Subject:
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Caster Substitute
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 7 Feb 1996 16:03:48 GMT
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Original-From:
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John Piccirillo <jpicciri@nebula.%stopspammers%tbe.com>
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Viewed:
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2323 times
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While there is some discussion on robot bases, let me add a bit about the
"third wheel", usually a caster, used on differential drive systems.
Casters have the advantage that they are plentiful, cheap, and come in lots
of sizes and configurations. They have the disadvantage that they exert a
sideways torque when the platform turns, bad for dead-reckoning and takes
needs more clearance on the undercarriage to operate. I have used two
substitutes successfully. The idea was to use a ball that would roll in any
direction. At first I used the ball from a roll-on deodorant applicator.
These are about 3/4" to 1" in diameter. I cut off the body, cleaned it out
and found that the top portion could be mounted by using a 1 1/4" hole saw
to cut an annulus in the wood mounting stem. I hot-glued it in. It worked
fine but was a little "draggy" since the plastic parts weren't polished nor
could be lubricated without making a mess on the traveled surface. Next I
ordered a ball bearing mounted "roller ball" (called a ball transfer
conveyor) that is used for material handling, i.e. a large array of these is
used to side boxes over (UPS uses them for instance). These balls were also
about 3/4" in diameter. They come with both flange and stud mountings.
They are made of steel, can support 60 lbs and are relatively heavy, about a
1/4 to 1/3 lb. However, they also come made of nylon (support 20 lb. -
flange mounting only) for the food handling industry. I couldn't find a
source to buy these individually, so I bought a small "drop in plate" that
had six mounted on a steel frame for about $ 35 from Grainger. The flange
mounted are about $ 3 apiece, the nylon about $ 7 apiece.
I hope this helps.
John-
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