Print PDF
Favorite
Email
Step 3Leg Design 2 - Hypothesis***y is there a hypothesis at this step?
***why are the ideas being reinvented in the middle of the instructable (organization needs to be reworked)
After examing the geometries around the second part of the leg design I have come up with a more mathmatically sound hypothesis. When the leg is positioned as in the previous step (femur perpendicular to the ground and knee joint rotated until end effector touches the ground) a triangle is formed.
Theoretically the distance from the center of the hip joint to the end effector could be considered a Moment Arm. Therefore the idea of torque and force can be applied here and instead of saying:
"This requirement is that the end effector can be positioned beneath the knee joint or can be positioned under the knee joint with minor hip rotation."
one could say:
"The end effector must be able to be positioned so that the distance between the hip joint and the end effector create a moment arm that is short enough so the force produced by the hip servo is greater than the downward force produced by the body (distributed amongst all four legs)"
See the following diagrams:
New values for this calculation are:
Number of legs considered = 4
Weight carried by each leg = 25.2 oz
Hip Servo Torque = 183 oz in
Moment Arm = Torque / Force
Moment Arm = 183 oz in / 25.2 oz
Moment Arm = 7.2 in
Therefore, the actual hip-end effector distance was 7 inches.
As long as the hip-end effector distance does not exceed this distance, the hip should always be able to support the robot (whether getting up or standing upright).
After examing the geometries around the second part of the leg design I have come up with a more mathmatically sound hypothesis. When the leg is positioned as in the previous step (femur perpendicular to the ground and knee joint rotated until end effector touches the ground) a triangle is formed.
Theoretically the distance from the center of the hip joint to the end effector could be considered a Moment Arm. Therefore the idea of torque and force can be applied here and instead of saying:
"This requirement is that the end effector can be positioned beneath the knee joint or can be positioned under the knee joint with minor hip rotation."
one could say:
"The end effector must be able to be positioned so that the distance between the hip joint and the end effector create a moment arm that is short enough so the force produced by the hip servo is greater than the downward force produced by the body (distributed amongst all four legs)"
See the following diagrams:
New values for this calculation are:
Number of legs considered = 4
Weight carried by each leg = 25.2 oz
Hip Servo Torque = 183 oz in
Moment Arm = Torque / Force
Moment Arm = 183 oz in / 25.2 oz
Moment Arm = 7.2 in
Therefore, the actual hip-end effector distance was 7 inches.
As long as the hip-end effector distance does not exceed this distance, the hip should always be able to support the robot (whether getting up or standing upright).
| « Previous Step | Download PDFView All Steps | Next Step » |
 |
Add Comment
|
