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Thread: Next steps with a PhantomX AX Hexapod Mark II & BBB

  1. #21
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Thanks. Actually, last night I installed a Raspberry Pi 2. It's compactness along with no longer needing the Xbee (I'm using a Bluetooth Sony DS4 controller now) cleaned things up a good bit.

    I'm still using the Murata regulator though, and at 1.5A max it is a little lean on current capacity. Fortunately, I'm not using wifi at the moment which consumes a lot of power. I never had any issues with it, though, in the past. I'm on the hunt for something better. I had a RC car BEC which would be great, but for some reason it died and I haven't bothered with them since. I may go back to it.

    For the old Pi, yeh, I powered through GPIO. It bypasses the fuse, but hey what could possibly go wrong! The Murata acutely has output short circuit protection so it will turn off if a lot of current is pulled. I'm sure it trips at a higher current level than the Pi's fuse, though, so it isn't as protective.

    For the Pi2 install, I'm powering through the MicroUSB connector using an old cable I cut in half. It worked out neatly with this setup.

  2. #22

    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    For what it is worth, on my hexapod, I am using one of these: http://www.amazon.com/Castle-Creatio...4638280&sr=8-1
    Which is a 10amp BEC. Currently I have it setup with the connector for an ODroid XU3, but before this when I was using an RPI I used the appropriate connector for it. On the input power side for the BEC, I used a AX cable, connector (cut wire in half), and I plug this cable into an AX powered hub, which is where I feed the power in from the battery or wall wart...

    1.5Amp would probably be sufficient for just the processor and maybe few things in the USB, but my guess is it would it would not be enough for WIFI, BT and camera and...

    Oops actually remembering back with my RPI setup (Lynxmotion T-Hex) - I had problems with what I said due to USB power issues on RPI, so I instead routed the power to a dumb USB powered hub, and then ran a USB cable from the hub to the RPI, and also connected the a USB cable from RPI to source of HUB... Worked with dumb USB hub, smarter one did not turn on until it had source signal from host so chicken and the egg... But I think these issues have improved with later RPIs...

  3. #23

    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    I had problems with what I said due to USB power issues on RPI, so I instead routed the power to a dumb USB powered hub, and then ran a USB cable from the hub to the RPI
    I've found it much more reliable to feed 5V into the Pi using the GPIO header. A single OKI-78SR can drive a RPi with some amount of USB devices and a PiCamera. For something heavier, I'd expect a OKY-T/3-D12P to perform OK (3A) and the T/5 version (5A) to be overkill even when also feeding a 3.3V converter separtely (like a 78SR or LXDC or whatever.)

  4. #24
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    I've had issues with powered USB hubs on the BBBk previously, only solved by blocking the +5v line from the hub back to the BBBk, but doesn't seem to be an issue on the RPi2 so hopefully resolved.

    Like Dan I'm powering the RPi2 using a cut in half micro USB cable.

    I like the look of the BEC example you've listed, might switch to something like that when I try to reduce the size of my current build.

  5. #25
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Things are progressing well, though slowly, with Jim Bob. The following functionality has now been achieved using bespoke code cobbled together in Python on the RPi and various sketches on the Arbotix-M and Arduino board. Locomotion is provided by the Phoenix code base running on the Arbotix-M

    • Obstacle avoidance via the ultrasonic and IR sensors, including a stairwatch sensor I added after close call with the staircase
    • Tracking and following objects using the Pixy
    • Voice outputs
    • Ability to head in specific directions using the mag sensor
    • Basic distance scanning via LIDAR lite


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    Current block diagram

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    I originally had all sensors directly connected to the Rpi via an AD and logic level converter but had trouble getting the LIDAR and Pixy working consistenly with the Rpi, so dropped an Arduino board back in to handle the various sensors.

