-- Abstract and requirements:
A self made tadpole trike is a construction highly subjective. To be satisfied from your venture, you must do research for what others have done. Beyond that, you may not be a mechanic with special technical experience, but you must:
1. have good experience on all the technical matters of bicycles. That is to say practically, to be able to dismantle your normal upright bicycle to the smallest bit, fix problems, service, and make it up again as a safe vehicle ready for action in perfect condition.
2. have a general "technical perception" -- what makes you able to imagine simple solutions to complex technical problems.
Still more, you must fully understand your responsibility. You are not going to make a toy for your backyard, but you will make a vehicle to get out there on public roads! You are not going to be alone there! You will not be responsible for your own life only! You will be held responsible for others' lives as well! If you want to commit suicide, please do it alone, if so this will be much appreciated by anyone!
This page was made with two objectives in mind:
1. To help you decide, if you make a tadpole trike by yourself.
2. If the answer is yes, then to possibly offer some ideas.
English is not my mother language but i'll do my best on that.
-- A short evaluation of the tadpole trike:
First of all, what is a tadpole trike? Here is one:
https://www.atomiczombie.com/streetfox-tadpole-trike-diy-plan/
Before diving in the construction, you might want an opinion about this vehicle by someone who has used it for various purposes and in various conditions. So, i am an old cyclist who has cycled for ~1 million kms in ~45 years on upright bicycles for any imaginable use: commuting, carrying things, sport, travelling (cycle touring). I decided that i might want a tadpole trike when i learned of some advantages regarding health problems (posture). In the meanwhile i got rid of my back problems adopting physical action, but the wish remained and i decided to make it.
Firstly i made a test frame, not being careful with the geometry, just to see if i can do it right. Not having a workshop, i worked in my warehouse and backyard with basic hand tools. I had not ever used an angle grinder, so i borrowed an old one from a friend (in the process i destroyed it and had to buy a new one). That funny frame came out to be non symmetrical on any angle or distance on it! I composed the frame with the necessary components and cycled around, that day was a memorable one, yes it worked!
Not only it worked cycling around for a few months, but i decided to load that thing heavily for a 10-day travel on a very hilly area of the country, just as a final total hard test before seriously making the good thing. It was an amazing experience. Lots of camping gear for a super time, and safe rides on the hardest slopes uphills and downhills, no damage, no problem on me either considering tiredness or health in any sense. The rig weighed ~70 kilos in total, and one day with this weight on a long downhill i saw my speed at 58 kms/hour! I have never been in the cockpit of a Formula 1, but going with that speed sitting 30cms of the ground and having no protection around you was absolutely thrilling...!
I wanted the construction to be robust and reliable for any possible use except racing/fast driving: for enjoyment, commuting, carrying daily loads, travelling with loads. No mistakes on all that, period. The project took me a whole year -- ~4 months of research to see what and how can be done, and then 8 months of construction building and editing and experimentation and testing. Now after all, this is what i can say in short:
On the positive side:
1. It is the anthem of comfort. No posture or contact problems on any point on your body. No bump on a saddle. No stress in the back. No twist in the neck. No strong holding on handlebars. Just like sitting in your beloved armchair, period. Even if you push hard uphills, when you stop you will not feel stressed on any point, you will only feel the work done on leg muscles - which is quite fair. It is ideal for excercize for people that want just the gain of the physical action, that is to say they concentrate on the cardiovascular and respiratory systems.
2. It is appropriate for a wider range of people, safe for people with equilibrium or other special health problems. One day a disabled person living on a wheelchair asked me for a ride, and managing to cycle around, i could see that the feeling he got on that thing was priceless.
3. You take the perfect seat to enjoy the world. That panoramic view is priceless. You easily look in front, left, right - i even check my back in the mirrors. The open view offers the greatest enjoyment on any environment, both in city and in nature.
4. Compared with the upright bicycle in terms of speed, it is slower under these general rules:
- downhills, it is apparently faster,
- on flats, it is ~15% slower at worst,
- uphills, up to 60% slower at worst, that is to say in steep uphills, but with an important note: you push against the seat with your back, so you can apply more pressure on the pedals, so you go slowly BUT you can climb very steep slopes. There is actually no "minimum speed" with this vehicle, you can move very slowly, but you climb steep roads more safely.
On the negative side:
1. It takes more space and weight. Count that for storing, for parking, for transport. And possibly in town, it is less flexible inside the heavy traffic. Not critically much though, i can live with.
