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Two wheel non-balancing robot

  1. Sep 3, 2009 #1
    Me and my team are working on a two-wheel simple robot having two motors and 12v 1.5amps supply for a small intra-college robo-race.
    The wheels are 10cm diam. and we have a cylindrical body between the two wheels with 8cm diam. The setup is all wired, nothing wireless( with the remote ).
    We have less time and no money(india), so we went wired. Anyways the problem is, when we turn on the motors, the entire cylindrical body moves but not the wheels. Note that the wheels are little heavier than the main body. We made the cylindrical body out of PVC and other two bowl shaped PVC structures to cover the motors.The axis of the motors is screwed with the wheel.
    In short, the torque is not being transferred to the wheels but the motor itself.
    Any help would be appreciated.
  2. jcsd
  3. Sep 3, 2009 #2
    I'd go for a leading 3rd wheel. Like a strut from the middle of your cylinder that goes out horizontally with a free rolling wheel attached. Note this will only work for forward motion, unless you make the wheel in such a way that if you reverse the strut flips over as the cylinder rotates and comes into contact with the ground again.
  4. Sep 3, 2009 #3
    Simple solution is to make the body heavier.
  5. Sep 3, 2009 #4
    yes we thought about that,i agree to that. one of my team member thinks it won't work smoothly on rollers that are on the tracks (rollers to decrease the speed of the robot), also on "U" turns..what do you think? as you said, we can go for a 4th wheel for both forward and reverse motion. we can attach a rod through the center of the body and attach two small wheels that can help stop moving the rotation of the cylindrical body..what say?

    yes, i did though about that but some idiots in my team thinks it wont work.Thanks for the help chris.
  6. Sep 3, 2009 #5
    I assume that both are roughly circular, all you have to do to convince your tesmmates is show them he Moment of Inertia equation.

    The fact taht the motor will rotate the easiest thing (this you can prove by holding the body (where your wrist is resisiting the torque, if you made it heavier the moment of inertia does the same job).

    Make body MOI > Wheel MOI and the wheels will rotate.

    The above solution is by no means technically brilliant, but it will solve the problem.
  7. Sep 3, 2009 #6
    ok, i can do that, chris. i even demonstrated the same thing to them. that is-
    "( where your wrist is resisiting the torque, if you made it heavier the moment of inertia does the same job)"

    only thing remaining is to see it work
  8. Sep 3, 2009 #7
    The extra weight wouldnt work. Your wheels will turn but also the cylinder, their velocities proportional to moment of inertias. The wheels have esp high mom of inertia because most of the weight is on the outside. In the end, you would get little velocity. To get reasonable acceleration, the cylinder has to be very heavy, which again will counteract linear acceleration due to increased total mass.
    Go with the third wheel.Or if you can do this.
    Have your two wheel setup, stop (or reverse) one motor while running the other, then switch them.You will get the necessary support from friction to go forward. Do this switching very fast and you can run smooth and straight.
    Last edited: Sep 4, 2009
  9. Sep 6, 2009 #8

    Anyways, have you heard of caster wheels??
    http://img2.tradeget.com/huiqiang5/2Y2AYE951wheel.jpg [Broken]

    And, as Emreth explained, making the body heavier isnt a smart solution.
    you are not in the business of guessing anymore. Get mathematical:wink:
    Last edited by a moderator: May 4, 2017
  10. Sep 7, 2009 #9
    india? yea, its a **** place sometimes.

    caster wheels looks promising but as i said we are out of money.
    im getting 2 small wheels from some **** old toy car and trying to fix them to the cylinder.
    then see how it works..
    thanks for the help ank.
    Last edited by a moderator: May 4, 2017
  11. Sep 7, 2009 #10
    Yea I know, but i didnt laugh at India, that "so we went wired" was soo darn funny:biggrin:. Anyways, there are not many hobby shops around here to get your hands on one of those cool futaba radios.

    Come on dude, it only costs 10 bucks(~0.20 USD). One of the pics has it in place, the other one is a more common Castor, costs even lesser

    Attached Files:

  12. Sep 9, 2009 #11
    :D sure thing!
    anyways we are now couple of days away from our final day, we finally attached two small wheels from the middle of the cylinder. That solved our problem, but there is another problem now. We have a 12v limit and we need to climb a gradual 30deg elevation, we tried to do that and the bot stops half-way. We need more torque for that. I am now thinking of getting another motor for the back wheel, which will help climb.
    Thanks again for the pics ank!
  13. Sep 10, 2009 #12
    @bloshe1, I left you a message. Check your inbox
  14. Sep 12, 2009 #13
    if speed or time is not a concern you could also use gears to increase torque, that is if getting another motor isnt easier to do. but the best and absolutely free solution is to lighten up the assembly as much as possible which would decrease the downward force. try taking off the 4th wheel, every little bit helps. drill holes etc.
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