Underwater Solenoid Valve Remake

Posted on by
Reply

I tried a solenoid I scavenged from underwater valves on my 3D printed valve system and it didn’t work (duh).  It was just too weak.  The original valve spreads the force from the high-pressure side across a larger area, so I guess the spring return can be comparatively weak.  My design didn’t do that.  I also didn’t cut my compression spring down very much, but I qualitatively determined that the solenoid wasn’t generating a useful amount of force by holding it on the magnetic core while turning the power on and off a bunch of times.  I am a terrible engineer.

So I went back to square 2 and decided to remake the original brass valve body in lighter ABS plastic using our Makerbot 3D printer.  The beta version looked like this: Continue reading →

Cravenly resorting to commercial solutions in underwater solenoid valves

Posted on by
1

I’m having trouble with the upper valve that will allow air to be released from the hull (thus decreasing buoyancy and giving some downward thrust).  I mean, I’m having trouble with everything, but that’s why I’m doing this, right?  Anyway, I decided to order a couple underwater solenoid valves in the hope that I could stick one in the robot and have it work (hahahahaha).  I found several suppliers in China listed on this site alibaba.com, and settled on Nuoling Pneumatic.  Most of the other options either weren’t waterproof, were too big, didn’t support a 12 V power supply, or had a large minimum order size. The two I bought were $12.35 each, which is less than I was expecting (although the shipping was $55 for two units).

Underwater solenoid valve from Nuoling Pneumatic

Underwater solenoid valve from Nuoling Pneumatic

The valves were a lot bigger and heavier than I expected.  You can see it’s basically a big chunk of brass connected to the waterproof electrical components.  Fortunately it’s easy to take apart:

Continue reading →

Un-improving range on the infrared channel

Posted on by
Reply

It turned out doing software UART was a terrible idea.  The processor is way too slow to support a reasonable baud rate.  I did figure out how to use a comparator though: the key phrase I was missing was “rail-to-rail.”  That means that inputs can be in the full voltage range from ground to Vcc.  Another handy phrase is “push-pull,” which means that the comparator can output 0 and 1; in contrast, an “open collector” comparator can only output 0, and needs an external resistor to pull the output to 1.

I bought a rail-to-rail push-pull comparator, the MCP6541, and tried it with the receiver circuit, and sure enough it increased the maximum range significantly.  Unfortunately it also increased the minimum range significantly.

Continue reading →

Improving range on the infrared channel

Posted on by
1

The range on the infrared channel, which I discussed in the last entry, is probably enough; but I’d like to increase it a bit.  With more range I can space modules farther apart if needed, and hopefully be able to have a wider angle between the transmitter and receiver.

Fortunately the signal output by the Darlington transistor pair on the receiver is a pretty clean digital signal.  At full power it ranges from (a little above) 0 V to (a little below) 3.3 V.  As the transmitter gets farther away the digital signal remains but the low voltage increases beyond the UART receiver’s ability to read a 0.  For example, at a large distance the UART signal might range from 2.5 V (logical 0) to 3.3 V (logical 1).

There are several options I’ve considered:

Continue reading →

Finished 3D-printed AUV hull

Posted on by
Reply

The hull is done for now.  As I mentioned before, I have some improvements in mind (mainly to get rid of the outer bolts), but it took about 34 hours to print all eight pieces and I’m not eager to do it again.  If I ever get around to putting motors on this thing then I will have to re-print at least four of the semidemihemispheres, as the current ones don’t have any mounting points for motor attachments.

Pictures and video follow:

Continue reading →

What I learnt making a 3D printable AUV hull (Part 2)

Posted on by
Reply

I printed four copies of the semidemihemisphere and refined it a bit as I went.  Here’s the whole thing, including the hull that I covered in my last log entry.  The only difference in the hull is I removed the top hole, as only two of the semidemihemispheres need it (as valve mounting holes).

Tweaked version of the AUV model.

Tweaked version of the AUV model.

I made a few interesting changes to the cutaway portion though:

Continue reading →

What I learnt making a 3D printable AUV hull (Part 1)

Posted on by
Reply

I did a bit of testing on my AUV hull design, and finally got a prototype ready to go.  I’ve been working on the design for several months in Autodesk 123d, which is a pretty great program if you can put up with the crashes, corrupt save files, and slowness (hey, it’s beta).

Here is my current design in full, including the support structures:

Spherical Autonomous Underwater Vehicle hull

The 3D model for my spherical AUV hull.

This is one eighth of the hull; I call it a semidemihemisphere.  Eight of these will make a sphere 18 cm in diameter.  I split it up into eighths because I’m using a Makerbot 3D printer and its build platform is limited to a cube about 10 cm to a side.  Also, this way each piece can be identical (or nearly so).

One limitation in the Makerbot is that it can’t print overhangs very well, so I had to add some support structures that can be cut away.  In this entry I will ignore that and focus on the hull design:

Continue reading →

Poor man’s IrDA for intermodular communication

Posted on by
Reply

If all goes extraordinarily well, the AUV will have the following modules sitting in the hull:

  • Acoustic modem
  • Motor control
  • Depth control (buoyancy control and pressure sensing)
  • Master controller

Rather than wiring everything together, I plan to give each module its own power supply and use an optical communication protocol to connect the modules to the master controller.  The inside of the hull will be cleaner and more solid than if everything was wired together, and waterproofing will be easier.  Here’s how it works:

Continue reading →

Sure enough, ReplicatorG reads 123D-generated STL files at 1/10 scale

Posted on by
Reply

Update: 123D beta 5 uses the proper units for exporting STL files, so the scaling operation is no longer necessary.

As I noted previously, objects in STL files created by Autodesk’s new 123D CAD program are not correctly scaled when loaded into ReplicatorG (at least not for me, I’m using the public beta from a few weeks ago).  Eyeballing it, I guessed the object in RepG was about 1/10 the size defined in the 123D model.

To test this hypothesis, I designed a rectangular prism, 50 mm by 25 mm by 10 mm (yes, the temptation to go 90x40x10 was strong).  Results follow:

Continue reading →