Underwater ROV controller question

[CrazyCossack]

Thanks for that. These seem suprisingly expensive, is there one that will perhaps work for 3 DC motors? Since this seems like we'll have to buy one that controls 2 motors (Sabertooth dual 5A motor driver ) and one that controls the last motor (SyRen 10A regenerative motor driver) at the cost of over $100?

Also how do these work? They connect into the serials and on the other end onto the motors and can somehow be controlled be controlled through the serial?

[madsci1016]

I agree with Admin, Dimension makes really decent motor controllers, for your need, specifically this one:

http://www.dimensionengineering.com/Sabertooth2X5.htm

Slightly expensive at $60, you would need two to run three motors. (They are dual channel each). They communicate over serial and can be daisy channel in 'packetized' serial mode, so you would just connect both of them to the Arduino's Uart TX pin. The Arduino will send data packets that would tell the motor driver what to do, including reversing direction. The motorcontroller would get power directly off your 12V battery.

Most Arduino's have their own voltage regulator on board, meaning you can connect their "Raw" power pin to 12V and it will step it down to 5V for the Microcontroller's use. I wouldn't power anything else off the microcontroller directly.

If you have other parts that need power at 5V, you can either build yourself a power regulator board, or if you do use the Dimension motor controllers, they provide 5V out for anything you might need it for.

[madsci1016]

There are cheaper non-digital alternatives out there, but the trade off is that they are much more complex to integrate. They would require many more IO pins of the Arduino to be used, and would require you to build some additional support circuitry to use.

For example, This one is $23

http://www.pololu.com/catalog/product/1212

But look how many wires it needs:



And that's just for one motor.

While the Sabertooth would just be serial and ground to both.

[Admin]

I agree with madsci1016.

They may be more 'expensive', but if you pay twice the price for twice the quality and capability, then its worth it.

This is an example of me using a DE motor driver:

How to Make a Robot with Axon II MCU

[CrazyCossack]

Makes sense, we'll definitely go with the Dimension controllers then. Thanks so much guys, really invaluable help! It would have taken me eons to figure this all out if I did it without asking questions (and a lot of wasted money buying the wrong stuff too).

[CrazyCossack]

Hey guys, just a small update, we've *basically* finished the build except for the electronics. The only thing that remains is to find a good propeller, a local hobby store sold one that seemed decent but was slightly too small so we're going to go back and test a larger one. Issue is even the small propeller need a much larger shaft than the bilge pump motor's shaft was, and the larger ones are even more so. We need a propeller about 2.5-3in in diameter, they might not have one at the hobby store that large and might need to look online (unless we want to pay 3X $45 (no way) for a big fancy metal one).

Just to run it past you guys one more time before I do a massive amount of online purchases, here is what I plan to get:

Overview of parts:

Robotics:
E-shield: http://www.robotshop.ca/adafruit-ethernet-xport-shield-kit-arduino-6.html
Arduino: http://www.robotshop.ca/arduino-usb-microcontroller-board-1-4.html
2X motor control: http://www.robotshop.ca/Sabertooth-2x5-en-1.html

Camera: http://www.bhphotovideo.com/c/product/654971-REG/Trendnet_TV_IP501P.html#accessories

10/100 switch: http://www.amazon.ca/TRENDnet-5-Port-100Mbps-Switch-Plastic/dp/B000M2TAN4/ref=sr_1_1?ie=UTF8&s=electronics&qid=1277240876&sr=8-1

Cat6 cable:
http://www.deepsurplus.com/Network-Structured-Wiring/Ethernet-CAT6-Patch-Cables-300ft/300ft-Yellow-Cat-6-Patch-Cable-Molded;jsessionid=0a0105531f4330b4b62fbc61470c8cadbe10d24accee.e3eSc3uRax8Te34Pa38Ta38Rc350

[madsci1016]

Looks like your Ethernet Shield you linked is just a breakout, and actually requires you to buy another circuit, the actual ethernet chip, to be completed.

This looks like a complete Shield.

http://www.robotshop.ca/arduino-ethernet-shield-4.html

[CrazyCossack]

Ah-ha, thanks again, good catch. Good thing I posted to confirm. I'll probably be asking a lot more questions once we figure out a circuit diagram haha.

Cheers.

[madsci1016]

Crazy

How much programming experience do you guys have? Have you thought about what is going to be on the surface that sends commands to the ROV? A computer program, another Arduino?

Just things to think about while the stuff ships.

[CrazyCossack]

We've planned to use a laptop on the surface that'll be running a program/as well as showing video.

We've got some basic experience in java, C++ and Visual Basic (doesn't really count). Been a while since we've programmed though so all the syntax runs together in my head haha. I've checked out some programming with the Arduino and I'm not too worried, seems like there are good online ressources for the syntax but I'm not sure how we're going to network this with the 10/100 switch. I'm not sure how much GUI capability there is with the Arduino as I've only seen command prompt-type UI.

But I think making a GUI with the video feed from the camera embedded in the GUI might be a little of a nightmare with the switch, if I do that it'll be later after we have the basics down. I'm sure the camera has a crappy little program that should let us at least do the basics: see what we're doing, and record video for later.

