Positive directions for thrust

Hi there, I am building an ROV and have a query about which direction thrust should go. It is an 8 thruster model (vectored6dof). I can see the configuration page where it shows the direction of rotation of teh the thrusters, but it does not show which way the thrusters should be mounted.

I assume, for positive PWM (1500 to 2000), the lift thrusters should push water downwards.

What about the forward / back / sideways thrusters? I there a diagram showing for positive PWM which direction they should push water?

Hi @ausdroid, welcome to the forum :slight_smile:

The thruster orientations and the output PWM signals are somewhat decoupled, because the thruster windings don’t have a consistent order (which is why Motor Setup allows reversing the direction of each thruster, and automatically detecting if any have their directions flipped).

That said, the thruster bodies do have intended orientations (which can be seen in the frame images as well as our BlueROV2 and BlueROV2 Heavy product pages, and the 3D models in their Technical Details sections). For our T200, the front is the more rounded and elongated side, with the cable coming out of it.

The input controls also have specific orientations, which I believe should match what’s documented here, but I’ll need to confirm.

ArduSub uses signals in the 1100-1900 us range, to match the inputs of our BasicESC.

Thanks for getting back to me.

So, the vectored6dof setup has the lateral thrusters with two facing forward and two facing backwards. So, I would assume that in forward motion, the front two are in reverse and the back two are in forward, or Vice versa. But you are saying it doesn’t matter as you can reverse the direction of each thruster in the firmware.

Is positive PWM pushing thrust toward the pointy end? Or the round end?

Thanks for your help.

That’s correct.

Because the windings aren’t consistent, and because the thrusters have different propeller options (clockwise and counterclockwise), some thrusters will go forwards with 1500 \leq PWM \leq 1900, while other thrusters will go forwards with 1500 \geq PWM \geq 1100.

The thruster direction matters because forwards has higher thrust, but the PWM control values aren’t consistently the same for “forwards” and “reverse” across thrusters. In ArduSub we handle that by having a software toggle that indicates which region is positive/forwards for each thruster.