Difference between revisions of "DEWBOT IX Caterpillar Drive"
MaiKangWei (talk | contribs) (→The Math) |
MaiKangWei (talk | contribs) (→The Math) |
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We started by looking at the [[media:Climb_Power.xls | geometry, power and normal force]] requirements for climbing the pyramid's corner pole. It turned out that at a linear climbing velocity of 6 in/s (which was as fast as anyone was comfortable with), either a single CIM or MiniCIM could provide the necessary power. Traction would require that we increase the normal force between the robot wheel and the pole by at least 100 lb<sub>f</sub> above the force provided naturally by gravity. | We started by looking at the [[media:Climb_Power.xls | geometry, power and normal force]] requirements for climbing the pyramid's corner pole. It turned out that at a linear climbing velocity of 6 in/s (which was as fast as anyone was comfortable with), either a single CIM or MiniCIM could provide the necessary power. Traction would require that we increase the normal force between the robot wheel and the pole by at least 100 lb<sub>f</sub> above the force provided naturally by gravity. | ||
| − | Taking this analysis a step further, we adapted the team's [[media:Drivetrain_Model_DB9_Pyramid_130209.xls | drive-train mathematical model]] to the pyramid climb. We ultimately settled on a single CIM motor reduced by a 54.4:1 ratio driving 1.1 inch effective diameter wheels. Terminal drive speed is calculated to be 4.6 in/s. The CIM should run at 26.9 amps during the climb. | + | Taking this analysis a step further, we adapted the team's [[media:Drivetrain_Model_DB9_Pyramid_130209.xls | drive-train mathematical model]] to the pyramid climb. We ultimately settled on a single CIM motor reduced by a 54.4:1 ratio driving 1.1 inch effective diameter wheels. Terminal drive speed is calculated to be 4.6 in/s. The CIM should run at 26.9 amps during the climb; pretty close to optimum efficiency for the motor. |
==The Design== | ==The Design== | ||
Revision as of 15:47, 18 March 2013
Achieving a 30 point climb was a key aspect of 1640's game strategy for Ultimate AscentSM, with a strong bias towards climbing on the pyramid outside (thereby enabling other alliance robots to also score 30 points).A number of concepts were considered and evaluated. The Caterpillar Drive approach was selected because it was perceived that:
- The climb time could be relatively short, allowing significant scoring with Frisbees;
- the climbing mechanisms would not interfere with a shooter; and
- the concept was consistent with a low center-of-mass robot.
The Concept
The concept of caterpillar drive was to "simply" drive up the pyramid's corner pole: a slick, powder-coated 1½" steel tube at a 60° incline from grade, interrupted by two horizontal corners extending 2½" from the corner pole's surface. So this becomes a drive-train problem.
In order to cross the two horizontal corners, three (3) drive wheels oriented along the robot's drive axis will engage the corner pole. Each of these three drive wheels may be independently disengaged and lifted away to allow a portion of the robot to cross over a horizontal corner; only one drive wheel will ever be disengaged at any given time while climbing. Each wheel has a "claw" to hold it to the pole and to also provide the wheel with the normal force needed for traction. The claws terminate with bearings so as not to impede the climb with friction.
Skids on either side of the drive axis will rest against at least one pyramid horizontal at all times to prevent the robot from rotating around the pole. Since the robot chassis is shorter (27.75") than the distance between horizontal pyramid members (34.5"), the skids need to extend during climbing to insure that at least one pyramid horizontal is in contact with the skids.
The Math
We started by looking at the geometry, power and normal force requirements for climbing the pyramid's corner pole. It turned out that at a linear climbing velocity of 6 in/s (which was as fast as anyone was comfortable with), either a single CIM or MiniCIM could provide the necessary power. Traction would require that we increase the normal force between the robot wheel and the pole by at least 100 lbf above the force provided naturally by gravity.
Taking this analysis a step further, we adapted the team's drive-train mathematical model to the pyramid climb. We ultimately settled on a single CIM motor reduced by a 54.4:1 ratio driving 1.1 inch effective diameter wheels. Terminal drive speed is calculated to be 4.6 in/s. The CIM should run at 26.9 amps during the climb; pretty close to optimum efficiency for the motor.
