Estimating the Efficiencyof a Parallax Servo

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Calculating Servo Efficiency

Energy to Lift Weight

We know that energy is lost due to friction in the gearbox and that “losses” occur in the electric motor.

The overall efficiency of the system is . . .

electrical energy used is determinedthe same way as for pump project

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𝜂=𝑤𝑜𝑟𝑘𝑟𝑒𝑞𝑢𝑖𝑟𝑒𝑑𝑡𝑜𝑙𝑖𝑓𝑡 h𝑤𝑒𝑖𝑔 𝑡

𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙𝑒𝑛𝑒𝑟𝑔𝑦 𝑖𝑛𝑝𝑢𝑡 𝑡𝑜𝑚𝑜𝑡𝑜𝑟=

𝑊 ∙ h𝑉 ∙ 𝐼 ∙𝑡

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Making a Pulley from a Wheelwheel is grooved using a lathe

hole drilled through wheel for attaching lifting string (fishing line)

original wheel

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Servo Efficiency Assignment• Wrap fishing line around a grooved wheel, and attach a weight to the end of the line • Turn on your servo to lift a weight• Use five different servo speeds during lifting:

• servo pulse width=1500s for no servo motion• servo pulse width=1700s for full speed counterclockwise• choose five values between 1500s and 1700s

• Measure the vertical distance traveled by the weight• Use the millis() command to determine the time elapsed during lifting (print to serial

monitor)• Compute efficiency

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1540 1.541580 1.581620 1.621660 1.661700 1.70

Electrical Power

(W)

Electrical Energy

(J)

System Efficiency

(%)PULSOUT Argument

PULSOUT Width (ms)

Height Change

(cm)Lift Time

(s)

PE Change of Weight (J)

Voltage (V)

Current (A)

Spreadsheet for Computing Efficiency

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Create the following plots:

1. “Potential energy change of the weight” and “electrical energy input” (both on y-axis) versus “pulse width.” Be sure to label each of these curves on your plots.

2. “System efficiency” versus “pulse width.”

1540 1.541580 1.581620 1.621660 1.661700 1.70

Electrical Power

(W)

Electrical Energy

(J)

System Efficiency

(%)PULSOUT Argument

PULSOUT Width (ms)

Height Change

(cm)Lift Time

(s)

PE Change of Weight (J)

Voltage (V)

Current (A)

Recommendations• Secure your robot in a vise or at your table (take one wheel off the robot and let the pulley

wheel hang over the edge of the table, holding the robot during lifting.

• Measure the weight of an object to lift (cell phone, several sets of keys, purse), and attach the weight to the end of the fishing line provided.

• Write a Arduino sketch that allows servo speed to be controlled and wheel motion to be activated using the robot whiskers.

• Measure voltage and current for different servo speeds; you will need two multimeters.

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tie fishing line to pulley

Please return the pulley to your instructor, and clean up any messes that you made.

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