Embedded Files
Torso Turntable Redesign
Torso Turntable Redesign
As the bearing used in the original design could not bear the weight of the shoulder and above, it began to loose. The old bearing on the torso-turntable was found to be wobbling (about 10°), so a new slewing bearing was required. Since we calculated the maximum tilting moment caused by the arm is about 22Nm, we decided to replace the previous turntable by a big slewing bearing from Igus. This bearing can resist a maximum 800 Nm tilting moment. A 3d-printed spacer is placed under this bearing to enable the inner ring to rotate without friction with the supporting aluminum plate below. A new motor hub for the shoulder blade is also designed to adjust the new size of rotating bearing.
Figure 14: CAD overview of the new torso and turntable design.
Figure 15: CAD of the slewing bearing (table) installed.
Replace turntable with slewing bearing which can withstand tilting moment
Shoulder blade is directly mounted on slewing bearing with new designed hub to motor shaft
Installed Slewing bearing
Installed Slewing bearing
Side View
Side View
Top-Front View
Top-Front View
Top view
Top view
Before Redesign
Before Redesign
11.3° deflection
After Redesign
After Redesign
3.4° deflection
Breakaway Joint
Breakaway Joint
A breakaway mechanism at the upper arm segment is required for animatronic figures. A breakaway joint can be used to simulate breakaway events for various motion profiles under controlled conditions without damaging figure. The old breakaway joint was using a flaxmag link, which breaks in one direction and under a certain force. The new breakaway joint uses an electromagnet which also breaks in one direction but under different forces. It accomplishes the objective to simulate and analyze the breakaway event under different force conditions.
Figure 16: CAD overview of the breakaway joint.
Components:
Left Part and Right Part: mount the other components on the upper arm of the robot. (Left = 103 g, Right = 83 g).
Electromagnet: changeable pull force with different PWM from the Arduino. Maximum pull force is about 65 lbs = 289 N. (273 g).
Gusset: Mount the steel plate on the Right Part. (51 g) .
1018 Steel Plate: To let the electromagnet attach to it. (310 g).
Spring: prevent the damage on the arm when breakaway happens. (5 g).
Electromagnet Calibration
Electromagnet Calibration
Relationship between magnet power and pull force is about linear. We use this graph to convert the PWM value to corresponding pull force by the electromagnet.
Breakaway joint no breakage
Breakaway joint no breakage
Breakaway joint breaks
Breakaway joint breaks
Control System
Control System
Schematic for control system.
Figure 7: Control System Diagram
Control system Implementation
Input the motion profile parameters (final position, torque limit) in Matlab.
Matlab calculates position for each time step.
Outputs values to the corresponding motor via Arduino to move the arm.
Read current position to calculate the next motion step.
Control System Workflow
No breakaway
No breakaway
(0.5x speed) Profile 1 under 50% magnet power. Acceleration = 429.2 deg/s2, max velocity = 137.4 deg/s.
(0.5x speed) Profile 1 under 50% magnet power. Acceleration = 429.2 deg/s2, max velocity = 137.4 deg/s.
Breakaway
Breakaway
(0.5x speed) Profile 2 under 50% magnet power. Acceleration = 1716.6 deg/s2, max velocity = 137.4 deg/s.
(0.5x speed) Profile 2 under 50% magnet power. Acceleration = 1716.6 deg/s2, max velocity = 137.4 deg/s.
No breakaway
No breakaway
(0.5x speed) Profile 2 under 60% magnet power. Acceleration = 1716.6 deg/s2, max velocity = 137.4 deg/s.
(0.5x speed) Profile 2 under 60% magnet power. Acceleration = 1716.6 deg/s2, max velocity = 137.4 deg/s.
No breakaway
No breakaway
(0.5x speed) Profile 3 under 60% magnet power. Acceleration = 2574.9 deg/s2, max velocity = 219.8 deg/s.
(0.5x speed) Profile 3 under 60% magnet power. Acceleration = 2574.9 deg/s2, max velocity = 219.8 deg/s.
Dynamic Model (Simulation) - Profile 1
Figure 17: Breakaway Moment along with Time at v = 164.9 deg/s, a = 858.3 deg/s^2 - PWM: 0.5
Figure 18: Comparison of Simulation & Actual Motion Profiles of Test 1
Figure 19: Velocity along with Time at v = 164.9 deg/s, a = 858.3 deg/s^2 - PWM: 0.5
Dynamic Model (Simulation) - Profile 2
Figure 20: Breakaway Moment along with Time at v = 164.9 deg/s, a = 1287.5 deg/s^2 - PWM: 0.5
Figure 21: Comparison of Simulation & Actual Motion Profiles of Test 2
Figure 22: Velocity along with Time at v = 164.9 deg/s, a = 1287.5 deg/s^2 - PWM: 0.5
Dynamic Model (Simulation) - Profile 3
Figure 23: Breakaway Moment along with Time at v = 164.9 deg/s, a = 1716.6 deg/s^2 - PWM: 0.5
Figure 24: Comparison of Simulation & Actual Motion Profiles of Test 3
Figure 25: Velocity along with Time at v = 164.9 deg/s,a = 1716.6 deg/s^2 - PWM: 0.5
Page updated
Report abuse