Frankie
In the pursuit of the simplest and cheapest way ever to build a recumbent trike
Recumbent trikes are fun to ride, comfortable, fast - and quite expensive really. I knew I wanted one, but I didn't have a spare $2500 that I'd have to pay for one. Of course, they are really worth it, lightweight, sturdy, well-designed and all. But for a poor student, the cheap alternative would do. Trying to copy a commercial design would be way beyond my skills, and some parts are difficult to get and expensive - it wouldn't be any cheaper in the end. So a new design had to be found, preferably one that does not need special parts, and is solely build from scrap parts of old bikes.
One of the expensive components is the stub axle hub in the front wheels that are commonly used in recumbents. I wanted to use a normal hub (admittedly also because I was thinking about putting in electric hub motors into the front wheels some day...).
One more problem though: I bought an electric arc welder, but have never done any welding before. I decided that I should get some practice on scrap metal, to learn welding. As I didn't feel like random scrap welded together to bigger scrap, I thought that I could start with random scrap welded together so that it vaguely resembles a trike... this is what this page is about. By now the name of the trike should be clear - Frankie. Made from the dead bodies of two kid's and one adult bicycle, and brought to life (hehehe)!
The unique difference of this design is that the wheel fixtures and steering joints are borrowed from existing bikes - no complicated bearing arrangements to be self made, and it takes standard 16" wheels. I started welding the two 16" frames to the cross tube.
The first problem can be seen here: as I
started with scrap, I couldn't find two exactly identical frames - the
right one is a bit shorter. I compensated by shifting the bent bit of
the cross tube to the right, roughly aligning the front wheels (would
anyone please take care of all the mechanical engineers in the back row
that just fainted??). The second problem is less obvious in the picture
- as I didn't bother to clamp down the parts, the frames distorted
during the welding. One wheel is a bit lower (2cm!!) than the other...
oh well, it's just supposed to be a welding exercise, isn't it, and
this one is never going to work anyway... or is it??
Moving on to the rear wheel assembly.
The thin tubes were stuck into fitting holes in the cross tube, and
welded. Argh, welding tubes is hard!!
A "rollbar" was added which is supposed to hold the seat and the rear wheel together:
A "rollbar" was added which is supposed to hold the seat and the rear wheel together:
At this stage I was still very proud.
Only later I realised that due to the silly positioning of the rollbar
(too high, too far to the front) there was no space for any sort of
comfortable seat... But this wasn't going to stop me now. Quickly
another thick tube was welded to the cross bar to hold the pedals. A
part of an old road bike frame provided the crank bearing attachments,
cranks and pedals. A few details followed (chain, wheels, gear shifter,
and ackermann steering), and the thing was ready for a test ride!!!
...or, almost. No brakes!!!!! but who
needs brakes anyway... apart from that it works! still a lot of room
for improvements. The improvised seat had to go. Brakes were added
after the first test rides, making it a bit safer. The front tube from
the road bike was not stiff enough. A thicker tube provided
reinforcement; the road bike tube was glued in with epoxy and fibre
glass. A luggage rack made from webbing as the final touch, and
voilà, the vehicle that got me to uni and back for a number of
weeks:
And then a weld cracked. It was the weld fixing the long front tube with the pedals to the cross tube. Inspection revealed that the forces were so great that the rather thin cross tube collapsed. Just welding it again wouldn't solve the problem for very long.
What started as a saturday on which I just wanted to fix a flat on my roadbike took its course. Instead, i was looking at my trike, thinking that it's such a shame that i can't ride it, and that I should fix it. The frame would have to be reinforced. Also, I wasn't happy with the seat position - too upright, and the thing looks a bit like a wheel chair. Plus, it had the nasty habit of tipping over the front wheels when braking hard... Another flaw was the steering angles: the front bike frames are tilted forwards, making the steering too steep, with almost no rake.
