Building A Square Bicycle

Square Bicycle Design

Inspired by [Michael Ubbesen Jakobsen’s] BauBike design, [Aaron Seiter] decided to try building his own.

The entire frame was made out of 1″ square steel tubing and welded together in no time at all. Actually intending to ride this bike, he had to make a few changes to the original BauBike design. Most importantly, he raised the seat up to allow for proper leg extension while pedaling.

The funny thing is most people on Reddit thought it wasn’t going to work, so shortly after posting the gallery to imgur, [Aaron] also uploaded a short video to YouTube to prove, yes, he can actually ride it. Stick around after the break to see it in action.

Bicycles are one of the best modes of transportation by leveraging enough mechanical advantage to make the human body efficient enough to go long distances with ease. So naturally, people love hacking them. Reverse tricycle anyone? And in case you missed the recent Backwards Brain Bicycle, it’s also definitely worth a read.

30 thoughts on “Building A Square Bicycle

  1. Would it have worked had the forks be square to the main frame rather than at an angle? IOW, the whole steering bar and forks just go straight down. I don’t see why not, but I’m curious why that piece is mounted at an angle. Is it simply so that the steering bar wouldn’t be too far from the rider while giving the front wheel some space away from the pedals?

    Nice work. I wish I’ve fabrication skills so I can try things like this. (c:

    1. They can be straight down, that’ll work fine until you try to steer.

      Steering geometry is a whole universe, it summarizes down to ‘trail’ –

      Basically the distance from the steering head to the wheel axle sets how ‘twitchy’ a bike is; the longer the less twitchy but slower steering. For motorbikes a sports will have ‘fast’ steering (less trail) making cornering really fun while a cruiser, eg Harleys, often require you to dismount and push the bike around the corner.

      (That’s why you only see HDs on highways – few corners)

    2. Engineers long ago in the 1800’s designed the fork to turn forwards because that auto-levels the wheel towards the center when in motion. The reason ‘trail’ bikes don’t is because they need to move more ‘erratically’, and are often at or close to a standstill obviously.
      A real normal use bike for the roads should have the fork always non-straight in relation to the road.

      If the fork would be straight down he could not likely ride it hands-free either..

    3. Imagine the forks that go to the front wheel axle, instead are attached to a vertical strut. This is while standing still. If you use vertical forks then turning the handle bars does nothing to your dynamics or balance. The strut just rotates in the vertical axis. If the forks are angled forward, then turning the handle bar forces the bike to the left or right and also lowers it. If you change the strut to a wheel, then the point of contact also moves as you turn the bars and it starts to get a little complicated – you can get the old flipped-over-the-handlebars maneuver on a more vertical setup like a mountain bike. Always a hit on Ridiculousness. Just as in dirt bikes where power is your best friend when things start going wrong (leave that brake alone!), so going against intuition and powering through the start of a fall also works for muscle power. Speed in the cornering is what provides the force that lifts you out of the fall – the centripetal or centrifugal. You now, the M(dv/dt). Without the delta v, g wins and the M goes down hard.

  2. The front fork could be an L shape instead of slanted.

    But the steering hingse should also be slated. This can be achieved by making the hinges part of the frame:


    At the + signs a vertical to the front wheel. The axle of the wheel should be in front of the line through the two hinges. So either extend the frame or attach an L for the front wheen. Extending the frame will be stronger.

    The o’s are hinges in the frame. They are offset to achieve the specific slant when steering.

  3. Why does he have a little square under the seat? He should have just lengthened the distance between the seat and and front wheel and put the seat over the pedals, save some steel.

    1. Because it’s a structural member that stiffens the rear frame square. Otherwise it would turn into a lozinge at the first bump.

      It’ll probably still break because that’s a horrible structure for a bicycle frame. It’ll tear itself apart.

        1. More or less. There’s a tremendous stress on the welds at the corners, because an un-braced square tends to collapse with any load that isn’t perfectly perpendicular to the sides and through the center.

          Here the bottom horizontal beam of the frame slides back and forth relative to the top as much as the corners will give, pivoting the two vertical beams. It will eventually tear the welds on the inside corners due to metal fatique.

          An ordinary bicycle would place the wheel at the corner of a triangle, because that configuration is mechanically stable. There’s no torque acting on the ends of the beams because they each stop each other from pivoting, and so there’s none of this back-and-forth twisting on the welds.

  4. Doesn’t anyone know how to make a bike that’s comfortable to ride? What is with the low handlebars and high seat that force the rider into a back breaking, hunched over position while being constantly kicked in the crotch by the seat?

  5. It doesn’t take an engineer to see that this bike may work, but not for long. There are too many very high stress areas where the entire loaded weight of the vehicle, plus stress loads, are hung across a single right angle weld. I’m surprised that it tolerated that guy on it as long as it did, and I would never trust it with my considerable bulk. The front half of the frame, the part connecting the steering head to the rest of the bike, is especially bad. I wouldn’t build a table that was cantilevered out like that, much less a bike which needs to handle dynamic loads in several planes.
    This is just plain unsafe, in my opinion.

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