Having trouble with 12v motors and reversing

Discussion in 'The Projects Forum' started by Ulfr, May 27, 2015.

  1. Ulfr

    Thread Starter New Member

    May 27, 2015
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    I am pretty new to electronics and have decided to tackle the MIT Sea Perch ROV. I've altered the design a bit. It calls for 3 motors and one of them (the vertical control) uses an SPDT push button switch which allows for the motor to reverse itself. I really like this idea and am attempting to alter the design to use 4 more SPDT switches for turning and forward/reverse.

    What I've done is I've designed the control box to sort of emulate an old NES controller. What would be the D-pad is 4 SPDT switches and it is here that I am having trouble. Forward, reverse, and turning on the Sea Perch is done via two 12v motors at an angle. Just powering one will rotate the Sea Perch and giving power to both will let it move forward. What I'm trying to do is have these 4 SPDT switches control the forward, reverse, and rotation. Here is what I am after:

    "Up" will power two motors and move the Sea Perch forward
    "Left" will power one motor and rotate the Sea Perch left
    "Right" will power the other motor and rotate the Sea Perch right
    "Down" will reverse the power to the two motors and allow the Sea Perch to back up

    I've got the first 3 to work via diodes but I am unable to figure out how to wire my "down" so it will do what I want. Right now it does nothing. This is my first attempt at such a thing and my first time making a post like this so I apologize if I don't show everything necessary for help. But I'll give it a shot.

    I have my GND, PWR, and ACC wired for my left and right rotations. From my ACC I have my positive lines going to the motors. The lines from these ACC terminals have diodes to prevent feedback. I also have the positives for both motors on the "up" button on the ACC terminal. These also go through diodes to prevent feedback. On my "down" button, I have the negative for both motors in an attempt to allow it to work in reverse. What I figure is that the diodes are preventing the negative signal from being used through the "positive" lines to the motors so it won't allow it to spin the other way. But for the life of me I can't figure out a way around this. I have the feeling that the solution is staring me in the face but I'm just ignorant enough to not be able to see it.

    Any advice/help would be greatly appreciated.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Can you sketch out what you have so far?
    Max.
     
  3. Ulfr

    Thread Starter New Member

    May 27, 2015
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    Ok, my first schematic! Possibly a million things wrong with it but hopefully it will get my point across :).

    Does this help?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You need to draw a better circuit diagram than that, it doesn't make sense....
     
  5. Ulfr

    Thread Starter New Member

    May 27, 2015
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    If you could tell me what to correct and/or clarify, I'll gladly do it. Just telling me I need to make it better doesn't help because I don't know what needs to be done or what you are looking for. It makes sense to me, but then I'm the one who made it. Until I know what is tripping you up, I don't know how to address it.
     
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Here is the assembly manual for the Sea Perch. ETA: Manual is outdated.

    Below is the wiring diagram as it was designed (before Ulfr modified it.) ETA: Diagram is outdated.

    Sea Perch ROV Circuit Diagram.PNG
     
    Last edited: May 29, 2015
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    As shown in the diagram in the previous post, the Port and Starboard Switches are DPDT toggles. What is not clear from the diagram is that they are three position switches with a center off position. That is what allows the motors to be switched between off, forward, and reverse.

    If I understand what you want, it is to be able to do that with a pushbutton switch. Correct? Please describe the pushbutton switches. I don't know what an NES controller is.
     
  8. Ulfr

    Thread Starter New Member

    May 27, 2015
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    NES stands for Nintendo Entertainment System. I'm looking to sort of emulate the use of an old school controller for this. The pushbutton switches I am using are single pole double throw (SPDT) from here (http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_28063_-1). What I'm wanting to do is use SPDT switches for everything. I've already wired my vertical motor as originally specified in the MIT Sea Perch diagram and it works perfectly. What I'm wanting to do is do this very same thing with my FORWARD and REVERSE where each button pretty much does the same thing that the vertical buttons do...press one and you go forward and press the other and you go in reverse. This will be done by activating the other two motors. I can do that...simply wire it the same way the vertical one is done but just send the power to two motors instead of one. But where it gets tricky is I want to have my LEFT and RIGHT buttons only power one of those motors to allow the ROV to rotate.

    Does this help clear it up?
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I think so, but I'll have to do some schematic doodling to see if I can do it with a diode matrix. It would be easy with a microcontroller; does that hold any interest for you?

    ETA: On second thought, a uC would increase the component count excessively.
     
  10. Ulfr

    Thread Starter New Member

    May 27, 2015
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    A microcontroller interests me VERY much...I definitely want to work with them but I'd hoped to maybe avoid it this go-around and use one for version 2.0 with a handful of other ideas I've come up with while making this one :).
     
  11. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I have thought about the Sea Perch quite a lot, and as usual, things are not as simple as they seem at first glance.

    First of all, the wiring diagram in post 6 shows the starboard switch controlling the port motor and vice-versa. This bothered me, and I located a later version of the construction manual that corrected this error.

    Then, I noticed that in some of the figures, the thruster assemblies were mounted at an outward angle from the long side of the frame, and some figures showed them mounted at an inward angle. More reading revealed that setting the angle of the thrusters is part of the learning process, thus the angle is adjustable. My assumption is that since the ROV does not have a rudder, the best compromise between thrust and maneuverability will come with the thrusters angled out slightly. (Perhaps some of our seafaring members will confirm or correct that assumption.)

    Then, I began thinking about the fact that the two motor control switches each had three possible settings, and that meant that there were nine possible combinations of the settings, each of which would produce a different result. I created the table below to document the possibilities in speed and direction. Again, I am no expert in submersibles or dual prop rudderless boats of any kind, so maybe someone here can point out any errors in the table.

    Sea Rover Thruster Control.png

    After considering this table, I believe that using DPDT center off toggle switches was done for a good reason, and that attempting to use SPDT pushbutton switches would seriously compromise the maneuverability of the ROV (not to mention the considerable increase in design complexity.)

    One possible option is to orient one of the thrusters parallel to the long side of the frame, and the second at a right angle to the long side of the frame. The first would be to provide forward and reverse thrust, and the second to provide right and left steering. My guess is that overall speed would be reduced significantly, but I think that would allow the use of SPDT pushbutton switches.
     
    Last edited: May 29, 2015
  12. Ulfr

    Thread Starter New Member

    May 27, 2015
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    First off, now I don't feel so bad for not seeing what I thought was a potentially easy-for-a-newbie-to-miss solution. I think I might see about going the DPDT route. Need to study the design again since I've veered off so far into the SPDT-only territory. But on the subject of microcontrollers...I've dabbled a bit with a small robot kit so I may have something that can be used here. I'm a decent programmer and have tinkered a bit with the code in the microcontroller but I'm not proficient with it. Any advice for going along that route?
     
  13. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    The easiest and least expensive uC to start with is a PICAXE; check it out at picaxe.com. Driving motors from uCs usually requires an H-bridge for each motor; H-bridges can be constructed with discrete components and are also available as integrated circuits. There are some decent you-tube videos that explain H-bridges.
     
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