September 15, 2007 D.Giandomenico More than you wanted to know about Robot Winch Design David...

September 15, 2007 D.Giandomenico

More than you wanted to know about

Robot Winch Design

David GiandomenicoLynbrook High School Robotics

FIRST Team #846DGiandomenico@lynbrookrobotics.com

(408)343-1183

A few common tasks robots might do:

• Robot may move itself

• Robot often has an arm to lift or grasp objects

• Robot might have to lift itself or pull an object

Three functions we may consider:

• Design a robot arm• Design the drive train• Design a lifting winch

We will consider the winch, which is arguably the most simply specified of the three robotic functions.

2004 FIRST National Robotics Competition

• Endgame Task: Robot must suspend itself from a bar located 10 feet above the floor

• Our task: Design a winch to lift robot

Design Criterion for the Winch

• How much weight to lift?

• How far?

• How fast?

What We Want.

• Weight:

• Distance:

• Time (speed):

130 lbs

1.5 feet

5 seconds

What we have:(Some of the Motors supplied in FIRST Robotics Kit)

All data approximate at 12 VOLTS

Bosch, motor only - - 0.65 114 A 20,000 RPM 2.5 A 340 W

Bosch, motor/gearbox in high

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

Bosch, motor/gearbox in low

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

Fisher-Price, motor only - - .36 N-m 57 A 15,000 RPM ? 140 W

Fisher-Price, motor/gearbox

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

Delphi Sliding Door Motor (Mfg: Taigene)

- - 35 N-m 40 A 75 RPM ? 69 W

Globe, motor only - - .21 N-m 21 A 11,500 RPM .82 A 63 W

Globe, motor/gearbox 117:1 77% 19 N-m 21 A 100 RPM .82 A 50 W

Delphi Seat Motor (Mfg: Keyang)

- - 2 N-m 20 A 600 RPM ? 31 W

Delphi Window Motor (Mfg: Valeo)

- - 12 N-m 20 A 70 RPM ? 22 W

data from www.usfirst.org

FIRST MOTOR COMPARISON (2002-2003)

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

- - 35 N-m 40 A 75 RPM ? 69 W

- - 2 N-m 20 A 600 RPM ? 31 W

- - 12 N-m 20 A 70 RPM ? 22 W

“CIM” Motor Specification

“CIM” Motor Performance

Winch DesignInput parameters

Weight to lift (lbs) 130Height (ft) to lift in time T 1.5Time to lift seconds 5

Convert to MKS (metric system)Mass to lift (Kgs) 59.1Weight To lift (Newtons) 579.1Height (m) 0.457Time to Lift 5

Potential EnergyKp = mgh (Joules) 264.8

Power needed to gain above energy in time TP = Kp / T (Watts) 53.0

Weight & Mass conversions:1Kg = 2.2 lbs-mass

Weight in Newtons = mass x 'g'where g=9.8 m/s/sso a 1Kg mass weighs 9.8 Newtons

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

- - 35 N-m 40 A 75 RPM ? 69 W

- - 2 N-m 20 A 600 RPM ? 31 W

- - 12 N-m 20 A 70 RPM ? 22 W

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

- - 35 N-m 40 A 75 RPM ? 69 W

- - 2 N-m 20 A 600 RPM ? 31 W

- - 12 N-m 20 A 70 RPM ? 22 W

Choosing a motor based onMaximum Motor Output Power

• The max power of a DC PM magnet motor cannot be sustained without burning out the motor!

• As a rule of thumb, operate motor at 70%-80% of theno-load speed.

• Power output = Pmax * 4(1-) where % no-load speed

• Coincidentally, At 75% no-load speed, Pout = 75% Pmax

• Need to consider losses in Gear sets

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

- - 35 N-m 40 A 75 RPM ? 69 W

- - 2 N-m 20 A 600 RPM ? 31 W

- - 12 N-m 20 A 70 RPM ? 22 W

20:1 80% 10 N-m 114 A 1,000 RPM 2.5 A 260 W

64:1 70% 29 N-m 114 A 300 RPM 2.5 A 230 W

147:1 65% 35 N-m 57 A 100 RPM ? 91 W

- - 35 N-m 40 A 75 RPM ? 69 W

- - 2 N-m 20 A 600 RPM ? 31 W

- - 12 N-m 20 A 70 RPM ? 22 W

Estimate gear loss for a large gear reduction

Consider a large gear reduction of 1200

First, estimate number of small gears sets(Typical gear sets might have a ratio of 3:1)

Second, estimate the loss in for n gear sets

Gear loss estimate for a set of gears

Suppose we have n=3 inline sets of gears, each with a 4:1reduction. What is the total efficiency if each gear set loses 4%?

T = in

T = (100%-4%)3 = 88.5%

Estimate of how many gears to make a large gear reduction.

• Suppose we want a gear reduction of 1200. How many gear sets with a reduction of 3 do we need?

