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.
Linus Penzlien and I have been working with Rusty at Blue Robotics to properly configure the ArduSub firmware to appropriately drive the horizontal and vertical Thrusters in my six thruster configuration depending on the desired ROV motion input from the GCS (QGC) gamepad joystick inputs.
Validation of the BBBMINI six servo outputs, when driven by the GSC gamepad joystick inputs, was accomplished by communicating with the BBBMINI over a UDP LAN connection and using a R/C receiver PWM output tester to verify the servo PWM output values in relation to the expected PWM values.
An example BBBMINI servo output verses expected output Correlation Chart is in an attached pdf file below. It can be seen that the BBBMINI servo outputs verses expected outputs are not correct for Thrusters 1, 3, and 4 for the Forward ROV direction. This discrepancy can be easily corrected using the MOTOR_MOTION parameters in the QGC default parameter list to reverse the BBBMINI servo PWM outputs to achieve the correct Thruster output direction.
Having validated the ArduSub firmware for my six Thruster ROV configuration, I moved on to completing the Navigation Controller Tray that will reside in the Navigation Controller WTC.
The Blue Robotics ROV-side Tether Interface Board and the BBBMINI are attached to a removable sub tray that is attached to the main Navigation Controller Tray. The Signal Junction Board is permanently mounted at the rear of the Navigation Controller Tray and is not attached to the sub tray. See photos below:
The next step will be to complete the mechanical and electrical installation of the Navigation Controller Tray in the Navigation Controller WTC. This will include connection of the Signal Junction Board individual thruster PWM control signal cables to their respective Thruster Cable Penetrator Control Signal cables, connection of the Tether four twisted pairs to the ROV-side Interface Board, and the connection of the ROV-side power input cable to the Cable Penetrator Power Cable wires coming from the Battery Compartment WTC.
More to come.
My Project Discussion Thread will be continued here
Tom C AVD