 12" or so until I've used up the strand. Alternatively, you can wet the entire strand before wrapping, but I found this was much more messy and didn't really provide much benefit. Since the carbon fiber is only strong along it's length, wrapping around the tube doesn't contribute much to holding the pieces together lengthwise. So after completely wrapping your joint going around the bamboo, you'll want your next layer to be oriented along the length of the bamboo. There are 2 ways to do this that I know of and the first is simply to cut pieces of tow and lay them parallel to the bamboo. The second, which I did on this trike, is to purchase unidirectional carbon fiber tape which has long strands running the length of the tape. I bought 3" wide 12K tape from Fiberglass Supply (pic 4). http://www.fiberglasssupply.com/Product_Catalog/Reinforcements/Carbon_and_Kevlar/carbon_and_kevlar.html The tape worked great and made it easier to keep everything as parallel as possible to the bamboo as I wrapped over the top of it. Two pieces of tape the length of my joint covered it very well. I apply the tape dry to the top of the wet joint and then make sure the tape is completely wet using a foam brush. With the lengthwise oriented pieces in place, I began wrapping 24K around and around over the top. Initially I apply 4 alternating layers (2 around and 2 long) and then wrap the joint with electrical tape sticky side out. The electrical tape provides compression so there are no spaces within the joint. I drill 1/8" holes in the electrical tape before applying it so that excess resin can escape during compression (pic 5). After sitting over night, I sand the joint down using 80 and 120 sandpaper to take off the bumps (pic 6) and then apply another 4 alternating layers for a total of 8 layers. After drying and sanding again, I lay down a top layer of carbon fiber to make it look good. If I have uneven spots (which I always do) I put short pieces of tow in them to level up the surface before the final layer. This is only cosmetic and doesn't contribute much to strength.
Before going further, I cut the rear (short) end to 19" at 30° angle. You can make this piece a bit longer depending on the size of your tire, but 19" left an 1" gap between the tire and the bamboo on my trike.
Step 10: Positioning the Main Beam on the Assembly Table
Once you're happy with the wrapped joints, you need to get the main beam fastened in place on the assembly table. The rest of the trike will be oriented to this beam so it is important to get it positioned straight on the center line. To get the correct height for the piece I built a box 5" tall and around 30" long and bolted it on the center line of the table. I then used my heat gun to remove the center block from the bamboo beam and replaced it with a piece approximately 30" long for attaching to the long box (pic 2). Make sure you mark the center of the 30" plywood ends so you can position it correctly.
Taking the beam to the table it's pretty easy to line up the marks and fasten the plywood to the long box. This technique not only gets the center piece on midline, but also insures that the end pieces aren't listing right or left. Straight down the middle & straight up and down.
5" box + 3/4" plywood + 1/4" wrap = roughly 6" of ground clearance.
Step 11: The Really Tricky Part
These two pieces are the trickiest part of the build and very easy to mess up. You will definitely need your PVC model for this part. The key is to cut the center piece first as it has compound cuts on both ends which are in different planes. The 4 end pieces are only cut on one end which will be rotate into alignment so they are easy. Getting the correct orientation on the center piece is the key. All of the cuts are the same: saw blade angled at 10° and tilted at 10°. The pieces are 1 1/2" diameter x 7" long, but I would make the 4 end pieces longer so you can cut them to length later.
What I did to make this easier was to use the PVC model to cut an exact copy of both center pieces in 2x2 wood. The left and right pieces are different in the way the cuts are oriented. Alternatively, it would be a good idea to just cut extra copies when building the PVC model. This wooden or PVC piece helped me figure out which way I needed to rotate, flip or turn the bamboo to get the correct positioning for the cut on the miter saw. (I'm getting a headache just remembering this part.) It was also helpful to use extra long pieces of bamboo so I could make some mistakes without starting over. Once I knew for certain the cut was correct, I positioned the bamboo the same way on the saw and cut it to 7" long.
When you make a cut be sure to mark a horizontal line across the end of the cut. These lines help immensely when you are joining the pieces together. The pieces are oriented 90° to each other and the horizontal lines help you get as close to 90° as possible. Once you've made all the correct cuts and things line up, glue the pieces together (pic 1). I will confess that I couldn't figure out how to clamp the pieces together so I actually superglued them and just held them in place. I guess that tells you how much I think the glue accounts for the strength of these joints, but it's was hard to come up with another way. In retrospect, I may have been able to glue each joint individually with a different glue, but it's hard to do. Since I superglued these pieces together, I did apply some paste epoxy to the outer surface of the joint (pic 2).
