I am sure that many of you have heard of the OpenROV Project which involves building your own ROV from a kit. I am an experienced model builder with plenty of experience and a reasonably equipped workshop, but I was a little taken aback at the complexity of assembling the OpenROV from their kit of parts. It seemed to me to be a high school to college level project requiring a small team of experienced modelers to successfully put the OpenROV together though I could be wrong.
It appeared to me that there were a number of critical assembly requirements that had to be performed spot on as there was no going back to realign or reseal once the assembly was completed. Therefore I have been looking around to see if there might be an easier way to design and build a ROV similar to the OpenROV without having to perform some of the critical assemblies required to complete the OpenROV.
One area of the OpenROV design that I took exception to was the thrusters. They were not going to last very long when immersed in seawater due to the exposed bearings and stator/armature. To me this was a kind of deal breaker as to the questionable lifespan of these thrusters. I know that commercial thrusters are not cheap (think Seabotics or CrustCrawler) and the OpenROV project was just trying to overcome the high price of commercial thrusters with their homebrew design. Still the unknown lifespan of the OpenROV design did not leave me with a warm feeling to say the least.
Then came along Blue Robotics and their T100 Thruster KickStarter Project Link. Their design approach looks good and they have actually tested and characterized prototypes of the thrusters they will deliver to the pledgers. With the addition of the in-thruster water cooled ESC this design becomes very attractive in that it reduces the number of wire penetrations in the Water Tight Compartment (WTC).
Great! Now we have a source of reasonably priced thrusters so what is next? Well, that is where you, the ArduBoat members, come in.
Let's start thinking about the WTC, navigation controller, communication, power, ballast, buoyancy, etc. and attempt to come up with a reasonably priced ROV that the average ArduBoat member might want to consider building.
Hi Tom / Rusty,
I guess you are talking tether strain relief, you could also use a prussick knot setup with a small dia dyneema rope & bridle to the frame.
I'm with Kevin, I highly recommend a disconnect fitting at both ends of your tether. If you don't you'll wish you had. My Deep Trekker didn't have one and it was a PITA to have to spin the ROV around to take out all the twists at the end of every dive.
Rusty's also correct. You will want to make sure that the strain on the tether goes directly to the ROV's frame. Lots of ways to do it, take a look at some of the commercial ROV's to get ideas.
That's a great idea and I'm sure we can integrate that into the software.
A turns counter is a useful addition, but on a battery powered micro ROV where your source of power is limited I think a disconnect is still the better way to handle this... although an even better solution would be to have both. :)
Linus Penzlien and I have been busy porting the ArduSub firmware over to the BBBMINI and have been achieving a few successes so far.
We are presently using the latest version of Debian (2016-02-16) recommend by Mirko on the BBBMINI, QGC version 2.9.4 for the Topside Control, and the latest daily build of ArduSub for the ROV-side Control.
We have calibrated the BBBMINI's accelerometers and compass and are presently in the process of calibrating the radio using a gamepad input (Xbox Controller). We would have been much farther along by now, but we had a problem where the accelerometers on the BBBMINI were not calibrating according to QGC even though there were accelerometer offsets and calibration values in the QGC parameter list. The reason for the calibration failure was due to the fact that QGC had two INS units enabled while my BBBMINI presently only has one INS (MPU-9250). Once that error was corrected QGC indicated that the accelerometer calibration was successful as was the compass calibration.
I have also setup a Topside to ROV-side test bench on which I have mounted the Blue Robotics Topside and ROV-side Interface Boards and connected their Tether interfaces with a short piece of CAT5e LAN cable. I have successfully used QGC to communicate with the BBBMINI, running the ArduSub vectored thruster configuration firmware, through the Topside to ROV-side Interfaces and a 5 vdc to 3.3 vdc level shifter connecting the output of the ROV-side Interface serial port to the BBBMINI telemetry connection. A picture of the test bench setup can be seen below:
The Topside Interface Board has a USB connection that allows QGC running on either a PC or a laptop to communicate with the Topside Board,
Once the gamepad calibration is complete we can move ahead with testing the functionality of the ArduSub firmware using QGC.
More to come.
Tom C AVD
Today I have managed to get my Xbox 360 joystick calibrated in the QGC ground station. I was not as successful when calibrating the Radio using the joystick as the calibration failed when trying to calibrate the pitch and roll axis joystick.
However all was not lost as I was able to turnoff all of the pre-arming checks, which includes the RC Radio Check, and was then able to Arm the ROV. Rusty has suggested that the RC Radio Calibration be taken out of ArduSub for the ROVs.
After arming the ROV I proceeded to determine what RC output channels on the BBBMINI corresponded to which axis on the Xbox 360 controller:
On RC 1 I had pwm output when I moved the right joystick yaw axis.
I had throttle axis pwm output on RC 2 when I moved the right joystick throttle axis.
I had pitch axis pwm output on RC 3 when I moved the left joystick pitch axis.
I also had throttle axis pwm output on RC 4.
I had roll axis pwm output on RC 5 when I moved the left joystick roll axis and finally I also had throttle axis pwm output on RC 6.
I am now waiting on word from Rusty as to whether I have the correct RC output for each axis of the two controller joysticks.
More to come.
Tom C AVD
It turns out that we had the wrong thruster configuration version of ArduSub loaded on the BBBMINI. Once we corrected that issue, joystick input to QGC from the Xbox 360 game pad appears to be driving the BBBMINI thruster pwm outputs correctly for forward/reverse, yaw, and vertical assent/descent.
I have put together a wire harness that will connect the BBBMINI servo outputs to the Signal Junction Board that distributes the individual pwm signals to each Thruster. I created the wire harness by crimping seven servo female pins to a 7 wire cable to be able to connect the BBBMINI 6 servo pwm outputs plus ground to the BR thruster Signal Junction Board. I then soldered each wire in the cable to its appropriate pad on the Signal Junction Board and will be able to hopefully begin testing the six Thrusters this weekend.
More to come.
Tom C AVD
Getting closer! I just received my parts from Rusty and am waiting on a PixHawk that should arrive next week. Once I have everything it'll be time for me to sort out the electronics for my build. Got to say I'm pretty impressed with both the hardware and software for ArduSub so far.
After having second thoughts about powering the Power Control Board wit a live LiPo battery, I remembered that I have an AC powered 12 amp peak 13.8 vdc battery eliminator, complete with overcurrent and short circuit protection, that I can use to check out the integrity of the Thruster Power cable penetrator cable connections to the Power Junction Board. If all goes well, then I can switch over to the LiPo battery to simulate actual ROV operation.
Good news, there was no smoke and fire when I powered up the 6 Thrusters with the DC battery eliminator power supply which means the bullet connector connections between the Power Junction Board and the Thruster power cables have no shorts or opens.
I then hooked up my trusty servo tester to each Thruster PWM control input and tested each Thruster briefly as to CW and CCW operation and all of the Thrusters were found to be functional.
Now I can setup the Navigation controller and see if I can use the Gamepad along with QGC to command the BBBMINI to drive the Thrusters.
More to come.
Tom C AVD