Dyne's LD-F1 (D-O concept) build

[Dyne]

T-Minus 2 weeks (Yikes)

Between last Monday's countdown post and last Thursday, I ...

• Printed the front body shell of the droid, as previously mentioned
  
• Did a lot of chassis design
  
• Finished adding the various pivot points to the rear body shell
  
• Changed the electronics arrangement
  
• Printed replacements for the red 42T and 60T HTD belts that I'd previously been using.  The new ones are 40T and 58T respectively.  This is to help with tensioning, as the old ones were a little too loose.  They seem like they'll work, but I also printed 41T and 59T belts in case I need a size in between.  I really should design motor sprockets and intermediate sprockets with more teeth so they mesh with the belts better (10 is a bit too few), but that'd alter the gear ratio of the drive.
  
• Printed 12 TPU traction pads
  
• Printed 11 of 94 PETG traction pads
  

When deciding how many TPU pads to print, I also had to decide how to arrange them.  My tracks have 53 links each, each link with room for a single traction pad to be attached.  Making the tracks somewhat consistent in both the amount of friction and in the appearance would be ideal, so I wanted to work it out so the TPU traction pads are relatively evenly spaced. The extra friction of a single TPU pad compared to PETG isn't HUGE, but it is noticeable.  They also differ in color from the more metallic PETG pads (Silver PETG), though oddly they are a very close match to the color of the track links (Silver PLA).  

Unfortunately, 53 is a prime number, so the only factors are 1 and 53.  I'll have to settle for a varying pattern.

For example, I could start off treating each track as having 52 links to get better factors to split the track up into segments with, and then put the single leftover link somewhere in one of them.  The factors of 52 are 1, 2, 4, 13, 26, and 52.  I'll ignore the option of 1 or 2 (too few TPU pads), and 13, 26 or 52 (more than I want).  If I went with 4 pads per track, they could be spaced as follows (each "1" being a TPU pad, and the other numbers being PETG): 1, 12, 1, 12, 1, 12, 1, 13.

By coincidence, the contact surface of the track is more or less 13 pads long.  That means the above pattern would have a point in every rotation where there are briefly zero TPU pads on the ground.  This could lead to inconsistent traction.  Since that 13 link gap wouldn't line up between the left and right tracks for very long, it could also cause the droid's direction to vary when trying to go in a straight line.  I don't expect it'd be a major problem, but I'd just as soon avoid it entirely.

Which is why I chose to use 6 TPU pads on each track.  That allows me to separate each by only 8 PETG pads, except for the last group, which is only separated by 7.  (Six sections of 8 PETG = 48, plus six TPU pads at the start of each segment = 54.  That's one too many links, so remove one PETG.)  There will still be occasions when only one TPU pad is on the ground and other occasions where two are, but that's less problematic than none at all.

With 12 out of 106 pads printed in TPU, I only needed 94 more in PETG.  I previously said that they took 45 minutes, but I tweaked the profile a bit and got it down to 39.

If I printed them one-by-one, that would work out to 94 * 39 / 60 = 61.1 hours of print time, or roughly 61.1 / 24 = 2.54 days of nonstop printing, not counting setup time.  However, printing ten of them would only take 6.25 hours, which in the long run saves 2.35 hours of raw print time (94 / 10 * 6.25 = 58.75) and potentially a lot of setup time as well.  It would also give the little pronged clips on the pads more time to cool.  In any case, as mentioned earlier, I'd printed 11 of them by Thursday.


Then on Friday, I made another executive decision:  Faced with the prospect of 83 more traction pads, and seven chassis parts that individually would take a significant portion of a day to print, I went ahead and swapped nozzles to 0.6 mm.  I'm glad that I did, because that cut my print times nearly in half. Since then I've managed to print:

• The remaining two sprocket wheels
  
• The rear body shell
  
• The electronics box
  
• The electronics box lid
  
• Both rear inner side plates
  
• Both rear outer side plates
  
• 15 more traction pads
  
• 6 of the idlers
  

Most of the larger pieces were finished by Saturday afternoon.  And here is a dry fit of the chassis with the parts I've got so far:






With the new nozzle, the individual traction pad print time has also been reduced to 22 minutes, cutting the max print time for the 68 that I still haven't printed down to 25 hours ... less if they are done in groups.  I can likely knock those out here and there this week.

(I would have had ten more traction pads already, but I encountered one of the evils of cardboard spools.  Apparently a piece of the inner cardboard on my silver spool lifted up, and then the filament got caught behind it as it turned.  That prevented the spool from turning further, and so the printer stopped extruding plastic right before the main body of the pad itself finished.)


That leaves only the idler mounts, the side plates, and the rest of the head as major prints.  I am printing the left-hand idler mounts right now and the right hand will soon follow.



The front-most idler (on the right) is missing because that one is different and I still need to model it.  I need it to have a smaller diameter so there's more space between it and the intermediate drive pulley.  Speaking of which, you may notice that the outboard idler mount has a little arm passing behind the yellow pulley. That has a matching slot for the axle for said pulley to help keep it straight.  Which I just now realized will only really work in one specific position (the one that I modeled the droid in) because the pulley moves with the front section of the droid, and the idlers are attached to the rear section, and these can slide in relation to each other.  I knew that before now; what I just realized is that I forgot I was going to design to accommodate it.  Big oops. Ah well, I may get lucky and not need to tension the tracks that way (Denial: it's not just a river in Egypt).

I still have to wrap up the design on the side plates and the rest of the head, but they are well on their way and with luck I may be able to get the side plates printed by next weekend.  Ultimately, though, I can do without them for now since they are just decorative parts.  Even with the new nozzle, the other section of the head will take most of a day, so that may be next weekend's big print.

