Procurement

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The hardware haul from The Yard. Not bad for an hour of digging. Total cost was $52.

To kick off this Labor Day weekend I did some shopping. Wichita has a cool little place aptly named The Yard, which sells everything from screws, casters, foam, you name it. And because most of it is surplus, the prices are great, too.

When I design things, I start out planning to source everything new, and I record the price of every component I call out on the design. This information was immensely helpful as I dug through bins of screws. I had a price to beat on every component I was shopping for.

And as usual, The Yard came through. For example, a 5in long socket head cap screw, 5/8-11 thread was $5.80 through McMaster. The same screw at The Yard was $1.99. I found some 5/8-11 lock nuts for $0.68 a piece. McMaster quoted me $0.92 a piece. This was typical of all the hardware I was able to find there. Shopping at The Yard also saves me shipping, a cost I’d incur buying through McMaster or some other online source.

The Yard even cut some 3/16 chain for me. They charged me for two feet at a total cost of $2.50. I even got to keep the extra links. Not too shabby!

Those pennies add up. There are some components I’m going to have to shell out a lot of money for, like the hubs for my drive wheels. The bad boys below cost just shy of $50 a piece, and after shipping it was $120 to get them.

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The drive wheel hubs. Finding one with a 17mm ID shaft with a 2.75in bolt circle was not easy.

Harbor Freight had a sale on their cheap 10in diameter wheels, and I picked up four of them for $3.99. However, I think Harbor Freight is always having a sale on those tires. Their regular price is still dirt cheap.

Each tire comes with two hub pieces. One hub piece has two flanged bearings pressed into it, the other has no bearings. You can see the two hub pieces from one tire in the picture below.

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The wheels disassembled. Deflating them makes disassembly easier.

I took two hub pieces with no bearings in them and made a “drive wheel” tire. I took the remaining two hub pieces with the bearings in them and popped one of the two bearings out. You don’t need a total of four bearings for one tire, and I have plans for these extra bearings.

I had to drill a hole in the hub piece with the bearings so the nipple on the innertube had a place to protrude from. You can see the hole in the hub without the bearings in the picture above.

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I had to drill a hole in the hub piece with the bearings in it. This was my first time using the new drill press! 

After I drilled the holes and put the wheels back together I had a pair of “caster wheels”, a pair of “drive wheels”, and four extra flange bearings. I had to bend the innertube nipple on the caster wheels to get a bicycle hand pump on the nipple so I could inflate them.

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The “caster wheels” are the two at top. The “drive wheels” are the two at bottom.

The four extra flange bearings are going to be used to mount the stem of the casters into.

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The mounting method for the casters. The extra flange bearings get used here.

The Yard also has a vast selection of steel and aluminum raw stock. They didn’t have the 2in X 2in X 0.25in square aluminum tube I was after, but they did have some 2in X 2in X 0.1875in square tube. I think this will be easier to weld to 0.125in thick aluminum sheet metal anyway, so I had them cut several sticks for me.

My only complaint about The Yard is that they won’t do angle cuts for me. I’m either going to have to get my miter box and hack saw out, or find someone with a nice band saw to get them cut.

Overall, I think this is a good start to getting the prototype robot lawn mower fabricated.

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