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Thread: Self-erecting, self balancing 'bot

  1. #11
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    Re: Self-erecting, self balancing 'bot

    I always assume that "slim margins" can suddenly turn into "no margins" - and then the magic smoke gets released.

    Weight is not a problem, and I'm not planning to make 100M of these, so a bit of over-engineering won't hurt. I'm planning to use Pololu drivers rated at 1.5A w/o fan or heatsink, and .4A steppers, so I'm not super worried about heat. On the other hand, a small fan and light-weight shrouding can turn a minor "probably not a problem" into a "not a problem at all".

    I just can't yet judge the heat issue...

    I may be over-thinking this...

  2. #12

    Re: Self-erecting, self balancing 'bot

    1.5A driver, 0.4A stepper, should not need a fan!
    And, the less that can fail, the fewer Murphy moments you will have ...

  3. #13
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    Re: Self-erecting, self balancing 'bot

    Ok! Fan-less it is!

    I may stick on a small heat-sink while no one is looking!

  4. #14
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    Re: Self-erecting, self balancing 'bot

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    Metalwork arrived. My Maker buddy with his CNC equipment, and a can of black spray paint, does a very nice, tight job!

    The Teensy 3.2 - based PC board has just gone out for fab. Features include: Dynamixel driver, XBee interface, lots of LEDs, battery voltage-sensing & mosfet power control (it can turn itself completely off), stepper interfaces, and a separate console interface for logging.

    I have the MPU interface working. While I'm waiting for the PC boards I'm going to start to work on the stepper functions.

    Fun!

  5. #15

    Re: Self-erecting, self balancing 'bot

    Putting all the holes in the correct locations is a lot easier with some CNC help :-)

    I'm glad you have the MOSFET power control; every time I've "saved time" by not adding that, I've ended up "losing batteries" by forgetting to manually turn it off when something interrupts me. So, good for you!

  6. #16
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    Re: Self-erecting, self balancing 'bot

    I learned to protect the battery here on this site!

    I went a little crazy with voltage sensing, single-button off/on, & power control. I think next time I'm going to devote some time to using an Amtel microcontroller for this function. I lost a ton of board space to resistors and steering diodes for this. But it was fun! There's such a close line between developing hardware and developing software - it's all logic!

  7. #17
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    Re: Self-erecting, self balancing 'bot

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    PC board has arrived! I've checked out the power bus's, and I'm ready to warm up the old soldering station. SMT devices first, then the power components, the LEDs, and then the rest.

    I've noticed that different color LEDs need different-valued current-limiting resistors for similar brightness, so this time I'll characterize the LEDs with a pot so I can pick brightness's I like. Not like the Teensy-based board I did for my hexapod - the green power led was so bright I'd wake up at night and think aliens were landing...

  8. #18

    Re: Self-erecting, self balancing 'bot

    different color LEDs need different-valued current-limiting resistors for similar brightness
    Yes. The yellows are always anemic. Also, they have different forward voltages, and thus the same resistors will give different amounts of current to different LEDs.
    I've always found the blue ones to be the brightest, with the caveat that their forward voltage is really high (about 3.1V) so the same resistor will give them less current for a given input voltage (3.3V or 5.0V.)

  9. #19
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    Re: Self-erecting, self balancing 'bot

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    I've populated the board. LEDs work. Motor drivers work. Wheels turn. There's several issues with the board, but I'm going to work on software for a while, making sure I know of all the board issues before I send out for new copper.

    The black cable is the FDTI cable. I use one of the Teensy's extra serial ports for logging; it's nice to be able to see what's on its mind while debugging!

  10. #20
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    Re: Self-erecting, self balancing 'bot

    Holy heatstroke, Batman! Those stepper motors get hot, hot, hot! And I was worried about the drivers! You learn something new every day!

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