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Thread: Falling-Up Robot Project

  1. #11
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    Re: Falling-Up Robot Project

    Sweet project! I love how massively tall this robot stands. Might be pretty crazy to scale it wider and make something like wall dividers that you or two people could push around.
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  2. Re: Falling-Up Robot Project

    Quote Originally Posted by tician View Post
    NEMA sized hybrid stepper motors may be a bit heavier and lower power, but they are inexpensive, accurate, and can use small, inexpensive micro-stepping drivers for accurate position control without any gearing. The extra weight of the stepper motor is coaxial with the wheel, so has very little effect on the pendulum's moment of inertia and ultimate payload. If you absolutely do not want any gearing, you are pretty much stuck with stepper motors. There are low backlash gear boxes and/or roller chain / timing belt setups that would enable hobby BLDC motors to provide similar performance to a heavier stepper motor using direct drive, but they can be expensive and/or bulky.
    Very low backlash gearmotors are available, but are very expensive, upwards of $200 USD depending on desired specs. And the torque at low speed is still low compared to steppers.

    The NEMA23 3A stepper motors used on the Falling-Up Robot have a max holding torque of 270 oz-inches without a gearbox. So there's no issue with wearing out gears. The torque combined with zero backlash results in very nice stand-still performance. For high rate corrections, the steppers are very responsive:

    https://forum.pjrc.com/threads/41442...l=1#post132162

    For those who attempt stepper motors, driving them is not as straightforward as a DC motor with PWM control. Also, steppers induce more mechanical vibration that DC gearmotors. Microstepping is necessary and I recommend stepper drivers with sinusoidal current control. Filtering the accel & gyro measurements is also a must.

  3. Re: Falling-Up Robot Project

    Quote Originally Posted by r3n33 View Post
    I love how massively tall this robot stands. Might be pretty crazy to scale it wider and make something like wall dividers that you or two people could push around.
    I didn't have the heart to cut the 6 foot long aluminum extrusions. It turned out that It makes for a very interactive robot because it stands with you. And the main microcontroller board is at desk level, so it's convenient to work with, without taking precious space from my desk.
    Extrusions are great for making very light and stiff robot frames. It's easy to add parts without having to disassemble your project. They're like legos for adults.

  4. #14

    Re: Falling-Up Robot Project

    It makes for a very interactive robot because it stands with you
    That's a great observation!

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