Dec 30, 2018

Mitch's AR2 Build Log

43 comments

Here's the start of my build log - at long last, after having the parts waiting for a very long time!

 

To celebrate, I had the kit parts anodized; I picked them up from the anodizer yesterday, they came out great. I was tempted to pick another color, but the black hides some of the machining marks from the fabricator. I'll print the plastic pieces in green to hopefully give it a cool look.

 

It's still going to be a slow build; FIRST kickoff is next weekend, but hopefully I'll get enough time in over build season to finally get my AR2 up and running!

 

/Mitch.

 

 

 

Anodized parts from the kit

 

Plastic parts will be green PLA

 

 

Dec 30, 2018

Wow that’s going to look awesome. Thanks for posting and keep us updated.

Yeah, I'm very pleased with how it came out. It was a great excuse for me to go meet the andodizers; they sponsor our FIRST team (we anodize most of the robot). Super nice folks, anyone here reading who lives in the SF Bay area I'm happy to refer you to them.

 

I should have started printing the plastic parts sooner, they're bigger than I remembered - the printer will be busy for days :-).

 

My model files do not include the file for "J6 Limit Switch Tip" - is that somewhere?

 

I'll definitely post progress as I get things assembled!

 

/Mitch.

 

I think the color scheme is going to work :-)

 

I have access to a laser cutter, so I might cut the flat covers out of translucent green or solid black 3mm acrylic. Printing a 1/8" thick flat plate's going to take a while compared to the laser...

 

I've got this neat translucent green that will show the mechanisms inside; if that doesn't look good the solid black will go with the anodized material.

 

Onward!

 

/Mitch.

 

 

 

green with black

 

Dec 30, 2018

Hi Mitch the limit switch tip is in the download for AR2 print files on the downloads page. I was just about to reply to your email and I will also attach this file for you.

More printing underway tonight, attempting to print both J5 side spacers at the same time, we'll see what happens.

 

Meanwhile I have cut the flat covers out of acrylic in both translucent green and smoked gray. We'll see how well they work, if they don't flex they won't break, but the holes are so close to the edges that the acrylic might not hold up.

 

I love the translucent green stuff; the photos below don't do it justice but the material seems to pick up just about any ambient light and it glows along the edges. We engrave the sponsor panels on the students' robots with this stuff and sometimes the robot inspectors tell us to turn the sign off :-).

 

I might just use the smoked gray though, it seems to look better than the two tones of green.

 

Once all the 3D printed parts are done I think i'm ready for some real assembly!

 

/Mitch.

 

 

translucent green

 

 

smoked gray

 

 

Edge glow

 

 

Dec 31, 2018

Tough choice, those both look nice. Can’t wait to see it complete.

Hmm. Looks like I won’t be able to heat the material to get the bearings to fit. Heating anodized aluminum will cause the finish to crack since the coating is brittle.

 

Therefore I’m printing a tapered jig to mate with the cup and will attempt to use an arbor press to get it in there. Might still freeze the cup.

 

You say the fit is a light press fit, has anyone used a press or have all used heat and cold?

 

/Mitch.

 

 

Looks like, at least for my aluminum kit, the hole for the cut-off square head M8 screw is not tapped in the J1 Platform part.

 

You might want to check other kits if this is not a known issue.

 

 

Missing tapped hole

 

Happy New Year All!

 

I'm making good progress on my build; after a little research and some experimentation with some other anodized parts, I tried the heat expansion technique. I only raised the housing temperature to 150F and dropped the bearings to 0F in the freezer, and it dropped right in.

 

Therefore: You don't need a huge temperature difference to get the bearings to drop in. No damage to the anodizing.

 

I may need to disassemble partially as my limit switches aren't here yet, but I hope to make significant progress today!

 

 

3D printed arbor to press bearings in; wasn't really needed

 

 

Bearing installation going smoothly

 

 

so cool.

 

Assembly has been smooth so far ....

 

 

Actobotics timing pulley installed

 

 

Starting to look like a robot!

 

The J2 spindle is putting up a fight to get the 30206 bearing onto it. Trying a more extreme temperature difference, but I may need to throw it on the lathe to turn it down a little.

 

Wow, that J2 spindle is a real troublemaker! :-).

