Wright State University

1
Wright State University

• Jenny Broering
• Mike Hill
• Rahul Shah
• Michael Wasco

2
Problem Statement

• The purpose of this project is to design and
  manufacture robotic manipulator to assist younger
  patients with daily activities, such as
  retrieving things from the ground or immediate
  environment.
• Basic Requirements
• 0.75 m reach from front of wheelchair
• Each linkage must move no more than 0.25 m/s
• Lift 0.5 kg mass (1.1 lbs.) with 7.5 cm in
  diameter
• Maximum cost of 4,500 (excluding controllers)

3
Agenda

• Design Constraints
• Robotic Arm Design (detailed)
• Conclusions
• Questions

4
Design Constraints

• Arm, including motors, must weight less than 30
  lbs.
• Keeps wheelchair balanced
• Dimensions of arm/base must not exceed 6 inches
• Wheelchair must be able to fit through standard
  doorways

5
Design Constraints

• Keep shoulder and elbow motors at the base
• reduces weight on arm itself
• transmit power to elbow via shaft
• Aluminum 2024
• High Strength-to-Weight ratio
• Lightweight compared to steels (2770 vs. 8030
  kg/m3)

6
WSU Arm Design
7
Orientation of Base Motors

• Mounting position
• Length along chair allows space for base plate
• Straight layout allows for easy mounting
  possibilities
• Two large motors displaced from arm
• Reduces torque
• Makes links slimmer and lighter

8
Base Configuration
9
Shoulder Motor

• Required Torque 465 in-lbs (7433 oz-in)
• Speed Requirement 2.65 RPM
• Suggested motor and gearhead
• K D Magmotor servo motor
  (model C33-I-200E08)
• Carson 34EP100 NEMA 34 gearhead (1001)
• 477 in-lbs provided

10
Shoulder Motor

• Servo amplifier suggested to slow speed down to
  required speeds
• connecting directly to 24 VDC will give an output
  of 10 RPM
• connecting 24 VDC to a servo amplifier, we can
  set a speed from 0-10 RPM

11
Shoulder Motor Dimensions and Costs

• Motor
• 5.15 length
• 3.38 diameter
• apr. 5 lbs.
• 134.00

• Gearhead
• 5.43 length
• 3.25 diameter
• 9.68 lbs
• 700.00

• Amplifier
• 439.00

12
Elbow Motor

• Required Torque 237 in-lbs (3797 oz-in)
• Speed Requirement 4.4 RPM
• Suggested motor and gearhead is the same as
  shoulder motor
• K D Magmotor (model C33-I-200E08)
• Carson 34EP100 NEMA 34 gearhead (1001)
• 477 in-lbs provided

13
Elbow Motor Dimensions and Costs

• Motor
• 5.15 length
• 3.38 diameter
• apr. 5 lbs.
• 134.00

• Gearhead
• 5.43 length
• 3.25 diameter
• 9.68 lbs
• 700.00

• Same as Shoulder motor choices

• Amplifier
• 439.00

14
Upper Arm

• Comprises of two links
• Dimensions 410 x 50 x 5 mm.
• Weight 0.8772 lbs.
• Advantages
• slots cut to reduce the weight
• Provide support for the shaft and the lower arm
• encompasses the parts

15
Upper Arm
16
Bearing Plate

• Provides structural support
• Slot provided for compact closing of the arm
• Dimensions 100 x 50 x 10 mm.
• Weight 0.23 lbs.

17
Elbow Joint

• Elbow motion using the shaft, bevel gears and
  rod.
• Weight
• Rod 0.045 lbs.
• Shaft 0.614 lbs.
• Bevel Gears 0.0278 lbs. each

18
Elbow Joint

• Advantages
• eliminates the motor-on-joint assembly.
• reduces torque on the shoulder motor.

19
Lower Arm

• Single shaft design
• Two slots
• decrease weight
• Symmetric placement between the two upper arm
  links reduced unwanted torsion.

20
Lower Arm

• Dimensions 320 x 50 x 5 mm.
• Weight 0.3498 lbs.

21
Differential Assembly(wrist)

• Motor-on-Gear Design
• Off the Shelf vs. Machined
• Dimensions

22
Design

• Two Axes Movement
• Gears spin in same direction, gripper pitches
  up/down
• Gears spin in opposite directions, gripper rolls
  cw/ccw
• Motor-on-Gear Design
• Gear is attached to motor shaft
• Motor shaft/gear have same axis of rotation

23
Off-the-Shelf vs. Machined

• Currently searching for off-the-shelf models that
  can be incorporated into the design space
• Machined differential will drive the cost up
  significantly

24
Dimensions

• Approx. Size (w/o motors) 162x120x50 mm
• Weight (w/o motors) 1.7 lbs

25
Differential Assembly(wrist)
26
Differential Motors

• Orientation of motors provide a direct
  application of the gear movement
• Differential design allows motors to work
  together thus reducing the size and cost of motors

27
Differential Motors

• Torque requirement 107.2 oz-in
• Speed Requirement 15.7 RPM
• Suggested motor
• Barber-Colman permanent magnet DC Motor with
  gearhead (model EYQF-33300-661)
• 12 VDC
• 160 ozin
• 9 RPM

28
Differential Motor Dimensions and Costs

• Motor
• 2.5 length
• 1.5 diameter
• weighs 9 oz.
• 74.00 ea.

29
End Effecter(Gripper)

• Motor-screw powered movement
• Three Fingers
• Dimensions

30
Gripper
31
Motor-Screw

• Powers the closing action
• Will weigh less then 1.5 pounds
• open/close control
• variable closing pressure

32
Three Fingers

• Better stability
• Pick-up a wide variety of sizes 7.5cm-.5cm
• Middle finger has lip for round objects
• Fork lift design
• Non-slip cork/rubber padding

33
Dimensions

• Each finger is 95 x 25 x 2 mm
• Weighs only .333 kg w/o motor-screw
• Hollow casing 50 x 95 mm
• 2 mm wall thickness

34
Torque Calculations

• Note that the weight of the materials were taken
  to act at the farthest distance possible

35
Motor Speed Calculations
? L/V
0.1524 m
0.542 m
0.902 m
36
Summary

• Main motors placed at base
• Design uses 5 motors
• Design gives 5 axes of motion.
• Upper arm is slightly longer than lower arm
• Differential Design
• Three finger Gripper

37
Summary

• Motor cost 2768.00
• Material cost 150.00 (est.)
• Machining cost
• Total weight. 36 lbs

38
Disadvantages

• Improper folding of arm
• not certain if folding is within 6 in.
• motor placement on differential makes wrist bulky
• Overall assembly is overweight by 6 lbs.

39
Advantages

• Meets nearly all of the constraints /
  requirements.
• Shaft
• allows transfer of more power to the lower arm
• allows reduction of torque on the shoulder motor.
• Use of plates instead of tube reduces overall
  weight considerably

40
Advantages

• Can lift objects from the floor or from
  table-tops.
• Torque requirements met by motors.
• Versatile gripper.
• Use of Aluminum 2024 in most parts
• consistency in material
• high strength to weight ratio (used in airframes)

41
?? Questions ??