Water Rocket Launcher 3.0 :: The Plan

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.

HT Controller : Overview

Ok, this is a quick post to index the previous posts relating to my Home Theater controller build for later reference.

Project Goal(s):

  1. Mostly to use the CNC machine to make something new, with materials other than wood.  Learn in the process.
  2. Fix a previous project that broke.  I had a power strip that turned on my amps sequentially but the voltage regulator burned up (no heatsink)
  3. Address the problem that my cable modem is behind my theater equipment rack, and when it needs to be reset it’s a pain to get to.

With that in mind, here are the posts covering the basic steps – in order:

  1. Learning to make a circuit board.  Isolation routing one and two.
  2. Cutting the front/back panels out of acrylic.
  3. Assembling the innards of the controller, and connecting input/outputs.
  4. Troubleshooting the things that went wrong.
  5. Final pics and video of completed project.

HT Controller : Complete

I got the controller installed in my media cabinet.  Connected the cable modem and router to the outlets on the back, and the db9 over to the powerstrip all the theater amplifiers are plugged into.  Pretty happy with the fit, and it will be nice not having to pull my equipment rack out to reboot the cable modem.

Besides, it seems to add a little flair when firing up the system to watch a movie.

—-=== VIDEO ===—

 

HT Controller : Troubleshooting

So I had some issues when putting the final product into use.  Which is to be expected, but this bugger had me opening the case at least 6 seperate times..

Issue 1 : when the 5v relays would kick in, it my 7805 voltage regulators didn’t have the reserver to engage them both at the same time.  I needed to add a capacitor.  I did it the easy way, and just screwed it into the terminals.  The +5v is wired in parallel so both relays benefit.

Issue 2 : I used digital pins 0 and 1 on the arduino to control the relays.  Turns out those pins are used for serial communications.  So when updating the board the relays woudl clickclickclickclick like no tomorrow.  No good, had to use different pins.  Obviously I didn’t account for that on the board creation, so they got solder to the pins directly.  Picture is a little out of focus, but it is the orange/yellow leads in the foreground.

Issue 3 : In the external power strip where 6 seperate relays live and are controlled by the arduino here, I made a mistake in that I didn’t have any 10k pull-down resistors on the 6 control lines.  I should have put them in my original circuit, and instead I added them via a little ‘daughter’ board I added to my original circuit board.  Oh, and if you actually jump to read about the external power strip know I took the power supply and arduino out as they are replaced by this build.  All that is left is the transistors and relays.

Ribbon cable removed, and ‘riser’ pins installed:

Daughter board freshly machined:

And installed:

Lessions Learned :

* Patience.  I had to keep telling myself that there was no way I would get everything right on the first try.

* That a 7805 regulator needs a headsink in most cases.

* That a 7805 also needs filter capacitors.  You can’t just plop it in a circuit and expect clean output.

HT Controller : Assembly

Installing the various components to get the HT controller to work was probably my favorite part of the build.  Something satisfying about seeing everything coming together.  At a high level these are the key components:

Arduino : Brains of the operation

Custom circuit board : Connections out from arduino and 5v power regulation

Relays : control each of the 2 outlets (cable modem and router)

Scavanged switching power supply : 120v ac to 12v dc

DB9 : connection out to the power strip where a relay controls each of 6 outlets/amps

So everything was installed on nylon spacers, with small machine bolts coming up through the bottom.  That can be seen well on the relay installation:

And here is the custom circuit board I created in my isolation routing tutorial.  All wired up to the front panel, buttons, db9, and relays:

Overall unit in early assembly:

And (almost) final:

Primary lesson learned on this assembly was when routing a circuit board that you are going to attach ribbon cables to, ensure the holes are lined up straight.  Do not stagger them as I did, it makes it very difficult.

I also learned that when soldering to plain copper boards you really need Flux – more than than what is in your solder.  I had good luck with some acid-based plumbers flux I had laying around.  I put that on the board where the pads where, and then tinned them.  Don’t forget to clean it of with rubbing alchohol or acetone.

HT Controller : Panels

So for my home theater controllers I needed front/back panels.  I knew I wanted to make these out of acrylic sheet, and that I wanted to use the CNC to cut them out.  One of my drivers was that in the past button layout was always a bit tricky, using the drill/dremel it was difficult to get everything lined up right.  So with that said, here is where I ended up:

Getting the actual panel cutout was pretty straighforward.  Measured the case, and setup the outside dimensions and then measured out where the controls would be.  The biggest challenge was the cutout for the outlet.  For that I traced an outlet cover plate, scanned it in, and imported the scan into my cad software.  This is the backplage all coutout.

This chassis has been used in previous projects.. so never mind all the fan cutouts!  Used to hold 4 500gb drives which was a HUGE storage array (in its time).  I didn’t quite get the speed/feed for cutting the acrylic down – so that is a continuing learning opportunity.

Same panel painted with spraypaint (on the inside):

and installed using clear silicone as an adhesive:

The front panel had some text v-carved around the buttons as labels.  This was done with a 60 degree v-carve bit, then filled in with white crayon.  Worked out quite well!  Again, the back is painted black and the text is engraved in the front.  Only the right button is crayoned at this point:

Only other task I had that was panel-related was to route a spacer out of 1/8″ hardboard for mounting the LCD panel.  This got sandwiched between the LCD and the front panel (with clear silicone) to make the LCD be flush with the front.

Primary lesson learned : When cutting thin 1/8″ material (acrylic in this instance) do NOT use an upcut bit.  It will pull the material up off the table and into the route.  This would be a use case for a downcut!

