The physical launcher was pretty straightforward. I cut out a few legs from 1/2″ ply and assembled them to a couple of wood rings. Its about 3 feet wide, which should provide a very stable base. There is an initial coat of carnival red paint, but that will get additional coats if the trial run actually works..
I then picked up a few plumbing parts and assembled it up. Key pieces were a big 2″ cap with a hole drilled in the end, and I stacked that against a 1/2″ coupler to provide a stronger base.
The cap was mounted open side up. Then when you put the bottle, mostly full of water, on the launcher this cup should hold the water in the bottle. Then as propane is pushed it, some of the water should bubble out of the bottom. At least that’s the plan… You can also see the ‘feed tube’ which is where the propane will be pumped in. It should come in under the water line, then bubble up to the top mixing with the air present.
Not complete by any means, but there it is with a bottle on the launcher, sans fins of course.
I haven’t have much experience with high voltage, but wanted to be able to generate a good spark to facilitate ignition of the water rocket. I took the easy way out and picked up a cool little spark generator at (of all places) sparkfun.com. Creates a scary loud mean-sounding continuous spark.
To put the spark in the bottle I used the cnc machine to route a ‘plug’ of sorts to go in the top of the 1/2 pvc pipe. Drilled and tapped a couple holes for stainless steel cap screws I had lying around and I had a pretty good start. I had to bend the left one a bit to ensure they didn’t touch at the top where the caps are.
I probably went a little overkill, but I used some 12gauge house wiring I had for the leads going to the screws. I didn’t want the sparks ‘gapping’ inside the launch tube. I used the mini-torch and soldered the copper wires to the screws and shrink-wrapped them up.
And here was a quick test to see if it was sparking ok. Pretty small, but continuous and hopefully will make ignition happen!
Been launching water rockets with the kids for a few years, and thought I would try to amp things up a bit this year. I have been using the air compressor to generate the launching pressure, and the 80psi or so I get makes for an impressive launch – but I think we can do better. I have also been trying to make an electronic push-button type launcher, little kids have trouble pulling the rope to release the wrocket sometimes.
So I thought I would take a different approach and try to generate the pressure internally via combustion. That way the bottle would be basically sitting on the pad, not under pressure until ignition. I had previously thought I could generate H2O via electrolysis but thought that may be too dangerous to have 120vAC in the mix.. 🙂
So new plan is to use propane. I think if you start the bottle with x amount of air, then add propane until you hit the right mix and ignite you should be in business. The wrocket will either fly or blow up! Hopefully after a few tests I can identify the right mix.
Or maybe it will just blow up each time. Should be fun either way.
I wanted to see if i was on the right track before putting much more effort into this project. So, I filled ‘er up with some tap water and double-checked the resistance between the pos/neg posts to make sure there wasn’t a short. There was about 180k OHMs of resistance – not sure if that is good or bad. So I then jumpered in some temporary leads and threw the switch.
The bubbles coming off the plates was immense! You couldn’t even see in as the water was so frothy with them. That lasted for about 10 seconds until my 20amp shop breaker tripped. The water, electrical leads, and alligator clips were pretty hot too. So, with that I’d call the trial run a success – but I really hope I can bring down the current draw using distilled water and (limited) baking soda or I will have to resort to other measures to limit the current…
The picture below is from when it was all over, I wasn’t brave enough to stand close on the first run.
Most info online show using a car batter / charger to do elecrolysis… I didn’t want to deal with that so I am going to give 110v a shot. Here is how I will turn it to DC which is what is required. 35A rectifier bridge on a old CPU heatsink. Hopefully I can control the current by the amount of baking soda in the distiller water. Let me know if you think this is a bad idea for any reason.
We did a lot of water rockets at the cabin last season but were always limited by the compressor up there. It would only generate 80psi or so. After reading about using electrolysys to make hydrogen / oxygen for rockets in my make magazine I thought I would give it a go.
For the electrolysis I used stainless steel outlet covers on stainless bolts. I kept them seperated by nylon spacers. Two sizes if spacers kept them apart as well as protect the bolts from touching the plates they went through.