I want to fill the chamber with out opening it.

Remember that part of filling the chamber includes both a fresh charge of fuel and the proper amount of fresh air. How do you plan to purge the chamber of burnt fumes if you don't open the chamber? Air compressor?

The original plan fails when you try to stop the counter mass. Works if it keeps going, but not if it comes to a stop.

Yes it matters. Google Gas Gun Design Tool (GGDT) and play with hypothetical cannons to fine tune your design before building it.

When using a boring bar, be sure it is sharp, keep it well coated in lots of cutting oil for cooling. Unlike tools cooled by the tool post, the bar has a long thermal path. Use the correct cutting speed. Remember to reduce speed as the diameter opens.

Frost free fridges include the wattage of the defrost heater. This may overstate the compressor requirements.

I've had good luck simply using a sabot. This can take the force of a large area and apply it to a small dense projectile. This was done in a thread for the max damage to a AA battery. http://www.spudfiles.com/spud-cannon-related/topic21827.html http://www.spudfiles.com/resources/the-foam-and-batter...

The wire size and length is very important for high power applications. A long run or a small wire gauge will cause enough voltage drop to alarm the inverter on low voltage. I visited a welding shop and bought welding wire instead of using the light gauge wire that came with mine. I sized it for a 2...

Most fridge compressors will run on a 1KW inverter. My Prius inverter setup ran a full size fridge for a weekend during a power outage. The issue with inverters is two fold. The compressor uses a higher start current than the run current, so the inverter must be big enough to handle the start watts ...

It does need to be prevented from blowing out. It does not need to be glued. On a pneumatic I made, with a 2 inch screw on barrel (ABS) a golfball barrel simply slid inside as an insert with a flange on the end so it could not fall on through. I'll see if I can find a pic and post it later. Edit, Di...

Way back, I saw a coax design that used a soup can in a 3 inch chamber with a rubber gasket bolted inside the can and covered with felt to adjust the fit. This can piston apparently worked well. I don't remember the barrel size. Think it was 1.5 inch or 2 inch. I'm not going to try to find a thread ...

I stepped in too. My excuse, same as everyone else. I haven't "push a tater through pipe" in a while becaue of it. Youngins, work, farm, work, bills, work. Did I mention work? BUT, summer time is fast approaching... Hmm, I was trying to remember the last time I pushed a tater through a pipe.. I thi...

There is a sticky on how to make small rubber face pistons on a drill press. You can choose from several suitable materials. http://www.spudfiles.com/forums/files/15_935.jpg Making a small piston that seals well is not too hard if you have the tools. http://www.spudfiles.com/forums/tutorial-making-a...

Here in the US, I can pick up used G band routers for $10 as people upgrade to N. You don't need to buy new equipment. Before buying anything, be sure to check your coverage. Some floors don't kill the signal much, so a router on the main floor may be able to penetrate through the floor to the basem...

This is why BBQ tanks have overfill protection float valves, and disposable tanks are filled by weight and are not refillable, legally anyway. For safety the design must not exceed 80% full by volume to ensure the expansion space for warm weather.

Remember that is is not a broadcast transmitter. It is packet radio, so it must switch from Transmit to Receive fast enough to handle packet handshakes. Again as in my first post in this thread, forget a linear amplifier. If your laptop in the garden does not have high power too to link back, it won...