Home        Store        Docs        Blog

Towed ROV with ArduSub?


(Aleksander Øyen) #1

We are building a towfish type ROV and I am using a pixhawk to controll it.
The frame has two rudders in the front, aileron/elevators, v-tail and two thrusters.

the rudders are mainly there to be able to move the towfish out of centre from the boat during towing.
ailevators to control roll and altitude/depth.
vtail to stabilize pitch and course/yaw.
thrusters are there mainly to test a theory :stuck_out_tongue:

I have been looking around the documentation for ardusub but I don’t really find any info around control surfaces and towed application.
I am using bluerobotics pressure sensor for depth control.

Am I better of just using arduplane, or is there a way to make this work in ardusub, or have I just overlooked some info in the documentation?


(Jacob) #2

Cool! Do you have a picture of the vehicle?

There is no concept of control surfaces or ‘forward flying’ type vehicle in ArduSub right now, but it may be adapted to work. You would need to produce a custom frame configuration as outlined here. This configures the outputs depending on the forces they produce on the vehicle when actuated. ROVs produce roll movement by actuating thrusters, you will do it by actuating control surfaces. This will only work for you when the vehicle is moving forward, but I think it can work while the ArduSub firmware is blind to this detail.

There is some discussion on a similar topic here:


(Aleksander Øyen) #3

I can share pictures of our 1:4 scale prototype in a couple of weeks, it is currently under a NDA.
we are using Ardusub on our prototype, final product will have a system we will build from the ground up.

I will take a look at the info you provided and do some testing :slight_smile: thank you!


(Aleksander Øyen) #4

I can share some pictures now :slight_smile:
The ROV (TAUV) is towed behind a trawler, and travels between the trawl and the trawler, delivering fish without needing to take the whole trawl-bag to the surface.


#5

I am working on a similar towed system. However I’m missing the skills needed with regard to writing code. My towed system (without thrusters) utilizes a Vee tail configuration. The wings which provides down force are without ailerons. Wing dihedral keeps the wings to perpendicular to the tether.The system has been tow tested while using radio control to actuate the Vee Tail and the system responds beautifully.
Now she needs a brain. I need a simple autopilot which will maintain a set depth (she has a Blue Robotics depth sensor). She also needs to maintain the last magnetic heading command from my transmitter. I.E. hold a heading until she is told to change direction…
A standard Vee tail configuration using a pix hawk controller would work perfectly except for one element of the system’s behavior. That is, the tether angle when in use will vary radically in the roll axis. As the system rolls, IE tether angle changes, control authority of the tail fins (pitch and yaw) must be allocated based on roll angle. For instance when at a 45 degree roll angle one fin has 100% pitch authority and the other 100% yaw authority. Simply said the system is flies in a rolled attitude based on the tether angle which is constantly changing .
My system is ready to go and all I need a a piece of software to add to my Pix hawk. Any ideas on how best to accomplish this? I think I need someone to write some code for the project but I don’t have a clue as to whom to ask or where to look for a person with the requisite skills. Any help and or ideas will be greatly appreciated. Thanks in advance!!!


#6


(Jacob) #7

Why/how is the towed vehicle’s roll attitude coupled to the tether angle? Is this behavior desirable, or do you want the vehicle to stabilize level all the time?

When you say at 45 degree roll, one v fin has only pitch authority, and the other only yaw, this ‘pitch’ and ‘yaw’ is in the boat frame. The stabilization will be done in the vehicle frame ie, the vtail fins always have the same pitch/yaw authority regardless of the vehicle’s attitude.


#8

Jacob: Thanks for the reply, my apologies for the late response. The tether angle is variable, and it is an endemic element to the system. Tether angle is relative to an earth centered system. Tether angle in the roll axis with respect to the towed body is constant, in that the tether is always perpendicular to the towed body’s wings, regardless of tether angle relative to the earth centered system… When I say the different control fins are assigned pitch and roll authority is based on tether angle, that is also earth centered.
That explanation is a bit clumsy, an analogy would be an aircraft flying level but in a rolled attitude. An aircraft with a Vee tail which has its tail fins at 45 degrees to the wing span. When flying level with a 45 degree roll angle one fin would be horizontal and the other vertical. This explains how and why fin authority for pitch and yaw is based on roll angle in my system. For instance if the wings are level then both tail fins have equal authority over pitch and yaw.
It seems the formula for calculating the fin authority based on roll angle would be fairly simple? Applying that in code that another more complex issue. However I don’t have the skills to sort out either issue much less applying it to a drone controller. I apologize for being somewhat vague about the application of my system but I cannot reveal that at this time. I can say that I am using Blue robotics products in the system and they have worked flawlessly.


(Jacob) #9

I think we are on the same page @Skoony.