Onyx X build thread

[jwatte]

The upcoming Robogames kicked me in the butt enough to dust off my Onyx X plans.
You may recall, I was too busy with the robomagellan last year, and couldn't get Onyx in shape.
This time, I'm prioritizing the other way around -- magellan is standing aside, and I'll re-build Onyx based on learnings from before.

I have a bunch of interesting things I'd like to try, from "stabilized turret based on belts and brushless motors" to "on-board aim assist with Raspberry Pi," but in order to make it to this year, I've decided to hold myself to the simplest possible scheme.

Main problems to solve:
1. read-back of stats over XBee just doesn't work -- it is so slow turning around the on-air interface
2. the frame was really narrow and couldn't fit the target plates. This was great for maneuverability.
3. also, the frame took a bad fall, and is a bit twisted
4. the 5 GHz video would fade in and out, and all monitors I have at home cut out when sync isn't perfect
5. the head/turret would shake around more than I like when walking -- it was fairly top heavy
6. screws would come lose and be left on the floor all over when walking too fast
7. various bits (including the camera lens!) shattered from the airsoft pellets

Planned solutions:
1. I will build just a forward control this time, and if I have time left over, send read-back using another mechanism (second Xbee, WiFi, etc) Keep It Simple Stupid!
2. I can spare an extra inch in width/height to put the plates on the body.
3. I'll have to build a new frame to solve the space problem, so Tormach mill, here I come!
4. I'll throw money at this problem and buy a drone-approved video display that presumably doesn't lose composite sync from noise
5. Moving the plates off the turret will help. Also, while two guns looks awesome, I'll go for a single gun this time.
6. Threadlocker, every screw, every time. There is no such thing as "just testing and I'll do it better later" -- do it as if it's final every time.
7. Delrin is easily laser-cuttable, and can also be heat-strip-bent in a pinch. 1/32in delrin sheet is cheap and doesn't weigh too much. I'll build a shell of Delrin, and then add some 1/32 transparent polycarbonate around the bits that need visibility (camera, indicator LEDs)

Also, the previous body was smaller, and needed the turret heading servo to be mounted on top of the top plate, which meant the turret was high up, contributing to the jittery balance. This new body puts the servo in the same plane as the hip heading servos, inside the body. This leads to a lower center of gravity.
If I have time, I may build the infrastructure to support the turret with an external thrust bearing, but for now, the thrust washer on the heading servo will have to take the load. Because the servo is advanced from center of body, this means it may take some radial load, which is not great. Or I'll move center of gravity forward, and adjust the gait to compensate.

I'm thinking I'll post pictures here as things develop, to keep me honest and on-track. If anyone actually bothers reading and sees me deviating from the KISS principle, a swift kick would be much appreciated!

[jwatte]

First pictures:

I've used to use Inventor for my mechanical drawing, but was recently turned on to Fusion 360.
I tried an early version many years ago, and didn't like it, but Ah-mah-gerd! It's great now!
Integrated CAM, straightforward simulation set-up, sketch mode flows smoother than Inventor, and yet it seems to share a lot of genes with it. Oh, and it's free. What's not to like?







You may be able to see that there's a version of the tibia that bolts one slot (22 mm) higher up on the knee servo.
In that configuration, the toe of the tibia is higher up than the hip elevation joint. This means there would be a minimum distance away from the mech that I could touch down, and the femurs would have to splay out a lot when getting really close.
However, that mechanism may actually end up being more nimble in actual walking -- we'll see.

And how do I make the pictures be appropriately wide for the post? Right now you see the left half of each picture ...

[GhengisDhon]

http://rteamrobotics.weebly.com/

Looking good.

Looks like you have a lot to do. Let us know if there is anything we can do to help... even if its just moral support.

[jwatte]

Moral support would be great :-)

Machining very thin, large objects is hard for me -- about 6 inches is the max size, and the new plates are more like 8x8.
I'm thinking of sending them off to Big Blue Saw. Or maybe I'll just use 3/32" Delrin for those plates off the laser...
(I tried using the waterjet at Tech Shop, but the aluminum sheet I have "bubbles" during pierce-through; looks like de-lamination.)

The other thing I'd love to have is better situational awareness. At least distance sensors for either each of the sides, or each of the legs, so I know if I'm trying to walk into a building sideways.
But, that both requires a working telemetry system, AND additional parts to integrate. Firm NO on that!

[Zenta]

Looking good!

[tician]

Attempted last night to get a kogeto dot to also provide an image in the unused center of the optical assembly, but did not know enough about its construction to get it working quite right. With some corrections, I hope it will be possible to add an external flat mirror above the center to get a plain directional view in the center of the panoramic view. If not, I might try making a simpler (3D printed?) version with only a single top-mounted convex mirror for downward looking panoramic view (very good view of robot) and a single flat mirror above the hole in the center of the convex mirror.

