Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Want my robocar to turn

  1. May 24, 2008 #1
    I am ona project of making a robocar and I want it to turn.
    After my first attempt I realized that it should be a three wheel car with a ball bearing in the front as the third wheel.
    But I want to make it a four wheel drive and the problem is:
    I use simple motors and they are free to rotate in both directions.So Even if I stop motors on one sid's set of the wheels tehy continue to move in the forward direction.
    Any suggestions??????
     
  2. jcsd
  3. May 24, 2008 #2

    Danger

    User Avatar
    Gold Member

    To start with, you cannot have 4-wheel drive on a 3-wheel vehicle.
    If you insist upon using a ball bearing as your 3rd wheel, I'd recommend using an inverse version of a computer mouse. (ie: Put drive wheels where the sensor wheels would be on a mouse.) That, combined with differential braking on the back wheels, should give you all of the manoeuvrability that you could hope for.
     
  4. May 24, 2008 #3

    rcgldr

    User Avatar
    Homework Helper

    Assuming these are DC type motors, you need a speed controller that shorts them out (or a low resistance connection) to get a braking effect.
     
  5. May 25, 2008 #4
    Please elaborate

    "To start with, you cannot have 4-wheel drive on a 3-wheel vehicle."

    As four your comment, I am not trying to use a four wheel drive on a three wheel robocar.
    I have used a three wheeled robocar previously and now I wish to use one with four wheels.


    "Assuming these are DC type motors, you need a speed controller that shorts them out (or a low resistance connection) to get a braking effect."
    I am using DC motors,but I don't understand how to do that braking effect. If you are saying to connect a shunt across the motor then also the motor would stop to rotate but the wheels of the other side would tend to pull it along, and as there is no restriction on the rotation produced mechanically, the wheels would continue to move even when motors on that side has been turned off or has been shunted.

    There is another technique:
    Make one motor move forward while other moves back, which wolud make it turn on the same place, but I dont wish to use it.
     
  6. May 25, 2008 #5
    With regular DC motors, shorting them is not the same as turning them off. DC motors act as generators and when they are shorted, it is pulling a larger load and acts like a brake.

    I do not know how much you will see it with cheap or small motors but it is there. For example, with Lego motors if you cut the cable and short it, they stop immediately and are very hard to turn.

    If you are more interested in why, let me know. Basically, it has to do with the motional emf and if current flows then back emf is created. It isn't complicated but i have to read about it again.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?