I do have some concern that my idlers may be too narrow ... not so much a problem for the droid's stability, but more for the tracks.  The idlers definitely don't (and can't) extend the full width of the links, but I could extend them outward a bit (as long as they cleared the traction pad clips).  In that case, I'd have to redesign and reprint a few things, make a few bolts longer, and make a few mounting posts shorter.



Apart from the failed traction pads, there were a few other hiccups.  The rear shell warped a bit across the part's width.  You can see the curvature on the right in this photo:



I used the heat gun and some 1-2-3 blocks to encourage it to straighten out a bit.  I also had to do a major support-ectomy to get that material out of the gap between the hinges.  It was also a pain for the Electronics Box.  I need to adjust my profile to make it a bit easier to remove.

In fact, the rear body shell nearly failed, because I totally forgot to build in the built-in support like the ones I did for the front body shell, which I realized just as it was about to start curving toward the relevant overhang.  I ended up supporting the overhang with my bed scraper until the plastic was rigid enough to support itself.  It's a little rough in that area, but that's fine.





Earlier I mentioned I'd changed the electronics arrangement.  Specifically, I moved the ESP32 microcontroller to a removable panel just forward of the opening for the Electronics Box Lid and the fuse box.  The ESP32 is a bit offset on the panel to hopefully allow USB to be plugged in (most likely it'll need a 90 degree adapter).  I'll have to be careful to turn off the droid if I hook it up to USB (supplying it with two sources of power is a good way to fry it, I believe).



While putting it in the "brain box" like I originally did would be cool, having ready access to the main power switch is more important.  I've gone with a 40 amp DPST rocker switch for that purpose, which was the largest rating I saw that was likely to fit.  I still had to be careful with the switch placement to make sure that it didn't obstruct the front axle and would fit under the cover, so I elected to make an angled platform for it (Which is also visible in the screenshot above).  Even so, I will have to make sure the wires clear the switch, and I had to put my voltmeter in sideways.


On the physical hardware front, I've cut my front and rear axles to length, and installed what feels like a million heat set inserts.

Here is the list of the inserts I've designed for so far (assuming that I haven't forgotten about some).  A few are M5, but most are M3, so if I don't specify, they're M3.

• Two Front Inner Side Plates (3 each)
  
• Front Bottom Plate (4)
  
• Front Body Shell (4)
  
• Electronics Box (4x M3, 6x M5)
  
• Rear Bottom Plate (12x long M3, 4x short M3)
  
• Two Rear Inner Side Plates (5 each)
  
• Rear Upper Crossbrace (4)
  
• Upper Stalk (4)
  
• Two Lower Stalks (6 each)
  
• Four Sprocket Bodies (6 each)
  
• Two Inner Idler Mounts (2 each)
  
• Two Outer Idler Mounts (2x M3, 4x M5 each)
  
• Head (2x M3, 2x M5)
  

Note: I have two types of M3 inserts ... the short ones that have straight vertical ridges, and longer ones that have helical ridges.  I got the longer kind fairly recently, so I designed some of the parts for the short ones, e.g. the various stalk parts.  I also used the small ones where space is a concern (e.g. the two rear wings on the rear bottom plate).


Awhile back I bought 30 608zz skate bearings to add to four that I already had handy.  The build currently uses 32 of them (that I can remember), so at the moment I have enough.  However, the idler mounts on each side have the option of adding two more idlers between the main three, so that'd be 40 total.  I'll need to order some more for that.

• Eight Idlers (2 each) = 16 (24 with the four optional idlers installed)
  
• Four sprockets (2 each) = 8
  
• Two lower stalks (1 each) = 2
  
• Upper stalk (2)
  
• Neck rotation (2)
  
• Rear Body Shell (2)
  

The new bearings came lubricated with grease that is meant for rapidly turning parts (it thins out as the bearings get hot) ... a lot more rapid than this droid is likely to run.  This makes them stiffer than the other bearings I already had.  Soaking them overnight in gasoline helped dissolve the original grease.  I lubricated them afterward with white lithium grease, and now they're a lot more free spinning.  But they also smell like gasoline, so I'd air them out for awhile if you attempt it.

As I recall, I've also used 10 623zz bearings.  Two in each of the intermediate pulleys in the drive system, two in the rear shell/upper stalk pivot, two in the pitch arm, and two in the tilt arm.  Actually, I've misplaced a few, so I also have to order another set of these.


Once I get the idler mounts printed, I can start actual assembly and testing.

Having done a couple of test fits, I can tell already that the rear body shell is going to be a pain to install.  There are two bearings (one in each hinge arm) and four spacers (red and blue discs in the screenshots) to hold in place while the axle goes through the chassis.  





I could put a bolt through the opposite side to meet the axle and hold the parts in place, backing the bolt off as the axle advances ... except there are lock nuts on either side of the assembly, so putting either through isn't going to be a picnic, much less both at the same time.  I'm considering tape to hold the parts in place, something that I can pull free later.


Wiring is also going to be a bit difficult.  The droid's design is quite interlocked (e.g. the front axle), so the order of operations will be important.  I designed some attachment points on the idler mounts for a few extraneous PCBs (such as audio) but I'm pretty certain right now that if this droid has audio at all during its initial run, it's going to have to be a Bluetooth speaker.

And I still haven't even modified Penumbra's code to deal with the head servos and neopixels.  It'll work for driving out of the box, but the other features involve adding in the i2C and Neopixel libraries and coding stuff for those.  It never ends...