At the moment I'm more worried about how the electronics are going to work as that's the area that we really don't have much experience (except basic stuff we can barely remember from grade 10 physics haha).

So we have:
3X motors at 12v 3amps each.
Camera at 12v 9amp.
Edit: and LEDs at 4.5v at 1.7amp
Arduino 5v...and ?
And no idea if the motor controllers, e-shield, and the 10/100 switch take any power.

So basically we have to decide on what batteries we're going to buy for this. Moreover, how will they be configured? I've read putting the microcontroller on a separate battery from the motors is a good practice? I'm really lost as to how power is going to work with the Arduino, usually I'd expect the Arduino to directly be feeding the motors power....not sure how one could get them running on a separate battery and taking orders from the Arduino...

[Razor Concepts]

....not sure how one could get them running on a separate battery and taking orders from the Arduino...

Arduino runs on separate 5v source. Motors and motor driver runs on separate 12v source.
Connect ground of the 5v source to the ground of the 12v source.

This way, they are on separate batteries, but the Arduino can still talk to the motor controller.

[madsci1016]

Alright, Lets break down your power system a bit.

First off, the battery. My suggestion would be a Hobby Li-poly battery like This One. The reasons are they are cheap, and support large currents. You mentioned you are using bilge pumps, which can draw large currents. I know the 12V one I have for my saltwater change system can draw 3-4Amps under load. So worst case for you, 3 pumps at full load would be 9-12 Amps, which other battery types would have a hard time sourcing. However, they can be dangerous, and you should definitely have a something like a 15Amp fuse in-between your battery and ROV electronics.

I tried having separate batteries for electronics and motors before, but got tired have having issues on which battery was dead, and having to keep two different chargers around. For the folks around here, it's just a matter of opinion. I reduced my SAGAR robot to one system battery and had no problems.

For the devices:

The motorcontrollers are self powered, they just required a direct connection to the battery (through a fuse), a connection to the motor, and Serial in and signal ground.

The Arduino can also be powered from 'raw' battery voltage, as it has it's own power regulator that can take up to 20V. The Arduino has nothing to do with motor power, that's all taken care of by the Motor Controllers. The Arduino just commands them to give a certain amount of power to the motors.

The network switch will take power. If it runs of 12V, you should be ok powering it off the battery voltage. If it's 5V, you will need to see how much it draws. If it draws less then 100ma, you could run it off the 5V output of one of the motorcontrollers. Same for the camera. If you end up having a lot of equipment (or servos) that runs off 5V, you might consider a switching regulator like this. The would give you a 5V source up to 1 Amp.

For the LED, another adjustable voltage regulator Like This would let you dial in the right voltage for your LED array, and support the large current it draws.

All these switching regulators are expensive compared to cheaper Linear regulators, but the trade off is much better efficiency performance and longer run times.


You really don't need to worry about the 10/100 switch as far as programming. It is invisible to all the devices connected to it, all it does is make sure all the device can talk to each other. So you could use the camera software running on your topside computer to bring up the camera. Then you would just need a program that opens up a TCP or UDP connection to the Arduino, and sends commands to it. You just need to make sure all devices are on the same subnet, IE all have IP address like 192.168.1.x .

I think I got it all. Man that was a long post. You are making me want to build an ROV now, it's a shame the waters near me are about to be all dark with oil. Stupid BP.

[Ro-Bot-X]

You can power your Arduino (and all 5V electronics) from a 5V switching regulator by plugging the output from the regulator to the 5V pin (and GND to GND) if you are using a 12V battery. This way the electronics are not influenced by the motors starting up as the switching regulator will output a steady voltage until the battery is completely depleted. You need to make a battery sensor to be able to command your ROV to come back to shore before the motors can't push it any more.

Also, you can use the 3A adjustable switching regulator as madsci recommended to power your servos and adjust it to 6V, instead of using a second battery on the robot. A second battery plus charger will be more expensive anyway and will complicate charging.

[CrazyCossack]

Thanks for the info guys, that was very helpful. What about capacitors? With a quick discharge battery like that perhaps they won't be needed? I'll probably also throw in a few transistors here and there to make sure things don't go boom.

I'll try to get back to you all with a shitty circuit diagram you can all tear apart haha, eventually we'll get it right though.

[madsci1016]

No problem.

Most of these devices already have power cleaning caps already, no need to add more. Arduino cleans it's own power. The camera and switch will expect to get dirty power from dirty wall warts. LEDs won't care.

I'll probably also throw in a few transistors here and there to make sure things don't go boom.

What do you mean by this? Did you mean fuses instead of transistors?

[CrazyCossack]

My bad, I mean to say diodes, but then realized that the motor controllers/micro controller can probably deal with that on their own circuits, though switching the direction of current is probably unlikely.

We'll get back to you guys with a circuit diagram soon!

[madsci1016]

The battery I linked for you has a polarized connector, so it's physically impossible to connect your battery backwards. There's no need for an energy wasting diode.

