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Making this my rover thread. First test of selected motor. A tiny compact N20 reduction motor geared down 298:1 with integrated quadrature sensor. Rover motor test. It’s noisier than I expected.
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Previously on vgr builds a rover... adventures in discovering turnbuckles
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Bought a pair of these tiny turnbuckle rods with spherical joints for the 3-link differential mechanism on my rover design. They’re used in RC monster trucks for something. Found via a video of a rover build by a random hobbyist. Internet+capitalism = answer for everything.
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Next challenge: assembling a wire harness for these tiny components and thin 24 awg wires is gonna be a bitch. Anyone have tips? Will need to crimp in tiny connectors that connect to a cable attached to board at other end (the pin count is off by 1 here but ignore that)
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These tiny connectors are really a pain to take apart. Only careful way I can think of is with 2 needle nose pliers. Is there a better way? 🤔
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ngl this project is like 100x beyond my starting practical engineering skill level. It’s truly full-stack engineering from mechanical design to Python embedded control code. But I’ve already at least 3xed, so only another 33x to go. Goal is autonomous drive test by year-end.
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But in my defense, I’m the only one trying to build maximally from scratch 😎. Of the 5 others in out build party, 3 are using off the shelf robots and focusing on software, 1 is using an ESA open-source design but focusing on a RISC-V board, and one is using a kit robot.
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We’ll see. Place your bets: what are the odds that I will achieve my drive test goal for the year: an autonomous rough figure 8, including climbing over a 30-degree slope obstacle. I give myself 22.3%.
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Rhett has a super-minimalist build going
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The varying approaches have been fascinating as we all approach "Rover" with whatever part of the problem seems most interesting. I of course couldn't help myself from building a Flight System from scratch. github.com/rhettg/stubborn
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Continuing rover adventures, since my main robot design, Nature is Murder, is a complex 6-wheel rocker bogie, I decided I needed a very simple test chasis just to work on the motor control and programming in parallel. I decided to call it... Accessory Before the Fact 🤣
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Unlike NIM, ABTF is not a production robot. It will have 4 driven wheels, each with an SG90 steering servo attached to a wheel unit with an N20 drive motor (4 corner holes), and a Beaglebone Blue board (4 posts)
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It should be able to drive around fine, enough to test motor control, but probably can't handle significant obstacles or hold much by way of sensors and things... the mounting posts are to raise the board above the chassis, leaving room for a battery below
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Printed and tried a partial ABTF assembly. Wanted to use 4x M3x20 flanged bolts and nuts to secure the board to the posts, but had to use unflanged for 2 because the mounting holes are cramped and right next to some components that don’t allow a flange or washer. Works though.
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Next up: designing the drive motor housing and assembling the whole 8-motor beast. After which some janky JST wire harness assembly and adding a 7.4v lipo battery pack. Then the Everest... actually programming the Beaglebone Blue. I’m frankly intimidated by that.
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Side quest: misadventures in learning to crimp.
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Little thread on what’s one of the harder hands-on engineering things I’ve done in my life. A real test of dexterity and eyesight: crimping a wire to put in a connector. A JST PH connector to be precise. What’s crimping? Here is an expert tutorial iotexpert.com/jst-connector-
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The trick to efficient OnShape cad design, I’ve realized, is to design each component in an assembly spatially in place using offset planes etc. That way alignments are visible as you build. You can check assembly view as you work on the part view, to make sure holes etc line up.
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It’s interesting how much this is an REPL like in programming. I literally had calipers handy and was measuring COTS components as I went, like the 2s lipo battery (2 blue cylinders), turnbuckle link, and ball joint between rocker hinge and body, to make sure it would fit.
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You discover design constraints/needs as you do this. For example, that white connector on the battery is supposed to plug into the 3-pin header on the board near it (this is a Beaglebone Blue robotics board). But it’s too short to come around from the bottom the way I’d planned.
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So either Plan A: add an extension cable (which needs room) to keep the battery on the lower deck or Plan B: put the battery above the board, raising the center of gravity and making the rover more top-heavy than it already is.
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Two more. In assembling-while-designing, I realized my original plan to have a completely covered top deck wouldn't work. The BBBlue antennae need to stick out there, plus need top access to gpio headers to connect stuff on payload deck. So ended up with a nice big hatch hole.
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The second one: while sketching this out, I hadn't factored in that the turnbuckle (red rod a few tweets up) is too long for the differential bar to be on the main body... so now I had to add a tail plane to hold the differential bar (on perseverance this is in the middle)
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Whew, finally figured out how to do mate connectors correctly. Now I have this aluminum strut mated via a slider joint to the rocker hinge
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My rover body is going to end up tiny relative to the undercarriage. This is because my 3d printed part dimensions are limited by my printer's build plate (120mm square, but effective max more like 100mm square)
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Hehe triple-hybrid test assembly: CAD printout, pen lines on paper, some actual components. This could be an art form.
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The first complex thing I ever built was a model kit glider ~1988, that came with 1:1 scale drawings. This now-vintage one. I built it by using drawing itself as the construction template, with nails on a board,. It was all balsa wood cut-and-glue pieces. 1:1 is a great hack!
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