ROV project, looking for advice regarding the ROV "brain"

[Wanderer]

Hello Everybody,

A friend and I are starting a ROV project. It is for underwater filming and will carry a Gopro camera for that and another camera for piloting, we're looking at a build with 6 thrusters as to give us the following movement:

- Back and Forward
- Up and down
- turning (spinning)
- Side ways

The power will be provided by embarked 3 cells lipos (11,1V)
My friend is taking care of the building of the frame and myself of the electronic part. I already have some experience with a fixed wing UAV which use the Autopilot Mega.

For the "brain" of the ROV, I'm planning to use:
Control on the surface:
Arduino Uno
2 joysticks
A GUI displayed on LCD screen with feeds from the ROV on board sensors and joysticks movements

On board the ROV:
Arduino Mega, with the following shields:
Motor control,
Accelerometers, Gyros and Compas (all on 3 axis)
Depth sensor
Current sensor

I already spend quite some time reading this forum, and I got few questions, mainly regarding the shields I should go for:
We're planning to use bilge pumps as thrusters: what would be the best choice for the motor shield (correct me if I'm wrong, I have to use 6 of them isn't it?)
Regarding of the Accelerometers, Gyros and Compas, what would be the best for such project.

I'm looking forward to reading back from you, meanwhile I keep on doing research
Thanks in advance
With Kind Regards

Wanderer

[thegadgetguy]

Welcome to the forum. It looks like you have a good handle on the basics, and your control scheme looks pretty good to me at least. You may have seen this already, but here is a link to KR2_Diving's thread - he has a control system quite similar to yours.

http://homebuiltrovs.com/rovforum/viewt ... f=18&t=803

In regards to what shields would be best, definitely have a compass. The accelerometer may also be useful, to let you if you bumped into something. Unfortunately I'm not entirely sure how accurately you could navigate with accelerometer and gyro shields, if that's what you want to do. I know that is how it works on submarines, but I assume their equipment is a lot more accurate then what is available to us.

I haven't seen many Arduino motor driver shields rated for more than two amps. If you are using bilge pumps you are going to want something more in the 10-15 amp range, as bilge pumps can draw 5-8+ amps depending on what prop you have on them. If you went with brushless motors you could just use brushless ESCs and not worry about shields. This is becoming a more popular option, unless you dive in saltwater, as saltwater and electricity don't mix! There are brushed ESCs that work with bilge pumps, but they are becoming rarer and are quite expensive.

Well, I hope this answers at least a few of your questions! Again, welcome, and good luck on you build.

[Wanderer]

Hello thegadgetguy, thanks a lot for your answer, very helpful, I really appreciate

In regards to what shields would be best, definitely have a compass. The accelerometer may also be useful, to let you if you bumped into something. Unfortunately I'm not entirely sure how accurately you could navigate with accelerometer and gyro shields, if that's what you want to do. I know that is how it works on submarines, but I assume their equipment is a lot more accurate then what is available to us.

The idea of using the combo of gyros and accelerometers is for providing the pilot datas such as the attitude of the ROV, later that could be use for stabilizing a gimbal for a camera for instance.
I have found this one, which hold the 3 sensors (magnetometer, gyros and accelerometers) which looks quite promising:
https://code.google.com/p/ardu-imu/wiki ... uctionPage
I'm still looking for a depth sensor though

I haven't seen many Arduino motor driver shields rated for more than two amps. If you are using bilge pumps you are going to want something more in the 10-15 amp range, as bilge pumps can draw 5-8+ amps depending on what prop you have on them. If you went with brushless motors you could just use brushless ESCs and not worry about shields. This is becoming a more popular option, unless you dive in saltwater, as saltwater and electricity don't mix! There are brushed ESCs that work with bilge pumps, but they are becoming rarer and are quite expensive.

