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  1. Evaluating DC Motors Xác định momen thiết kế Acquiring the Data Data Requirements No Load RPM Stall Torque Caution: Wear Eye Protection. Work with Adult supervision.
  2. Graphing the Data Mark max Torque Y Axis Mark Max RPM X Axis X Connect the points with a straight line X
  3. Graphing the Data Locate the Mid Point RPM Trace a horizontal line to the Y Axis X This is the Design Torque Value X X Mid Point RPM Determining Design Torque ALWAYS Record, Describe and Date the Data
  4. Directly Measuring Motor Stall Torque is a Learning Experience. Sample Motor 12V Battery Voltmeter Ammeter NC MO Switch //-------------------------------
  5. Evaluating DC Motors Determining Motor Stall Current Measuring Armature Coil Resistance The Multi-Meter selector is set to read resistance in units called ohms Ω (The Blue portion of the selection dial) The selector is set to the lowest range (0- 200Ω ) The Value measure is 0.9 ohms.
  6. Measuring Armature Coil Resistance Set the meter to read ohms. Use the lowest range. Short the meter leads and record the value. This is the meter error value. Attach your meter to the two motor leads. Slowly turn the armature shaft and record values at 45° intervals. Average these values. Caution: Turning the armature shaft quickly, induces a current in the armature windings. This Will damage the meter. Calculate the Stall Current I= E Ohm’s Law The basic Algebra of electronics R I = Current in Amperes E = Voltage R = Resistance in Ohms, Ω
  7. Calculate the Motor Stall Current The sample motor yields an average measured resistance value of 0.6 Ω. The intended BattleBot power supply will provide 12 Volts emf (electro motive force). The meter error = 0.3 Ω E 12V I= 40 amps = R 0.6 Ω - 0.3 Ω Predicted Motor Stall Current = 40 Amperes Directly Measuring Motor Stall current is a Learning Experience. Sample Motor 12V Battery Voltmeter Ammeter NC MO Switch //-------------------------------
  8. Evaluating DC Motors Determining Motor Stall Torque and No Load RPM The Test Bench Set Up Requirements Securely fasten motor to the Test Bench. Use #10 AWG or larger, Multi Stranded Wire. Battery or Batteries similar to those intended for use in the BattleBot. HD Automotive Starter Switch Caution: Testing motor torque creates strong electrical and mechanical forces. Wear Eye Protection. Work with Adult supervision.
  9. Special Equipment Build a motor torque arm Use 1”x1”x1/16” steel angle 3/8” Shaft Collar Create the Stall Condition Wear Eye Protection 3 People should perform the test. Set up and hold the scale Mark the scale Energize/de-energize the system.
  10. Set Up and Hold the Scale Wear Eye Protection Scale with Taped Marking Torque Arm Retainer Motor Torque Arm Create the Stall Condition Wear Eye Protection Procedure Assume the stations; Energizer Scale holder Scale marker Energize the System Raise the Torque Arm with the Scale Mark the Scale Deflection De-Energize. ALWAYS Record, Describe and Date the Data
  11. Determining the Torque Value F = Force (lbs.) 3 lbs D = Length (ft.) .5 ft Q = Torque (ft.lbs.) F D Q= DxF 1.5 ft.lbs. = .5 ft. x 3 lbs. ALWAYS Record, Describe and Date the Data Measure No Load RPM Wear Eye Protection Procedure Mark Armature Shaft with Reflective Tape. Energize the System Read the No Load RPM De-Energize. ALWAYS Record, Describe and Date the Data
  12. Directly Measuring Motor Stall Torque is a Learning Experience. Sample Motor 12V Battery Voltmeter Ammeter NC MO Switch //---------------------------------------
  13. Evaluating DC Motors Determining Robot Speed
  14. Robot Speed Equations Use this equation to predict the BattleBot’s speed ALWAYS Record, Describe and Date the Data \\-------------------------------
  15. Evaluating DC Motors Determining Gear Reduction Determine the Required Tractive Force Procedure Load a wheeled drive platform with the design weight. Approximate the correct weight distribution. Drag the platform by a spring scale attached with a rope. Try to drag level with the floor. Tractive Force = 14 lbs. ALWAYS Record, Describe and Date the Data
  16. Calculate the Required Reduction Tractive Force Required (lbs.) Design Torque (ft.lbs. = Approximate Reduction Drive Wheel Radius (ft.) 14 lbs .75 ft. lbs = 4.6 rounds off to 5:1 .25 ft. ALWAYS Record, Describe and Date the Data