Very Tall Falling-Up Robot with Stepper Motors

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EVL
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Very Tall Falling-Up Robot with Stepper Motors

Post by EVL » Fri Feb 17, 2017 12:15 am

I'm developing the Falling-Up Robot, a very tall balancing inverted pendulum bot, using the Teensy 3.6 microcontroller with the Arduino IDE 1.6.12. I want to learn feedback control systems through practice & experience. It's tall so I can interact with it at desk level. So far, the brain and chassis is in place, and the basic balancing control system is in place to keep it from falling over.

https://www.youtube.com/watch?v=Xmt67HT ... e=youtu.be

I used stepper motors to take advantage of high torque at low RPM and zero backlash. This allows very steady stand-still performance. Dealing with the stepper-induced mechanical vibration was an issue, but was solved with analog filters on the IMU and an Extended Kalman Filter in software.

Aside from microstepping and sinusoidal current control stepper drivers, what more can be done to reduce vibration?

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haklesup
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Re: Very Tall Falling-Up Robot with Stepper Motors

Post by haklesup » Fri Feb 24, 2017 1:48 pm

pretty cool, looks like it works fairly well. Before I saw the video I was going to suggest you tune the mechanical system but I don't have many specific suggestions at this point. For example making the wheels larger might amplify the vibration but making them heavier should also dampen them by adding angular momentum to overcome. can't really go smaller and heavier as what would you use. Maybe a pneumatic wheel filled with a damping liquid, that's getting out there. perhaps some slop on the axel connection to the wheel like a limited slip clutch plate or spring loaded linkage.

Going back to the electronics, you could try different stepper motors with a little less torque or reducing the power to the stepper in an effort to reduce torque (sine wave drive did some of that).

EVL
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Re: Very Tall Falling-Up Robot with Stepper Motors

Post by EVL » Sun Mar 05, 2017 9:00 pm

haklesup wrote:For example making the wheels larger might amplify the vibration but making them heavier should also dampen them by adding angular momentum to overcome.
The mechanical vibration seems to be mostly driven by the NEMA23 motor case mounted to the robot chasis. Even if the motors are not spinning, there is high frequency vibration. I actually do have rubber dampers in-between to attenuate vibration, but vibration can still be felt everywhere. Without them, vibration is much worse, and gets even bleaker with simple stepper drivers (non-sinusoidal current control).

I might try softer rubber dampers. On the electronic side, can you recommend a good sine-wave driver that's also low cost?

EVL
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Re: Very Tall Falling-Up Robot with Stepper Motors

Post by EVL » Tue Apr 04, 2017 12:35 am

Okay, I got the XBEE communication working with the Teensy 3.6 mcu, and able to send motion commands to the Falling-Up Robot. Able to yaw and translate the 6-foot robot while maintaining tilt stability. It's no longer tethered to the USB port and the power supply unit. See latest video below. Recommend headphones.

https://www.youtube.com/watch?v=QHb9eYAyGJc

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