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Gotta break out the tiny hand drill and create a starter hole. Beginning to appreciate the value of having the right tools at hand. I bought this tiny jewelry hand-drill set a while back precisely for this sort of bs. But again, gonna design the hole into the print next time.
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Managed to strip the head of one screw in self-tapping false-start, despite using small screwdriver. But can tighten it with needle-nose pliers. Lesson: never force tiny parts, they strip easily.
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Next up, make axles for the 2 passive wheels. Hacksaw time. But first a short recess to go take a consulting call and make some money to pay for all these shady R&D shenanigans.
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The lessons never end. The shaft needs to be 26mm according to the design dimension, but the toothpick piece I used to test the assembly is 27.3mm. Which to use?
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I go with the toothpick. Figure the compliance of strut will create a nice compressive fit. But I forgot steel is much stiffer than wood, so it’s a tighter fit! Still it fits. Btw I’m very impressed with my hacksaw precision. I’ve matched the toothpick exactly 😎
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Second axle I decided to go a little shorter. Note the scratches on the shafts and leftover stock btw… hard to wield a hacksaw precisely without it jumping around a bit. Next time I’ll make a cutting guide or something.
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Replying to
Aaaannnd drive motors in as well 😎 The assembly is done! Note holes on drive motor strut fork caps… can add screws there if necessary but interference fit holds motor in place well enough. That was a bitch to get right btw.
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Let’s add the computer, battery and soft assemble the partial wire harness (battery and servos connected; drive motors not yet… will add 2x6= 12 more wires/4 more cables to this picture).
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Let’s power it up 😎 This is just led blinky running but it’s still neat. I got much further today than I expected. Now for toughest part… rest of wire harness. Unfortunately crimping and/or soldering may be needed and I suck at both. Then the hellish challenge: programming
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Back to the mechanical design of the main rover... just spent 2 hours figuring out how to get a mcmaster-carr ball joint and some standard nuts and bolts into my assembly, and detected some geometry issues that would have been annoying to discover after printing...
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Finally actually earning the mechanical engineering degree they gave me in 1997. I think the mechanical design is now about 60% done. I'm now aiming to build a model accurate enough to simulate.
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Turnbuckles and bogies need to be added, then the 4 drive units and 2 passive wheels. Another couple of days to rough it out, then 2 more to get all the finicky details doubled checked before I start printing.
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Another good day. Design is finally roughed out. Lots of the dimensions and stuff are tolerances, but now I have something I can refine.
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Especially proud of learning to integrate components from other sources properly. SG-90 servo motors are now in the design (random open-source), as well as a ball joint from McMaster-Carr
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I'm still astounded by how I can do all this insanely powerful engineering design work for free, and my only cost is materials and time.
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The turnbuckle was the hardest thing I've had to model. 2 ball joints at either end of a variable length rod... I left out the screw constraint and the lock nuts. Made it cylindrical joints instead.
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And FINALLY, the full assembly is sorta done with all major linkages and joints represented. It was a bitch to get this right... there's like 6 ball joints, and 5 pin joints here.
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The thing is, attaching the 2 turnbuckles would immediately mangle the assembly into a weird train wreck. Since the geometry is coarse, all lengths are rough approximations, and OnShape doesn't allow ball joints to be constrained, the constraint solver creates pretzels.
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And initially I had the turnbuckles set too long, so the thing would really contort. So I suppressed one end of each turnbuckle, rearranged the whole thing to look right, then manually adjusted the turnbuckle lengths and positions to be approximately right...
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Then I unsuppressed end connections and the solver "found" the nearby solution and didn't pretzelize the design. Then I used the measuring tool to measure the turnbuckle length, and went back to the part subassembly and constrained cylindrical joint to be a few mm around that.
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Effectively, instead of solving a hard 3d geometry problem to compute the right nominal length, I found it "experimentally" in the 3d CAD design. Now I have everything close enough that I can do projections and back out final actual geometry. 😎 🥳
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First attempt didn’t work because it turned out one of the 2 drive motors in ABTF build had terminals shorted 😭. Took a bunch of continuity testing to figure it out. Luckily I have 2 more plus half a dozen coming. They’re not cheap. $13 each, with integrated quadrature sensor.
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Feeling the urge to add a pair of RGB leds on my rover and have the leds go red for evil. In general I want to make my rover evil. You guys are lucky I’m pretty bad at this stuff.
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Next up: testing the quadrature sensor. 4 encoder wires hooked up to 4 encoder inputs with alligator clips ugh. Motor will run off dc supply for this test
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Back to rover after 6 weeks. I have 3 weeks to build a face-saving demo for demo day 😬 Dec 12. Printing parts for NIAM (Nature is Attempted Murder, the draft build for final build, Nature is Murder)
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Urgh. This part was sized big enough to hold the servo, but not big enough to allow it to be maneuvered in. 🤬
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Design for assembly is a bitch. I thought I had enough room to wiggle it in but no. Will try to saw in a compliance notch like I have on this mating connector. PLA is pretty stiff, but these notches work well.
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Alt solution is to mount with flange on the outside of the box, which wastes space and increases vehicle height by about 3mm but might be better than hacking away.
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Ah crap, this problem only affects the outer 4 wheels, and there may not be room to lower the middle wheels 3mm
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And FINALLY, the full assembly is sorta done with all major linkages and joints represented. It was a bitch to get this right... there's like 6 ball joints, and 5 pin joints here.
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