Underwater ROV serial communication and other questions
Andrew PArsons from Canada  [2 posts]
5 years
Hello all,

First I would like to say thanks to the community for helping me get this far in my project. In truth this is my first attempt at programming and using a micro controller to do my bidding. In the past I did everything using servos and switches. Although I have ran through the education courses with Parallax and have done all the projects.

I have tasked myself with making an Underwater ROV. I plan to use one are two Basic Stamp 2sx. One stamp (below sea-level) will read sensors and control 6 thrusters by using the Propeller Servo Controller to PWM to six ESC. I will also be using the Prop Servo Controller to manipulate an underwater arm. All the motors are brushless (Including underwater servos) and have been tested underwater. Each ESC will be powered from a 3s poly 5000mah battery that will be housed in Otter Boxes along with all the components. As for video I have not quite figured that out but it will most likely be a netcam with pan and tilt that I power below and break the lines out to the surface. If anyone knows how many pairs from the cat 6 a netcam will need please let me know?  As for communication from surface to the ROV I plan to use RS-485 Communication; actually this is one of my questions. Above I mentioned using 1 or 2 Basic Stamp 2 SX, does it make more sense to use a microcontroller on the surface with pots to control the ESC using RS-485 Signal? Or does it make more sense to use SparkFun BOB-09822 for communication and have RoboRealm to control the ESC and display sensor reading?

I am leaning toward using SparkFun BOB-09822 since I like the Idea of the increased resolution for the ESC compared to pots. So, If I do decided to go with BOB-09822 (already have 2 of them) how would I connect them in order to serin and out to the BASIC STAMP Below and use RoboRealm?
I know I have asked a significant amount of questions, and I do not expect one person to know them all. Also, if you have any suggestions on my project please post them.

 [29 posts] 5 years
This may not be the best forum for your ROV questions. Roborealm is more for computer vision-based applications – UNLESS- you are trying to make an autonomous ROV and navigate (in clear water) obstacles or object recognition.
I have built many underwater ROVs ranging from 150 feet to 1000 feet using Arduino and PIC microcontrollers and suggest the following considerations:
Your ESC need to be capable of driving your motors while under water as the back pressure resistance is much greater.  
Ensure your ‘underwater’ servos are rated for the depth/pressure you intend to operate.
As for our video dilemma; Look on eBay for two items; a mini “Spy” camera and USB Video Capture adapter called “EASYCAP” (~$7) http://www.ebay.com/itm/EasyCap-USB-2-0-Video-TV-DVD-VHS-Audio-Capture-Adapter-for-Windo-/230781521969?pt=LH_DefaultDomain_0&hash=item35bba69031. This is easily mounted on any pan/tilt and provides good video.
The camera should match your region (PAL or NTSC) and not have built-in LED lights as they will reflect off of your dome/window and interfere with the display.
Use external water/pressure proof lights if necessary.  You can use CAT5 cable and Balun Transceivers to help with sending video from the Spy camera to the surface. http://www.ebay.com/itm/Coax-CAT5-To-Camera-CCTV-BNC-Video-Balun-Transceive-/200683848101?pt=LH_DefaultDomain_0&hash=item2eb9b081a5. Remember to use a twisted pair for all our signal and data to reduce cross-talk interference.

Sending RS232 data via RS485 is very smart. I do the same. Look into “Port Powered RS485” modules;
http://www.ebay.com/itm/A-Port-Powered-CCTV-PTZ-Camera-RS232-to-RS485-Converter-Interface-/180860464353?pt=LH_DefaultDomain_0&hash=item2a1c1face1. This will eliminate the need to provide power to the signal. This device will use the transitioning data pulses to power the internal 485 chip.
My suggestion is to use two (2) controllers. One on the surface sending control packets and one on the ROV receiving the data and passing the commands to the Servo/motor controller. The ROV microcontroller can also send sensor data during times that you are not transmitting. However, think about a 232 to TTL converter to boost communications between the microcontrollers->(RS232/RS485)=>CAT5=>(RS485/RS232)=>Microcontroller-> PC?
http://www.ebay.com/itm/RS232-Serial-Port-To-TTL-Converter-Module-SP3232-With-Dupont-Cable-/221012565069?pt=LH_DefaultDomain_0&hash=item3375601c4d ( or similar)

Good luck!

Andrew PArsons from Canada  [2 posts] 5 years

Thank you very much for your help. More over I would like to further thank you for your help on the video side of things.

You are correct, my ESC are having a hard time running at low speeds not to mention high loads, the motor seems jolt at times. These Jolts, i fear, will be quite the issue when below 200 feet.

Currently my ESC and motors are not sensored, would thier be any point in going to a sensored type situation?

Again, Thank you.
 [29 posts] 5 years
You are most welcome.
Brushless motors are great for speed, but lack in touque unless adpted with some type of gearing or torque converter.
Have you considered brushed bildge pump motors?  http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=28499&catalogId=10001&langId=-1&storeId=11151&storeNum=50632&subdeptNum=50633&classNum=50637
I use the 1250 gph (gallons per hour) pump and maximize on amperage. They typically will draw about 2 to 4 amps from slow to full throttle. I've used three low-end motor controllers:
50 Amp ESC http://www.ebay.com/itm/Pro-Boat-50amp-brushed-ESC-water-proof-boats-forward-and-reverse-/330725578452?pt=Radio_Control_Parts_Accessories&hash=item4d00c7d6d4
or the popular L298 http://www.ebay.com/itm/1pcs-Dual-H-Bridge-DC-Stepper-Motor-Drive-Controller-Board-Module-arduino-L298N-/261002237340?pt=LH_DefaultDomain_0&hash=item3cc4f2159c
Here is a YouTube video of the adapted motor and hobby boat propeller http://www.youtube.com/watch?v=Ca2WIb6lR7gIf
If you start your project carefully and have your materials thought out, you will have a better ROV with less headache, about the same amount of money and better performance.
Conduct a search on YouTube and Google for home-made underwater ROV. There is a lot of information out there. You may conact me offline if you need assistance. I don't think we want to saturate RoboRealm forum with ROV stuff. By the way, you can view a few of my projects on my YouTube Channel at "Scruffman2001".
SERGIO DA CONCEIÇÃO from Brazil  [1 posts] 5 years
HOW TO INTERFACE THIS http://www.dfrobot.com/wiki/index.php?title=MD1.3_2A_Dual_Motor_Controller_%28SKU:_DRI0002%29



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