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#1 2014-08-01 15:21:12

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

NanoSeeker (Tiny Autonomous Underwater Vehicle)

I've started re-working an old project of mine, one that I last worked on about five years ago, called NanoSeeker.

NanoSeeker is a very small autonomous underwater vehicle, six inches long (150mm) and one and a quarter inches in diameter (32mm). The new version will be slightly longer, about 8 1/4" long (210mm), but the same diameter. Most of the new length is in the extended nosecone and tail section.

Here's a picture showing the old version above and the new version on the bottom:

IMG_20140718_122715.jpg

Here's a few videos of the old sub in action:

https://www.youtube.com/watch?v=IGX4m9Avs6w
https://www.youtube.com/watch?v=jf1Gg0e7EPQ
https://www.youtube.com/watch?v=Q9qbflEoz1E

Most of the parts for this submersible are 3D printed in ABS. The new shell tube is clear, so you'll be able to see the electronics and LEDs on the board.

I'm redesigning the board entirely from scratch, to use a 32-bit ARM chip running MicroPython, as well as more modern sensors that are available now.

The sub has 3 actuators - a center thruster for propulsion, and two hand-made linear actuators to control the dive plane and the rudder. The two linear actuators each use a magnet and an analog hall effect sensor for closed-loop position feedback.

For sensors, it will have a 9-axis IMU, a pressure/depth sensor, and a crude speed sensor (using a water-wheel paddle).

It will also have a bluetooth module, which will allow me to update the code on it while it is on the bench, without having to open the shell to get at the USB plug on the board.

You can read mode about this project as I update it on my blog, http://blog.huv.com.

- Jon

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#2 2014-08-01 20:16:20

Odysseus
n10b
Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Hello Jon,
This is an impressive job!
I was wondering if you need to put some weight to your AUV. According to your specifications, your NanoSeeker is approximately 130 cm3. Since it is made of ABS with air inside, I guess you need to put some kind of weight to reach the 130 g necessary to make it dive. Am I right? Is weight something critical for your NanoSeeker versus engine thrust (to go up and down)?

Last edited by Odysseus (2014-08-16 02:07:53)

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#3 2014-08-06 13:39:18

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Hi Odysseus,

Yes, I have to add weight internally to make it more or less neutral. I modeled a 3/8" diameter hole into the bottom part of the nosecone (inside) to hold a piece of tungsten (which is somewhat denser than lead). I also will be attaching weight to the underside of the PCB, behind the battery.

If you look at the third video above, you can see black electrical tape wrapped around the front and back of the sub - that was a quick and dirty way to get the weight & balance just right, on the first (and only) time I had it in a pool.

Sorry for the delay in responding - I assumed it would automatically subscribe me as the thread author, but apparently it doesn't.

- Jon

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#4 2014-08-07 22:58:04

Odysseus
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Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Hello Jon,

JonHylands wrote:

If you look at the third video above, you can see black electrical tape wrapped around the front and back of the sub - that was a quick and dirty way to get the weight & balance just right, on the first (and only) time I had it in a pool.

You've tried your Nanoseeker only once! Why so much work for a single time?

Been able to update your NanoSeeker code live is definitely a major and clear enhancement on the previous design. On the other hand, I am not clear why you have decided to change the nosecone shape and have a longer ROV vehicle especially if you have tried your NanoSeeker only once!

Did you see a major flaw in your first design?

Last edited by Odysseus (2014-08-07 23:11:24)

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#5 2014-08-08 00:06:42

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

The main flaw in the last design was reprogramming the AVR required me to take the thing apart, which was a major pain.

Plus, I didn't have the depth sensor mounted, so the only "sense" it had was compass bearing.

I made the new nosecone longer so it would fit both the depth sensor and the paddle-wheel speed sensor, as well as having a separate place to put weight for balancing the sub.

The tail section is also longer, to allow more water flow into the thruster (which was also a major design flaw in the last one).

- Jon

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#6 2014-08-12 01:06:12

Odysseus
n10b
Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Did you make any kind of CFD simulation to have a gut feeling of your new design?

Lot of torpido like design, have a thruster similar to this Bluefin Robotics design:

BF9M-Architecture.jpg

Your second design seems better but I am pretty sure water is not flowing smoothly in front of the thruster.

