Loading ...
Sorry, an error occurred while loading the content.

Re: [SeattleRobotics] Problems in Timing Belt drive system in 6WD robot

Expand Messages
  • twcarroll@...
    Alan, Ackermann steering will be a bear to implement with your present arrangement. The model race cars and off road car people use Ackermann steering as
    Message 1 of 41 , Jan 25, 2013
    • 0 Attachment
      Alan,
           Ackermann steering will be a bear to implement with your present arrangement.  The model race cars and off road car people use Ackermann steering as they use an entirely different way to steer.  The R/C transmitter has a twist knob to do the steering.  As a judge at our Seattle Robotics Society's RoboMagellan contest at Robothon, I've seen many Ackermann steered robots in the competition.  The geometry and motor driving is different from Differential steering, that's all.  I've also seen many six wheel robots in these contests, also.
           Just for the heck of it,- try removing the two center wheels and see if it stops the tooth-jumping action.
           Good Luck,
           Tom
      Hi Tom,

      Yeah, I was just considering "lightening" the springs on the center two
      wheels in the last post.  Maybe removing them as you suggest is a good
      temporary solution as well.  But after seeing DPA's 'bot doing its
      stuff, I really want my "HexaTraxx Moose" to be able to do the same!

      Does anyone see a difference between my 'bot and DPA's 'bot?  Besides
      the WHEELS.  I followed all is pictures...

      Yes, that's exactly what I'm seeing and the reason for the slipping
      belts.  Even 'tho my belts are 037 (3/8" width) and DPA's look like 1/4"
      width!

      Ackerman steering is quite interesting.  I've got Traxxas steering gear
      that could be added to both the front an the back (4W steering!),
      although adding it to my chassis (12" wide inside suspension, 20"
      outside wheels) would be quite a bit of work, even with the parts, as
      the width is different (longer tie-rod, mounting servo and two bearing
      posts).

      Is it ALL because of the TIRES?

      Alan KM6VV

      On 1/25/2013 2:02 PM, twcarroll@... wrote:
      >
      >
      > Just as Robert mentioned, looking at the photograph, it looks as if
      > you're using three solid shafts with the toothed pulley / wheels freely
      > spinning on each, and no differential.  6-wheeled robots have a problem
      > with this arrangement.  During turns, the robots basically tries to turn
      > around a point in the center.  The two center wheels turn the slowest
      > during turns, whereas the four end wheels are turning faster as they are
      > further away from the center of the turn.  If they are digging in the
      > grass or pavement, the force on the shaft and pulley is enough of a
      > difference between front and middle to cause the belt to slip off the
      > pulley a few notches or more.
      > Quite frankly, if you're 'under the gun' to get the robot completed in
      > time for the RoboMagellan contest, I'd remove the center wheels
      > entirely.  You're really not going to gain enough in traction with 6
      > wheels over 4 wheels to make any difference at all in the contest.
      > Ackermann steering is the best for this type of robot but that requires
      > a whole new set-up in your steering and control.  Six wheels look 'cool'
      > but are best used with differentials in the sets of wheels. Differential
      > steering, or as some say- "skid steering," with more than 2 wheels eats
      > up a lot of power when making turns.   That's why it is called skid
      > steering.  You'll never see a car with this type.
      > Good Luck,
      > Tom C.
      >


      ------------------------------------

      Visit the SRS Website at http://www.seattlerobotics.orgYahoo! Groups Links

      <*> To visit your group on the web, go to:
          http://groups.yahoo.com/group/SeattleRobotics/

      <*> Your email settings:
          Individual Email | Traditional

      <*> To change settings online go to:
          http://groups.yahoo.com/group/SeattleRobotics/join
          (Yahoo! ID required)

      <*> To change settings via email:
          SeattleRobotics-digest@yahoogroups.com
          SeattleRobotics-fullfeatured@yahoogroups.com

      <*> To unsubscribe from this group, send an email to:
          SeattleRobotics-unsubscribe@yahoogroups.com

      <*> Your use of Yahoo! Groups is subject to:
          http://docs.yahoo.com/info/terms/

    • KM6VV
      David, Thanks. I m still not finding the exact motor, http://electromate.com/db_support/downloads/PittmanExpress2011Catalog.pdf but I get the idea. 45 oz-in
      Message 41 of 41 , Jan 26, 2013
      • 0 Attachment
        David,

        Thanks. I'm still not finding the exact motor,

        http://electromate.com/db_support/downloads/PittmanExpress2011Catalog.pdf

        but I get the idea. 45 oz-in 142 RPM ??

        my 10 kgf-cm = 138.873866 oz-in. So maybe I've just got too much
        torque? I like my ground speed so far, should be 6-7 MPH with the
        1:1.533 gears I have. 1:1 gears would give me about 4.5 MPH.

        Alan KM6VV


        On 1/26/2013 4:13 PM, dpa_io wrote:
        >
        >
        >
        > Alan, yes motors are 24 volt Pittman GM9413J820 (or something like that) with 20:1 gear reduction and 500 CPR encoder.

        Drive pulley is 15 tooth and main pulley 30 tooth.
        >
        >
      Your message has been successfully submitted and would be delivered to recipients shortly.