2. On bad road or dirt track, you get quite a bit of vibration and shock. Now you do not have 2 wheels on 1 track, you have 3 wheels on 3 tracks. Simply put, this vehicle is not the best case for that (except for special commercial made ones probably). You can slowly pass a hard piece of road of course, though.
3. In the city you are less visible, since you are lower to the ground. But you can do something for this, have flag or light as high as possible. From my experience in months of everyday use, i never had a problem and as far as i get it from motorists and pedestrians, it is a rather unusual vehicle that they do not expect to see, so they naturally take attention of it.
-- The construction:
My objective was clear, i knew what i wanted:
- reliability: the trike must be strong enough to withstand stress,
- modularity: as many separate parts as possible, so as to be easily maintained/serviced/edited/changed,
- modest appearance: in order to discourage thieves, it should apparently seem to be a custom made construction,
- simplicity: the ability to fix problems with simple hand tools.
If someone gave me as a present the "best" (the most expensive) trike in the world, i would not accept, because that would not be what i need. From the above mentioned properties, simplicity is the most important at any level from construction to use and maintaining. I like to use bicycle trash, or any discarded trash, to exploit useful materials (not only for the cost). I like to cycle around the country knowing that i can fix possible problems in small villages along the way. I do not like to wait for special components made by special companies to arrive from the other side of the planet. I want to be able to fix problems in the middle of nowhere with tireups and my little tool pouch.
I learned how to use an angle grinder, but i never knew welding, and realized that it is not an easy thing, and that it is something i am not interested. But this is what good friends are for. Through a friend i got a new one, who works as a professional welder in the industry. One day inside a huge factory in the industrial area, this excellent man was straight to me, promising that he will do all the weldings for my trike as good as they can be and as many as needed and for free, but with the term that i promise that if ever he decides to make a trike, i will be the one to guide him precisely. The deal was perfect, both for him, and for me.
Get the plan and study it thoroughly. Process to the construction if and only if you fully understand possible implications. Let me do a copy/paste: Still more, you must fully understand your responsibility. You are not going to make a toy for your backyard, but you will make a vehicle to get out there on public roads! You are not going to be alone there! You will not be responsible for your own life only! You will be held responsible for others' lives as well! If you want to commit suicide, please do it alone, if so this will be much appreciated by anyone!
The "plan" is not exactly a mechanical plan, but it serves absolutely the important purpose of offering you the design principles of the specific vehicle in terms of safety and mechanical correctness. Supposing that you know well the plan, here are some ideas that i think worth of.
> Making the front wheels:
The first thing to do is the two front wheels, since their geometry will affect the geometry of the cross boom. Not an easy task, it took me time and experimentation. I found two 20 rims in bicycle scrap, opened holes on them for a 36-spoke wheel (a usual 20 wheel has 28 spokes). Precision for the positions of the holes does not matter if you are good at wheelbuilding. (Note: to protect the inner tube, the spaces between the spoke nipples inside the rim must be properly filled flat.)
I got two cheap hubs for disc brake, 36 holes, kicked out the ball races on both sides, measured the diameter of the gap, it was 29,5 mm. I wanted bearings inside there. I can find them at 30mm, or 28mm, external diameter. I found cheap 28mm ones. To fill the thin gap, i tried steel blades with the proper thickness (again, it is called "experimentation"). In the next image, a "6902" bearing inside the hub, fixed with a circular stainless steel blade 0.8 thick. Blades of 0.8mm thickness seemed OK, fitting very tightly. To secure them from active displacement, i used 3 of the disc-brake rotor screws, with the help of little pieces of brake rotor.
On the other internal side, i tap 3 5mm holes on the aluminum body, for the same purpose.
The axles are 14mm BMX, the 6902 bearings are of 15mm internal diameter, i need there also thin blades for the axle.
Along the axle the bearings are properly spaced with pieces of a hard plastic plumber tube, which fits snugly on the 14mm axle.
The hub should be as closer to the frame tab -small space in the internal side-, because you should have a center point steering angle as smaller as possible. Mine came at ~8 degrees.
Note: After 3 months of relentless use, the cheap bearings are still showing no sign of malfunction -- and they can be changed in half an hour.
> Making the frame:
I found simple iron tube 38X38 mm with 1,2mm thickness. I would like it a bit thicker, but in action i think it is fine after doing what is explained below.
