The Big Think

December 21, 2015

R2 Update

Filed under: The R2 Project — jasony @ 7:57 pm

More work on the R2 front. A lot more since my last update. The frame is pretty much finished except for the laser etching (which I’m still contemplating and, actually, reconsidering). So I’ve moved on to R2’s leg assemblies I have put a total of 43.5 hours of work into them so far (not counting stare-at-the-wall-and-think time).

Here’s what I’m trying to make this year.

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and is comprised of these sub-assemblies (including the feet and battery boxes as well as some other details). I’ll need to make two of these and a shorter center leg.

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The entire leg assembly has 30+ individual parts. I have to make a left leg and a mirrored right leg (as well as a less complex center leg). The part I’m working on right now is the “inside” main frame assembly of the leg that supports everything else. It’s made up of a top plate, bottom plate, four side “walls”, a curved top piece, and couple of bottom pockets that hold the side details (which I also have to make). Here is the basic structure

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I designed the files in Fusion 360 and exported them as .ord files to set up on the water jet.

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I took one of the two plates of 1/4″ aluminum I got for free from the anodizers (yes, they gave me about $150 in aluminum after I paid them the extremely low rate of $70 to anodize the frame (should have been $500 but they were jazzed about it being R2) and carefully positioned it on the water jet. I had to be really careful since all of the holes in the plate made it difficult to work around. In the end it took me almost an hour to get things lined up correctly.

Then I discovered that the water jet is misaligned. Whoops.

It’s actually a pretty big discovery at the shop and solves several mysteries around there. Turns out the underwater bed of the machine is off in the Y axis about 1/2″ over the 6′ front-to-back span. Seeing how the water jet has to be focussed about 1/8″ above the bed with a tolerance of around 1/16″, this was obviously not going to work. So I tore down my assembly and rotated everything 90 degrees, thus minimizing the error. I also had to regenerate a brand new water jet file. All told, I took about 2.5 hours on what should have been a 30 minute setup.

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After doing a dry run to make absolutely sure everything worked, I held my breath, started up the machine, and hit “execute”.

Here are a few videos of the machine in operation. It may be a costly beast, but what it can do in a very short period of time is just amazing. I really couldn’t do this without spending weeks in the machine shop, and even then I might get it wrong with my level of skill. The water jet is truly amazing.

23 minutes later I had one of the legs! Success!

Here’s a shot of the final plate with the legs cut out (after I washed it off with some water):

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Or… so I thought at the time.

Since everything was already set up and looked correct I went ahead and plopped the other plate down on the machine, calibrated and clamped it down, and cut a second set of leg plates. The pump mysteriously shut down halfway through (we think that the switch has a short in it) but a quick restart and I was back in business. Total cut time was just over 47 minutes. *whew*!

Unfortunately, upon my test assembly I realized that I had used the *wrong file* and my ‘side-wall’ rectangular pieces were cut .25″ too wide! This was a much better mistake than cutting them too short however, since I needed to mill off the taper that is introduced by the water jet anyway. Well, I thought it wasn’t going to be too big of a deal. I went back into Techshop early this morning and ended up spending about 8 hours in the shop slowly milling off that extra .25″ of width. So yeah…. lots of labor to correct a silly mistake, but ultimately I got some good manual mill practice as well as some really nicely made parts. I’m very happy with the way things are shaping up.

The next step is to decide how I’m going to make the top curved piece of the legs. I’m probably going to water jet that as well (to a man that has only a hammer, every problem….). I’ll have to come up with a 1.25″ thick piece of aluminum that’s big enough for the 6″ wide piece. It’ll be a chunk of change but I might be able to find it in the drop bin at the metal place (sold by the pound). Cutting something that will be a beast, too, but it’s the only way I can figure now.

Speaking of which, I spoke to the machining instructor, Jack Withers, at Techshop about the leg “horseshoes”:

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I’ve been through three or four ideas about how to make these but the best idea I’ve come up with is to make the 1/8″ slices on the water jet (yeah, yeah) due to the fact that the inside of the hub has those offset gear pieces. My concern is that the outside of the horseshoe will show those “bread slices” through the paint. But I think that if I lay down a coat of lab metal and then wet sand (and sand, and sand) then I should be able to cover up the slices.

Of course, doing it this way means that I have to drill and tap holes so that I can screw the slices together from the backside. But…. of course… the vice in the machine shop is 1/8″ too narrow for the horseshoes. So. I’ll have to disassemble the vice and figure out some way to make it slightly bigger in order to accommodate the wider stock. Always an adventure.

But that’s for later. Now I need to spend several weeks thinking about the leg assembly. There’s an interesting inside piece that you can just barely see that looks like this:

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How in the world am I going to make this? No idea yet…

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