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Thread: PhantomX controlled by a Raspberry Pi

  1. #71

    Re: PhantomX controlled by a Raspberry Pi

    Hi Kevin and others,

    I did update my git project with some of the simple performance improvements. Will play some more with it soon

    Kurt

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    Re: PhantomX controlled by a Raspberry Pi

    Quote Originally Posted by escott76 View Post
    Generally the "tidiest" way is going to be to make your own power distribution setup. Keep in mind "tidy" doesn't always mean compact and small, which may be more of a concern. You can solder and splice wires, or you could use a terminal block. When space/weight was at a premium in combat bots I would crimp, solder and heat shrink ring terminals to wires and bolt them together. Fan the wires out into two groups and you can slip a larger piece of heat shrink over it. You could also use liquid electrical tape.
    I get to spend part of my weekend trying to tidy up the pair of 2S LiFePO4 batteries into a single stick of butter (what it looks like) instead of using the gigantic and horrific looking series connection Y-cable I made. At least they were cheap and should not explode if I mess up.


    Quote Originally Posted by escott76 View Post
    If you are new to soldering and wiring, practice with scrap wires. Getting stuff to look neat is a matter of knowing what you want to do before you do it, which is always made better with practice.
    Indeed: PRACTICE, PRACTICE, PRACTICE. It is inevitable that one will mess up. If you are lucky you will only get a couple small solderflux splatter burns or ugly looking parts, instead of burning the house down.

    Quote Originally Posted by escott76 View Post
    Take your time, plan things out and make sure you do things like allow enough slack to disassemble components without taking everything else apart (never happened to me I swear ). Heat shrink covers a lot too, and is much better looking and longer lasting than electrical tape.
    Heat shrink really does look and work much better than electrical tape, but it can be annoying if you make the wires too short and it shrinks onto the wire while soldering. Even more annoying is forgetting to put it on the wire before you soldered connectors to both ends. (ಠ_ಠ)

    Quote Originally Posted by escott76 View Post
    Check your currents as well, I would avoid using a JST connector for anything that requires significant power.
    For high power connectors, I'm a really big fan of XT-60 connectors as they are easy to (dis)connect, easy to solder, and have nice little recesses in the plastic around the solder cups for heatshrink to slide into and completely envelope the solder joint. Not so much a fan of deans connectors, but unfortunately they are all that are used on the DARwIn-OP. Even really cheap bullet or spade quick-connectors usually work well enough for several amps without problems (usually more than JST or small Molex can handle).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

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    Re: PhantomX controlled by a Raspberry Pi

    Thanks Kurt I'll take a look. It's getting harder and harder to diff/meld our stuff. I've reworked a bunch of the commander code and I'm still using the old stuff you sent me via email to top it off! I'll try and find time this weekend to at least line up our commander code so at least that matches. Aside from the do/while in the main loop is there anything else big that I should take a look at outside of the xbee code?

  4. #74

    Re: PhantomX controlled by a Raspberry Pi

    I hear a LOT of folks who don't like the Deans ultras, I've used them for years with almost no trouble whatsoever. I think a lot of people try to solder them with way too small a tip. You *can* complete a solder joint with a tip that's too small, but you spend too much time doing it, bleeding heat off into the plastic the entire time. I tin the wire and connector end, then getting the joint heated enough to let the solder flow is quicker. I also try to keep a mating connector at least partially connected to hold everything stable. As with any soldering clean clean clean your iron! Before every joint!
    As for the heat shrink on a short wire, a wet paper towel can work wonders to keep that end cool.

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    Re: PhantomX controlled by a Raspberry Pi

    Quote Originally Posted by escott76 View Post
    I hear a LOT of folks who don't like the Deans ultras, I've used them for years with almost no trouble whatsoever. I think a lot of people try to solder them with way too small a tip. You *can* complete a solder joint with a tip that's too small, but you spend too much time doing it, bleeding heat off into the plastic the entire time. I tin the wire and connector end, then getting the joint heated enough to let the solder flow is quicker. I also try to keep a mating connector at least partially connected to hold everything stable. As with any soldering clean clean clean your iron! Before every joint!
    It's not that I have difficulty getting the connector or the wire hot enough, it is that the wire has to be soldered to a flat spot. ...and larger diameter wire extends beyond the edge of the plastic housing. ...and some of the connectors require a bit of dexterity to get correctly mated.
    XT-60 have nice solder cups milled into them, so I just heat the connector up and fill the cup about flush with solder. After that, use the soldering iron to push the wire into the nearly-molten solder and top that off with more solder. It is just really nice to be able to have the wire stay in place with only a little bit of pressure in a single direction instead of needing pliers to keep it from pushing itself off the connector (or up/down too far) before the solder solidifies.


    Quote Originally Posted by escott76 View Post
    As for the heat shrink on a short wire, a wet paper towel can work wonders to keep that end cool.
    I'll probably give that a try on the next harness not connected to a power source. The most recent heat-shrink problem was of my own making: I tried to connect a Deans ultra to an XT-60 with barely an inch of 12AWG.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  6. #76

    Re: PhantomX controlled by a Raspberry Pi

    larger diameter wire extends beyond the edge of the plastic housing
    Assuming you're using stranded wire (if not, why not?) then you can put half of the strands on one side, and the other half on the other. Just make sure you actually make a good solder connection in the middle of all that.

    connect a Deans ultra to an XT-60 with barely an inch of 12AWG
    That's why there's liquid electrical tape :-)

    Seriously, though, I made the Deans decision almost a year ago, and it's been OK for me, but if I were to make it today, I'd probably go XT-60. Not enough to switch at this point, though :-)

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    Re: PhantomX controlled by a Raspberry Pi

    To get this thread back on topic... So Kurt I'm integrating your changes into my code. What was your CPU load with your changes?

  8. #78

    Re: PhantomX controlled by a Raspberry Pi

    Hi Kevin,

    I think it dropped down into the 45%sh range when walking and about 20% when Commander is turned off. Both of these values can be made lower.

    A long long time ago, I remember some compilers allowed you to compile the code as to do code path timings and the like. I wonder if this compiler has any of that? May have to look...

    Things I changed:
    1) The simple loop you also noticed where we were simply hard looping until the right time.
    2) Playing around with the 2nd thread I used to read input from the XBee
    3) Run less of the code when the robot is logically turned off.

    Kurt

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    Re: PhantomX controlled by a Raspberry Pi

    So this is odd... check out these numbers.
    So when walking I'm at 22.3% CPU load.
    When it's standing there with no commander input I'm at 96%!
    When the commander is shut off I'm at 2%.
    So the standing there number is really shocking! I must have something odd running when it's still.

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    Re: PhantomX controlled by a Raspberry Pi

    So even better! I realized since I'm not interpolating on the CPU so I can usleep much longer. I can set a usleep(20000) without any noticeable difference to the walk. I tried 30000 and it became a bit jerky I assume from finishing the pose earlier than the usleep time. My CPU utilization is now down to 3% when walking! Though I still need to figure out why it's high 90s when it's just standing there.
    Last edited by KevinO; 04-13-2013 at 02:29 AM. Reason: Grammer

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