How does a pull-back car work? Illustrated teardown

This really needs to be done for a GLP-1 auto injecting needle.

Pretty sure it’s the same as an epi-pen as well.

It blows my mind. It’s a disposable, single use device that at the press of button:

1. Inserts the needle in your skin, 2. Slowly presses the plunger until the dose is injected 3. Then retracts the needle with plunger

Three distinct and seemingly opposing motions. With timing. All in a little plastic enclosure. It sure I can think of a toy with that kind of mechanism.

Oh, is that why when you "overwound" it it would make that rapid ticking sound? The outer end of the spring is falling into the next little slot, huh. Fascinating stuff.

What is the name for the sort of toy car you push in one direction and it continues slowly in that direction? These ones were usually styled as 4x4 vehicles and almost moved like a rock crawler with the 4wd set to low. They could be pushed forward or in reverse (and then would go in reverse).

I learned this when I was 4. We even had ones that shot sparks. America. The animations on this are really well done and I loved that trip back to childhood of pulling the car back and letting it rip. However, given the popularity, you should simulate what happens when you pull it back to the extremes over and over again and the spring gets stretched. It no longer kicks as fast as it used to and in some cases, it won't go at all.

If you have access to a 3D printer, this helps explain the basics too: https://www.thingiverse.com/thing:3308710

I guess as a kid I only had access to the cheap ones? Would pull back, not knowing where to stop, and there was eventually a crunching noise. Then I'd worry I'd ruined the thing!

I really love this site, it is obivous that the owner puts a lot of effort into this

Fascinating animation. But there is one thing I don't understand. What is the purpose of the left axle gear (green)? It is not fixed to the axle because it rotates in the same direction in both modes. Wouldn't is be more efficient to connect the wind-up gear directly to the right axle gear (blue) and through pushing to the left spring gear (red)?

We had these for my boys. The target age range of someone who can have fun with these ends at about the same age you learn to be careful enough not to break the motor.

Wow. I love being reminded of stuff like this. Those cars were so cool.

Edit: I took one of these cars apart as a kid to see how it worked. This site brought back a lot of memories. The little coil spring inside the gear. I have to get my hands on one of these now…

For a site that's named mechanical pencil, its mechanical pencil page is too simple. It should add the shake mechanical pencil and the rotating mechanical pencil where the tip rotates 40 deg or so on every click next.

I'd love to see one on the toy car where you rub the wheels across a surface several times in a row to get the engine going faster and faster, then on the last rub, you let it go and it zips away.

Cool write up and cool site. Off the top of my head the only other places I see spiral ribbon-springs like this are in a wall mounted thermostat.

Cool, I'm surprised they are a relatively newer invention (70's)

Of course they were bound to be surpassed by electrical cars with remote controls ;)

Looks like history rhymes

This doesn't answer the most burning question I have, which is why the wind-up gear has the spiral around the shaft...

Why is the wind-up gear needed? Couldn't the axle be connected directly to the spring gear?

It would be great if this was just a model running in a physics engine.

Love this site! Well done!

One of my favorite website ever. Delight as always.

absolutely love it! Gorgeous drawing, meticulous detail.

Great site!

Please leave my browser history alone