13 Mar 2016 - and a mystery. Test run gives a stubborn zero on our "force measurer"which is a luggage weighing scale. To get good performance we need 100W of electrical power to deliver a thrust force of 1N which would show on these scales as 0.1 kg force. Scale sits at zero all the way. Big under-performance challenge here!
Test 1 looked good - so there is something there.
I plan to follow-up by trying:
A smaller nozzle for more of a pressure build up,
Balancing the balance beam instead of measuring reduction of the weight force of a large counterweight
Measure other kinds of model thruster on this rig for comparison
Beam balance about 45cm long made of "Make-a-Bracket Carinya" steel shelving pieces.
Idea is to assemble the motor on the vertical piece at the end nearer to camera.
Rocket motor applies an up force - pivots in beam centre - giving a down force at the other end to be measured with an electronic hanging scale intended for weighing luggage.
A challenge, see video below, is a risk of "burnout". Normally the energy needed to change water to steam keeps the coil at 100 deg C or a little above. If we run out of water or lose water then the coil glows and can melt nearby plastic, or worse. I searched for fuse wire with the idea of making the coil out of a low melting point wire so it would act as its own fuse. This search found something better, the "thermal fuse". This sends current through a little bead of low-melting point metal. On temperature rise the bead melts switching the current off. This is used for a similar safety purpose in hair dryers and hair straighteners. Looks great - I am thinking of embedding this in the wall of a boiler made of epoxy resin - or in a cutout in a polypropylene tube reinforced with epoxy resin and carbon fibre. Example ref: http://www.jaycar.co.nz/Passive-Components/Circuit-Protection/Thermal-Switches-%26-Fuses/c/202E
I was going to keep Rocket Motor Number One as a historical treasure until I met ex student Dave who tells me he likes this blog and hurry up please to give us all Test Number 2 (This is Dave 2.0 - the number of interested people has grown to the point where there are 2 Daves) The quickest way to Test 02 is to modify the motor from Test 01. Ordering a few goodies online - like a pressure gauge and digital hanger scales for only about 5 dollars each which is a pleasant surprise. I checked out pumps but small electric pumps only go up to about 100psi and I calculate that tension springs or rubber bands acting on a syringe plunger can do better as well as being simpler, lighter and easier. Aiming for a static test of a more complete design with thrust and pressure measurements.
After the SpaceX historic recovery of a rocket booster for re-use, Elon Musk announced that he would not re-use it because it was of historic significance and should be saved for display like in a museum. http://www.popularmechanics.com/space/rockets/a18792/recovered-spacex-rocket-destined-display-case/
I am therefore inspired to save the rocket motor of Test Number One for museum posterity in case it turns out to be the start of something wonderful - or even the start of something.
Video of the first test run. Full version 8 min 34 sec includes setup and tech details.
(Short version in the previous post below is about 3min if you only want to see the motor running.)
