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Mission Planner Rover model skid steer vs differential steer?


(Ridgeglider) #1

I’m planning a surface boat cat-hull powered by mechanical configuration consisting of either two or four T200 thrusters with azimuth mounts similar to those described in the revealing thread: Azimuth mount for the T100 / T200 series

The simplest configuration would just use two T200s steered in differential mode. However, my boat needs to operate in a hover mode to maintain position, so I think four azimuth-controlled T200s (along w/ serovs to control direction) would produce much better results by utilizing full forward / reverse speeds aimed in a 0 - 180 degree direction. That way I could operate on long courses with all thrusters in zero to full speed forward speed mode, but with steering accomplished by the servos. This would be sort of like the control of a conventional multi-engine outboard, except that in my case the locations of the thrusters would be towards the bow and stern of each cat-hull.

Alternatively, in position-hold mode, the thrusters could be directed at the diagonal quadrants of the boat, with smal forward and aft speeds used to maintain position, largely to counteract currents or wind drag.

I’d like this craft to be controlled either via standard RC control or by an autopilot/computer pair, likely a Rasp. Pi3 and Pixhawk using ArduPilot Rover egBoat) / Mission Planner / MaxProxy / Mavlink and some python scripts. The radio control setup is pretty straightforward I think using most programmable eight channel+ RC radios (ef Taranis X9D or Futaba 14SG). The problem is with the ArduPilot Rover Boat model which only provides an either/or choice of differential skid steering, or fairly conventional speed on 1 channel, direction on 2nd channel control models. The problem is, I’, looking to do a multi-channel hybrid of both control models. Maybe the Ardusub / copter models would work if there’s a way to disable the 3D control.

Anyhow, looking for recommendations. Not sure how to categorize this thread, so throwing it into the General Discussion bin…

Thanks!


(Kevin) #2

Hi @hsharpe,
This sounds like an excellent project! Azimuth thrusters located in the bow and stern of a boat is very common for vessels that need absolute positioning control. I’ve seen these drives on offshore work vessels and oil rigs.

As for actually getting control with the Ardupilot firmware, you will have to do some modifications and some code writing to do what you want. ArduSub only supports fixed thrusters at this time and you need to chose between conventional or skid steer for ArduRover. A mix of both steering modes isn’t possible at the moment, and not for 4 thrusters.

As for recommendations, you can try doing R&D with ArduSub with 4 thrusters in a fixed vectored configuration. Just note that positioning flight modes are still in development with ArduSub: https://www.ardusub.com/developers/gps-positioning.html