Ring light for CNC

I recently put LED strip lights under the cabinets in the kitchen, and had a few left over.  They are pretty basic white 12v LED lights, similar to the ones you see here.  While milling a circuit board the other day, I found myself using a flashlight to see how things were progressing.  It was also hard to photograph the process, so I thought I would install some lights.  Pretty straightforward process.  The strips are made of small segments which can be cut off the roll.  I cut 4 sections off, and arranged them in a square.  Soldered the corners up and left a longer lead which would go through my cable raceway to the computer running the show.

The LED’s I had are backed with a 3m adhesive, so mounting them under my z-axis was pretty easy.  Peel and stick!

From there, I opened up the computer case and cut the leads off one of the molex connectors.  The power things like cdroms/hard drives, and contain both a 5v(red) and 12v(yellow) power source.  I connected the Leds up to the 12v, and now whenever the computer is on the LEDs light up the work piece.

 

New sign for the workshop

Took a shot at making up a sign for the workplace.  Learned quite a bit in the process, and wanted to document a few of those learnings for the proverbial ‘next guy’.

I used 3/4″ mdf.. and a 1/4″ upcut spiral bit to do most of the cutting.  The circle logo and ‘aperture’ letters are .4″ above the surface, and the ‘laboratories’ letters are .2″.  I profiled the letters after the overall pocket was created with a 1/8″ bit to get more definition.  This all worked ok except for a few things:

  • An ‘R’ and an ‘I’ in laboratories popped off.  The MDF doesn’t hold well when the letters get small.
  • I re-routed those letters and then glued them on.  In that process I realized that NEXT time i would just route all the letters out of another (thinner sheet) and glue them on.  It would save many hours of pocketing work.
  • Glueing the letters would also allow for easier painting as you could paint everything seperate and then glue them on.
  • On the topic of paint, for $3 for a 1/2 quart home depot will create color matched ‘sample’ paints… awesome for this kind of work.
  • Be careful when shopvaccing around the machine while its working.  At the end I looks like a skipped a few stepper moter steps on the x axis, so i have some rough edges on the right side of my letters.  I vaguely recall the router pinching the hose against a letter while vaccuming.. that may have caused it.  If it didn’t.. well thats a problem for another day.

So I learned a lot, and have a fun sign for the garage – its about 36″ long for reference.

Isolation routing

I had very good success with my isolation routing endeavor.  After having to remember how to do things in eagleCAD, the actual manufacturing process was very straightforward.  To start with, I got the eagle files for an arduino board from adafruit.  I needed this to ensure the through-holes would line up so my board would end up being an arduino ‘shield’.  From there I laid out my components.  I won’t get into the actual circuit, but a few things to note:

  • You will be well served by increasing the trace width to .032″.  The smaller traces I have (seen below) will machine, but are a little small for comfort.
  • When you do the wire layout wizard tell it to put wires on the bottom of the board.  One-sided.
  • For optimal wiring I needed a few traces that ‘crossed’.  Normally you would bring them to the top of a two-sided board.  I wasn’t ready to mill two sides and try to get them to line up.  So I basically put in a 0-ohm resistor as a ‘jumper’ to cross over traces.

So this is my diagram:

From there to get the gcode to mill your board you need to run pcb-gcode.  This is a eagleCAD addon that does a wonderful job of creating gcode.  Installation is well documented on their site, so I won’t cover off on that.  There is no shortage of options to configure, but I didn’t change anything other than my machine type (mach3).  To run the setup options you type “run pcb-gcode-setup” in eagleCAD.

From there you can do your configuration.  Mine is included here, FWIW.

After you have everything configured, you have it work its’ magic by typing “run pcb-gcode”.  The output will e a file showing what the board output will look like.  Remember it will be ‘mirrored’ as its the bottom of your board.  You can close the preview, and the actual gcode will be in your eaglecad folder.  There will be two files, a boardname.bot.etch.tap and a boardname.bot.drill.tap file.

I ran the etch file with a 60 degree 1/4″ v-carve bit.  I ran it on 1″ pink foam first to verify it wouldn’t crash, but then ran it on my copper circuit board.  The etch file was awesome, and everything went smoothly.

The drill file was a little weird though.  It kept going back to x0,y0.. I think maybe for bit changes?  Sometimes it would go back to x0,y0 with z0.. so it would drag the drill bit lightly along the surface.  So I ended up hand editing the gcode a bit.. removing all the tool changes.  I have never edited gcode before, and this was very easy to do.  Its basically just three steps that get repeated:

G00 Z0.1000 (raise bit)

G00 X-2.0000 Y1.4000  (move to new hole)

G01 Z-0.0320 F10  (drill new hole)

You just take anything extraneous out.  And then run it on your machine with the bit zeroed an inch up (air carve!) to verify everything looks good.  My drill/etch files are attached at the bottom of post so you can check them out.  Only other change was I must not have had the material thickness setup right in pcb-gcode, so the drill depth didn’t go all the way through.  Easy search/replace on the drill file to replace the depth with a new one.  That’s the (G01 Z-0.0320 F10) above.  Just change the -.0320 for example to whatever depth you want.

I used a .9mm drill bit for this task, and all my components fit well in that hole.  From resistors, to regulators.

BRIEF VIDEO

Snapshot of the board below.  You’ll see some scratches going to bottom-right (0,0) from the problem I noted above.  You will also see the size difference in the traces.  I will ensure I use all larger ones in the future.

Here is another photo after a light sanding to clean up the burrs.. pretty good!

Gcode:

motherShip_daughterboard.bot.drill.tap

motherShip_daughterboard.bot.etch.tap