Also I am wondering if your propeller is properly located...

I am looking at this article: Gimbaled Thrust and think that maybe your thruster should be moving (inside your tail) so that you could remove the little fin on the back.

Last edited by Odysseus (2014-08-12 01:40:45)

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#7 2014-08-12 16:28:12

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

I'm a much more "seat of the pants" kind of robot designer - I very rarely (okay, never) do that kind of analysis.

While a proper vectored thrust system (like the above Bluefin AUV has) would be awesome, I have no idea how to make it fit in the space available in NanoSeeker. I actually designed it based on a larger ROV a friend built, that had really good performance characteristics. The thruster sucks water in, so as long as the input ducts are large enough there won't be any issues with flow.

That was one of the issues with thrust on the original version of NanoSeeker - the input ducts were too short. I made them significantly longer on this version. The other thrust issue was with using a gearmotor instead of a straight motor with no reduction. On MicroSeeker (my larger AUV) I used a gearmotor, but I also used a larger diameter model airplane propellor, which (as it turns out) works really well underwater at slower speeds. (MicroSeeker for details on that robot).

- Jon

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#8 2014-08-15 13:54:44

Odysseus
n10b
Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Well you have already done a lot (from mechanics to electronics).

I did not find any reference to your CAD system but this link to the NanoSeeker shows that you are definitely using one.

I am not sure I understand; do you mean that the NanoSeeker is not using any reduction motor since the propeller is very small?

Did you try different propeller pitch and size to see which one was best suited for your motor?

It looks like you are using an homemade (3D printed) propeller. Did you try to make different propeller to compare thrust?

Did you try any commercial propeller?

Last edited by Odysseus (2014-08-15 14:24:07)

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#9 2014-08-15 15:40:04

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

I use Rhino3D for all my CAD work.

I tried several 3D printed propellers, with different number of blades and different pitches. What it came down to was the motor wasn't turning fast enough for the most aggressively pitched prop I could fit in the space. I also tried a commercial model boat propeller, which was the worst of them all in terms of thrust performance.

The new version of NanoSeeker will use a straight motor, with no gearbox, to drive the propeller.

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#10 2014-08-18 01:35:25

SherpaDoug
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Registered: 2014-08-17
Posts: 2

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

That looks like a nice little package.  What printer are you using for the 3D parts?  Do you have any problems getting the O rings to seal against the 3D printed surface?  Do you use any post-printing machining or coating?

One way to tighten O rings in the field that are just a little loose is to wind thread or fishing line in the corner of the groove.  That forces the O ring to ride a little higher and make a tighter seal.  Another way is to line the groove with lacquer like fingernail polish.

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#11 2014-08-18 13:36:19

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

I'm using a Stratasys Mojo 3D printer, which prints ABS.

I don't have any issues with sealing, because of the orientation of the parts as they are printed. I use grease to help the o-rings seal, but I don't do any post-print machining, just a bit of sanding/filing where the seam is.

I definitely don't need to tighten the o-rings, they are already very tight.

- Jon

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#12 2014-08-19 13:01:02

Odysseus
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Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Are you satisfied with the quality of your 3D printer?

Do you have to sand some parts like the nosecone to make it smooth?

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#13 2014-08-19 13:34:32

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

The Mojo is an awesome 3D printer. Of course, it is pretty much out of the price range of most hobbyists, but I have it as a part of my work.

The nosecone is pretty much as it comes out of the printer, except where the seam is (start and finish of each layer on the outer layer). I sanded the seam smooth, but the rest of it is untouched.

Here's a closeup of it, where I didn't do any sanding: http://www.huv.com/Nosecone-Closeup.jpg.

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#14 2014-08-26 20:36:10

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

The new boards showed up today! Hopefully I'll get a chance to put one together over the next day or two...

NanoSeeker v2 PCB

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#15 2014-08-30 13:18:57

Odysseus
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Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Can you tell me more about your board like input, output, wifi, programming. It seems pretty powerful.

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#16 2014-08-31 00:16:19

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

Its a pretty powerful little package. The processor is an STM32F405, which runs at 168 MHz, and has 192 KB of RAM, and 1 MB of FLASH. It also has hardware floating point, and is a full-blown 32 bit ARM7 microcontroller.