Have not chopped the optics in half (cross-sectioned) to be absolutely certain, but it appears to be a single injection molded assembly with two molded plated/silvered rear-surface mirrors and a large molded lens that forms the dome of the assembly. The larger mirror is concave and nearest the final corrective lenslet. The smaller mirror is convex and in a crater at the top of the large dome lens. So quite certain that the rays go through the lens to the larger concave mirror on the opposite side then reflect to the smaller convex mirror then reflect through the un-silvered center of the larger concave mirror to the lenslet that mates to the larger molded optical assembly.

The internal thread of the protective housing not only connects the housing to the phone bracket but also holds in the retaining plate for the actual optics, so you can just unscrew the plate instead of breaking apart the protective housing like I did. After disassembly, I removed a small circle (~2mm) of the mirror plating from the center of top dome. I went too deep with a plain drill bit hoping the optics were hollow and I would simply end up with a hole in a mirror surrounded by air, so I absolutely have to clean, polish, and backfill the hole with some sort of resin to restore the full vertical range of the panoramic view and then try to make that resin form the final corrective lens in the recess of the convex top mirror. Also have to repair some of the larger concave mirror that lost its silver, so might just try again with a new kogeto dot.

If you can produce a sufficiently polished surface with the cutting tool, then it should only need a small lenslet for final correction. I'm thinking a much better solution is to simply get a de-silvering agent to easily remove a small patch from the center of the top mirror and avoid the need to perform any surface polishing (if actual silver coating or if aluminum coating).

[jwatte]

I think you'd need some lapping and/or polishing to get good enough surface. Raw machining doesn't do it. (Well, unless you have a super nice face mill and only need it to be flat.)

Separately: I was going to build the host board for the OpenCM (so I don't have 10 little boards for hosting power / Xbee / voltage conversion / etc) and looked to re-install the Eagle I have paid for. But now, Autodesk owns it, and charges $500/year for the ability to make 4 layer boards. And killed the Maker version. So, KiCad, here I come! (one yak already! eek!)

[jwatte]

I have some time on the mill later today, to bang out the femur brackets. (8 total; two per leg)

I realize that the femurs might make the legs more rigid if I use some kind of connection between the two sides, but with the necessary clearances for full movement, there's not a great way of achieving that.

Also, the femurs in the picture above are 140 mm center-to-center. The ones I used on Onyx 3 were 80 mm, and I think those were too small -- the servos can lift more, and I can get some more speed out of them with a longer femur.
However, 140 mm seemed too much when doing some calculations on the IK and reach, so I decided to split the difference, and make them 110 mm for this go-around. Assuming the brackets come out usable today, I will be using them in April; no time to change too much!

I make these out of 1-1/4"x1/8" 6061 aluminum bar, which is almost the perfect size already. I'm planning to skim 0.08" from top and bottom to get a good finish (assuming it's flat enough!) for a total thickness of 3mm. This is thicker than I used before, but static simulation says a thinner femur will reach cracking strain if loaded by 6 kG alone. That's unlikely to actually happen on this bot, but I like safety margins. The thinning slots in the femur remove weight, at least!

I will have to make the outer servo connect to the tibia at 90 degrees to make sure I have clearance to move the femur straight up. I already did that for the 80mm version, so that's OK.
I may experiment with making the bottom servo also stick out at 90 degrees. The 80mm version had it in the upside-down position as in the picture above, and that works OK, but maybe I'll try putting that at 90 degrees, too. The Robotis C-bracket driven by the hip heading servo is already adding radius from the hip, though, so that extra inch may be a bit much, especially given that the body is now wider as well. We'll see!

[tician]

Could add some reinforcements to opposite sides of the femur (a little bit of C-channel on the body-side on top by 'knee' pitch and foot-side on bottom by 'hip' pitch) as long as they are able clear the edges of the servos when fully retracted. Basically a tube with multiple cutouts for clearing the servos when the leg is fully retracted, like some of the leg frames of the DARwIn-OP.

[jwatte]

Yes, I've looked at that. Ideally, I find some pre-made U or rectangular extruded channel/tubing that can be milled to the dimensions needed.
47mm inner distance only gives 1.9mm each side if I make it out of 2" tubing, and the next step up is 2-1/2" and that doesn't come in thick enough walls, so then I'm looking at milling out of solid stock, which seems very wasteful.

And 2"x1/16" rectangular tubing is almost a millimeter too wide on the inside :-(
https://www.onlinemetals.com/merchan...270&top_cat=60
It's cheap enough that maybe I should get some to try out, though?