Radial (star-shaped) engine.

I'm back～

"Look at this, Onee-san!"

"It's our masterpiece, Master!"

The engine blueprint they showed me had five pistons arranged in a star shape around the axis—a radial engine.

Amazing, I taught them the basics, but these two developed a radial engine. Enines like this were used in reciprocating aircraft engines back on Earth.

"If we start from the maximum or minimum with just one piston, it's unclear which way it would rotate initially, so by arranging multiple pistons and intentionally breaking the balance, we thought it could solve that."

"That's where I suggested the meteor design and it became this shape!"

Looking at the diagram, it seems like it could actually work if made properly.

These things won't move if the precision is off, but since I'll process it with Spatial Magic, that shouldn't be a problem.

In other words, this is a perfect engine blueprint.

"By having them pull each other, the pistons don't need to move in both directions; each just needs to move in one direction… Theoretically, it can run on a single Goblin's magic stone. Though we don't know how fast it would be."

Moreover, since it's a basic piston-only magic tool, the fuel efficiency should be quite good. Rotation magic tools require a lot of energy to increase output.

"… You look like you're itching to try the real thing?"

"Yes! Please, Karina-oneesan!"

Alright, Karina-chan is weak to requests from cute kids.

Let's make a model right away. Here we go, Spatial Magic crafting. Whoosh!

"It's a wooden model, but something like this. Printing the magic circle circuits too."

"Oh, Onee-san works fast!"

"As expected of Master!"

"Then, let's set a Goblin's magic stone into it."

A single magic tool connecting five pistons. I placed a tiny magic stone about the size of a pinky nail — a so-called scrap magic stone — but the shaft started spinning smoothly anyway.

"… It really moved! It's rotating!"

"We did it, Dea-sama! It's our victory!"

I don't know what they were fighting against, but Dea-kun and Aishia high-fived in joy. Can Onee-san join too? Yay～

That said, the rotation is surprisingly powerful. I tried gripping the rod, but it took quite a bit of force and bracing to stop it. To get this much speed and torque from one scrap magic stone… Wait, isn't this revolutionary?

"Ah… I heard a crack just now. Did a piston break?"

"Hmm. Wood can't handle the output in the thin parts. Impressive."

It was Treant wood, though. Hmm, now I want to make it with stronger material.

I remade it with stone. Natural stone should be sturdier than wood. I'd prefer metal for elasticity and such, but this will do for now.

I ran it via the same method and tried stopping it by gripping — again, it took considerable force to stop. No breakage this time.

"At worst, it could peel the skin off your hand. Amazing power."

"True. We can call this a great success."

Moreover, it looked like its power would just increase linearly if we chained two or three of the star-shaped units together. With gears, we could achieve quite high rotation speeds.

… Wait, we were just supposed to make a dummy magic tool, so why did we end up seriously developing an engine!?

"By the way, we also thought of a plausible magic circle to install inside the cart. A magic circle designed to amplify rotation. With eight amplification links, it should fool most. Though it might not pass with professionals…"

"Here, this part incorporates wind and fire motifs from my suggestion!"

Ah, not just the engine body, but even the camouflage magic circle inside the cart!

I was out for less than half a day, and they completed the work perfectly!!

Kuh, this is all because Dea-kun and the others are more excellent than expected! And cute!

I must give these two a reward…!

"Alright, then I'll make you two a special treat… Today, it's a pancake party!"

"Wow, Onee-san can make sweets too? I'm looking forward to it!"

"Thank you, Master!"

Incidentally, the radial engine model ended up being a mixer and was very useful for stirring the pancake mix after a few select adjustments.

… The box had the pancake mix ingredients list on it, so I could probably make more myself by referencing it. Though I'd need to figure out getting the baking powder.