Robot Electrical system Design

Discussion in 'The Projects Forum' started by BlakeA, Feb 23, 2010.

  1. BlakeA

    Thread Starter New Member

    Feb 20, 2010
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    Hey everyone! This is my first post but I have been lurking around the forums for quite some time here. Me and a group of students have decided to construct a small skid steer/weight lifting robot and I have been given the task of designing the controller/electrical system for it. This is my first time taking on a task like this and I wanted to get some people with more experience to check out my design for the system and give me some feedback.

    Some Constraints:
    The robot is going to have 5 movements (Left side forward/backwards, Right side forward/backwards, Lifter arm Up/Down, Full Forward, and Full Reverse). It will use 6 SPDT relays for actuation. The controller and robot will be connected by 28 gauge tether wires connected by a 9-pin connector. The power supply for the Controller will be a 9v battery and for the robot motors it will be 4 AA batteries.

    What I am really having problems with is Finding the right component specifications by calculating the current/voltage going through all the components. Any help or suggestions or comments would be greatly appreciated.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    The 225Ω relay coils will kill the 9V battery almost instantly. 4AAs are 6V, not 3V. If you can run the motors on AAs (which is doubtful), you certainly do not need 10A relays. Go measure the current that the motors draw, both stalled and running. I would use FETs to switch the motors.
     
  3. BlakeA

    Thread Starter New Member

    Feb 20, 2010
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    0
    Good reply,

    The 4 AA batteries consist of 2AA's in parallel providing 3V.

    The motor runs on 3-6V and will run with 4 AA. (tamiya twin gear motors)

    The 9V runs around 500mA hours and if we consider the most current draw to be when all five momentary switches are pressed there is 230 mA being drained from the 9V (please check me on this) meaning that the circuit should run around 2 hr's or so (Which is fine for our purposes).

    For the Motors stall current = 2100 mA
    Free run current = 150 mA

    Thanks for thaking the time to look at this Mike, more comments will be greatly appreciated.

    Edit: I agree 10A relays is overkill...what would you suggest for this circuit and how would i determine this?
     
  4. BlakeA

    Thread Starter New Member

    Feb 20, 2010
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    0
    On of my friends told me just now that the back emf of the relays could potentially damage electrical components and that i should put a diode somewhere attached to the relay to prevent this...I don't think this is going to be a problem with my circuit though, i would imagine that the EMF he is talking about is too small to do anything.

    I am still having trouble picking the Amp rating on the relays to safely transfer current. I would like a safety factor of 2-10
     
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