The chip is programmed over the USB port, and I use MicroPython. Once the firmware is flashed onto the chip, I can copy python source files (text) to the on-board flash drive, either through the USB connection (where it looks like a thumb drive), or (my preferred method) sending the new source file to the chip over bluetooth, and having a script save the source file to the built-in file system.

On the output side, it has motor control for 3 motors, and a serial link to a bluetooth module (BLE-113). No wifi. It also has four different colored LEDs.

For input, it has a 9-axis IMU (MPU-9150), the above-mentioned serial link to a bluetooth module, a resistor divider hooked up to an ADC input (allows me to directly measure battery voltage), a digital input from the speed sensor (which works like a low-resolution single-channel encoder). It also has a pressure sensor hooked up on the same I2C bus the 9-axis IMU is on, and a pair of analog inputs hooked up to analog hall-effect sensors that allow me to measure the angle of the rudder and dive plane.

I'm hoping to get some time tomorrow to populate one of the boards, and I'll report here with the results once I've done that.

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#17 2014-08-31 16:20:50

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

So here's the board, with all the surface mount components populated (except a couple 1206 capacitors I don't have - I'll do those by hand later).

I have to solder a bunch of through-hole stuff next, including the battery plug, the magnetic switch, and the voltage regulator. Those will have to wait until later though, since I have to head out now.

NanoSeeker PCB

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#18 2014-09-01 00:56:14

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

And here's a very quick video, showing the following simple script running on the board:

leds = [pyb.LED(i) for i in range(1,5)]
n = 0
while True:
  n = (n + 1) % 4
  leds[n].toggle()
  pyb.delay(50)

YouTube video link

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#19 2014-09-06 00:40:06

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

So I've been testing various components on the board, checking to see what works and what doesn't. So far, I've been able to test most of the components on the board, and with a couple exceptions, everything is okay. One problem is I didn't end up adding a simple 3.3 volt connection to the IMU chip, which is why you can see a small blue wire connecting a pull-up resistor to one of the caps near the IMU.

The other big problem is the bluetooth module. It is a Bluetooth Low Energy module, and as it turns out, they don't work the same as the old style SPP modules. I'm still investigating that, not sure what exactly I need to do to make it all work.

What I have verified is I can talk to the IMU (with the power shunt) over I2C. The analog hall effect sensors for the dive plane and rudder positions work properly. The two h-bridges to control the thruster and the dive plane and rudder both work, and the motors spin. The four LEDs on the board all work. The voltage divider that feeds into an analog channel works. The magnetic power disconnect switch works.

I haven't tested a depth sensor (because I don't have one by itself yet).

All in all, its not bad for a first revision board so far.

PCB

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#20 2014-09-06 00:59:16

Odysseus
n10b
Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

This is very impressive. Thank you for the nice pictures.

How did you learn electronics?

I read on your blog that you have a software background.

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#21 2014-09-06 01:47:25

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

I taught myself electronics, with a lot of help from various people and websites and magazines, and of course a lot of experimentation. I started doing electronics back in 1997.

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#22 2014-09-25 13:39:24

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

So, I've decided to redo the PCB, and use a different bluetooth module, one that supports SPP (virtual serial port) out of the box.

Bluetooth Module

I've ordered a couple from Digikey, and I'm going to experiment with it to ensure it works before I design the new board.

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#23 2014-09-25 13:52:04

Odysseus
n10b
Registered: 2014-07-08
Posts: 23

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

How much does Seeedstudio charge you to create a single PCB like this?

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#24 2014-09-25 15:10:44

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

This board cost $33.85 USD. The base price for that size was $18.90, plus $10 for a custom color (yellow), plus $4.95 shipping.

I've decided I'm going to try a different vendor this time (Dirty PCBs), since they offer free colors and have much better shipping options. The board will cost $25, and for $15 shipping I can get DHL China (3-9 days).

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#25 2014-10-15 14:45:29

JonHylands
AUV/ROV Expert
Registered: 2014-08-01
Posts: 19
Website

Re: NanoSeeker (Tiny Autonomous Underwater Vehicle)

So the new PCB finally arrived today... I'm pretty happy with how it looks. I'll hopefully be populating one tonight.

New PCB

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