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DC Motor Control in ROV

PixelBrine

Aug 15, 2012
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Hello. I am working on a project and I have run into my first real snag. The project is an underwater ROV that can carry a high def video camera. I have the frame built and I am installing the motors right now. I have two rear motors for Forward/Reverse and Left/Right

I have 2 DPDT switches that I have crossed the terminals on so that they reverse the current flow when switched from one direction to the other. I can get both motors to go in forward and reverse using just a single DPDT switch but I am having trouble when adding the second switch for Left and Right. Ideally Left would turn on just the right motor and Right would turn on just the left motor. (or even have the opposite motor go in reverse as well to aid in turning)

I am stuck adding the Left and Right functionality to the circuit Does anyone have any ideas on how this could be achieved? Or what I may be doing wrong? I have attached a poorly mocked up photo to describe what I have so far. Thanks.

qq3cdu.jpg
 

Harald Kapp

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Nov 17, 2011
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I can't think of a way to achieve what you want with 2 DPDT switches. The left-right switch would need a center position where both motors are active (assuming you want to go straight ahead, too).

A setup that works but need a bit more thinking of the operator could be made using DPDT switches with a central OFF position:
Use switch 1 to control motor 1 for forward-stop-reverse
Use switch 2 to control motor 2 for forward-stop-reverse

By cleverly combining switch positions you can achieve all possible combinations of motor directions and thsu steer your ROV.

If you need forward-reverse as well as left-right control, you will need a bit of logic to combine the signals from the switches into suitable motor control signals (a "mixer").

by the way: why don't you just use a ready made model RC control? The bettter ones have the mixer included.
 

PixelBrine

Aug 15, 2012
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Aug 15, 2012
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Wow the mixer idea might just work perfectly and even give me a bit more control. I don't need it to move forward while turning so that's not a problem. I thought about buying a control but all I could find were RC and the ROV needs to be tethered.

Thanks for the suggestion. I'll test it out in the morning.
 

Harald Kapp

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A simple mixer can be built from 4 relays, 4 pusbuttons and 8 diodes. Each pushbutton in connection with the diodes activates 2 relays. The diodes decouple the pushbuttons from each other such that different combinations of relays are controlled by one pushbutton each. The relays in turn control the motors:
attachment.php


[edit] You have to avoid to push more than one button at a time. Otherwise the relays will short the power supply (battery). A good idea would be to use an electromechanial joystick that allows only horizontal and vertikal movement of the stick. Thus at any time only one button can be activated.

Harald
 

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CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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Don't forget that you need opposite turning screws or your ROV is going to rotate.
 
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