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Thread: Onyx X build thread

  1. #81

    Re: Onyx X build thread

    Well, that's good for Onyx, because the current mounts for the panels makes aiming down hard. I get about 5 degrees of downwards angle. I'll just have to rely on being able to be far away at all times for people with low panels.

    (Also, considering the melee lances SOME PEOPLE are planning, that might be a good plan in general.)

  2. #82

    Re: Onyx X build thread

    Okay, everything tightened up again. I was all ready to set up for the qualification video, and then I realized I had forgotten to put in the code to actually move the turret in response to the aim commands :-) And then friend game night happened and I'll do qual tomorrow.

    Separately, I like the attempt to keep four feet on the floor as much as possible. Each time it lifts a pair of feet, the video jerks a little bit, so I'm going to try to shorten the time in the air for the feet. I may also be able to shift the center of mass to balance a little better once everythings in its right place.

    But, how much mass is really needed to make an effective gyro? I think it's more a quesiton of speed than sheer mass, right?
    When walking, I have clearance under the robot, and I do have a "pancake" brushless motor and a 20A brushless ESC laying around.
    I'll go research the math for gyros. I don't think I'll actually be able to swing it for this iteration, but it's certainly something to consider for next year! (That, and a stabilized gimbal for the turret)

  3. #83
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    Re: Onyx X build thread

    Quote Originally Posted by jwatte View Post
    But, how much mass is really needed to make an effective gyro? I think it's more a quesiton of speed than sheer mass, right?
    When walking, I have clearance under the robot, and I do have a "pancake" brushless motor and a 20A brushless ESC laying around.
    I'll go research the math for gyros. I don't think I'll actually be able to swing it for this iteration, but it's certainly something to consider for next year! (That, and a stabilized gimbal for the turret)
    That sounds like it would be some combination of mechanically questionable, computationally awful, and energetically impractical, so I look forward to you proving me wrong next year.

    In all seriousness, interesting problem. You could mount it vertically and leave it constantly spinning, which would be energy intensive, and the torques from precession would be a wonderful pain in the ass to model. You could mount two perpendicular to each other and spool them up and down as reaction wheels, which may or may not be less energy intensive. Or some combination of those schemes. Any way you slice it, its going to be a bulky, maddeningly complicated power drain. Sounds fun.

    Why not just pick a gait with 3 legs on the ground?

  4. #84

    Re: Onyx X build thread

    Also, when I start turning, I may actually first turn in the opposite direction than intended.
    The reason is interesting. (Well, to me :-)

    I turn by applying an in-phase rotation of the desired IK end position, around the center of the robot body.
    (This is different from just adding a hip servo rotation, because the hip servo is not at the center of the bot.)
    However, to get a good gait, the "center" of normal forward/backward motion does not put the legs 45 degrees out, but more like 30 degrees out.
    So, to take advantage of the full rotation angle possible, I make the rotation stroke extend in the whole 0 .. 90 degrees arc, which means it moves more "forward" than it moves "backward." If I didn't do this, I would get fewer radians per second of turning speed, AND I would hit the target plates between the legs because they would over-extend. (Let's say normal gait is between 5 degrees and 55 degrees of the hip servo, where 0 equals straight out.)
    So, because certain turns rotates the legs such that the are maximally rotated at the pessimal phase, I have the options of either shortening the default stride, or reducing the turn speed, or both. Or I extend the rotation more forwards than backwards, using the full 90 degrees. In the above case, the maximal rotation command would result in an additional 35 degrees rotation forward, but only 5 degrees rotation backward, with the 15 degrees offset (center) of that extra rotation added to the hip servo.

    When I fade in the rotation motion, that actuall may make the leg rotate "the wrong way" for a little bit, because of this offset from center. That is what causes the rotation to start out going in the wrong direction.

    There may be something smarter I can do, other than just shortening the strides (which reduces performance of the 'bot.)
    For example, I might be able to only change the amount of rotation applied while a leg is in the air. Because my step rate is about one step every 0.7 seconds, this would add some more latency to the control. I already have to live with 100 ms latency of the Xbee commands because that's how the 900 MHz modules perform.
    (You may recall I ended up using ESP8266 WiFi modules with UDP networking before, because they were actually much faster, as long as a working 2.4 GHz spectrum is available ...)

  5. #85

    Re: Onyx X build thread

    Also, situational awareness of quadruped legs around chairs and table legs is hard.
    Here's hoping the buildings stay in place when bumped in the arena :-)

  6. #86

    Re: Onyx X build thread

    Did you know that /usr/bin/sendmail moved to /usr/sbin/sendmail somewhere between Ubuntu Precise and Ubuntu Trusty?
    Well, neither did I, until I had to spend the evening debugging why emails suddenly aren't sending from some systems, rather than making a robot video.
    Oh, and Amazon/UPS re-scheduled the package containing the case I'll put my remote control station in, because weather in NY. Instead of arriving today, like I paid extra for, they claim I might conceivably still get it before the Robogames starts. Who needs time to build, anyway?

