Fine Tuning the Manifold Design

Between work, the Maker Faire I've had very little free time for the last two months. I finally got some time this weekend to work on Nassau's cannons. When I last tested them they seemed to be firing a little soft. Additionally, I noticed that at high pressures (120 psi) the rubber seals on my Chinese rotation bearings were blowing out.

Cranking up the Power

As I posted earlier I have good evidence that the apparently lack of hitting power is in the cannon's upper works. Even when used with one of Battleship Lion's accumulator, ball-valve, and risers the cannons are not hitting as hard as I expected. As I also posted earlier the barrels themselves are not a problem - in fact they appear to be helping things a bit. There is not much that can be done with the breech so the problem must be in the manifold

Increasing Flow Through Manifold

I guessed that the seals blowing out might be a symptom of the problem with power: pressure was building in the manifolds and not able to escape up the barrels fast enough. I decided to mount one of the manifolds on my rotary table and open them up a bit.

In the picture above the gray manifold to the left is what I original had; the charcoal manifold to the right has been opened up to allow more gas to reach the breach. It turns out that this did increase the power significantly but not up to my expectations.

Increasing Manifold Height

I didn't take a picture but I also made a spacer to increase the height of the manifold a tenth of an inch. I didn't expect this to help as the manifolds are the same height as the cannons in Battleship Lion - which are known to hit hard. Adding the spacer appeared to reduce the power of the cannon.

Checking Test Technique

I am quickly running out of things to try... I know the problem is not in the barrels, accumulator, ball-valve, riser or bearing because I am getting similar results when I swap all of those out for units that are known to be good. Tweaking the flow and volume of the manifold helped a bit but still did not get the power up to my expectations.

This suggested that my expectations are not reasonable. I decided to take one of Battleship Lion's turrets and test it exactly the same way I was testing Nassau's. I removed the magazine cover and fired away. Lion's results were slightly better that Nassau's. However, the results were much closer to Nassau's than to my expectated results.

I still do not really know what the problem is... I know that Lion can blow through 2" of foam but for some reason it does not in my test rig. That question will have to wait for another day though. I now have some confidence that the problem is in the test, not in the cannons

Bearing Blow Out

I still wanted to try and find out why the seals on the bearings where blowing out. One change I made in Nassau's cannons was to not have the bearing completely sealed by the manifold. I made this change to save some height - and because I didn't think it was really protecting the bearing from pressure. However, now the seals are blowing out... It seemed like the most likely cause of the blow out so I made a taller manifold that allowed the bearing to be sealed in.

The above picture shows the change. The charcoal manifold to the left is one of Nassau's original manifolds (with flow increased as described above). The gray manifold to the right is a more conventional manifold that does a better job of sealing the bearing.

Results

Unfortunately the results where the same. Enough gas escapes around the bearing to reach the seals. I also noticed that the seals in Lion's bearing never blew out during repeated testing of the original manifolds. I've decided for now to assume it is poor quality in the bearing itself. I have some 'lower quality' bearings which have nice metal seals... I will probably try them next and see how they work out. Here is one of Nassau's (increased flow) manifolds with one of these bearings in it.

The effort was not a complete waste of time. I discovered today how to make a manifold almost completely on the mill - and more quickly than I could using the lathe. I will save that for another post though