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