    To do:

    • Tidy up all the cables
    • Implement some form of voice commands
    • Expand the use of the LIDAR data
    • Begin conversion of current processes to ROS


    The one annaoying challenge I still have is the AX12's randomly reverting back to an ID of 1. Sometimes I can go for weeks without an issue, then other days it can occur multiple times. Always just one AX12 and seemingly random ones. I've seen a few posts on this issue, but so far have been unable to resolve.
    Attached Files Attached Files
    Last edited by CreedyNZ; 07-19-2015 at 01:48 AM.

  6. #26

    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Looks great!

    As for the Servo 1 issue, I have not done anything about it yet either. What I have considered doing was to update my hexapod like r3n33 did and not have any servo with servo ID 1 (rename it to 19 for example).

    Then could occasionally (or by command) have the code query for each of the servos. If it finds one servo with id 1 and one of the other servo IDs it expects, does not respond, then have the code update the Id of the Servo 1 back to what it thinks it is supposed to be.

    Again I have not done this as I was trying to keep the code compatible with standard Trossen configuration for the PhantomX.

    I know that it would be better to find out why this sometimes happens. My guess is either because the voltage drops low at some point, or potentially some message(s) get clobbered on the buss... But at least that approach may catch a majority of cases. Note: I have had a few occasions where I had 2 servos rename to 1... Which this could not properly handle, but maybe 1 went before the other one and as such could be...

    Kurt

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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Consensus for ID resets was 'brown-out reset' -> 'bootloader firmware update mode' -> 'invalid firmware update data' -> 'aborted update, so ID somehow reset to default'. Just updated the 'Diagnosing' sticky to include the suspected cause of ID resets, but forgot to add more about prevention by using thicker wires to provide power to each limb and possibly giving each servo in the limb a direct connection to a local powered hub instead of daisy-chaining them.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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  8. #28
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Jim Bob looks like a beast The sensory input is impressive and you are tracking and following objects with your Pixy! Cooool!

    I'm curious about where you mounted your mag sensor and did you have to perform a magnetic calibration? I've been experimenting with a stand that holds the IMU 100mm up from the body which helped a lot to get good readings and calibration from my magnetometer.

    So yeah I took some advice from the forums when I changed servo 1 to 19. Then at startup looked for a missing ID and would re-assign. This helped for most situations and if I detected two missing IDs I would halt execution and give myself indication that I needed to fix the IDs manually. This helped quite a bit and would at least give me indication when it couldn't automatically be resolved. I never did get to the root of the problem and after getting ROSie setup I haven't experienced a lost ID which is puzzling and leaves me with more questions than answers.
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  9. #29
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Hi,

    The tracking and following objects with the Pixy is a great party trick. It takes a while to calibrate properly for changes in light levels, but once set up works a treat. I'll make and post a video when I get the chance.

    I've mounted the mag sensor (LSM303HC) right at the top as far as possible above any magnetic/electrical interference. Having made, and crashed, a few drones I'd previously tried different ways of trying to shield mag sensors from magnetic interference but in the end, distance is the only thing that works (the inherent problem of course is that in trying to shield a mag sensor from unwanted magnetic interference usually results in also shielding out the very thing we're trying to measure)

  10. #30
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    Re: Next steps with a PhantomX AX Hexapod Mark II & BBB

    Quote Originally Posted by tician View Post
    Consensus for ID resets was 'brown-out reset' -> 'bootloader firmware update mode' -> 'invalid firmware update data' -> 'aborted update, so ID somehow reset to default'. Just updated the 'Diagnosing' sticky to include the suspected cause of ID resets, but forgot to add more about prevention by using thicker wires to provide power to each limb and possibly giving each servo in the limb a direct connection to a local powered hub instead of daisy-chaining them.
    Thanks, that's very helpful and might have hit on the problem. At the moment my power setup is like this:
    Click image for larger version. 

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    which I suspect is causing too great a voltage drop. I'll add another powered hub like this and see if things improve.

    Click image for larger version. 

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