Unfortunately, this ROV will be mainly used in salt water, so I thinks, we'll have to stick to the bilge pump option... And yes, those brushed ESC are pretty hard to find and quite expensive, especially when you need 6...
I found those shields:
https://secure.robotshop.com/pololu-dua ... r-14a.html
https://secure.robotshop.com/pololu-qik ... oller.html
I don't know if it's the right choice and if yes, which one to go for...

Thanks again for your help
Have a great day
Wanderer

[KR2_Diving]

Hey Wanderer,
I may be wrong, but I seem to think that running brushless in saltwater is not an issue. The biggest thing to remember is a good rinse after the dive.

At the moment, I plan on using an Arduino Mega inside the sub, controlling 6 thrusters, and communicating with the surface via RS485. On the surface, I will have an Arduino Uno connected to a PS2 controller for control.

At the moment, my tether is 2- Cat5e Ethernet cables. All power will be on board.

Each thruster is going to cost me about £40.00. (ESC $16.50 + MOTOR $12.00 + PROP $2.00 + misc parts.)

If you have any other questions, please feel free to contact me!

Ryan
"KR2_Diving"

[Wanderer]

Hey Ryan,

Thanks for your answer and for offering your help, I will definitely get in touch with you when needed....
I had a look on your thread about your building progress, very interesting, can't wait to read and know more about it

Hey Wanderer,
I may be wrong, but I seem to think that running brushless in saltwater is not an issue. The biggest thing to remember is a good rinse after the dive.

I've read the same and it's contrary which start to be really confusing.... I'll keep digging on the matter and see where it brings me

At the moment, I plan on using an Arduino Mega inside the sub, controlling 6 thrusters, and communicating with the surface via RS485. On the surface, I will have an Arduino Uno connected to a PS2 controller for control.

At the moment, my tether is 2- Cat5e Ethernet cables. All power will be on board.

Each thruster is going to cost me about £40.00. (ESC $16.50 + MOTOR $12.00 + PROP $2.00 + misc parts.)

If you have any other questions, please feel free to contact me!

Ryan
"KR2_Diving"

Seems I'm following your path there. I'm planning to have a gui on a 7inch screen, which will reflect, the joystick position, and datas from the ROV (attitude, depth, and current consomption...
Also, I'm planning to use 2 joysticks (coming from an old remote control) and a couple of switches instead of a PS2 controller.

One question though: when you're talking about Ethernet cable, does it means you're going to use them through a ethernet shield?
I'm looking forward to reading back from you
Thanks in advance
Have a great day, and keep up the good work

Wanderer

[KR2_Diving]

One question though: when you're talking about Ethernet cable, does it means you're going to use them through a ethernet shield?

Hello Wanderer,
No. At this time, I am not using any shields. I am only using the Ethernet cable as the physical medium for getting my wires from the surface to the ROV. I will likely be putting a more suitable plug on the cables. One of the cables is going to be used for video feeds. (3 of the twisted pairs will be directly connected to my on board cameras, with one spare twisted pair). The other cable will be my RS485 (2 twisted pair) with 2 spare twisted pairs.

I am still debating what I will use the spare twisted pairs for. I will likely have a hard wired water sensor connected to one twisted pair. I have even debated having a second RS485 connection for redundancy... but that might be a bit overkill for a DIY ROV.

Ryan
"KR2_Diving"

[thegadgetguy]

Where have you heard that you can run brushless motors in salt water , KR2_Diving? All I know seems to indicate that, while it would probably work, you would have pretty severe corrosion. I don't run brushless motors, so I really don't have any first hand knowledge of this. I would be really interested to hear what your experience has been.

[KR2_Diving]

To be honest... I have not tested brushless in salt water... I have read it somewhere... when I have a few minutes, I will have a look. It may have even been in this forum some where!

[KR2_Diving]

Here is a quick search result...
viewtopic.php?f=3&t=352&p=1179&hilit=br ... salt#p1179

[thegadgetguy]

If I'm reading the post correctly, greenkarson seems to have used freshwater during his testing. I'm really interested now to know exactly how conductive saltwater is.