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create fast accurate robot

Discussion in 'Robotics & Mechatronics' started by Daniel Zepeda, Jun 22, 2018.

  1. Daniel Zepeda

    Daniel Zepeda New Member

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    hello,
    I have to create a robot (less than 2kg) that goes in a straight line (10° accuracy) for 15 meters as quickly as possible. It also has to be autonomous. Any ideas?
     
    Last edited: Jun 22, 2018
  2. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Use two stepper motors and you should be able to accelerate to full speed, travel required distance and deaccelerate to a stop all in a straight line.

    Mike.
    BTW, 2kg is not a small robot.
     
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  3. Daniel Zepeda

    Daniel Zepeda New Member

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    Thank you for your reply. Do you think stepper motors will be better than rotary encoders?
     
  4. dave miyares

    Dave New Member

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  5. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    Stepper motors and rotary encoders do two completely different things. They are not remotely interchangeable.
     
  6. DerStrom8

    DerStrom8 Super Moderator Most Helpful Member

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    This sounds like a school project. You should be doing the design work yourself, and asking for help from your instructor. You should not be asking people on a forum to do your work for you.
     
  7. Daniel Zepeda

    Daniel Zepeda New Member

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    Yes I know, but I didn't quite get the difference between both things, stepper motors and rotary encoders. My robot has to be autonomous. Can you explain the differences?
     
  8. dave miyares

    Dave New Member

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  9. Pommie

    Pommie Well-Known Member Most Helpful Member

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    A stepper motor is a motor, a rotary encoder isn't.

    Mike.
     
  10. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

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  11. dknguyen

    dknguyen Well-Known Member

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    Isn't 2kg a small robot? Not tiny, but small. I consider that a small robot in the same way I consider cats a small animal and roombas a small robot, and both of those weight double that.
     
  12. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Just checked one I made for school. Two motors, motor controllers, Arduino, 4x20 display, distance sensor, ply frame and associated wheels, screws etc. Total weight 400g. And the commercial Zumo robots that we use come in at 300g complete with 4 AA batteries. So, I consider a 2kg limit very generous - assuming this is a school project. I also consider mercury to be a small planet.

    Mike.
     
  13. camerart

    camerart Active Member

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    Hi D,
    A stepper motor has steps in it's windings e,g, 200 steps. The controller 'steps' 200 times for one rotation.
    A servo motor, is a DC motor, and has feedback e,g, a disc with 200 divisions, which counts again e,g, 200/rotation.

    Your control program either (stepper motor) sends out steps to each motor, or (servo motor) turns on the current and counts from the disc.

    Unless you can place anything else in the room, such as a light to follow, I agree with the earlier suggestion, of a compass module.

    Good luck,
    Camerart.
     
  14. Pommie

    Pommie Well-Known Member Most Helpful Member

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    An alternative is a tricycle undercarriage. One front wheel driven by any motor and two back wheels. As long as it's built accurately it will have no choice but to go in a straight line. A stepper will still give you more control over acceleration and distance.

    Mike.
     
  15. gophert

    gophert Active Member

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    If you get to use an arduino, use a gyroscope shield. Easy, easy, easy.
    You should be able to stay within one degre over the 10 Onda née o o 15meters with a simple two motor robot. Just use a slider pin (small carriage bolt or plastic rod) for the third support. A caster or wheel is too complicated and creates errors.

    https://playground.arduino.cc/Main/Gyro
     
  16. Pommie

    Pommie Well-Known Member Most Helpful Member

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    Have you tried reading a gyro? The reading is the rate of change of the giro so you need to integrate the readings to get an angle. Plus, when the gyro is still it doesn't read zero!

    Not a trivial task for an experienced programmer and not easily accomplished by an beginner.

    Mike.
     
  17. tomizett

    tomizett Active Member

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    If it's just got to go in a straight line in the direction it starts off, then you can drive it without any direction feedback - your only concern is wheel slip. In that case, think about building it with tracks not wheels - they're really good at going in straight lines, and will have less tendency to slip.

    If you do need directional feedback then I like Pommie's idea of a (solid state) gyro. Although I don't see that you'd need any programming - you can get gyros with PWM outputs, so you could do all the processing analogue if you like.

    Maybe you could fit a real (big, heavy) gyro to a steerable wheel and have it navigate itself mechanically, like those things that they use to sail boats (whatever they call them). That'd be interesting!
     

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