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Comment by rich_sasha

15 days ago

As a cyclist, I tend to pay more attention to the bike shape than most people. Everyone knows what a bike looks like, but as with LLMs, most people would struggle to draw one - correctly connecting all the different tubes at correct angles etc.

I note that even these bikes are not actually rideable. For a bike to be stable, the front wheel axle needs to extend forward a little ahead of the fork - the fork must ”bend forwards”. This is what actually keeps the bike upright, not gyroscopic effects or some such. Given LLMs are generally good at basic maths, im surprised they get this wrong.

Maybe a bit less so in this case though. As per the announcements, the model was actually trained for this prompt, so was fed some training data. I can well imagine the data there was just not so good.

12 comments

rich_sasha

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adwn  15 days ago

> Given LLMs are generally good at basic maths, im surprised they get this wrong.

1. Modeling and analyzing spinning, three-dimensional objects goes far beyond "basic maths".

2. The prompt was for an SVG of a realistically impossible situation (pelican riding a bicycle), which together already implies a stylized depiction. Why on Earth would you expect it to generate a 3D model of a bike, do a physics simulation on it, iterate until it satisfies certain contraints which are only hinted at in the prompt, and then project it down to a simplified 2D cartoon drawing? That's not how LLMs work, and that's not how we want them to work.

Bedon292  15 days ago

I feel like perhaps this is a bit too nuanced of a critique. While I do see what you are saying on many images of bicycles, there are also many that that I do not see it on. Close to half of them, in a quick Google image search, have forks appear straight and the axle is dead center on the ends of them. If there is something there, I am not seeing it even when trying to specifically look for it.

I'll also note that, using a piece of paper as a straight edge against my screen, there is a very slight forward curve on the low and a bit more on the high responses. Medium does appear to be perfectly straight.

  • matsemann  15 days ago

    There are two things involved. What you are mentioning is the fork offset. Whether the wheel is mounted ahead of the steering axis. Either by the fork having a bend, or the mounting point of the wheel not being in the dead center of the fork. Note that this is measured in millimeters, and often not that visible in a picture. I'd say almost every bike except bmxes have it, but maybe not.

    But even with zero offset, there is another thing in play. The steering axis is at an angle, a fork never points straight down. So even with zero offset, you still get a trail, which is the difference between the contact point of the wheel at the ground, and where the steering axis meets the ground. This trail is really what matters in the end, not how you get there.

    See https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometr...

    But even better, play with (ctrl+f) "trail" in this simulation: https://ciechanow.ski/bicycle/

    There you see the point. Even with zero offset, there is still a trail.

saberience  15 days ago

Yeah but if 99.9% of people would get the bike totally wrong, why does it matter if the LLM doesn't get it perfect.

You're nit-picking on a detail no one actually cares about.

jonas21  15 days ago

If that's the case, how do bikes like this work?

https://www.walmart.com/ip/Huffy-26-inch-Rock-Creek-Men-s-Mo...

(apologies if I'm misunderstanding).