Day 26: 1 extra hour in each day is what I'm asking Santa for this year!

The 80/20 law is in full swing! 20% of the work got me 80% of the way there. Its getting down to the last couple pieces and now comes the hard part.

Drilling the injectors has proven to be more difficult than I anticipated. The oxidizer holes (inner ring) are 0.033 inches where as the fuel holes (outer ring) are 0.015 inches which is the smallest drill bit in the world. It is a #80 drill bit. I broke 2 of them before ordering one made of carbide. That broke too. I am convinced that it is simply not possible for me to drill these holes with the tools I have so I will be changing to a 6 hole pattern which will allow me to use 0.038 and 0.017 inch bits for the oxidizer and fuel, respectively. I am also going to start by drilling one small hole to start that way if I can't get the 17 thousandths bit to work I can go to a 4 injector set up.

The bottom left hole on the outer ring contains the offender!

This is the new injector plate.

Since I couldn't work on my injectors until I got a new plate finished, I started to test my electronic systems. I learned that not all nitrous solenoids are created equal. My fuel solenoid is not powerful enough to open against the 400 psi charge pressure. Should have figured that since car fuel pressure is only ~20-50 psi. So ordered a new one that is on the way now.

I  took the time to just sit down and learn everything there is to know about DC circuits and capacitor banks. Turns out that even though the steady-state requirements of my coolant pump is only 110 watts at 5 amps, the start-up surge can top 50 amps. Even if it is only for a split second, it still shuts my set-up-down. Geoff comes to save the day yet again with lawn mower battery that I can use to run the pump separate from the rest of the system until I can get a capacitor bank put together.

 Testing of the cooling system with the battery. Everything checks out.

 This is the man himself! This is Geoff helping me get my solenoid to seat properly.

 For some reason, our horizontal band saw has been taking FOREVER to cut so while I got the stock for the injector plate cut, I started to shape my next next rocket! This one will be 100 lbf and regeneratively cooled. More on that later!


Quick design notes for my capacitor bank (Warning: Hand-wavy math incoming):

The governing equation is Charge (Coulombs) = Capacitance (Farads) x's Voltage (Volts)

Capacitors in series have additive voltages. A common voltage is a 2.7 volts so I will need 5 of them to get higher than my 12 volt power supply. 2.7 x 5=13.5 volts maximum.

They need to all be able to store the same amount of total charge.

So the equations break down to:

Vt=V1+V2+V3+V4+V5
1/Ct=1/C1+1/C2+1/C3+1/C4+1/C5
Qt=Q1=Q2=Q3=Q4=Q5

It (amperage)=Ct*dV/dt
Stored work potential in the capacitor (joules) is W=1/2*Ct*V^2

So my pump needs 50 amps at 12 volts minimum. My PSU supplies 12.3 volts. Ebay has cheap capacitors that are 80 farads at 2.7 volts. Combining them in series gives me a maximum of 16 farads at 13.5 volts.

dV/dt is going to be limited by the rate at which my power supply can recharge the capacitor.

300 watt power supply can supply 300 joules/second.
If the total joules of energy in my full charged capacitor is W=1/2*~16*12.3^2=1152 Joules
If the total energy in the capactiors can be kept above W=800 Joules (~300 joules less than the full charged one), solving for V=sqrt(2*W/Ct)=sqrt(2*800/16)=~10 volts shows that my psu can supply about 2 volts/second to the capacitor. So my dV/dt is 2 v/s.

The amperage that my ebay capacitor can supply amounts to
It (amperage)=Ct*dV/dt=16*2=32 amps psuedo-continously but it is ok if the voltage drops for a little while until the motor gets spooled up so I think it will work.... "in theory"