Ok, so here's the plan: chop off the rear wheel assembly, somehow fix it 30cm further back and a bit higher. Fixing the wheel higher up would solve the steering geometry problem, making it longer would stop it from tipping forward, and would provide more space for a seat.
More confident with my welding by now, I decided to make a proper welded seat frame, which also would be an integral part of the bike frame. This provided extra stiffness and stability with little extra cost or weight.
Two afternoons later:
Summary:
Building a trike doesn't have to be hard nor expensive. I don't know exactly, but I think I spend only around $100 on everything (lots of stuff came from the junk yard). And how's the ride? Well, it's great fun!! It is a bit heavy (probably around 20kg), so accelerating is slightly slower than my road bike. But there's hardly any drag, so I can just keep pushing, and going faster. Cornering is good, though when overdone, the inner wheel lifts off the ground. It is easy to balance it out, and is a lot of fun. The only problem that is still there is the skewed steering geometry (nothing on this thing is even remotely straight or symmetric). The result is a slight steering wobble. It's fine as long as I have my hands on the control, but if I let go at higher speeds, the front wheels start oscillating left and right very quickly. I'm surprised it's not far worse, considering that I hardly ever used a tape measure while building it, and everything was done by "looks about right"...
The new seat is extremely comfortable. A nice side effect is that I always have a fantastically relaxing lounge chair with me. A few days ago I took my lunch to a nice spot next to the river, just stopped, and enjoyed the view while having my lunch and relaxing in the sun.
A comment I often hear is "aren't recumbents really dangerous, because of the low position and bad visibility?" I thought about that, but I came to the conclusion that recumbents (or any push bike) aren't dangerous at all. Cars are dangerous. Going past cars I realised that my head is about 20cm below the rim of the windows... However, the flag seems to work, and all cars keep a safe distance. The drivers are probably more worried that my fierce contraption of mild steel might scratch their paint, should they attempt to cut me off. So far I had no scary situations on my trike, compared to quite a few on my road bike... The gist is, some car drivers are a problem, no matter what sort of bike you're riding. Riding with caution and foresight pays off. I never assume that a car saw me or will stop, until it's very obvious. It seems to be a good strategy!
Building a trike doesn't have to be hard nor expensive. I don't know exactly, but I think I spend only around $100 on everything (lots of stuff came from the junk yard). And how's the ride? Well, it's great fun!! It is a bit heavy (probably around 20kg), so accelerating is slightly slower than my road bike. But there's hardly any drag, so I can just keep pushing, and going faster. Cornering is good, though when overdone, the inner wheel lifts off the ground. It is easy to balance it out, and is a lot of fun. The only problem that is still there is the skewed steering geometry (nothing on this thing is even remotely straight or symmetric). The result is a slight steering wobble. It's fine as long as I have my hands on the control, but if I let go at higher speeds, the front wheels start oscillating left and right very quickly. I'm surprised it's not far worse, considering that I hardly ever used a tape measure while building it, and everything was done by "looks about right"...
The new seat is extremely comfortable. A nice side effect is that I always have a fantastically relaxing lounge chair with me. A few days ago I took my lunch to a nice spot next to the river, just stopped, and enjoyed the view while having my lunch and relaxing in the sun.
A comment I often hear is "aren't recumbents really dangerous, because of the low position and bad visibility?" I thought about that, but I came to the conclusion that recumbents (or any push bike) aren't dangerous at all. Cars are dangerous. Going past cars I realised that my head is about 20cm below the rim of the windows... However, the flag seems to work, and all cars keep a safe distance. The drivers are probably more worried that my fierce contraption of mild steel might scratch their paint, should they attempt to cut me off. So far I had no scary situations on my trike, compared to quite a few on my road bike... The gist is, some car drivers are a problem, no matter what sort of bike you're riding. Riding with caution and foresight pays off. I never assume that a car saw me or will stop, until it's very obvious. It seems to be a good strategy!
