Recently whilst on a trip with some time to kill I revisited Rene Caldera's Micro-Hybrid website http://microhybrid.com where I was shocked to read that he was ceasing production and distribution of his material/plan kits for this interesting little rocket motor.

For those of you not familiar with the product, it's a 22ish mm diam motor that uses N2O from the little cylinders that are used to recharge whipped cream dispensers. Most people come across these at some point in their amateur rocketry hobby and spend many hours trying to work out how these might be used to make a mini-hybrid motor. Some of us even get as far as lashing something together before realizing that it's going to take a massive amount of work to get any sort of performance from these comparatively heavy cylinders.

We'll Rene stuck at it and put in that massive amount of work! He solved the two big issues:

a). How to puncture the foil seal on the cylinder without adding stupid amounts of weight in the form of carriers, threaded caps etc.

b). How to initiate the flow of N20.

His solutions to both of these problems are elegant, lightweight and easily available.

But this is not why I sent him an order....

I sent him an order because he not only managed to get the thing to work, but he created a niche product with almost a cult following. There are message boards and websites everywhere talking about these little things. Truly he created some rocket culture and that earns my respect....

Anyhow. A week or two later on a Friday afternoon the package arrives. I turn to the wife and say "Well, there goes the weekend!" before bolting for the shed and locking the door behind me.

First up, here is what you get from Rene:

Everything you need to build the motor and enough (non pyro) consumables for a fair few burns.

Now yes, you could just buy the plans and rummage through the junk box for the rest. But I have to say it was a pleasure to have all the materials laid out before the job started and know that all I had to add was time.

The first job was to fire up excel and convert all the inches, thou, and cubits to mm.. And they call us colonials!

The first swarf came from the snap ring grooves in the case...

So did the first problem! This thing is tiny! I didn't have a tool that would go up the bore.... I did have a spare Allen key though..

From here on it was easy....

The Al piston/piercer-injector carrier was easy, even the little brass piercer was straightforward. Rene discusses the machining steps in the instructions in a straightforward, unpatronising manner.

Now Rene's design is mature, tested and much discussed, so I pretty much left it alone. Except, that is, for the nozzle. His drawings have the graphite nozzle (quite a soft grade) sitting directly on the aft snap ring. Experience tells me that this may cause the edges of the nozzle to crack and chip. So I added a 1.8mm aluminum washer below the nozzle to spread the load from the snap ring. To keep everything lining up, I took half this width from the nozzle it's self and the other half from the fuel grains.

Here are all the machined parts, cleaned up and ready for anodizing (the big tabs in the casing are for electrical connections). All up it took me about an hour to machine on my little lathe.

Here you see the Al bits being anodized and the (mostly) finished product in the box. The square thing on the right is a little steel and brass punch I made to produce the burst disks from coke bottles (I told you it was simple and elegant)..

The missus is off overseas for a month so I should have plenty of time to cannibalize the digital kitchen scales to make a little load cell. The smallest test rig I have only goes down to about 5N that would give me 2 bits of resolution at full thrust from this thing...

More to come.