ENGR 100-600 | University of Michigan

ROV Controls Activity

To help get a high-level understanding of how to control ROVs, we are going to do a hands-on demonstration to show how your design choices will affect the abilities of your ROV. You will get some more experience controlling ROVs in lab this week.

Background

Here’s a video that shows an ROV doing an underwater inspection, similar to what your ROV will do at the competition. To design your ROV, you need to have an idea of the different ways it can move underwater (known as degrees of freedom) and how the placement of thrusters and limitations of the electronics will impact the ROV’s maneuverability. The following sections provide a little bit of background information on these concepts.

Degrees of Freedom

All underwater vehicles have six degrees of freedom, meaning they can move in six different ways (see Fig). The different motions are:

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An ROV’s six degrees of freedom. "Borrowed" from online because I didn’t have time to make a cartoon before lecture started.

Sometimes a vehicle moves solely in one way (e.g. forwards = surge), and sometimes it moves in two or more ways simultaneously (forward and turning left = surge + yaw).

Placement of Thrusters

Where you place your thrusters will decide which degrees of freedom your ROV can move in independently and how fast it can move in those degrees of freedom. Fig illustrates these relationships.

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Some cartoons showing how an ROV is able to move based on where its thrusters are as well as some general guidelines to follow when thinking about where to place your thrusters.

Some general guidelines for how the placement of thrusters impacts your ROV’s maneuverability are:

Limitations of Electronics

In general, ROV controllers have:

Examples of the buttons and switches we will use for this course are shown in Fig. Buttons can do “on/off” behavior (e.g. turning a thruster on or off). Toggle switches can do “on/off/reverse” behavior.

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Examples of buttons and switches that you might use on your ROV controller. Pictures from the internet because I forgot to take pictures of these in the lab.

The ROV controllers that we make in this course are hand-held. Controllers for larger ROVs are often built-in workstations that might look more like the dashboard of a car, bus, or airplane. Our controllers start with a plastic box, similar to what is shown in Fig.

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A plain plastic box that is similiar to the base of your future ROV controller. The box can be held pretty easily if you hold it on both sides… unless you’re like Laura and have really small hands for a grown person (bigger is NOT better for mobile phones!).

It is relatively easy to drill out holes in these boxes for the buttons, switches, access ports, etc. that are needed for the controller. Inside the controllers, an Arduino board and a breadboard (Fig) are mounted to provide the base electronics of the controller (its “brain” if you will). The buttons and switches are then connected to the breadboard, completing the controller.

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A breadboard (white thingy on the left) and Arduino board (red thingy on right) that will go inside your ROV controller and be its “brain”. The white thing with a yellow sticker on it is the battery that is connected to the Arduino board.

Your ROV’s payload has a circuit board inside that processes up to eight signals from your controller’s Arduino board. The base configuration of the Arduino board assumes the eight signals correspond to the “on” and “reverse” positions of each of the four thrusters (4 thrusters x 2 positions = 8 signals). A button can close one circuit, thus sending one signal, e.g. “on” or “reverse” for a thruster. A toggle switch can close two separate circuits, e.g. “on” or “reverse” for a thruster.

An ideal ROV might be one that can move in all degrees of freedom simultaneously. But this might require up to nine thrusters and 18 control circuits! And you only have four thrusters and eight circuits. Because you are limited by both number of thrusters and number of circuits, you will need to decide carefully which degrees of freedom you will choose to control directly.

Tasks

Your group is going to have two tasks:

  1. Create an obstacle for an ROV to maneuver around
  2. Determine how to drive an ROV around the obstacle

Take no more than 5 minutes to complete each task – this is a fast activity!

Task 1: Obstacle (5 min)

Your group will be given a type of obstacle to create. The types of obstacles are:

To create your obstacle, you may use chairs, tables, yourselves, whatever you can think of! Just do it quickly because you only have 5 minutes! Place your obstacle near the head of your table so that we have a roughly-ring-shaped obstacle course around the room.

Task 2: ROV Control (5 min)

Your group will be given a “controller” that says what degrees of freedom your ROV can move in (electronics limitation) and how fast or slow each of those motions can be performed (thruster placement). For example, your controller might look like this:

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Now, Laura is going to be your group’s “ROV”. Look at your “controller” and practice telling your ROV how to move. Be precise so the LauraROV will know what to do! Some example commands, based on the sample controller above, are:

You don’t have to use exactly these commands; figure out what phrasing you think the LauraROV will be able to understand the easiest. :) But be quick! You only have 5 minutes to figure this out.

Testing Your ROV (5 min)

When the 10 minutes have passed (5 minutes for building the obstacle + 5 minutes for figuring out your ROV controller commands), Laura will start at a randomly selected group. That group will control the LauraROV using its ROV controller commands. When the LauraROV makes it past the first obstacle, she will go to the next and the next, etc. until all obstacles have been tried.

As the LauraROV tries to tackle the different obstacles using different ROV controllers, take note of what obstacles she can get around easily and which ones are harder given her ROV abilities (degrees of freedom + thruster placement + electronic limitations).

Debrief (5 min)