The end of bamboo which will be attached to the main frame is cut at roughly 120° (pic 3). Because I would be wrapping carbon fiber over the end of the culm, I filled the end with expanding foam before making the cut. This cut was made on the bandsaw.
Now that your cuts are made and all the pieces glued, you know what to do......start wrapping!
Step 12: Making the Dropouts
Now that we have 3 pieces, we need to get them attached to each other and the rear wheel. For that we'll need some dropouts. I purchased 2 dropouts from Nova Cycles Supply. http://www.cycle-frames.com/bicycle-frame-tubing/DROPOUT-WITH-DISK-TAB.html (pic 1) One side is made for attaching a disc brake and I whacked that part off so both sides matched and could fit inside the bamboo. Unfortunately I don't have pictures of the next step, but the short lower arms on the dropouts needed to be lengthened. I used similar size metal about 2 1/2" long and extended both pieces. On the outside surface of the dropout arms, a 2" piece of 3/4" square tubing was welded along the length of the arm (pic 3 & 4). The arm and tubing slide inside the bamboo and are then pinned which I'll show later. The last pictures show the dropouts installed on the rear wheel and the angled pieces in place (pics 4-6).
Step 13: Attaching the Rear Arms
Before the 2 upper beams get in the way, it's a bit easier to go ahead and anchor the rear tubes to the main beam and dropouts. This was a little tricky because the carbon fiber tow wanted to slide off. It was also difficult to get the these large zip ties to not do the same thing so to solve this problem I used small brad nails instead (pic 2). Small holes were drilled into the bamboo and carbon fiber in a circle around all three beams and brad nails were tapped in. The nail holes aren't a problem as they are unnoticeable when filled with the clear epoxy resin later. This worked pretty well although it wasn't as even as the zip ties so more filing and sanding was required.
I also pinned this joint to make sure the arms didn't slip since there is a lot of dead space between tubes. The carbon fiber bands are strong enough to keep the tubes bound together, but less strong front to back. Again I used a 5/16" auger bit to drill out the holes and then tapped in 5/16" steel pins (pics 3-5). PC-7 (epoxy paste) was used to fill the depressions over the pin ends, sanded and wrapping was continued. These bands ended up about 1/4" thick and look pretty cool (that's important too). Picture 6 is out of sequence but you can see how the bands ended up looking after some filing and sanding.
To attach the rear arms to the dropouts, I used PC-7 and forced as much as I could into and around the 3/4" square tubing inside the bamboo. I finished the ends of the bamboo by rounding of the PC-7 beyond the culm end. Picture 7 is out of sequence also but you can see the finished epoxy end on the dropouts. All four pieces of bamboo attached to the dropouts were pinned with 1/4" steel pins after the initial carbon fiber wraps as previously described. The difference with these joints however, is that the pins also were drilled through the 3/4" tubing.
Step 14: The Front Wheel Arms
Next is building and attaching the front wheel arms. I think I probably overkilled this step but my concern was that the front wheels are only supported on one side of the wheel. If the bamboo arm going to the wheel flexes that would lead to major problems that would be hard to fix later. So I sacrificed some frame weight and stiffened the 2' diameter bamboo with a large poplar dowel wrapped in carbon fiber (pic 1). Once the carbon fiber/resin had hardened, I coated it with 16 pound expanding foam and slid it into the bamboo. 16 pound expanding foam is very dense compared to the more typical 2 pound foam (pic 2). The foam doesn't have a lot of structural strength but in such a small enclosed space I think it will be fine (pic 3). Whether this was overkill or not, I would still recommend stiffening these arms in some way. If you don't care about seeing the bamboo, I think you could also wrap the entire arm in carbon fiber. I didn't want to cover up the bamboo and opted for the big dowel. A carbon fiber outer wrap would obviously be lighter.