[CrazyCossack]

Thanks for such a quick reply. We've been trying to figure out how long one battery would last us in this setup. I think we'lll run the microcontroller off the main battery afterall. There doesn't seem to be any figures provided on battery life at any given current draw. If we were to have a camera running at 9amps + 1.7 amp LED, both on constantly, so 10.7 amp base, plus a variable average of probably 4.5-6 amps on the motors - how long would the battery last? This is in addition to the unkown current draw of the 10/100 switch and the Arduino.

[madsci1016]

I'm running out the door so I will have to come back with the math, but there's no way your camera is drawing 9Amps. Double check that.

[CrazyCossack]

Ah-ha, 9 Watts, completely misread that thanks for the correction. I thought that was a little much. And with it being 12v, that is 0.5 amp. Edit: though the web page actually says 12V, 1.5A on further checking.

[madsci1016]

Back.

I don't see your ROV moving all the time during your dives.

Really, with the price and size of that battery, i'd say get two and put them in parallel, for a total of 4.4 Amp Hours. That would power 4.4 Amps, for an hour. or 2.2 Amps for two hours, you get the idea.

There's really no telling how much average power your ROV is going to consume, and it will also vary mission by mission, if you are fighting a current you will use more power. My gut tells me that with 4.4Ah at 11.1 Volts, you would get 45-60 mins of run time, but that's a WAG (Wild A$$ Guess).

How about some pictures of what you have built already?

[CrazyCossack]

That was our best guess as well since the life of the battery at any Ah was not stated by the manufacturer. We'll probably end up buying three in case one craps out. So 15amp fuse still seems to be the best bet then. Would it make sense to put a large capacitor after the fuse to regulate the current? Or would that be counter productive?

Man I had totally forgot that you hadn't seen anything from the design, next time I'm at m buddies house I'll bring my camera and I'll take some pics.

[madsci1016]

Would it make sense to put a large capacitor after the fuse to regulate the current? Or would that be counter productive?

I wouldn't. Power cleaning caps only work well when placed near the device that's using the power, and all those devices already have those caps built into them. Just make sure you use decent wire, sized appropriately, and make good connections.

[CrazyCossack]

Alright good stuff then, should be a pretty easy circuit then, just plug-and-play basically. Only thing that remains is getting a (or a couple) switching regulators for the LED and maybe the 10/100 switch.

[Admin]

We've planned to use a laptop on the surface that'll be running a program/as well as showing video.

Reminds me of a funny story I heard where a guy didn't secure his electronics/laptop, and the tethered ROV decided to take everything into the pool with it . . .

[CrazyCossack]

Yeah I'll be sure to check to make sure that never happens to us!

First off, the battery. My suggestion would be a Hobby Li-poly battery like This One. The reasons are they are cheap, and support large currents. You mentioned you are using bilge pumps, which can draw large currents. I know the 12V one I have for my saltwater change system can draw 3-4Amps under load. So worst case for you, 3 pumps at full load would be 9-12 Amps, which other battery types would have a hard time sourcing. However, they can be dangerous, and you should definitely have a something like a 15Amp fuse in-between your battery and ROV electronics.

Hey, I'm having difficulty finding a good charger for this battery - would you guys have any recommendations?

[waltr]

I'm having difficulty finding a good charger for this battery

To buy or build?

To build check out the MCP7383x charge control chips from Microchip. These need a minimum of external parts.

[CrazyCossack]

At the moment I'm thinking buy, building something like that may be beyond our current capabilities haha.

[madsci1016]

Crazy,

I personally own and use This One. Seems to work fine charging the battery I linked, since I own that too.

Good for those on a budget, but the expensive ones take batter care of your batteries.

And before you ask Here's the connectors to mate to the battery.

[CrazyCossack]

Ah-ha, thanks very much. To my credit (or lack thereof) I did realize I needed connectors! Cheap is always good.

We're currently trying to find CAT5/6 available in Ottawa, most American retailers want to charge $40-$60 for shipping 300ft of cable, which is more than the price of the cable (~$40). We've not had any luck yet, seems like it's either 100ft or 1000ft, not sure that connecting three 100ft together would be a good idea, connectors might actually bump the price up to even with the 300ft, and might not fit in the tether. I will keep you guys posted though.

We're thinking of making the tether as done here (http://www.hobbyrov.com/index.php?option=com_content&view=article&id=47:umbilicals-and-tethers&catid=39:umbilicals&Itemid=29). Though finding that length in hollow braided rope might be tricky.

On the propeller front we've tested small (and cheap) propellers 3/16" size, they worked well, but our cover for the thrusters allows for 3in diameter blades. We also tried plane props with the full size 3in, and interestingly the smaller 3/16" props meant for water vastly outperformed them. The local hobby place had metal ones, but for a lot of money, like $40 each. Seeing as we have 3 thrusters that is quite expensive, I think we would rather pay like $5 for plastic ones with probably less power, than pay $120 for slightly more power. So if anyone knows any place that sells cheapy plastic props with a 2-3in diameter that would be so helpful.

And suprisingly, that's about all the materials we need before we're done material wise. The only issue that really remains is getting the wires into the electronics area, we'll probably use a threaded plumbing fitting. Looking forward to getting this all setup! And I haven't forgot about pictures.