Design Challenge #1

[steph]

Trebuchet battle, love it!!

@likeablejerk

It’s amazing that such a small kerf makes such a big difference

Truer words have never been spoken, @likeablejerk!! My first real laser cutter project was to make an interlocking waffle model of a 3D form out of chipboard. Of course, they told us nothing about kerf, so when I went to make all the finger tabs, I made them all as wide as the material itself. Since I was using 1/32" thick chipboard, my tabs were so big and my material so flimsy that the whole thing just would not stay together no matter how hard I tried…pieces would fall off that thing left and right if anyone so much as looked at it

[johnwills]

Sounds like that was an effective lesson.

[ihermit2]

I don’t think a trebuchet could be done without an axle to rotate about since it converts potential energy from weights. A more classic catapult or ballista maybe. They seem to use wooden arms bent to store the potential energy. Rubber bands are also a good energy storage that can act directly.

But that’s just limiting it to siege weaponry, I know of.

I’m sure there are people waiting to submit less violent submissions? Anyone?

[likeablejerk]

[joe]

Hmmm, I might have to put in a trebuchet design as well.

[polarbrainfreeze]

Here’s my attempt at a design. I did not have a lot of time, so it’s not very big. I went for style over substance this time.

I put together a wind-up toy car. It will use an elastic to propel the car forward. It uses Ikea pencils (or probably any #2 pencil) as the wheel axles.

It stacks several layers of 1/4 in material.

It could be cut out of wood, with the “flames” engraved on the side. The different colors could be done by staining the different parts after they are cut (thus everything on one sheet).

Or it could be cut out of different colors of plastic (which would go against the rules of only using one sheet of material, since you would need to use different sheets for different colors).

You can see at the bottom, there is a hook for an elastic.

The elastic winds around the back axle, and hooks onto the hook. If you do it right, the elastic only catches on the pencil if you turn it in a specific direction. It’s loose when the pencil turns in the other direction (google “elastic powered toy car” to see how people do it). So theoretically, you should be able to wind the car back, and let it go so it moves forward.

I’ve never tried this, so I’m not sure if it will work or not.

It all EASILY fits on one sheet of material. I quickly calculated this (it’s missing the flames):

I still have LOTS of room, so either I could make the car bigger, or design another one (or two) to go with it so you can have races.

I’ve yet to cut it, so I have no clue how it will perform.

[steph]

Haha, sort of. Mostly just frustrating…imagine 30 newbies all trying to use a laser cutter within a small window of time before the next group of 30 had to use it. Then pair that with the fact that this was our first time using 3D modelling software…a crazy week to say the least!!

Though I never (okay, mostly never) forgot about kerf again!

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[likeablejerk]

This is great! I love the idea of having multiple cars cut from the same sheet for racing.

Also, I appreciate that you sculpted seats into the cabin cavity. It’s such a great detail.

[johnwills]

Oh, I like that! It’s got my mind racing on adapting the design to look like my 1952 Willys truck or any number of other classic cars and trucks.

[likeablejerk]

Go for it! Also, we should put wheels on the trebs so that @polarbrainfreeze’s hot rods can tow them.

[karaelena]

Nice!

As soon as I get done with my current project- I design and post my idea.

[polarbrainfreeze]

Do you have a picture of your truck? Or an image on Google that looks like it?

If I find the time, I’ll probably design another one or two different cars to fit on the same sheet.

[johnwills]

This is my truck…

Here’s a Skechtup model of a similar truck. I used this model to cut a 2.5D sign on my CNC router.

1960 Willys Jeep Truck

Here are other angles of other 52 Willys trucks.
https://www.google.com/search?q=1952+willys+jeep+truck&espv=2&rlz=1C1CHWA_enUS633US633&biw=1920&bih=911&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj8k6yApa_NAhUIcj4KHWT2CyUQsAQIKQ

[likeablejerk]

It turns out that converting mine to work without the pencil was not much trouble. I just swapped in square axles with Chinese coin style collars on them to give a round surface to pivot on at the necessary spots.

And just not adjusting for kerf on the round discs and holes should give it enough play to rotate freely.

ETA: the larger collars on the outside ends of the smaller pivot are just to keep it from walking side to side.

[polarbrainfreeze]

I was thinking of doing the same thing for the axles on my car design, so it can all be cut on the GF. But I’m afraid the “square” axle will grab the elastic when the car is moving forward. I wanted something a little more round.

If I had a laser at home, I would try it with the round pencils and the square laser-cut axles and see if they both work.

[likeablejerk]

@ihermit2

I don’t think a trebuchet could be done without an axle to rotate about

They can’t. But the fun is finding a way to make functional axles with a laser

[likeablejerk]

I suppose you could made enough stacked “coins” to make a fully round axle where the rubberband wraps, though it might make it too beefy for your current design scale (mine are about 1/2"D so ~30% bigger than a pencil.)

[likeablejerk]

[johnwills]

That’s great!

[cbarker]

@likeablejerk

Go for it! Also, we should put wheels on the trebs so that @polarbrainfreeze’s hot rods can tow them.

On our way to pumpkin chunkin!