The length of the arms and the angle of the center cuts will vary depending on the set up of your front axles. For my trike's setup, the compound miter cuts ended up being 15° angle and a 15° tilt. The arms angle forward at about 65° from midline and up to the wheel at about 15°. On the wheel end, a 1 1/4" hole is drilled with a Forstner bit (pic 4). The hole is centered on the bamboo 7/8" from the end. Typically this end of the arm would have a fish mouth cut and not a complete hole. A hole has an advantage in strength and it makes it easier to wrap in my opinion. The hole also aids you in aligning the center line cuts since the arms are held by the headset tubes at the wheel while you tinker with the compound miter cuts. It is very important to have a plywood block glued to the bamboo for correctly orienting the drilled hole and the angled cut to each other. Without the block it is virtually impossible to get your angle cuts together on midline (pic 5&6). Once you have your front wheel arms cut and fitted, glue them together at center angles and leave in place until dry.
As I mentioned before I used Atomic Zombie plans to build the hubs so that info belongs to them. So I'd recommend either purchasing their Warrior Trike plans (www.atomiczombie.com) or use kingpins (http://www.fleettrikes.com/tthindex.htm.) Either will work.
Step 15: Epoxying, Wrapping and Installing the Front Arms
At about this point in the build I discovered a 2-part paste epoxy called PC-7 (pic 2). http://www.pcepoxy.com/our-products/paste-epoxies/pc-7.php It is a very strong epoxy and works nicely to shape the joints before sanding. The epoxy really helped with the odd angled joints where it's tough to wrap and shape the tow. When you mix the 2 parts it becomes a gooey sticky paste but it is easily sculpted using denatured alcohol. As the build progressed, I spent more and more time shaping the epoxy around the joint using alcohol because it significantly decreased sanding time. I purchased PC-7 at Ace Hardware. Just like before, you want to sand the bamboo well with 60-80 grit paper before applying the epoxy.
On the ends of the arms I used a bit different approach on the wraps by including carbon fiber woven tape instead of unidirectional tape (pic 3). Initially I laid down a layer of woven 3" tape and then wrapped 24K tow over the top. In the "V" shaped areas where it was difficult to wrap, I used short pieces of tow to fill the voids and let it dry. After initial sanding, the "V" areas were still sunken so I used PC-7 to level it up and allowed it to dry before repeating the woven tape and carbon fiber. I really like the end result and found this to be an attractive solution to this difficult joint.
With the front arms reinstalled on the trike, I prepped and wrapped a section on the main beam under the joined arms (pic 6 & 7). Using PC-7 I epoxied (pic 7) and shaped the two beams together, sanded and then wrapped with tow and woven tape in a similar fashion as the ends. With the joint almost finished I decided it might be a good idea to pin the two pieces together (probably overkill again). Using a 5/16" auger bit I drilled a hole all the way through and drove a steel pin into the joint (pic 8). Make sure the pin is slightly shorter than the entire length so it doesn't protrude. You can PC-7 any recess from the hole, do your final sanding and wrap the last layer over the top.
Step 16: The Upper "Seat" Beams
The upper seat beams are pretty quick and easy to make since they are flat 2 dimensional pieces. I followed the steps previously described for cutting, glueing, epoxy pasting, sanding and tow wrapping. Measurements for the pieces are in picture 2. The bamboo is 1 1/2" diameter. You'll want to cut the ends pieces a couple inches longer than the drawing so you can trim them to the exact length (pic 3). Remember these 2 pieces are not the same -- there is a right piece and a left piece. As you can see in picture 4, the ends of these tubes are cut in opposite directions to match the front arms. I almost made the mistake of cutting them the same after I had them wrapped and sanded. Crisis avoided thankfully!
One of the problems I noticed on my first trike was that the front boom flexed up and down as I pedaled. Even after heat treating the bamboo retains a lot of flexibility so to fix this issue I braced the front boom back to the front arms (pic 5). These 2 pieces of bamboo are about 10" long and I simply cut them where I thought they looked about right. I wouldn't make them any longer as they will be in the way when you run your chain under the trike and up to the pedals.
Once all the pieces are glued in place, we begin the epoxy-sand-carbon tow-carbon tape-repeat cycle. Lots of sculpting, sanding and wrapping. I followed the same procedure for the upper rear dropouts as I did the lower and pinned them.
Step 17: Connecting the Beams to Form a "Truss"
If you remember, the problem with the first trike was a single beam can flex up and down, side to side, and twist along it's long axis. Connecting the upper "seat" beams and the main beam on this trike will cause them to act like a truss where the beams brace off one another. So instead of having 3 separate beams, they will actually behave as one wide and tall beam that won't flex much at all. My original plan was to add a lot more bracing than I ended up using. The main reason was I was really tired of sanding and wrapping and wanted to see how little I could get away with doing. Full disclosure here;) I would estimate that greater than 50% of the time it took to build this trike was spend on sanding and wrapping. It's a marathon, not a sprint. I lopped a couple miles off the marathon by doing some trial and error. Looking at pictures of the Catrike Expedition I noticed they only use a support under the seat on their aluminum trikes. So I decided to begin by putting bracing under the seat bottom and just in front of the rear tire and see how rigid the frame became.
