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Re: [HBRobotics] RE: #25 chain and sprockets

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  • KM6VV
    I did open up the files below. Thanks again for the link. I have independent suspension on all six wheels, so I m probably prevented from using a bow-tie. I
    Message 1 of 1 , Jul 27, 2013
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      I did open up the files below. Thanks again for the link.

      I have independent suspension on all six wheels, so I'm probably
      prevented from using a bow-tie. I do have two spans of timing belt
      between my three axles, but I drive the left side wheels from the front
      end of the timing belt chain, and the right from the rear. Not quite a
      bow-tie. Each wheel has a U-jointed drive shaft running from the timing
      belt chain down to the wheel.

      Ethel looks quite stout! A little more room and flexibility. I'm
      hampered with the spacing of the timing belt pulleys, motors and all
      that. Even the 24 V battery had to be split up and sandwiched between
      the timing belt runs.

      My HexaTraxx Moose seems quite stable, and can climb stairs; although I
      reluctant to try it much until I've been able to thoroughly check out
      the drive, and maybe compete in a Robomagellan!

      Yes, drive trains and their study are quite interesting! But I need to
      get on with the electronics, computers and software!

      Anybody ever compare a #25 chain against an XL .375 drive? I guess I'll
      get a chance to see.

      I've been putting off buying another set of wheels and tires; but that's
      probably the next step.

      Alan KM6VV

      On 7/27/2013 4:54 PM, Steven Nelson wrote:
      > On the Bobcat page you can view the pdf files farther down the page for
      > free. Also on a true Bobcat there are no master links in the chain and
      > there is no adjustment. The chains are pre-stressed and are also in an
      > oil bath. For my robot drive trains I just use slots in the bearing
      > mounting brackets on the axles to adjust the chain and of course a good
      > chain lube. I always allow for 1-2 chain links of stretch. I have often
      > seen about 3/4 of chain link stretch after testing and definitely after
      > heavy abuse in combat after that they pretty much settle down. On a 6wd
      > like (Sewer Snake) Matt uses the Jack shaft to support the center tire
      > and wheel and also uses that shaft to drive the other two wheels in the
      > Bow Tie configuration. Although he has tried a couple of other
      > configurations from time to time. One thing I did discover is the Bobcat
      > tread width center to center VS axle shaft center to center ratio is
      > usually 1.34 to 1 or so. This is a good ratio for both quick turning and
      > fore/aft stability. It's a very good starting place for 4wd skid
      > steer. When I built Ethel I took her to 1.7 to one and she is less
      > stable in fore and aft motion than what I used in several combat robots.
      > She tends to rock so I added wheelie bars for safety and to prevent face
      > planting. If you use a ratio of like 1.2-1 or less on 4wd they don't
      > turn as quick although some folks like the stability but they sacrifice
      > turning. I've measured a lot of combat robots in the pits and have
      > driven or watched them drive and after awhile I could tell how a robot
      > will perform just by looking at this ratio. Another trick that some have
      > used on 6wd is to over inflate the center tires with few extra lbs of
      > air or to mount the center axles 1/16 in to 1/8 inch lower to aid in
      > skid steer turning on hard surfaces. That helps a bit at least when
      > using a non active or solid axle mount. Drive trains are an endless
      > journey into the realm of Trial and Terror...
      > http://www.teamkiss.com/etheltherobot/etheltherobot.html
      >
      >
      >
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