• Solve 3N = 1200

• N = ln(1200)/ln(3) = 6.45

In the final design, N must be an integer, but for the interim design, this method conveniently allows us to estimate the loss without committing to a specific gear selection.

Gear loss estimate

From before, we need around n=6.45 gear sets. Assuming a loss of 4% for each gear set,

T = in

T = (1-4%)6.45 = 76.8%

Fisher Price Motor Data 2004

All data approximate at

12 VOLTS

Fisher-Price, motor only

- - .36 N-m 57 A 15,000 RPM 2 140 W

Fisher Price Motor 2004

From FIRST_MOTOR_CALC.xls

2000.0

4000.0

6000.0

8000.0

10000.0

12000.0

14000.0

16000.0

Torque (N-m)

V=12VDC

Speed decreases as motor is braked

What is Torque?

dFW inline

But isn’t that “Work”

Units of Work vs. Torque

• Work (Energy)

• Torquepound feet(lbf-ft), ft-lbf, oz-in, N-m etc.

ft-lbf, Joules (=N-m), KWh, etc.

Power, Torque & Speed

RPM 2TP

tdFP /

trFP /)( trFP /

Torque (N-m)

V=12VDC

Speed & Torque in a DC PM Motor

• Let ={0,100%}

such that

2000.0

4000.0

6000.0

8000.0

10000.0

12000.0

14000.0

16000.0

Torque (N-m)

V=12VDC

Speed & Torque in a DC PM Motor

Or, w/o calculus, Max occurs between two roots of quadratic, at =0, =1 that is,

=½ or equivalently, when =50%

)()()( TP

Using calculus, Max Power occurs when:

)21()(

)1()( ssTP

Torque (N-m)

V=12VDC

Max Power in a DC PM Motor

Fisher Price Motor Data 2004

All data approximate at

12 VOLTS

Fisher-Price, motor only

- - .36 N-m 57 A 15,000 RPM 2 140 W

CURRENT

Torque (N-m)

V=12VDC

Power input into a DC PM Motor

Device Under Test (DUT) conditions:V = 12VDC (fixed)Load is varied using some type of brake

Under these conditions, a good model for the current is:

)1)(()( oso IIII

Power input into a DC PM Motor

)]1)(([

osoDCIN

Power is small when =100%, and increases linearly as decreases

CURRENT

Torque (N-m)

V=12VDC

Torque (N-m)

V=12VDC

EFFICIENCY

Torque (N-m)

yV=12VDC

DC PM Motor Summary

• Max Power occurs at 50% No-Load Speed

• Best efficiency typically occurs at about 75%-85% No-Load Speed

• Most DC PM Motors cannot sustain operating with full voltage applied at speeds less than 50% No-Load.

Putting it all together

1. Choose a winch drum size

2. Calculate the drum rpm

3. Choose the % motor operating speed

4. Calculate the required gear reduction to operate at that speed

5. Verify the output winch line force meets or exceeds the original specification, including gear box losses

Winch Design Specification

Input parametersWeight to lift (lbs) 130Height (ft) to lift in time T 1.5Time to lift seconds 5

Convert to MKS (metric system)Mass to lift (Kgs) 59.1Weight To lift (Newtons) 579.1Height (m) 0.457Time to Lift 5

Winch Drum SpeedWinch Line Speed

Distance (m) 0.4572Time 5Speed (m/s) 0.0914

Drum size (dictated by factors such as cable)Diameter (inches) 6Diameter (m) 0.152Circumference (m) 0.479

Drum speedRevolutions / second 0.191Revolutions / minute (rpm) 11.46

Determine the Gear ReductionDrum speed

Revolutions / second 0.191Revolutions / minute (rpm) 11.46

Motor spec at 12VDCNo load speed 15000 RPMStall Torque 0.36 N-mPout max 141.37 W

Motor speed and torque% motor speed 80%Motor Speed 12000Torque 0.0720 N-mRequired Gear Reduction 1047.2

Gear Loss Estimate

Required Gear Reduction 1047.2

Loss estimate assuming 'n' small gear setsIndividual gear set reduction ratio 4 times% Loss per gear set 5%

Number of gear reductions 5.016Total estimated gear efficiency 77.31%

Verify We Meet or Exceed Pull Strength Specification

Total estimated gear efficiency 77.31%

Winch line output at speedMotor torque at speed (above) 0.0720 N-mTorque after gearbox (no loss) 75.40 N-m

After gear box losses 58.29 N-mForce on Line 765.00 NForce on Line (lbs) 171.74 lbs

Feat Accomplished!

• 171lb exceeds required spec of 130lbs

• What does this mean?• Things to think about:

– Could it be that we overdesigned the winch?

– How will the winch respond when lifting 130lbs if it is pulling with 171lbs?

– And of course, how do we build this winch?

More than you wanted to know about

Robot Winch Design

David GiandomenicoLynbrook High School Robotics

FIRST Team #846DGiandomenico@lynbrookrobotics.com

(408)343-1183

September 15, 2007 D.Giandomenico More than you wanted to know about Robot Winch Design David...

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