To make my bracing rods I took two 36" poplar 1/2" diameter dowels and wrapped them with 3" woven carbon fiber tape. To do this I laid a long piece of wax paper on my bench and wet out the 36" long piece of cf tape with epoxy resin. Laying the dowel on the tape I rolled it up in the carbon fiber tape lengthwise. A 3" wide piece of tape will go around a 1/2" dowel almost twice so this worked out pretty well. I then wrapped the tape and dowel with electrical tape with the sticky side out as before. After the resin dried, it was time to start cutting these crazy little pieces.
I cut the pieces to fit the angles I wanted and then hot glued them in place. A triangle is always stronger so all the bracing was done in a triangular pattern. I put small zip ties on the dowels to give me a definite stopping point as I wrapped since I didn't want to cover up the woven tape on the dowels. The end result was not only a nice edge, but also the appearance that the dowels where held by small carbon fiber fittings (pic 5). It added a nice detail to the frame. All the joints were then epoxied, sanded and wrapped, etc. Pictures 2-5 show the progress of the bracing under the seat.
Pictures 6-12 show how the rear bracing was accomplished. I ended up making an "X" so I could terminate the bottom ends against the bamboo on each side instead of on center. A lot of epoxy was used on that "X" and the space below it before wrapping. It took a lot of patience but the end result was very strong and looks good as well.
After adding these braces I set down on the trike and rolled around the shop. The frame was very solid and didn't budge when I forced it laterally or bounced on it so I stopped there. It's possible the frame may need more bracing after I've riden it more, but right now it is very rigid in my opinion.
Step 18: Adding the Bottom Bracket and Pedals.
Just when you thought the frame was finished, there is one more joint to wrap and that's the bottom bracket. I purchased my BB from Nova Cycles Supply http://www.cycle-frames.com/bicycle-frame-tubing/73mm-LUGLESS-SUPER-LIGHT-BB.html I had a piece of bamboo which was very close to 1 1/8" so I decided to bond it to the BB for the derailleur. If you only have one ring, you won't need a derailleur, but other wise we need something to mount it to. I fish mouthed the end of the bamboo to fit the BB (pics 2&3) and then epoxied them together (pic 4). Before I applied any epoxy, I reassembled the axle, cups and bearings into the BB to prevent epoxy from getting in the threads.
One of the flaws of this design is that it's made for a single rider of a certain height as there is no adjustment for the seat. Since I'm 48 and have completed my long bone growth this isn't a problem;) Trike manufacturers solve this problem by using a telescoping front boom which I might try on my next build. You'll need to figure out where you want the BB and pedals and make a fish mouth cut in the main boom (pic 5). This part is a bit tricky since you want the BB level horizontally, square to the main boom and the derailleur bamboo at 70° to the main boom. Takes a little bit of messing around with it to get it close, but I never got it perfectly fitted. The picture looks better than it really was. Once again I used hot glue to hold it once I got it in the correct place and then double checked everything. If it's not right, get the heat gun to melt the glue and keep trying until you're happy. I found it really helpful to have a block cut at 70° and hot glued to the main boom (pic 6). Once hot glued in place, I applied and sculpted the epoxy around the joint with the cups in the BB to keep the threads clean (pic 7).
If you have a good eye, you may have noticed the 70° looks a little thin. That's because I built mine at 55° thinking I knew where my chain would be running. Typically the derailleur post should be about 90° to the chain. When I added the two 10" pieces to brace the front boom it changed the angle of the chain from where I had originally planned it to be. Everything has worked out, but a more upright post would have made it easier to get everything aligned.
Wrapping the BB with tow and tape was the same as previously described. This time however, I didn't want have the resin to glue my cups and axle in so I opted for large fender washers on each side secured through the middle with a bolt. An added advantage to this was that the fender washers prevent the tow from sliding off the edge which helped build-up (pics 8-10).
