Testing in Cayuga Lake


#1

Here are a couple of pictures of testing in the lake. I ran the OpenROV for around 40 min. with no brown out or resets. There were a couple of ducks around but they stayed clear of it. The North end of the lake still has ice on it. I stayed in the boat dock area as it was much calmer. It was a lot of fun to see the OpenROV in operation.

John

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#2

Hi John,

thanks for posting this. I also saw your Lake Cayuga video which David posted in the blog. I think there should be a lot more videos and photos from guys that already have operated their ROV out there!

After having switched from Alkaline to NiMH cells, I ran a bathtube test successfully on the last weekend and I hope that I can do my first 'real life' outdoor test on the upcoming weekend.

Now I run NiMH 8 cells in series (providing 9.6 V) and I had no brownouts so far. I even reduced the scale values in ArduinoPhysics.js to -30/+30 and I had the impression that this would give enough thrust to the ROV at full speed. Running all three motors at full speed (under water) made the ROV consume 4.5 A in total, which makes me confident that I'll get a sufficient total operating time with my 4500mAh cells. Due to the heavier NiMH cells, for bouyancy compensation, I had to add a small air container to the top side of the ROV.

Btw, is that black thing on top of your ROV some kind of bike tube filled with air? Doesn't this make it difficult to hover at a constant depth, when the air gets compressed and has a variable volume depending on depth?

-Stefan


#3

Love the video and Pictures, can't wait for me to get the remaing parts to finish my Build.

Boyancy I was thinking that if you had two pvc tubes with screw on caps on each end with a compartment seperating front and back that you could mount these on the top of the ROV. This way you could allow water into each compartment of the tube to ballance it.


#4

It is an inner tube. I tried ping pong balls but needed more than 5 and that is all the holders I had printed, so I when back to the the inner tube. Yes it is hard to hover! I was thinking I need a setting on the open cockpit screen to be able to set my vertical thurster on a little bit. It is too hard to do this with the X'box controller. Like a radio control trim adjustment.

I am running 10 NiMH cells in series. Five in each battery pod. I have posted pictures before on how I made my tubes. All I do is cut new tube lengths and pust the ends back in. I think I have 5 sets of tubes at this point. The design of the ROV makes it easy to attach different length tubes and adjust for balance.


#5

Hi John:

To amplify what Stefan said, have you done any in-water testing with 8 NiMH cells? The motors will run just fine on 9.6V, and it should help your buoyancy issues a lot. Buoyancy is always going to be an issue with NiMH since the cells are denser than Alkaline or Li. With the low series resistance of NiMH cells I don't think you'll have any problems with the BB browning out, but it will be something to check at low levels of battery charge. I'm guessing in the end all you lose is the 20% of the energy represented by the 2 extra cells.


#6

I switched back to 8 batteries and the ping pong balls and will give it a try.

thanks!

John


#7

I manged to do the first "real life" test at a nearby pond last weekend.

All in all I can say that manouverability was better than expected! I used the gamepad for proportional control (I don't really think that using the keyboard is more than a backup option). I also have to say that I bypassed the motors "smoothing" code that was introduced with the last Arduino firmware update, because it is not necessary when controlling the ROV with the gamepad (It makes the ROV response very slowly and ruins the advantages of using the gamepad). I found it very easy to hover the ROV with the vertical thruster.

I reduced the throttle value range to -30/+30 (in my scale function in ArduinoPhysics.js) for all 3 motors and found that this quite enough for giving the ROV some speed while making the control of the ROV easier by using the range of the gamepad joysticks better. The lower throttle values will also prolong operting time, so I'll probably stay with this setting.

I had not a single failure or brownout during the whole runtime of 1 hour and 10 minutes (also better than expected). I used 8 NiMH cells with a capacity of 4500 mAh. I measured a maximum overall current of 4,5 A when operating all 3 motors at full speed (under water) with the -30/+30 limit.

