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Monday, May 24, 2010

ELB early May

The hubs are the parts that adapt from the axle to the stator. Some people combine the axle and the hub into the same piece (think BWD), but I couldn't do that because longboards have trucks. Trucks are somewhat complicated hunks of metal that allow skate/long/mountain-boards to turn. They also have axles embedded in them meant for non-hub motor wheels, which means I have to have an adapter if I want to use stock trucks. I probably could have made my own, but that would have required a lot of design time and money (large chunks of aluminum are expensive), and I'm a firm believer in "simpler is better" when it comes to engineering. Read the design review for more details on the trucks I used, but for now, here's a picture:

Anyways, back to hubs:

 Front hub design. The rear differs only in length thanks to some stupid brackets welded on the axles I'm using- see the pic of the trucks above.

They are made out of T3-2024 aluminum, which has high shear strength. The hub slips over most of the axle and then threads onto the last half inch. Two grub screws bite into two flat spots ground onto the axle, thus keeping the hub from unscrewing and falling off. The largest diameter surface is a press-fit for the stator, and the groove in that surface is for a rollpin (Ohhh! That's what the round groove in the inner surface of the stators is for...). The thin grooves on the bearing surfaces are for snap rings, i.e. bearing retainers. The four holes that go through the thickest part of the hub are my way of avoiding having to grind a flat spot in the hub under a bearing for wires to route through. The drawback of this plan is that I have to have a massive bearing on the deck-facing side of the motor. Oh well, at least the larger bearing will handle shocks from the horrible Cambridge streets/sidewalks better.

I began by cutting down the stock into pieces slightly longer than the total length of the front hubs. The plan was to make four identical hubs and then cut off some of the end on two of them to make the rear hubs.

 My mess. The second step was to do the boring and threading. Two are finished with that step in this picture.

Mark (the Edgerton Student Shop guy) wanted to use the CNC lathe for the outer surfaces, so I of course agreed (soo much less work and more precise). After about three minutes of CAM, the lathe was ready to go. Check it out:

One of the half finished hubs. S'up Mark.

Four half done! This took maybe 30 minutes. It would have been much quicker if I didn't have to be so careful about not taking too much off of the bearing surface.

Next step was to flip them around and do the other half.

Left: one of the massive 1" x 2" bearings. Top: One hub with the surfaces done.

4 with finished surfaces. You can see the inner threads in this pic.

The next step was cutting snap-ring grooves, one 5/8" and one 1" in each. Mark has an awesome bookcase full of engineering reference guides, and one of them happened to have everything you can imagine about snap-rings in it. He also has some cutting tools specifically designed to cut very very thin grooves.

 So shiny... Note the snap-ring groves.

The next steps were all mill work, and were done later in May.

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