Control Systems - Control a sub with a PC104 stack?

[reverendryan]

I'm thinking about building a completely custom sub that uses a PC/104 (or similar) computer and acoustic modem rather than standard radio controler (although this might be used as a fallover).

What would be the disadvantages of such a setup? Could motor noise, as well as orientation of the sub have an impact on communication?

Also, how would this impact hull design since this would require a larger than normal hull diamater (6"-1')?

Thanks for your help/ideas.

[interpol]

Going acoustic will cost you

Going acoustic will cost you alot.

I have been experimenting with my own stuff, but to no avail. The noise generated by the sub interferes with the acoustic data. Not only that, but you will need a spread spectrum in order to compensate for the movement of the boat.

Buying an acoustic modem, well, lets put it this way. It's five figures in USD.


Benefits of an acoustic control system? Range - an acoustic setup could yield hundreds of meters of control underwater. But it will cost you.

[roboticsubs]

Hello,
I'm not very knowledgable about

Hello,
I'm not very knowledgable about acoustic modems, but couldn't you operate on subsonic frequencies and then filter out all other frequencies (such as motor noise)? Just and idea!
I have been thinking about trying to do something like that as well (using an acoustic modem), but have not started researching or experimenting yet.

Hey Interpol, what do you mean by "you will need a spread spectrum in order to compensate for the movement of the boat"? Like I said, I don't know much about this yet.

[interpol]

Excuse me, I didn't mean

Excuse me, I didn't mean to say that you will need Spread Spectrum to allow for movement of the boat, I meant to say you need spread spectrum to eliminate interference.

I was editing spots in my post, and didn't realize I left that in.


Spread Sprectum is just taking a narrow band signal and spreading it out. Kind of like frequency hopping, or instead of hopping you can just do it in a predetermined sequence. It really gets rid of alot of noise in the signal this way, since so many bands are used. It's alot more efficient, but alot more expensive also.

Like I said, there are companies out there with acoustic modems that might fit in an RC Sub (if you have at least a 10" beam), but they are five digit cost, and that's for the low end models.

Unless someone develops the "sliced bread" equivalent for us, than I don't see us using acoustic to control our subs for a while.

[reverendryan]

Thanks, Interpol. I'll look into

Thanks, Interpol. I'll look into finding a used/grey market modem, but I think I'm going to rethink the control system. I would still like a compuer- perhaps using radio.

I wonder if 802.11b would penetrate the water very far... Perhaps I'll run some tests on that.

[interpol]

Unfotunately, the wireless LAN freqs

Unfotunately, the wireless LAN freqs are not going to do much good for you. The higher frequency gets absorbed even faster by the water.

Think of it like this. Your radio signal is an alka setzer tablet. The higher the frequency, the smaller the tablet. So, when your signal/tablet goes through the water, it gets absorbed by the water. You need a LOWER frequency to get more range. The more water you have to go through, the more signal loss you will get. This is because water(not pure water, but most water, like lakes, sea water, etc) is slightly conductive. Therefore it absorbs the energy from a radio signal while the signal traverses through it.

As far as radio control goes, you should get decent range with a standard 75MHZ radio. If you wanted to do a wireless video system, 900Mhz or 1.2Ghz is your best bet. Just make sure you check your countries laws on radio use, and that you aren't stepping on someone's frequency, or you could get into a lot of trouble.

If you wanted to get really crazy, you could do what the navy does to send one-way info to actual subs, by using real low frequency, like 15-20Khz, and lots of watts. But that probably wouldn't be legal.

[reverendryan]

I think if I tried

I think if I tried ELF pulses around here (puget sound/WA) the local bangor base would be on me quick

For now I'm going to table the comm issue, and focus on getting this thing designed. Its going to be big enough that I can throw in a regular radio with very little extra concern for mass. Perhaps I'll find a way to link a reguar 75MHz receiver to the PC/104 stack. (Read: I need to do anthro reading for my test next week =P)

Thanks for all your insight, Interpol.

[interpol]

I am currently working on

I am currently working on a slightly oversized 1/48 sea wolf. I have just finished cad'ing most of it in Inventor. It is scale for the most part, with the exception that I increased the beam by a "skoch". You can't really tell, but it allowed me to fit the next step battery into it.

I will be using 75Mhz for a control radio, and 1.2Ghz for the video and onboard telemmetry for depth, heading, etc.. Its a little over 7ft long, so I have plenty of room for everything. I am actually using a different kind of motor this time, I am using an electrocraft, instead of the run of the mill rc motor. Its about the size of a coke can, takes 12VDC, and has so much torque that you can't stop the thing with your bare hands. It spins at about 1100 rpms, so no gear reduction is needed.

My only concern is EMI from the motor, so I am building a seperate "engine room" and completely shielding it off. But yeah, it's all in design right now, I have the electronics done, just need to build it.

If you find a cheap way to get acoustics done, let me know, i tried and couldn't find any way to do it cheaply(that I would trust my sub with).