Virtual spring test

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For SC 751 series code

The purpose of this page is to discuss how to run the virtual spring test of the robot w/the testjig. Specifically, setting of the testjig and robot.

initial robot configuration

• disable SM updates to the MC w/command 127 0
• w/testjig, position robot to the zero position
• (optional) run command 104 w/repeat to confirm that the robot position is near zero (|3rd number| <100), and that the SM state (2nd number) is as commanded (3 initially, 13 later)
• zero (adjust) the K and B for the VS w/command 131 0 0
• increase the overload limits w/command: 1122 30000 30000 9000 9000 (last number is continuous ~amps*1000)
• command SM to enter the virtual spring state w/command 170 13 (confirm w/cmd 104)
• enable SM updates to the MC w/command 127 5

testjig config

• range 0 to 64000 (this is inital and final)
  • because jig doesn't return to zero, for now run w/ plantarflexion and a range of 0 to 64000 (where zero is near ramp engagement, and is also the zero position for the ankle [where it was boot])
• set (de)acceleration, ~10 rads s-2 (or maybe larger? 20 rads s-2)
• RPM 1111 for stiffness test, 4444 for damping test
• set passes to a multiple of 2 (VERY IMPORTANT, otherwise, might stop at 64000)
• 1 second delay between passes (will allow fuse to re-zero)

some experiments at 1111 rpm

• low stiffness w/command : 131 1000 0 (appx 100 nM/rad)
• med stiffness w/command : 131 2000 0 (appx 200 nM/rad)
• high stiffness w/command : 131 4000 0 (appx 400 nM/rad)

some experiments at 4444 rpm

• moderate damping w/command : 131 0 400 (appx 40 nM/rad sec)
• moderate stiffness and damping w/command : 131 4000 400

results

• K value is approximate 12% small, or appx 20% greater when the effect of K2 is considered
• B value is approximate 20% larger, or +-10% when estimated robot screw friction is removed.
• RE40 to EC30 ratio is appx 3.3 to 1 (based on moment arms of 112mm vs 37 mm, and RE40 ratio of 22/20)

other

• 130 can be used to read the VS parameters (the first 2 are relevant in this experiment)
• 131 sets K and B : eg 131 K B
• 1120 can be used to read the electronic fuse parameters (first two values are maximum sums, the 2nd two values are the decay rates in q15)
• 1121 can be used to monitor the electronic fuse (first 3 values are the present sums, 2nd three values are actual current in q15)

limits

• testjig : use 1111 rpm, ~10rad s-2 acceleration, position of 0 to 64000, 2 passes, 1 sec between passes
• set fuse to ~9 amps w/command 1122 30000 30000 9000 9000
• VS K: don't exceed 400 nm/rad (eg 131 4000 0) - can result in oscillation or overload.
• VS B: don't exceed 40 nm/rad s (eg 131 0 400) - can result in oscillation