AMP-1 Rocket Engine

Here are a number of pictures depicting the machining process for the injector cap. The two sides were faced off and then the center was drilled and bored out to .750". A centering plug was made to center the part in the rotary table to drill the bolt circle and mounting holes.  Machining the Centering Plug

One of the things that will be slowly worked on over the next few months is the creation of a Bill of Materials and a Spending Spreadsheet to more thoroughly track this project. Otherwise, over the past few weeks, numerous tooling additions, parts and testing equipment were purchased to accelerate this project to completion. A tentative test fire date of March 22, 2019 is now on the books and what I will be shooting for.

In preparation for welding the fuel tank together, more practice welds were conducted on aluminum blocks. The blocks chosen were of similar thickness to the components that would be welded together. Furthermore, two deep chamfers were added to the blocks to thoroughly simulate the welding conditions that will be seen on the real thing. Pictures below are to two welds. First one was not ideal and the second attempt showed much better penetration into the joint.

Original Amplifier Shield Setup After ordering a proper amplifier shield to boost the small voltage changes that Wheatstone bridge on the load cell gives off, some Arduino programming was done to interpret the voltage as load. Fortunately, the amplifier shield purchased was configured to output a boosted voltage that the built in Analog to Digital Converter could read and convert to integer values (0-1023 for a 10 bit system). However, this was found to be inadequate for the load cell and could only give an accuracy of 1.54 LBS per integer value. In other words, a 5V input divided up into 1024 sections yields a readable voltage change of 4.9mV (5V/1024=0.0049V). The load cell is capable of reading changes much smaller than 4.9mV so some changes were in order because the system needed to be more accurate than 1.54 LBS for measuring the rocket engine thrust. Amplifier Shield coupled with the 16 bit ADC So, to make this more accurate, a 16 bit Analog to Digital Converter was use...

Final steps were taken to finish up the servo mount that interfaces with the high pressure ball valve body. The top plate was drilled for M4 screw clearance and a 1/2" thru hole was drilled to accommodate the servo spindle. Four M4x0.7 threaded holes were tapped into the top of the two vertical pieces to bolt the entire assembly together. The next item to complete is the coupler between the servo spindle and valve stem. 

Yesterday, the other vertical piece of the servo mount was machined in the same fashion as the first. Here is a few photos:

Some work was done on creating a proper mount for the servo and high pressure ball valve to be rigidly connected. There is a finished drawing in the Documents section for the Servo Mount. The sets of photos below visually document the construction of the first vertical piece. The only thing that is of worry at the moment is thin sections that run along the sides of the valve body. With an extremely high torque induced from the servo, it is of concern being that there is a sharp corner, that the aluminum mount might shear. A bolted bracket may be constructed to span the length of the bottom just to insure that the sides of the new part will not flex outward and shear.