Thrusters placement

[theinlinaung]

So we are just starting up and planning for placement of the horizontal thrusters.

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#1. Pros
Visually symmetrical
Small turning circle
Cons
Only half of thrust force applies to forward thrust due to 45’ angle. The lateral thrusts balance out making the forward propulsion system less efficient. The motors must be far enough.

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#2. Pros
The thrusters in the middle are rotatable making the thrust force exert on any direction.
Turning circle could be made small.
Cons
Adds complexity in rotating mechanism and more controls to the operator.

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#3. Pros
Cost efficient and could use higher power motors. The thrusters could still produce couple moment by propelling opposite directions.
Cons
Is turning reliable? Lateral motion is impossible.

What do you think?

[thegadgetguy]

Firstly, welcome to the forum!

The first thing you will need to decide is what the intended purpose of your ROV will be. There is no one 'best' thruster configuration, only the best configuration for your application. For instance, if you want to build a small observation-class ROV primarily for looking around and exploring underwater, setup #3 is probably your best bet, possibly with the addition of lateral thruster to allow you to strafe left and right. It's simple, easy to set up, and provides good basic maneuverability in most instances. If you want more maneuverability for use with a manipulator to pick stuff up or something, then the vectored setup #1 might be a better choice. In my opinion, any effort getting the thrusters to move in setup #2 would be better expended building a vectored setup like in #1, but that is just my opinion.

Secondly, you need to figure out if your control system will be able to support the thruster configuration that you choose. Setup #3 can be controlled well by almost any control system - switches, switches/relays, simple proportional, fully proportional w/mixing on one stick, etc. On the other hand, you really need proportional control with a bit of logic to get the most out of setup #1. You can do it with switches or switches/relays if you want, but you're really missing out on the maneuverability a vectored setup can give when combined with proportional control. Setup #2 could vary complexity wise depending on how you might set it up, but will be more complicated then setup #3 in virtually all cases.


To respond directly to your last Con...

#3. Pros
Cost efficient and could use higher power motors. The thrusters could still produce couple moment by propelling opposite directions.
Cons
Is turning reliable? Lateral motion is impossible.

I've found turning to be quite reliable in this setup. Setup #1 has an advantage here, but it is not a night and day difference. Lateral motion can easily instituted by the addition of a single lateral thruster. Look at the 9th, 10th, and last pictures on this web page for a good example: http://homebuiltrovs.com/seafoxretrofitthrusters.html

Well, I hope this will help get you started . Hopefully some other forum members can chime in and give their opinions.

[theinlinaung]

Well, I hope this will help get you started . Hopefully some other forum members can chime in and give their opinions.

Thank you for your response. We are excited to make a test prototype for the thrusters. And we discovered a new type of design from CornerStone Electronics. But we are curious that lateral movement would produce a turning torque that turns (rolls) the vehicle which is undesired. It can provide direction control with just four motors though.

Vector Thrusters 2.PNG (174.5 KiB) Viewed 7008 times

[ArduROV]

I am using exactly this thruster placement in my ROV. The lateral movement with the vertical thrusters is possible.
But it is important to know about the turning torque of the thrusters. You have to place all the heavy stuff (batteries, etc.) to the bottom and all the buoyant stuff to the upside to make the ROV very stable in the water.


https://www.youtube.com/watch?v=Aj737G6bZE8

In this Video at 0:40 min you can see a small lateral movement with nearly full thrust to the right side. You can see the turning movement to the right but the ROV is still stable in the water. If you are interested i can make a few more lateral movements in my next excoursion to the lake and show it in the next video.

[theinlinaung]

Hi ArduROV,
Thank you for your response. We'll test the design with a prototype.