Drive Motor Sizing:
Mass:
Angular Velocity:
Oversize motor by at least a factor of two
Chassis Team Voltage supply = Vs = 12 V
Oversize motor by at least a factor of two
Chassis Team Voltage supply = Vs = 12 V
Calculations for drive motor assumed one motor.
Drive Motor Capability Analysis:
It is likely the robot will encounter small obstacles while still operating on ideal surfaces. For example, tiles, small stones, dirt, very small inclines, etc.So a worst case scenario will be considered where the robot is stopped and has to climb over debris. The worst Case scenario for the inclined plane will be when the robot is stopped. Also an analysis of the time required for the robot to deceleration to zero velocity will be done.
Selected motor Specs: 50:1 Micro Metal Gearmotor HP
Gear ratio: 50:1
Free-run speed @ 6V: 630 rpm
Free-run current @ 6V: 100 mA
Stall current @ 6V: 1600 mA
Stall torque @ 6V: 15 oz·in
Debris:
Required force to lift robot directly up:
Maximum height of debris that still allows forward motion from stand-still:
(1)…….
Solving for gives
Determining the maximum height of the debris that could be climbed over from stand-still:
Redoing the calculations using results in a debris height:
Inclined Plain:
Determining the max angle of inclined plane that can be climbed from a stand-stillw/ payload:
Determining the maxangle of inclined plane that can be climbed from constant velocityw/ payload:
Redoing the calculations with no payload results in a :
Redoing the calculations using results in a :
Deceleration:
Using the specs from the motor:
K is a proportionality constant.
Solving for armature resistance:
Solving for torque:
For deceleration the supply voltage (VT) will be zero because the terminals of the motor will be shorted.
Since the torque-speed equation is linear the average speed of the motor can be used to determine the average torque which acts to decelerate the robot.
to come to a full stop from 1 m/s.
(#) are assumptions which must be verified.
Maximum height of debris is very small which could cause undesirable operation on RIT’s floor surfaces.
Ability to climb a handicap access ramp ( per the American Disability Act) cannot be achieved with the current selection of motor and wheelcombination.
To ascend a handicap access ramp the wheel radius can be decreased, the mass of the system can be decreased by removing the payload, or the motor size can be increased. The easiest and cheapest change would be removing the payload.
One drawback to changing the wheel diameter to from is a lower top speed of .
Steering Motor Sizing:
(1)…….
Required Power:
(2)…….
5
Oversize motor by at least a factor of five halves or 2.5
Calculations for steering motor assumed two motors.
(#) are assumptions which must be verified.