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Steering Mechanism

  1. Nov 7, 2009 #1
    Hi,
    I'm building an battle robot. The total weight of the bot is round 40KG. I want to implement an steering mechanism for my bot. For that i found Rack and pinion arrangement. But the problem in that is, how to make an DC motor to rotate just for a few revolutions?

    Another method which can be used is an servo steering mechanism. But since most hobby servos are made out of nylon gears, i don't know whether they will be able to handle the stress? Is there any schematic diagram for an steering arrangement using an servo motor?

    Thanks!
     
  2. jcsd
  3. Nov 7, 2009 #2

    Danger

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    Welcome to PF, Ukesh.
    As to your first question, you might want to look into stepper motors. I don't know anything about them, but some of the guys here can totally fill you in. You could also run a geared-down transmission between the motor and the pinion. That should slow the response speed enough for you to maintain control.
    My personal approach would be to use a lead-screw rather than the rack and pinion. It gives high force at moderate speed. Intermediate gearing can be used in that configuration as well, if appropriate.
     
  4. Nov 7, 2009 #3
    some thoughts-

    Control of a DC motor can be done with an optical encoder using quadrature output to clock a counter up or down. For pure digital control, a comparison is made to a control number sent and the motor is powered in the appropriate direction until the numbers match.

    There are some very powerful hobby servos for r/c models but they are not so cheap.

    You may be able to make use of the worm drive motor/gearbox of an electric window from the automobile junk yard to operate a simple and powerful steering linkage. This could be connected to the pot of an r/c servomechanism and operated as a servo, too, (with power FET to deliver the amps to the motor).
     
  5. Nov 8, 2009 #4

    Danger

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    Excellent suggestion. I love using car parts. A power-seat adjuster system might also be quite suitable for this application.
     
  6. Nov 9, 2009 #5
    I would build the thing on the z-rider lawn mower style (zero radius) that way you steer with the difference between tire rotations like a bobcat. @ motors, 2 motor controllers
    that way you:
    1; saves engineering/ build costs on any steering
    2; gives an additional channel for weapons
    3; makes the robot 1/3 less vulnurable

    as far as weapons, I always wondered why no one used a hollow spike with saltwater injection, or EMF/ tazor zap.

    oh, know, I'm thinkin again, better go....

    dr
     
  7. Nov 11, 2009 #6
    thnx for your reply guys!
    well first thing is i want to keep my design as simple as possible. So I'm looking to make the steering mechanism either using a Rack and Pinon or using an servo. And i will be controlling the servo or the motor via a standard RC controller. If I'm opting for the rack and pinion type im thinking of using an motor with 10 rpm, so that the rotation of the shat will be less. My doubt is that, if when rack reaches the extreme end of the pinion, say i provide stoppage of some sort, will the gears undergo backlash or will the gears get mismatched? My guess is that since the rpm of the motor is less, provided the stoppage is efficient and the meshing of the gears is okay, the motor will stall rather than undergoing physical changes.

    And the problem with servo is that, I couldn't find a way to use the servo for the mechanism i need. I've seen in RC cars, mostly newer models use servo for steering mechanism. But those links are complex! can someone guide me for creating an link mechanism to be used with an servo?
     
  8. Nov 12, 2009 #7
    many (especially low buck) servos have very little "throw force" we have been doing some experiments with riding lawn mower (for mower war usage...lol) conversion to R/C and that has been the stopping point. The servos you can buy are pricey, and pull a good amount of current, reducing battery life.

    dr
     
  9. Nov 12, 2009 #8
    hmm..the servos i can afford just give torque around 16kg/cm. I dont know will that be enough. the wheels each weigh around 300gm (made of metal). so combining with the links etc will increase the total weight! Can this 16kg/cm servo handle this much?
     
  10. Nov 12, 2009 #9

    Mech_Engineer

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    For a BattleBot, zero turning radius is definitely bettwer, otherwise you'll be much easier to pin against a wall or in a corner.

    That being said, for a 40KG bot you probably have room for several pretty big servos, so you could use a 1/4 scale servo like a Hitec HS-805BB which puts out 24.7 kg-cm (343 oz-in) and only costs about $40. Using two of these on a steering linkage would give you a good amount of force for steering. Still, I think your best bet is to just have independent control of the drive wheels on the left and right sides of the bot, and reverse the wheels on one side of the bot if you want to turn.
     
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