For bouyancy compensation, I added a 200 ml air tank at the top side of the ROV (see attached image). It's just a PVC rigid pipe from a hardware store with 2 PVC endcaps, which gives some 200g additional uplift. It's not 100% water tight yet, but I think I'll just epoxy the endcaps to the tube instead of dealing with o-rings. The surplus uplift can easily compensated by adding some extra nuts to the threaded bars at the bottom (front or aft, left or right - however you want to trim the ROV). Or by adding additinonal hardware, sensors, etc., of course.

One disadvantage of the tether coming with the kits is that its not floatiing and therefore can easily get entangled in obstacles at the bottom. I'd like to make it slightly positive bouyant - has anybody ideas for that (like using plastic or wooden pearls with a hole in it every 50cm or so)?

-Stefan

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#8

Eric once showed me a design idea he had for tether floatation pieces. I'll ask him about that.

A few other things:

- Thanks to the homeplug adapter, we've had success using an even thinner two wire tether. So if it's buoyancy that's your main concern, there might be options there.

- I've noticed the same thing when flying ROVs - that it's easy to get tangled up in your own tether if you're not careful. I think a visual cue on the cockpit that shows how much the ROV has rotated would be useful to help avoid too much of this.

- The ROVs that James Cameron used on the Titanic played the tether out from onboard the ROV. If you're trying to get into tight spaces, you might think about rigging up a way for a section of tether to unspool from the ROV instead of only topside. That make sense?


#9

David,

while playing the tether out from the ROV would really be nice (it won't have to drag all the lenght of tether behind it), I can't image a practical way to achieve this with openROV...

But it would really help if the tether would float at the surface instead being dragged over the bottom by the ROV. It's not that I'm afraid that the ROV itself gets tangled up in the tether, but that the tether gets caught by some obstacles on the bottom (like trees, branches, sharp-edged rocks etc.). The risk for that could be minimized it the most part of the tether would float on the surface.

Does the thinner tether that's being used together with the homeplug adapter float? If not, isn't the risk that it gets caught or even get torn apart by a sharp rock even higher?

I thought of equipping the tether with wooden pearls like these, but I'm afraid that tether drag will get significantly higher.

-Stefan


#10

I was thinking about floating the tether as well. I was going to try using Ping Pong Balls, these should withstand the pressure although they would need to be tested. It would be great if they could be placed in that pressure pot to see how much pressure they could withstand before crushing. I would like to see one placed about 15 or 20" from the ROV this would keep the tether off the bottom and then additional ones along the wire as needed. I am not sure how much drag this will put on the ROV but thinking back when I go fishing with a bobber it could be significant, We may need to come up with a torpedo shaped floater so as to have less drag. Will be interesting to see what folks come up with.


#11

See my comment which talks about ping pong balls and their crush depth, http://openrov.com/forum/topics/getting-neutral-and-a-prop?commentId=6365107%3AComment%3A35647

Short answer ~35 meters


#12

John,

I have been diving wrecks in Cayuga Lake this summer. Some of them are historical and "semi-lost". IE precise location not known to diving community. I could definitely use the assitance of an ROV hobbyist. In particular, I was contemplating a dive this weekend.

Let me know if you are anyone you know might be intrested.

Marc D. Johnson


#13

Shipwreck hunters seek Cayuga Lake’s treasure. Took our ROV to the lake last month to do a little surveying and documenting of a few of the object we have found on the bottom of Cayuga lake. The week long expedition went well, I was able to tryout the new floating tether from OPEN-ROV and it worked extremely well. that combined with the new elevator I built made the exploration much easier and not having to worry about the tether getting hung up on objects around the shipwrecks we were exploring. I downloaded the new software flash image 30.0.2
it appeared to work fairly well with the exception of not being able to connect after a while. not sure what the issue is what we are unable to ping the ROV unless we reboot five or six times. at this point we had to go back to 2.5.1 release for reliability. here is a link to the newspaper article about our exploration where they mention the use of the underwater robot.