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I'm using wheels from McMaster-Carr.
Their are two types, both are Thin-Tread Mold-on Rubber. The wheel itself
is cast aluminum, with a rubber tread, and includes roller bearings. Their
are 8 total, all 6" diameter. 4 are 1 1/2" wide (#2354T32), 4
are 2" wide (#2354T34).
The rubber on these is pretty grippy, with a durometer hardness of 70. |
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I'm linking these directly to
the axle shaft, so roller bearings won't work. I used a piece of wood to
knock the bearings out of the wheels. The diameter of the aluminum hub
itself is approximately 1 3/16". |
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Here is the wheel separate from
the bearings. The bearings use a plastic housing with stainless steel
rollers. A split blue-steel sheath surrounds the bearing, and washer-like
caps are on each end. |
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Their is way more aluminum here
than I need, so I'm removing some. I created a template to remove six 1
1/4" diameter holes. |
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I don't have any fancy milling
tools, so I clamped the wheel on the 12" drill press and used a 1
1/4" hole saw. The teeth would clog up occasionally, so I would stop
and knock the build-up off with a hammer and screwdriver. |
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The first hole usually wasn't to
bad, but as the aluminum heats up, it got more difficult. I would usually
only do two or three holes before the wheel go to hot to handle and I'd
have to set it aside. The drill motor would get pretty hot also (started
smoking the first time I tried to do about ten holes in a row), so I ended
up doing two at a time, and finding something else to work on. |
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Don't know why I didn't think of
this, but my friend Bryan mentioned I should be using oil when I'm drilling
metal. I had already bought an oil can for drilling steel, just never
thought to use it with the aluminum. I tried it and it made a huge
difference. Much less heat, cut much faster, teeth didn't clog up. I was
able to knock out all the rest of the holes in less than an hour. |
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Here's one of the wheels with
all 6 holes removed. I figure I saved about 2 pounds total removing the
holes from all eight wheels. |
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The wheels are listed as either
1 1/2" wide, or 2" wide. As you can sort of see in this picture,
the aluminum rim is that wide, but the tread is actually narrower since
the rubber tapers down. Since size and weight counts here, I'm getting rid
of anything extra. |
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I used a utility knife to trim
off the tapered area of the rubber. Hard to see here, but now all the rubber is the width of the tread, with the aluminum rim almost
1/8" wider on each side. |
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I used an angle grinder to
remove the extra rim material. I also ground the hub in the center down to
the same width. |
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I used a file to level
everything out and smooth it down. |
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Hard to tell in this picture,
but here it is with the extra material removed. I'd guess doing this
on all the wheels saved around one pound. |
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Here's another view. You can
kind of tell if you compare to the two other pictures that the taper is
gone. This will also allow the wheels to fit closer together, allowing a
narrower bot, with less gaps for debris to get caught in. The 1
1/2" wheels weight 20oz each, the 2" wheels weight 24oz each. |
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The next step is to provide a
link between the motors and the wheels. I'm using McMaster-Carr sprockets
for this, which will have their hubs inserted into the hubs of the wheels,
with the sprocket portion protruding from each side. These are 3/4" bore, 1 1/16" hub, 3/4" wide, 1.5" OD, 11 teeth, steel
(#6280K113). |
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If you're on the ball, you might
notice that the ID of the wheel hub is 1 3/16", and the OD of
the sprocket hub is 1 1/16". Couldn't find a sprocket the exact size
I needed, so I'm trying something that feels a little half-ass, but what
the hell. Many of you are familiar with JB-Weld, well McMaster-Carr has
something similar, using aluminum instead of steel, in larger tubes
(#74575A93). |
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Here's the missing link. 1 roll
of .051" diameter copper wire. This will take up most of the extra
space between the wheel hub and the sprocket hub. |
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I wrapped the copper wire around
a wooden dowel a little smaller than the ID of the wheel hub. |
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Here is the copper coil removed
from the dowel. |
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I clamped one of my 3/4"
steel keyed shafts into the vice, and slid (hammered actually) one of the
sprockets onto the shaft (with the key in place). |
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Mixed up some of the Aluminum
Paste Epoxy, about two inches from each tube. |
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Smeared the epoxy on the hub of
the sprocket. Note that I did rough up the hub with sandpaper first to get
the best bite I could. |
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Smeared the epoxy on the inside
of the wheel hub as well. |
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Inserted the copper coil into
the wheel hub, and smeared it with epoxy (not as easy as it sounds). |
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Slid the wheel over the bottom
sprocket on the shaft, then smeared the upper sprocket hub with epoxy and
slid it on the shaft. |
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Used wooden spacers to keep the
proper distance between the wheel and the sprocket, and try to keep
everything in the same plane. |
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Here's the wheel after the epoxy hardens, and
the spacers have been removed. |
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Some epoxy needs to be cleaned up from the
hubs of the wheel and the sprocket. I used a chisel to break epoxy from
the steel sprocket, and a file to remove the extra from the aluminum wheel
hub. |
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The wheel after having the epoxy cleaned from
the hub. |
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The four driven wheels after cleaning up. |
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To help strengthen the wheels, and guard
against the epoxy breaking, I'm inserting a metal pin. I drilled through
the set-screw hole in the sprocket and into the aluminum hub of the wheel. |
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Here's the pin, a nail hammered into the
hole. I then cut the nail off with a jig saw, and filed the pin smooth. |
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The 4 2" wide wheels are being attached
to each other in pairs. the same epoxy mixture I used earlier is applied
to the aluminum hubs and rims of the wheels |
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The wheels are pressed together and zip ties
are used to hold them together. |
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The wheels after assembly. The zip ties will
remain as a backup in case the epoxy fails. |
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I'm using the same sprockets I used for the 1
1/2" wheels as the fill in the hubs. |
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I put the sprockets onto a shaft... |
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and using one of my favorite tools, the reciprocating
saw... |
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Cut the sprocket part from the hub. |
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Using the same techniques as above, I created
copper coils to use as filler. |
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I placed the steel hubs onto the axle at the
correct distance apart. |
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I coated the hubs with the same epoxy used
above. Slid the copper coils onto the hubs, and again coated them with
epoxy. |
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The trick is getting sliding the wheel over
all this. Their is little room to spare, so it takes a bit of coercing, as
you can tell by the epoxy all over everything. |
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After the epoxy hardens, I knocked the shaft
out with a hammer, and cleaned the hub up with a file. I strengthened
these with a steel pin, as I did with the 1 1/2" wheels. |
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Here's the completed wheels after sanding the
epoxy off the rubber with some 120 grit sandpaper. |
