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  • # of motors that one motor controller can handle

    Does anyone know whether it is legal and/or electrically advisable to hook up 6 motors (3 to each side) to a single motor contoller.
    We want to use six motors to power our drive train and therefore want to send the same signal to two sets of three motors.

    I can't find anything in the rules that specifically does not allow this... the motor controller package states that a four motor robot can be built by paralleling two motors to one channel but doesn't specifically say whether you can use three per channel.

    Waiting for your words.... please limit this to fact and not just opinion.

  • #2
    The disadvantage of running multiple motors from a single motor controller port is that it splits the voltage. Essentially you get 3 motors running at the same speed, with one-third of the power compared to if you only ran one motor from that motor controller port.

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    • #3
      Originally posted by Elpreyday View Post
      The disadvantage of running multiple motors from a single motor controller port is that it splits the voltage. . . .
      The controller package describes connecting the motors in parallel (not in series), which results in splitting the current from the controller, not splitting the voltage.

      If you want to parallel three motors instead of two, the question is whether the controller can handle the 50% increased current draw (relative to the two motors in parallel, for which the controller was apparently designed). With one or two motors, if a motor stalls, the motor(s) typically burn(s) out, not the controller. With three motors in parallel, maybe the controller would give up first.

      You could test the motors yourselves to determine their current draw at stall, for example, and you could open up a controller and spec out the compenents inside to get an estimate of what current rating might apply to the controller as a whole. But As far as our team is aware, the electrical specs for the tetrix DC motor have never been published, by Tetrix or by any team, and the same for the controller--no specs have been published by Tetrix or by Hitechnic or by any team, as far as we know.

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      • #4
        This is slightly off topic but for some reason I have been unable to start a thread. Our team has 3 tetrix motor controllers, and two have failed. I'm just wondering if other teams are having similar problems.

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        • #5
          Four. Stalled motors draw 2 amps; Motor controller channels can output 4 amps (not sure of this statistic; correct me if I'm wrong).
          Max Bareiss

          FTC #248 Fatal Error (2009-2013)
          FRC #3142 Aperture (2009-2012)
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          Rowan University Baja SAE

          And mentoring for life.
          --
          11 seasons of FIRST in 6 years, as a student. Many more as a mentor.

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          • #6
            We are using fused wiring for our motors and every once in a while- gremlin like- the motors go on the fritz and it seems that the in line fuse is clicking on and off which makes the robot go crazy- so to speak. Do the fused wires have a limited life? we have 2 robots and -1 robot has 6 motors and has more wiring issues but our other robot is prone to these intermitant electrical problems? ANy suggestions?

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            • #7
              So to clarify; a motor controller is built to hold 2 motors. Two pairs of +/- leads on it. However, you can safely put four, two motors in each +/- pair. But not six, three on each pair, since that would overload the amperage of the controller. This is assuming you split the leads, so that it will put all the motors in a +/- slot to the same power (due to the way electricity works). The alternative, chaining them, where the wiring goes to the first motor, then from there to the second, and so on until it comes back to the +/- slot, can hold as many motors as you want, but will quickly lose the ability to power motors beyond the first one.

              My own question; how does this effect the lifespan of the controller? The batteries? The motors in use?

              Correct me if any of that is wrong, that is purely what I got out of this thread, and not based at all on my own testing or knowledge. (though I will be testing this, as soon as I can convince my teacher/parts supplier that this will work without burning anything out)
              Last edited by FTC3053; 05-03-2011, 11:53 PM.

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              • #8
                We ran with 3 pairs of motors on a single controller for the iSpace Championship and the World Festival. We had no issues. Power and speed were not a problem for us. Soldered connections seemed to hold up fine. No wiring issues. And it made for simple programming for our 6 motor 6 wheel drive. We used the heat fused wires on all our drive motors.
                Jamie Diamond
                Cougar Robotics Team (Get Over It! #4251)
                (Smart Moves #127, Climate Connections #437, Power Puzzle #1470)
                coach@cougarrobot.com
                http://www.cougarrobot.com

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                • #9
                  Originally posted by 2010FTC4251 View Post
                  We ran with 3 pairs of motors on a single controller for the iSpace Championship and the World Festival. We had no issues. Power and speed were not a problem for us. Soldered connections seemed to hold up fine. No wiring issues. And it made for simple programming for our 6 motor 6 wheel drive. We used the heat fused wires on all our drive motors.
                  Originally posted by Skinkworks View Post
                  Four. Stalled motors draw 2 amps; Motor controller channels can output 4 amps (not sure of this statistic; correct me if I'm wrong).
                  So can the controllers actually handle 6 amps per channel? Or did 4251 never use each motor to the full amperage? (sorry if I got my electrical terms wrong, I do programming, not wiring)

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                  • #10
                    Originally posted by 2010FTC3053 View Post
                    So can the controllers actually handle 6 amps per channel? Or did 4251 never use each motor to the full amperage? (sorry if I got my electrical terms wrong, I do programming, not wiring)
                    We really don't know. Our robot weighed about 23.5 lbs. We were more than average in pushing matches. But wheels would typically spin before motors would stall. Another item which might be related is our motors were geared to our wheels at 3 to 2 ratio. i.e. 3 turns of the motor shaft would drive 2 turns of the wheels.

                    Again, no problem with motor controller, no problems with motors, no trips of our fused motor wires.
                    Jamie Diamond
                    Cougar Robotics Team (Get Over It! #4251)
                    (Smart Moves #127, Climate Connections #437, Power Puzzle #1470)
                    coach@cougarrobot.com
                    http://www.cougarrobot.com

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                    • #11
                      My guess is that when the motors run at full capacity, two is the safe maximum. But, if you don't stall your motors, you can get 3. The trick now is testing this without burning out any motors or controllers.

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                      • #12
                        4311 runs eight motors on a single DC power controller, although no more than 6 are moving at the same time. We didn't have any problems with the controller. (3 drive motors on each side of the chassis, wired in parallel, and 2 motors controlling an arm for dispensing).

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                        • #13
                          OK, now I'm confused. A single DC motor controller has two "motor ports" right? So do you have all 6 wheels on one port? or left wheels on one port and right on the other? If so how are you controlling the arm separately from the wheels?
                          Jamie Diamond
                          Cougar Robotics Team (Get Over It! #4251)
                          (Smart Moves #127, Climate Connections #437, Power Puzzle #1470)
                          coach@cougarrobot.com
                          http://www.cougarrobot.com

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                          • #14
                            Your arm should then be moving at the same time as your wheels. Do you have any closeup pictures of your bot? I remember your bot, just I don't think I ever examined your wheels that much.

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