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Caution: First dive from my experience

(Cory) #1

Just wanted to share with everyone my experience on my first dive. Unfortunately, my first dive was terrible. I deployed my blue rov from shore. Precheck dive - everything looked and operated ok, when the rov was on the surface the motors responded to controls, I was able to stream video from the rov to the laptop. I was using an F130 controller.

I set my rov in the water where it sat on the bottom awaiting for my commands. The second I armed the ROV. It went nuts!! From the documentation it’s because it was trying to stabilize at the current depth. The motors continuously run and they don’t stop unless you disarm them :-/. The show stopper was when the back vertical thruster sucked up rocks that got stuck in the thruster. After that point, the motor has failed to operate correctly, as it constantly clicks and twitches but does not spend.

Secondly, I would recommend some sort of mesh cage around the thrusters because strings of algae gets tangled in some of the motors. :frowning:

The thrusters are no doubt very powerful, but I question the default code to run the thrusters when armed, I would prefer that when armed, the motors are at rest waiting to receive commands.

(Paul) #2

Wow, that’s really unfortunate. I think it’s worth while noting that it’s always a good idea to fly any new ROV for the first time in a controlled environment, such as a swimming pool or similar. There are just too many things that can go wrong for the first few flights that you want to minimize any risk of damaging the ROV as much as you can.

I’ve not had an opportunity to try the ArduSub software yet, but it’s pretty typical for functions such as auto depth and auto heading be -off- by default when starting up a ROV. If this is not the case with ArduSub, then I would recommend they change the software accordingly.

(Rusty) #3

Hi Cory,

Bummer! That’s not a great way to get started.

I’m curious why it went nuts. The ArduSub code should attempt to stabilize the vehicle, but it should stabilize fairly quickly. What flight mode were you in?

Thanks for the feedback on the rocks and algae. As Paul mentioned, I’d recommend testing for the first time in a slightly more controlled environment, but it’s definitely important to be able to handle those things long term. We’ve done most of our dives from boats or beaches but we only arm it once we’ve pushed it past the sand and rocks.

@Paul - The ArduSub code defaults to stabilize mode, which will attempt to level the vehicle. It must be armed to activate the motors so you can easily prevent the motors from running until you’re ready.



(Cory) #4

Thanks Paul and Rusty for the comments and feedback! Yeah, that was me learning the hard way :-/ Heh, I agree with you guys about the swimming pool, unfortunately where I live the pools are still closed since it’s still pretty chilly up here :stuck_out_tongue:

But yeah, Rusty, I was surprised too. Before I placed it in water, I did a dry/surface run where I armed it and all the motors were spinning. So then I disarmed it, did my final checks on each plug to make sure it was tight and then placed it in the water. It was sitting on the bottom and submerged, I armed it and it was in ‘stabilize’ mode. When it ran, it was as if all the motors were at full speed, water was splashing all over the place, as I was trying to gain control of it, it was rolling and twisting. When I pulled it to the surface, I noticed big rocks were stuck in each of the four gap/hole of the thruster number five. And then the vertical thruster number two was stuttering as well. I proceeded to disarm and pulled out the rocks, and armed it again. Thrusters 2 and 5 were stuttering. :frowning:

I never gain or had control of the rov on the first dive at all. Before I deployed it in the lake at the back of my house, I tried it in the bathtub, I noticed all was doing similar behavior, but figured the bathtub was not the best place to test out the simple controls (I just wanted to check it to do simple forward and backward movement), the thrusters were just too powerful water was splashing everywhere…I definitely made a mess of the place :-D. Things didn’t get better when I deployed it in the lake.

My setup was: Raspberry Pi 2 connected to Pixhawk with ArduSub default firmware code with controls config for the F130 controller, for my tether it was was CAT5E cable.

(Rusty) #5


First of all on the ROV behavior on power up - I think something was probably wrong. Either a thruster was spinning the wrong direction or the IMU was not calibrated to level and so it powered up quickly. Normally when we power up an ROV it might very gently try to correct for attitude but not dramatically.

Can you verify that the IMU was properly calibrated and showing level attitude?

I suppose that could also be caused by incorrect joystick outputs. Did you check the joystick outputs in the MAVLink Inspector in QGC? Make sure you have “Full down is zero throttle” selected in QGC - otherwise you will get all the vertical thrusters starting at once!

It’s very strange that the two thrusters are stuttering. Even sucking in a bunch of rocks shouldn’t cause that unless they made it inside and damaged the wires. Have you looked at these more? Any news? If you can’t figure out, shoot me an email and we can take a closer look at them to figure out what’s wrong.

For the record, the ROV should be calm enough that you can perform initial testing in a bathtub. I would make sure you can get to that point before trying again!



(Richard) #6

Rusty I am not familiar with the “plug and play” of the Blue ROV, but can he individually test the T200’s using your simple test program? This would eliminate something awry coming from the “box”.

(Rusty) #7


Yes, they can be tested separately with the example code or a servo tester. That’s a good idea.


(Jacob) #8

Did you save the telemetry log from qgroundcontrol after the mishap? If not, try to identify which log file on the pixhawk corresponds to the event, and upload it. We may be able to determine the issue with that.