Choosing the right motor

This topic contains 4 replies, has 3 voices, and was last updated by  Vishal 2 days, 20 hours ago.

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  • #3048

    Vishal
    Participant

    Hi everyone,

    I’m a solo roboteer, and it’s my first time at Pi Wars and also my first time designing a chassis completely from scratch! I am a bit confused about what type of motor to use and which motor to use…

    I think I will be using a geared DC motor as it has a good torque and high speeds. Although, I want it to be encoded motors so that I can use them for autonomous robots as well. Unfortunately, a single encoder motor cost around £12 and is very hard to find a suitable one that I can trust as most of them don’t have any reviews at all!

    So if anyone could give me some guidance on recommended motors and where I may be able to buy them, it would really help a lot! Are there any good motor models anyone knows of (and suitable drivers)?

    Thank you!

    #3050

    StuartL
    Participant

    Encoded motors only ‘help’, they don’t solve all of the problems. Wheels will slip on the variety of surfaces in these very physical competitions and dead reckoning (where you trust where you are based upon how far a wheel has turned) is not reliable. It’s a useful input but it cannot be trusted.

    Go for motors which give you the performance/size/cost you wish for and look at the autonomous challenges differently… how could you use a more trustworthy source of information to figure out where you are? Ultrasonic or time-of-flight sensors? Cameras and OpenCV? CMUCam Pixy? A mix of all three?!

    If you really want to have rotary encoders you could fit some retrospectively to the motor or output shaft.

    #3051

    lwr20
    Participant

    I’m a big fan of motors with encoders. We’re sticking with built-in encoders this year too.

    For places to buy: try RobotShop and TME.

    Choosing a motor is hard. You need to take into account:
    – How fast you want the output shaft to spin on your robot
    – How much torque you want. This is strongly related to:
    – How much power you can supply. In practice this is volts and amps. Think about your motor controllers, your battery, etc.

    Find a motor which spins at no-load a bit (maybe 2x) faster than you need for your robot and has a stall torque which is higher than you need (again, maybe 2x).

    Then read this: https://www.pololu.com/product/1575/faqs – this tells you how to estimate the curves for your motor and figure out where it will be operating and decide if that’s right for you.

    If you want to see how other people choose motors, try these excellent blog posts from previous competitors:

    Driving onwards

    Pi Wars-drivetrain

    #3052

    lwr20
    Participant

    Oh – and buy a spare or two – nothing worse than having your robot break a gear or a motor in the last week before the competition.

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