Step 19: Wrapping the End of a Bamboo Culm
Finishing the ends of bamboo can be a little difficult and I figured out a way to make the end of the derailleur bamboo look a bit better. First I plugged the bamboo with a piece of foam (pics 1&2) and then poured 8lb expanding foam in the end. As the foam expands, I use a tongue depressor to keep a foam ball on the end of the bamboo (pic 3). After the foam sets up, it is shaved and sanded into a nice rounded end over which carbon fiber can be applied (pics 4&5). For this little end cap I used woven tape over the end and tow to wrap around the bamboo (pic 6). I like the rounded end a lot better than a flat end. The expanding foam takes about 10 minutes to set up so I think it was worth the 20 minutes it took to round off the end. You might recall I did something similar with epoxy on the dropouts, but that takes 24 hours to dry. On the dropouts I needed epoxy inside the bamboo, but for this little decorative end I'm not worried about strength so the foam was quick and easy.
Step 20: Finishing the Bamboo
I sanded the bamboo again to remove any epoxy and remove blemishes. To protect the bamboo I applied 3 coats of Spar varnish with 220 grid sanding in between coats. Alternatively, you could use an oil and wax combo to protect the bamboo.
Step 21: Chain Idlers
With the frame finally build, one of the remaining things to do is run the bike chain from the rear wheel, under the trike and up to the chain rings in front. To do this we'll need two pulleys attached to the frame to guide the upper chain. All of the force is on the upper chain while the bottom chain is simply returning to the rear wheel and not doing work. The lower chain needs a guide but it doesn't necessarily have to be a pulley. You can purchase pulleys from various trike dealers and manufacturers but they are quite pricey. You can easily spend $100 for a pulley and a mounting block which fits 2" pipe. Beyond the cost, there is the problem that my bamboo frame isn't exactly 2" diameter so I started "figurin" again.
www.mcmastercarr.com is a fabulous hardware resource for any project. After looking around a bit, I purchased two rubber coated 3/8" stainless steel u-bolts to fit 1-7/8" outer diameter pipe (part #30555T43) for $12 a piece (pic 1). I also purchased two 4" nylon v-belt idler pulleys with a 3/8" center hole (part #6234K45) for $10 a piece. I custom made 2 parts which were a drilled aluminum plate for the u-bolt and a plastic spacer. The plastic spacer was cut from a 1/4" think black kitchen cutting board I bought at Wal-Mart. Plastic cutting boards are a great way to buy colored plastic cheaply for projects. Picture 2 & 3 show how the pulleys were installed.
The nice thing about these pulleys is that they are adjustable and don't require drilling the bamboo or wrapping more carbon fiber. Adjustability is nice when you're figuring out where the pulleys need to go. Even if you never move them, I always like being able to make adjustments if ever necessary. With the plastic spacer in place behind the aluminum plate, these idlers are solid and I'm very happy with how smooth they are for under $25 a piece.
Step 22: Adding Chainstays & Guide Tube
While trying to figure out how I was going to guide the chain back to the rear wheel, the use of chainstays hit me. So I build a couple out of 1/8" aluminum using the drawing in pic 2. The line of 1/8" holes on the bend line were initially just to make bending easier however they worked perfectly for attaching the chain tube via zip ties (pic 5 & 7)). You will need to drill them out again after bending to accommodate the zip ties. An 1/8" & 1/4" thrust bearing (bronze washer) were needed on both sides to prevent the chainstay from touching the wheel (pic 6).
The black poly tube was purchased from Lowe's and it's just water line. Was able to purchase a 3' section and flare the ends with a heat gun. I made a wooden tool out of a dowel by sanding the end with my Dremel sanding drum (pic 8). Worked very well and the poly pipe is easy to heat and flare. The flare will help the chain slide and reduce noise a bit.
Step 23: Let's Ride
And that is that! Please let me know what you think about this trike and how I might improve it. It took a while to build but it's all worth it. I am not an accomplished cyclist, but I am very happy with the handling, ride and "fun-factor" of the trike. I hope to post a video soon of me riding it when the weather improves.
To build the curved seat, here's my instructable: https://www.instructables.com/id/Building-a-Recumbent-Trike-Seat/
Don't forget to vote in the Shopbot Challenge. If I were lucky enough to win a Shopbot, my first project would be a velomobile cover for the trike! Along with an instructable of course. Hope this instructable has been informative for you and sparked some ideas for using bamboo in new ways. Let's ride!
Runner Up in the