 

I turned it down in the lathe, then found out that the non-flange end is not tapped for M3. You might want to check your newest batch to be sure the vendor did not miss it.

 

 

Setup for thinning

 

 

Done, fortunately this will be hidden.

 

 

 

So *that* is why the screws won't go in! :-)

 

Thank you for the heads up. I just went through my stock and all appear to be tapped. Im sorry about the hassle on that. Is there any chance the anodize has filled the threads? I'll send a message to my vendor and make sure this is double checked on the next batch. Build looks great BTW - keep the pictures coming. Its cool to see it come together.

Greetings Chris,

 

It's possible that the anodizing killed the threads, but it didn't affect any of the the other M3s there. Andoizing does add thickness, but a very small amount (under a tenth).

 

I think my J2 spindle is possessed.

 

Looks like I need to take it off *again*. The bore for the motor isn't big enough for the stepper shaft. I could probably "force" it but I won't. Given all the things wrong with this one part, I am wondering if I got a bad one.

 

So, J2 spindle is headed for the lathe again, I hope I have a boring bar long enough to get in there from the flanged end, since that'll hold more true in the lathe chuck.

 

So for J2 spindle I've had to : turn down the OD, tap the holes, and now turn the ID for the motor shaft.

 

I might need to pick it up in the morning. Since I took the little powder coat oven out to heat the bearings, it's a good opportunity to powder coat the guitar pedal my son built while home from school.

 

/Mitch.

 

Final status report for New Year's day:

 

I believe I have finally won my battle with J2 Spindle, I was able to get it mounted on the lathe and centered well enough to bore a little out of the inside, now the stepper shaft has a nice snug fit.

 

When installed, however, the J2 motor needs five washers, not three, to keep far enough away from the J2 gusset for the set srews to clear the motor. No biggie, I have lots of M4 hardware. Swapped the silver nuts for black ones while I was at it.

 

Photos below.

 

/Mitch.

 

 

progress !

 

 

progress !

 

 

need 5 washers for proper spacing.

 

 

set srews now just clear the motor

 

 

Jan 2

The anodising looks great. How much did it set you back?

Here in the Silcon Valley (South SF Bay) I paid $120 to have 24 pieces anodized. It was the minimum charge from the vendor, mostly to cover the setup costs. Relative to the rest of the robot's cost, it didn't seem like a big number. I'm very happy with how it came out.

 

I asked the vendor to be the absolute last priority, schedule me when they could, and I chose black, a color that they always have ready. Given how close to Christmas I sent the parts, they got to it within a week.

 

If you do anodize, defintiely choose a dark, opaque color like black. The kit parts are all machined a little differently, and there are witness marks from the tooling everywhere that you can see through the anodizing. I had to reassure the vendor that I'd be pleased with the results :-).

 

I colored only the parts that would be visibile from the outside, so some of the tiny ones didn't get anodized.

 

Clean the parts thoroughly with acetone or mineral spirits before you drop them off.

 

It should go without saying that best practice is to be nice to your vendor, especially if they're used to much larger jobs. Very often these people make thousands of the same part, so when you show up with 24 unique pieces they will need to track them carefully not to lose any.

 

Anodizers have other metal finishing services as well; I could have had the parts bead blasted first, which would have removed the witness lines,

 

/Mitch.

 

Jan 7

Thanks for the feedback Mitch. $120 is extremely reasonable espicially considering how well it turned out. If I build another robot I will for sure anodize it.

Couple of things for the next manual update:

 

- (pg47) : My keyed shaft is 50.24mm long, so it is a little hard to cut down to 53mm. I think that I'm ok with it, seeing how it is used I think the missing 2.75mm should not present an assembly issue.

 

- (pp45-45): My kit shipped with two different sprockets, with two different bores (same # of teeth though). I'm not sure I need to modify one of them, will know when I get there :-).

 

I have a #25 chain breaker/assembler; it should be close enough to the 6mm chain that I can use it to make the chain loop without needing the master link.

 

 

Thank you, I apologize - I do need to update the manual. I did shorten the length to 50mm as this is a standard length I can split shafts into and there was no need for the 53 - its just what I ended up with when I made the first one.

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