Home        Store        Docs        Blog

Help me to build my project please


(Darryl) #1

Hi Josh, Joe and all scubcribers

I am a complete novice in the ROV/AUV arena. I am trying to build a two thruster deltawing (triangular shape) AUV (?) that is autonomous - meaning, with my limited knowledge - that the AUV contains its own power supply built into the wing. I visualise that I will need two t-200 thrusters with integrated ESC, a compact battery (that will provide the optimum performance i.e. running time at average thrust/speed), a suitable micro-controller, an external waterproof ON/OFF switch, externally mounted LED battery condition/status lights, a GPS transponder and ?? (what other electronics will be required for the basic operational system?)…

Please help. Thanks

Darryl


(Rusty) #2

Hi Darryl,

Thanks for posting! Sounds like an interesting project. There are a few things to consider.

  1. Are you planning to have control surfaces like an airplane? If not, how will you control the AUV?

  2. There are lots of battery options. We are using lithium polymer batteries. The size required depends on your desired endurance and expected average thruster speed.

  3. GPS doesn’t work underwater since radio waves don’t travel well underwater. Subsea vehicles have to navigate via other means, usually sonar or dead reckoning.

I’m sure others will have thoughts to contribute as well!

-Rusty


(Harold Scadden) #3

Darryl,

First, all of Rusty’s comments apply … but here are some thoughts that you can expand on. Please grab dinner and a cup of coffee, I can type for a while at times!

As Rusty said, the GPS is not going to work under the water … heck enough tree coverage will knock out the standard GPS signal to a receiver. One thing you could do if you still wanted some sort of positional control is to use the GPS to obtain a position fix while you are on the surface and then you would have to use dead reckoning under the water. What you could do is use the dead reckoning to setup a boundary for the device to stay within and in the event that it goes so far outside of the fence, you force it to surface. If you are wondering, well I am driving it … how is it going to go outside … think of ocean currents, set and drift etc. that can push your unit outside of an operating area with or without the thrusters running.

Waterproof ON/OFF switch, EASY … you can use something as simple as a reed or Hall Effect switch and a magnet to trigger on/off with. By doing that, you can eliminate wiring penetrations for a switch or having to worry about the switch itself.

Any reason why you want to do the Delta wing thing? Rusty brought up an excellent point about control surfaces. Are you planning on trying to use the thrusters to vector yourself, if so, you are going to need more than two to do total attitude control.

Just read your post again, you said GPS transponder … ok, you are hunting for an ET phone home and tell me where I am at so I can come pick you up. That can be easy to do but with all GPS systems, wave height can be something that will eat you alive on getting a fix. You might want to actually have a whip style antenna for this thing.

How about some more info on what your dream toy is going to do besides punch holes in the water?

 

 


(Darryl) #4

Hi Rusty and Harold

Thank you for your quick response. To provide more insight into my project, I am building this 1.5m “wing” for my daughter who is an avid snorkeller/scuba diver. It will be her propulsion device in, and under, the water. I feel sure that two T-200 thrusters would be sufficiently powerful to tow her through the water. If this is successful I will be building quite a few wings for use in Mocambique.

So, to answer to your points:

  1. Yes, the wing will have flaps that will enable the operator (snorkeller/diver) to control their direction of travel.

  2. Space is at a premium and weight is very important. The entire wing is constructed from aluminum. Therefore I need a compact, lightweight battery that will enable the two T-200 thrusters to operate effectively at peak output for a minimum of 1 hour. That is an exageration as operating at peak performance will be the exception rather than the rule but I have to factor that possibility in if I don’t want to end up “dead in the water”. Ideally, I would like the battery to provide 2 hours of use, or more, at an average output (i.e. idling along most of the time with occasional bursts of peak thrust). That would be a real bonus.

Based on your experience and expertise in this field, could you suggest a suitable battery that would give me this type of performance?
<p style=“text-align: center;”>3. Yes Rusty, you are correct on the GPS. Harold hit the nail on the head here tho. The GPS transponder is to locate my wing/s should it/they go “missing” for whatever reason. “Here I am, come get me” :-)</p>
As regards the rest of the electronics - ESC, controller, battery status indicator, etc. - can you spec these components and give me a price for a complete system inclusive of the two T-200 thrusters?

Harold, thank you for the answer on the ON/OFF switch. As mentioned earlier, I am totally in the dark when it comes to electronics… can you specify something that I can investigate?

Thanks again, guys. I know I will get “there” with your help.


(Harold Scadden) #5

Darryl,

That is a big wing! More questions … I am assuming that your daughter would have some sort of hand holds on the wing … is that a fair statement? If so then I wouldn’t worry about steering controls because she can change the attitude of the device if it is balanced all the way around so if will just “sit” in the water in a level plane. That would reduce circuitry requirements.

I have no experience diving etc, will the T-200’s provide some sort of decent forward movement or is the device to act as supplemental power to pull her along while she is swimming etc with it?

I am still trying to get a picture of the construction model that you might have in your head. Will the Wing be free flood or is it going to be a sealed shape? The thing I am trying to figure out is how much displacement you are going to have in water and how much positive buoyancy that you are going to have just from the Wing before you start stuffing whatever else you want into it.

