Anyone else want a 'slower' ROV for survey work?

propulsion

#1

I've noticed that even thrust factor 1 is a bit speedy for my starfish surveys and maneuvering to get footage of specific objects. I feel like i'm blasting along UW like a maniac :)

I was wondering if anyone else would have use for a .5 thrust or something like that? Maybe a 'survey mode' plug-in (I have no clue how to make plugins, so just coming up with ideas) that has low end small increments on the thrust factor.


#2

Hi Laura:

I think much of the speediness that you're seeing is a result of running your ROV on 12 Volts while the throttle settings are tuned for the stock 9.6V.

If you'd like to tinker with the throttle settings, it's easy enough. They are in the file rovpilot.js, near the bottom. If you're using the new 2.5.1RC5 software, I believe the pathname to the file is:

/opt/openrov/cockpit/src/plugins/rovpilot/public/js/rovpilot.js

Tinker around with that for a while and let us know how it goes. BTW, are you using a gamepad to control the ROV? That should give you some added control at each throttle setting.

-W


#3

Ah, good point, I went with the extra cells because I was worried about having drop outs with the rechargeable NiMH under a load.


#4

so i went back to my 4 per battery tubes and instead of reading 'full' (the battery indicator) it reads 9.8 and two bars. The batteries i'm using are 5000mAh NiMH's X 8 total. I think this is what lead me to think i wanted the other two batteries. If I have 10 cells powering the system the little battery bar reads 'full'.

I also switched props and reversed thrusters, and either way I spin it (forgive the pun) the left motor has slightly lower power than the right when under control of keyboard/joystick.

To diagnose about how much, I put it in the bucket and since humans are reasonable at telling the difference in how something feels, i used diagnostics panel to dial the power up and down with both until they "felt" the same. When the port motor is a .38 and the starboard motor is at .27 then they feel 'equal'. Is this something I can tinker with when calibrating or a setting when programming? (set the starboard motor 10% less?)

Thanks!

-Laura


#5

Hi Laura:

Wow, that's a big difference.

It couldn't hurt to go back and recalibrate the ESCs, especially the port one. The calibration sets the incoming pulse-width range to 1000-2000 usec, while I believe they come from the factory set for a somewhat wider range. So perhaps the port thruster lost its calibration, and is running at a lower power than what you are commanding it to be.

If you have a programming box for the ESCs it couldn't hurt to check that they are still programmed correctly. Several people have had issues with the ESCs forgetting their programming, though I don't think that's an issue here. BTW, on the new OpenROV 2.7 announced today, we've ditched the old ESCs altogether and have gone with a version that is programmed via the controller board's arduino. The controller board will come from the factory with the ESCs pre-installed, pre-programmed, and pre-calibrated. We're hoping that this significantly cuts down on the ESC issues going forwards.

Also, while you have the E-tube open, see this post and check the wire resistances.

If neither of those things work, then........ I don't know.

As to the "gas gauge" bars, on older software builds they were calibrated for the old C-cells, which had the ROV running at 12V. The newest build (2.5.1RC5) has a feature where you can calibrate the gas gauge for whatever type of battery you are using.

-W


#6

Even with the bigger batteries, if you use a gamepad instead of the keyboard you actually get a range of thrust ( if on power 1, pushing the gamepad stick 50% forward = half the power of what the keyboard would thrust.).


#7

agree, I use the Logitech 710 wireless controll.
http://www.ebay.com/itm/Brand-New-Logitech-F710-USB-Wireless-Gamepad-Controller-for-PC-Windows-game-/321575491820?pt=US_Video_Game_Controllers&hash=item4adf6498ec

It gives me step-less adjustable thrust control :)


#8

I also agree, I was in the same boat until I got a game pad!


#9

I see two obvious solutions for your question.

The onle already posted, by including a "fine tuning" motors control, and the one based on the propellers.

It all depends on what the versatility of the ROV is wanted to be.

By only reducing RPM, propulsive power gets reduced and hence, range could be increased.

By changing to a more suitable propeller for your needs, would allow for more "towing" power, while moving slower. Range would have to be re-calculated, and the speed would be permanently reduced.

Regards

As everytime when making this kind of choice, speed, thrust and requirements must be balanced.


#10

Ion,

Yes, this is a similar discussion we deal with when utilizing Underwater Propulsion devices (AKA scooters or DPV) for scuba. Of course there you also have the added variable of the human underwater and how comfortable it is to be dragged along at assorted speeds, and at what point regulators free flow uncontrollably :) My favorite scooter (the SUEX) has ultra fine tuning of the motor which comes in very handy for video work and a prop that can be swapped out (a tractor prop vs. a speed racer prop) use dependent. At end of day, speed, although entertaining for drag racing is not as beneficial except for short bursts, compared to having a scooter that was designed with the ability to go fast and strong but be used in its 'sweet spot' from an RPM and load point of view, which gives it great range. we see both brushed and brushless motors, and 24v and 42v systems.


#11

Hi Laura:

Before my climbing accident I was a regular diver (Im completly recovered and rebuilt, don't worry :-), but my diving days are over due to pressure balancing problems at the screws and metal plates placed on some of my bones, it hurts a lot.

But ......... I can Climb, and keep on climbing. hehehe

Anyway we solved the free flow issue at high speeds by a re-design of the low pressure regulator stage tap, in such a way, that the dynamic pressure effect is kept under control.

May be having two different sets of propellers for the ROV, could be the "wise" solution.

Regards.