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Feb 15, 2017, 07:58 PM
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The 2nd stepper motor


Hobbyking 18A driving a stepper motor (2 min 28 sec)



There was 1 rewound motor left from 2014. Even though the requirements were never met, it was worth documenting what it did. Drove it at 16.8V to simulate a 4S battery. Set the load to 140g. Hard coded a jumping movement which powered it for 250ms at full power & a holding movement which powered it at 50% power for 1700ms. This managed to keep it from burning out, but it heated up quickly. Care had to be taken to let it cool down & it could never hold the load continuously.


It never got the load to a parabolic trajectory, but it was an open loop programmed as close as possible to the ideal acceleration. A closed loop with encoder feedback might have gotten more acceleration to it. The bare motor was 70g, so the load simulated the motor lifting itself + any required accessories.


Rewinding the motor may have made it more optimal for holding loads at the expense of jumping movements. It might be better off with a higher KV.


It was around this time the lion kingdom finally read more of kaloucheThesis.pdf & discovered the Ghost Robotics Minotaur. That thesis is valuable reading for anyone interested in robot legs. It was exactly the envisioned vehicle, showing the limit of what brushless motor driven legs could do. With an unlimited budget, it could only go 4.47mph & it only lasted 20 minutes, so it would only go 1.4 miles. A reduced cost version would be even worse. It did show a robot with legs that only moved in 2 axes could still turn 360' in 6 seconds.


They provided some documentation on how the Minotaur worked: a 5.3Ah 4S battery, an STM32 realtime board, a blurry photo of motors which looked like t-motor U-10's. Unfortunately, you have to buy the robot to get the source code.
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