Another question … how far away from the Coast line, if this is even going in open ocean, do you expect to be? The reason I am asking this is when ET gets a fix on the satellites and wants to phone a position home, what will be your transmission method? Depending on your budget and what you might already own, I have some sleazy ideas on how to get you the position data. It is based upon a circuit that I built for a high altitude balloon project that we launched and tracked for hundreds of miles and recovered the device when it came down. Put it this way it went to a transmitted altitude of 103,258 feet … traveled at speeds in excess of 400 miles per hour … and covered down range distances of almost the State of North Carolina before it came down and we were able to locate it on the ground five hours later when we got to the landing site. You can check out the wiki for that project on our old Hackerspace page. http://757labs.org/wiki/Projects/hackerspacesinspace

I am game to help with any circuits and there are plenty of people on here with great ideas so your dream has a good chance of coming true.

 

 

 


(Darryl) #6

Hi Harold

I enjoy your humor, am impressed by your obvious knowledge and experience in this (AUV/ROV) and the electronics field and am encouraged by your willingness to assist me with my project. Thank you!

Yes, the wing does seem big but will definitely change now that I have settled on the Bluerobotics thrusters. I have looked at many different propulsion options from Tecnadyne (very expensive), Crustcrawler (less expensive), Trolling motors (powerful but too heavy and require lots of battery power) to modified Bilge pumps (2000gph Rule - a makeshift solution that I am not comfortable with).

The smaller wingspan will have two hand grips that will contain the ON/OFF switch in one and the Speed Control (deadmans switch style) in the other. Tilting both the handles up would point the nose of the wing down and visa versa. One handle up and the other down will send the wing in one sideways direction and the reverse action would send the wing in the other sideways direction. Think flaps, like an aeroplane.

The wing is a sealed shape, with internal struts covered by an aluminum skin along the lines of a normal aircraft wing. The leading edge will be curved, with the trailing edge tapering to the joining of the upper and lower aluminum skin. I anticipate having a watertight section in the centre/middle of the wing which will contain the battery, the controller and any other electronic components that are required. To counteract the weight of the thrusters, battery and other components I was considering injecting a buoyancy foam to give me the correct amount of positive bouyancy without compromising the dive capability/performance of the thrusters.

The wing will almost always operate close to shore in shallow waters (3m - snorkelers - 20m Scuba diver). My daughter is an accomplished swimmer (she owns her own swimming school) and Scuba Diver with night diving, wreck diving, rescue and a few other courses to her credit. Her husband is a qualified PADI Dive instructor with a number of courses to his credit. They will be my test pilots to put the wing through its paces.

Safety of the user is always a priority as the sea can be unpredictable and unforgiving with currents, winds, sealife, etc. ET will enable me to provide an extra margin of safety and confidence to recover, not only the user, but the wing as well in the event of a calamity. I would like to be able to track the whereabouts of the wing when it is on the surface through an internet connected laptop. Is that possible? I would assume so after reading your 757labs.org adventure.

Your balloon project is awesome! Which one of the two guys retrieving the balloon are you? One of the sections that caught my attention, altho’ they were all interesting, was the one about the battery. This is my concern as I would like the battery in the wing to run the two thrusters for an absolute minimum of 75 minutes (on full power if possible).

The content of certain comments you made may be relative to my project?

Your comments : This battery is capable of operating with a constant current discharge rate (my requirement?) over 1 Ampere for over 3 hours (nice extended time) at a final voltage output of 1.0 Volts. The idea was to be able to survive a high current drain (my problem too?) and maintain a total power pack voltage level above the projected Volt value (YES - required by the T-200’s) . This would ensure that we were able to provide a stable voltage source to all components (sounds good). The power for the camera was modified to run multiple twin cell packs in parallel to prolong the voltage level (this may be necessary for my wing?).

Thank you for your offer to help design the circuitry to make this work. I am super excited about the support you are providing and the possibility of making this dream happen.

Have a great day.

Darryl

 


(Harold Scadden) #7

Darryl,

In my opinion, you need to get the vessel configuration nailed down first. There are many issues that you have to address before you start to worry about other design integration issues with the batteries, electronics etc.

What is going to be the skin thickness of your wing and how do you plan on sealing the edges where pieces meet? Why I am asking this is to get some sort of feel on the structural strength of the wing submerged. You need to have a clue at what pressure (depth) that it is going to spring a leak.

I did some calculations based upon a tube made with 14 gauge 6061-T6 metal with a 12 inch ID and a length of 20 inches. Please understand that a tube will resist pressure better than a box will and a spherical shape will have the best chance of all to survive high pressure. The failure pressure is around 522 psi equating to about 1100 feet in depth. If the Wing goes that deep, you got other crap to worry about and hopefully the diver isn’t attached to it.

Since I don’t know the volume of your Wing I played around with a rectangular box of 59 x 24 x 8 inches. This comes up with a volume of 11,328 cubic inches of water displacement. The weight of the seawater displaced is a hair over 419 pounds. This basically means that your Wing and all of the accessories inside could weigh up to 419 pounds before you have to worry about foam etc. to make it neutral or positive.

Remember Aircraft Carriers are huge but they float for a reason … massive amounts of water displacement. The size of your wing might be your saving grace on being able to stuff it full of batteries etc. and all types of other toys.

 


(Harold Scadden) #8

Darryl, I sent you a private message … please go read it for some info.