  7. #87

    Re: Onyx X build thread

    So, the unopened bag of 5000 BBs I had in the box turns out to have bio-degraded all by itself in the bag. They're covered in sticky goo and smell of vinegar. It's about 1.5 years old, so I guess the freshness time on those is just a few months.

    I have a couple of BBs that have been out in fresh air, still biodegradable, but they seem to be in better shape. There's like 20 of them in a little tin on my desk -- probably enough to calibrate and do the qualification video (although I'll probably take y'all up on the offer to extend the qualifying video deadline!)
    Wal Mart doesn't carry airsoft in its NorCal stores, and the earliest Amazon can get new BBs here is Tuesday.

    Also, two nights ago, I focused my aiming laser to a nice dot at 10 feet, and hit the lens/focus insert with super glue. Today, it's totally out of focus, and it refuses to be re-focused, because super glue. Comedy of errors!

    Luckily, I have two spare red laser modules. Now I just need to disassemble the entire turret (again) to get to the point where I can swap out the laser.

    In other news, the graphics for the control station is coming along fine. Because software is easy :-)

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    Yes, I'm well aware that saying "software is easy" will cause Murphy to ensure I lose to some software glitch. Bring it on!

  8. #88

    Re: Onyx X build thread

    I've been building again! The case arrived, and I laser cut a plywood insert that I screwed a bunch of control-a-tronics into.
    It runs on mains or battery power; easy to transport and charge; under-voltage lock-out; 4A fuse on the battery (well, 4A hold, 8A trip, anything in between is debatable, because it's a polyfuse.)

    Raspberry Pi running the GUI; 5" 800x480 display using an Adafruit Kippah to reduce display bulk (this works out great!); XBee, 5. 8GHz 10" diversity receiver display; power control / battery protector board (re-purposed from my walnut/brass control panel two years ago; ATTiny85 based); voltage regulator and display for the Pi; Xbox controller; mini wireless keyboard; wired Ethernet extension/breakout.

    The case (yellow plastic) came with five crossed protruding 10 mm in the lid; perfect for mounting things. I tried drilling/threading the plastic, but it's polypropylene, which is tough but soft, so that didn't work out. Instead, I got some blade-time M3 brass inserts (intended for wood) and screwed them in; that seems to work much better.
    Also, everything connects to ground, and many things connect to each of the three power rails (battery/power adapter; 12V on/off/protected; 5V regulated.) I didn't want to solder everything to everything, because that will be a pain to service, so this is my first build using power rails! I got some ground bar at the Home Depot to screw everything into; it's designed for 14 gauge and thicker wires; I'm running 16 gauge, but the bar works fine for this application; connections seem tight enough. 16 gauge is as thick I want to go for these 1-2A curcuits; even that size is hard to jam into some of the receptacles it needs to go so I splice finer gauge for the final bit for a few things.

    Also, I got more BBs, because the old ones had decomposed (did I post about that already?)

    Also, the quality of the 900 MHz Xbee is going down. Used to be, I'd get 120 ms round-trip times, but now it's up to a second. Maybe some neighbor is talking on the phone or something ...
    I may want to also bring a pair of 2.4 GHz ones, and see which ones work better at the actual games.

  9. #89

    Re: Onyx X build thread

    Okay, so it all works okay now. I put some thin Lexan in front of the camera, and the metal focus ring in front of the laser, and the rest of the bot has hard surfaces, target panels, and heat sinks facing outwards. The one other thing I'm not sure about is the antenna for the video TX. I'll bring spares.

    The control center came out pretty well. I wanted to let the undervoltage board report the power voltage to the Raspberry Pi for display on the control screen ("POWER LOW!") and similarly let the Raspberry Pi tell the undervoltage board when it's time to turn off the power (after a shutdown,) but I think there are some bugs in the Raspberry Pi wiringPi libraries and/or GPIO utility that make it not quite possible to use the GPIOs available after the Kippah steals 95% of them in the way I want. It's not that important, and I ran out of patience to debug more. One constraint I put on myself was that I don't want to suid the control center to root, so I have to use the GPIO sysfs interface, and use the gpio tool to export GPIOs beforehand. But, as I said, I'm pretty sure it has some bug related to the difference between BCM numbering and WPI numbering, both of which are used in the API in different places. Maybe if there's downtime and no emergency repairs needed, I can noodle with it at the games.

    Aaaanyway, I'm pretty happy how it all turned out.


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  10. #90

    Re: Onyx X build thread

    BYI: regarding gyroscopes, keeping them spinning once they're at rate will take very little current! Think of the balancing gyroscope tchotchke you can buy in gift shops, that balance on a pencil tip and is started by a simple string pull. I think they can go for quite a while, as long as the bearings are good!

    Regarding the computation, I'd probably rather just engineer it, by adding a 6DOF MEMS sensor and simply counter-act the forces that are actually measured on the 'bot. After all, it's remote control, not autonomous, so I don't need any kind of precise odometry.

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