The frame has the weakest point of the trike, which is the junction of the two booms, the main boom and the cross boom. A funny story revealed to me that important truth. One day in the city, a stupid man driving his car hit me from the front, while i was standing waiting at the traffic light. This must have been one of the few times when a cyclist thanks the driver who hits him. The rest of the trike had no damage, only the main boom was slightly bent (the hit was strong), and the cross point was severely damaged in a way that showed to me clearly what i had to do next. By that time i had made the junction in a certain way, so as to experiment with the position of the cross boom, as shown in the following image.
After welding the two parts of cross boom, 4 flat pieces where added in the 4 right angles to make the junction stronger. These pieces were welded on the down point of the joint, in order to enhance the tensile forces exactly there. The welder told me that he guarantees the frame to travel to Siberia. I answered that he should think it over again because he might hear me some day asking him to escort me in Siberia. Here are two views of the junction, from above and from below.
The two other decisive points of the frame -and for the whole vehicle-, is the attachment of the front wheels. Of course this work must be done before the main junction. In order to achieve positioning precision for the welding of the two head tubes on every one of the two pieces of the cross boom, i made a special fixing structure to help me with this positioning. For this joint, two angles are critical, the center point steering angle, and the caster angle. I measured the former by drawing the geometry of the wheel (you can do it on a piece of paper, or on computer). The latter must be decided according to plan, i set it at 76 deg (taking into account that it will finally be a bit more, since the main boom is a bit inclined).
At first i fixed the center point steering angle once and for all, and then i had to do the work of shaping the square tube twice for the two welds, one for the left and one for the right piece of the cross boom.
A note for the amount of the track: I found ~80cm to be recommended. I decided mine at 73cm. My style of driving has not to do with racing or fast driving, but resumes to a few keywords: utility, versatility, safety, health. This is funny, i ended to this number after a short research about the width of doors in buildings. I do not want fast cornering, i drive safely and enjoy it anyway.
> Brake tubes and brakes:
In the next image, you can see the custom parts before the painting. Generally they follow the plan, except the two brake "forks". Let me show what i did with images.
Next problem was the double lever, that is how to connect two cables on one lever (so as to have two brake levers, one for the back wheel and one for the two front wheels). And at the same time i had the problem of the braking power, because it applies on two brakes so it drops in half, that is to say i must duplicate the force applied on the brake if possible. According to a law of physics, the lever arm and the actual force exerted are inversely proportional. A piece of aluminum was welded on the lever, so that the distance the cable shifts drops in about the half.
> The 2 handlebars and the "Under Seat Steering" position:
Each one of the two handlebars, the left and the right, is a piece of normal handlebar welded on a piece of fork stem (the one that is fixed inside the headtube). On the frame, i made the headtubes as short as possible, resembling the ones of the Warrior, for two reasons: a. to avoid unnecessary material/weight, and b. for the handlebars to be as low as possible (the fork stems as short as needed, as well). One half of bicycle scrap handlebar each, an appropriate curve included. This way the steering is low and in the most comfortable position, by your side and under your waist, resembling that of USS. This position can be precisely set to suit one's own body.
> The chain idler:
That was another interesting problem. I took a typical bearing from a closed-type bottom bracket, and i fixed a small 11-teeth cog sprocket around it with a 2-component epoxy cement, after making the surface to be coarse. Then it was easy to make a small construction and put that thing under the frame, fixing it with a 5mm screw. I did not fix the screw tight, so anytime i could turn the sprocket's angle a bit to achieve the best alignment, which of course is just where the least noise comes from the sprocket. For that noise, i also shaped the teeth with the angle grinder a bit to make its function smoother.
> Seat and extras...
The seat to be modular, i made it as two separate pieces. Each piece is a flat piece of wood fixed on its boom with two screws. I shaped them simply by gluing layers of foamy stuff one over the other. The cover is simply a cover of a couch pillow, which can be easily taken and washed.
A strong back rack was made from aluminum tube, and a "luggage carrier" made of reed to sit on top -- in the 3rd image above it was full of camping stuff.
A roof frame made of reed supports a rain cover for the very rainy days, or a sun shade for the very sunny days, and probably in the future some kind of solar panel. It is easily fixed/dismantled with custom elastic cords with brackets.
The last thing i want to say is: funny solutions to severe problems is great fun!
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